TULANG
Tulang disebut alat gerak pasif karena digerakkan oleh otot. Akan tetapi tulang tetap mempunyai peranan penting karena gerak tidak akan terjadi tanpa tulang. Jenis – jenis tulang
1. Tulang rawan (kartilago)
gambar:penampang melintang tulang rawan.jpg
Bersifat bingkas dan lentur serta terdiri atas sel- sel rawan yang dapat menghasilkan matriks berupa kondrin. Pada anak – anak jaringan tulang rawan banyak mengandung matriks. Pada orang dewasa tulang rawan hanya terdapat pada beberapa tempat , misalnya cuping hidung, cuping telinga, antara tulang rusuk dan tulang dada, sendi- sendi tulang, antar ruas tulang belakang, pada cakra epifis.
Matriks tulang rawan merupakan campuran protein dengan polisakarida yang disebut kondrin.
Tulang rawan ada tiga tipe yaitu: hialin, elastik dan serat.
Matriksnya memiiki serat kolagen yang tersebar dalam bentuk anyaman halus dan rapat. Terdapat pada saluran pernapasan dan ujung tulang rusuk. Tulang rawan hialin bening seperti kaca.
Susunan polikandrium, matriks , sel dan lacuna tulang rawan elastic sama dengan tulang rawan hialin. Akan tetapi serat kolagen tulang rawan elastic tidak tersebar dan nyata seperti pada tulang rawan hialin. Bentuk serat – serat elastic bergelombang . tulang rawan elastic terdapat pada epiglottis dan bagian luar telinga.
c. Tulang Rawan Fibrosa (Fibrokartilago) / Serat Matriksnya mengandung serabut kolagen kasar dan tidak teratur; terletak di perlekatan ligamen, sambungan tulang belakang, dan simfisis pubis. Sifat khas dari tulang rawan ini adalah lakuna – lakunanya bulat atau bulat telur dan berisi sel – sel (kondrosit).
2. Tulang (osteon)
gambar:Perkembangan sel - sel tulang.jpg
Bersifat keras dan berfungsi menyusun berbagai sistem rangka.tersusun dari bagian – bagian sebagai berikut:
a. Ostreoprogenator,
merupakan sel khusus yaitu derivate mesenkima yang memiliki potensi mitosis yang mampu berdiferensiasi menjadi osteoblas terdapat dibagian luar membrane ( periosteum)
b. Osteoblas
merupakan sel tulang muda yang akan membentuk osteosit.
c. Osteosit
merupakan sel – sel tulang dewasa.
d. Osteoklas
merupakan sel yang berkembang dari monosit dan terdapat disekitar permukaan tulang . fungsi osteoklas untuk perkembangan, pemeliharaan , perawatan dan perbaikan tulang.
3 . Pembentukan Tulang
gambar:proses osifikasi.jpg
Pembentukan tulang terjadi segera setelah terbentuk tulang rawan (kartilago). Kartilago dihasilkan dari sel-sel mensenkima. Setelah kartilago terbentuk, bagian dalamnya akan berongga dan terisi osteoblas. Osteoblas juga menempati jaringan seluruhnya dan membentuk sel-sel tulang.
Sel-sel tulang dibentuk dari arah dalam ke luar atau proses pembentukannya konsentris. Setiap satuan sel tulang mengelilingi suatu pembuluh darah dan saraf membentuk suatu sistem yang disebut Sistem Havers.
Berdasarkan matriksnya , jaringan tulang dibedakan sebagai berikut:
1. Tulang Kompak,
merupakan tulang dengan matrik yang padat dan rapat, misalnya tulang pipa.
2. Tulang Spons
merupakan tulang yang matriksnya berongga misalnya tulang – tulang pipih dan tulang – tulang pendek.
Berdasarkan bentuknya terdapat tiga macam bentuk tulang yang menyusun rangka tubuh, yaitu tulang pipa , tulang pipih, dan tulang pendek, selain itu ada pula tulang tak terbentuk.
a) Tulang pipa (tulang panjang)Berbentuk tabung dan biasanya berongga. Diujung tulang terjadi perluasan yang berfungsi untuk berhubungan dengan tulang lain, contohnya adalah tulang betis, tulang kering, tulang hasta, dan tulang pengupil.
Tulang pipa terbagi menjadi tiga bagian , yaitu bagian tengah disebut diafisis , kedua ujung disebut epifisis, dan antara epifisis dan diafisis disebut cakra epifisis.
Pada anak – anak cakra epifisis berupa karti;ago yang mengandung osteoblas, sedangkan pada orang dewasa yang sudah tidak bertambah lagi tingginya cakra epifisis sudah sudah menulang. Osteoblas menempati rongga yang disebut rongga sumsum tulang.
Tersusun atas dua lempengan tulang kompak dan tulang spons, didalamnya terdapat sumsum. Kebanyakan tulang pipih menyusun dinding rongga sehingga tulang pipih ini sering berfungsi sebagai pelindung atau untuk memperkuat , contohnya adalah tulang rusuk, tulang belikat, dan tulang tengkorak.
Tulang pendek berbentuk kubus dan hanya ditemukan pada pangkal kaki, pangkal lengan dan ruas – ruas tulang belakang.
Memiliki bentuk yang tertentu . tulang ini terdapat diwajah dan tulang belakang.
Tulang – tulang pada manusia selain menyusun rangka, juga mempunyai fungsi lain, yaitu:
a. Memberi bentuk tubuh
b. Melindungi alat tubuh yang vital,
c. Menahan dan menegakkan tubuh
d. Tempat perlekatan otot
e. Tempat menyimpan mineral terutama kalsium dan posfor
f. Tempat pembentukan sel darah
g. Tempat penyimpan energy, yaitu berupa lemak yang ada di sumsum kuning
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5. Hubungan Antara Tulang Hubungan antar tulang disebut artikulasi. Untuk dapat bergerak dibutuhkan struktur khusus yang terdapat pada artikulasi, Struktur khusus tersebut dinamakan sendi.terbentuknya sendi dimulai dari kartilago didaerah sendi. Terbentuknya sendi dimulai dari kartilago didaerah sendi. Mula – mula kartilago akan membesar lalu kedua ujungnya akan diliputi jaringan ikat. Kemudian kedua ujung kartilago akan membentuk sel –sel tulang , keduanya diselaputi oleh selaput sendi (membrane sinoval) yang liat dan menghasilkan minyak pelumas tulang yang disebut sinoval.
Adalah hubungan antar tulang yang tidak memiliki celah sendi, hubungan antar tukang ini dihubungkan dengan erat oleh jaringan serabut sehingga sam sekali tidak bisa digerakkan.
Ada dua tipe utama sinartrosis , yaitu suture dan sinkrondosis.
Suture adalah hubungan antar tulang yang dihubungkan dengan jaringan ikat serabut padat, contohnya pada tengkorak.
Sikondrosis adalah hubungan antar tulang yang dihubungkan oleh kartilago hialin, contohnya hubungan antara epifisis dan diafisis pada tulang dewasa ; hubungan antar tulang ini tidak dapat digerakkan.
b. Amfiartrosis
Adalah sendi yang dihubungkan oleh kartilago sehingga memungkinkan untuk sedikit gerakan. Dibagi menjadi dua, yaitu simfisis dan sindesmosis.
Pada simfisis sendi dihubungkanoleh kartilago serabut yang pipih, contohnya pada sendi antar tulang belakang , dan pada tulang kemaluan. Pada sindesmosis , sendi dihubungkan oleh jaringan ikat serabut dan ligament . contohnya sendi anatar tulang betis dan tulang kering.
c. Diartosis
Adalah hubungan antar tulang yang kedua ujungnya tidak dihubungka oleh jaringan sehingga tulang dapat digerakkan , disebut juga sendi.
Diartosis disebut juga hubungan synovial yang dicirikan dengan keleluasaan bergerak dan fleksibel.
Diatrosis dicirikan sebagai berikut:
i. Permukaan sendi dibalut oleh selaput atau kapsul jaringan ikat fibrous,
ii. Bagian dalam kapsul dibatasi oleh membrane jaringan ikat yang disebut membrane synovial yang menghasilkan cairan pelumas untuk mengurangi gesekan,
iii. Kapsul fibrousnya ada yang diperkuat oleh ligament dan ada yang tidak,
iv. Di dalam kapsul biasanya terdapat bantalan kartilago serabut.
Hubungan tulang yang bersifat diartrosis contohnya adalah sebagai berikut:
1) Sendi Peluru
Pada sendi ini kedua ujung berbentuk lekuk dan bongkol. Bentuk ini memungkinkan gerakan yang bebas dan dapat berporos tiga. Misalnya sendi pada gelang bahu dan gelang panggul.
2) Sendi Engsel
Pada sendi engsel kedua ujung tulang berbentuk engsel dan berporos satu , misalnya pada siku, lutut, nata kaki, dan ruas antar jari.
3) Sendi Putar
Pada sendi ini ujung yang satu dapat mengitari ujung tulang yang lain. Bentuk seperti ini memungkinkan untuk gerakan rotasi untuk satu poros , misalnya antar tulang hasta dan pengumpil, dan antar tulang atlas dengan tulang tengkorak. 4) Sendi Ovoid
Sendi ini memungkinkan gerakan berporos dua dengan gerakan kekiri dan kekanan , maju mundur dan muka belakang. Misalnya antar tulang pengumpil dan tulang pergelangan tangan.
5) Sendi Pelana atau Sela
Pada sendi ini kedua ujung tulang membentuk sendi berbentuk pelana dan berporos dua, tetapi dapat bergerak lebih bebas, seperti gerakan orang naik kuda. Misalnya sendi antar tulang telapak tangan dan tulang pergelangan tangan dan ibu jari.
6) Sendi luncur
Kedua ujung tulang agak rata sehingga menimbulkan gerakan menggeser dan tidak berporos, contohnya sendi antar tulang pergelangan tangan, antar tulang pergelangan kaki, antar tulang selangka dan tulang belikat.
7. Sistem Rangka
gambar:rangka manusia.png
Tulang-tulang dalam tubuh membentuk sistem rangka. Kemudian sistem rangka ini bersama-sama menyusun kerangka tubuh.
Secara garis besar, rangka (skeleton) manusia dibagi menjadi dua, yaitu rangka aksial (tumbu tubuh) dan rangka apendikuler (anggota tubuh).
Rangka aksral terdiri dari tulang belakang (vertebra), tulang tengkorak, dan tulang rusuk.
1,) Tengkorak
gambar:struktur tengkorak manusia.jpg
Tengkorak berfungsi melindungi otak. Hubungan tulang yang terdapat pada tempurung kepala bersifat suture, yaitu tidak dapat digerakkan.
Pada tulang belakang terjadi pelengkungan - pelengkungan yang berfungsi untuk menyangga berat dan memungkinkan manusia melakukan berbagai jenis posisi dan gerakar misalnya berdiri, duduk, atau berlari.
Hioid merupakan tulang yang berbentuk huruf U, terdapat di antara laring dan mandibula.
Hioid berfungsi sebagai tempat pelekatan beberapa otot mulut dan lidah.
4) Tulang dada dan tulang rusuk
gambar:struktur tulang belakang manusia.jpg
Berkas:Struktur tulang rusuk dan dada manusia.jpg
Tulang dada dan tulang rusuk bersamaan membentuk perisai pelindung bagi organ – organ penting yang terdapat di dada, yaitu paru – paru dan jantung. Tulang rusuk juga berhubungan dengan tulang belakang.
b. Rangka Apendikuler
Rangka apendikuler terdiri atas pinggul, bahu, telapak tangan, tulang-tulang lengan, tungkai, dan telapak kaki. Secara umum rangka apendikuler menyusun alat gerak, yaitu tangan dan kaki yang dibedakan atas rangka bagian atas dan rangka bagian bawah.
Tulang rangka apendikuler bagian atas terdiri atas beberapa tulang sebagai berikut:
1) Tulang Selangka
Tulang selangka atau tulang leher membentuk bagian depan bahu.
2) Tulang Belikat
Tulang belikat terdapat di atas sendi bahu dan merupakan bagian pembentuk bahu.
3) Tulang Pangkal Lengan, Pengumpil, Hasta
Tulang pangkal lengan bersama dengan tulang pengumpil dan tulang hasta menyusun alat gerak, yaitu tangan.
5. tangan
Tulang tangan tersusun atas tulang-tulang pergelangan tangan, telapak tangan, dan jari tangan. Tangan disusun oleh karpal skafoid, lunate, triquetrum, pisiform, trapesium, trapesoid, kapitatum, hamate. Telapak tangan (metakarpal) terdiri dari bagian dasar, batang, dan kepala. Jari tangan terdiri dari tiga ruas, kecuali ibu jari yang mempunyai dua ruas.
6. Kaki
Tulang apendikuler bagian bawah terdiri atas beberapa tulang yang menyusun kaki (alat gerak bagian bawah).
Kaki terdiri atas tulang kaki dan telapak kaki. Tulang kaki disusun oleh tulang paha , tempurung lutut, tulang kering dan tulang betis. Pergelangan kaki disusun oleh tulang tumit, kalkaneus, talus, kuboid, navikular, kuneiformis, dan jari – jari.
7. Kelainan dan Gangguan pada Tulang
Kelainan dan ganguan pada tulang dapat mengganggu proses gerakan yang normal. Kelainan dan gangguan pada tulang dapat terjadi karena kekurangan vitamin D, penyakit, kecelakaan atau karena kebiasaan yang salah dalam waktu lama.
a) Kekurangan Vitamin D
Vitamin D (kalsiferol) adalah vitamin yang diperlukan untuk kalsif ikasi (penulangan) pada tulang. Pada mamalia, vitamin D dapat disintesis oleh tubuh dari pro vitamin D dengan bantuan ultraviolet. Kekurangan vitamin
D dapat terjadi jika tubuh tidak menerima sinar matahari yang cukup. Kekurangan vitamin D pada anak-anak menyebabkan rakitis, biasanva terlihat pada pertumbuhannya yang terganggu dan kaki berbentuk O atau X. pada orang dewasa kekurangan viramin D dan zat kapur menyebabkan penyakit yang disebut osteomalasi.
b) Kecelakaan
Gangguan pada tulang dapat berupa memar dan fraktura seperti berikut ini:
1. Memar
Gangguan ini merupakan robeknya selaput sendi. Bila sobeknya selaput sendi diikuti lepasnya ujung tulang dari sendi disebut urai sendi.
2. Fraktura atau patah tulang dibedakan sebagai berikut:
a. Patah tulang tertutup bila tulang yang patah tidak merobek kulit.
b. Patah tulang terbuka , bila tulang yang patah merobek kulit dan mencuat keluar.
c. Fisura , bila tulang hanya retak.
c) kebiasaan yang salah
Kebiasaan duduk yang salah atau kebiasaan membawa beban disatu sisi tubuh saja dapat menyebabkan kelainan pada tulang seperti berikut ini:
1) Lordosis
Adalah jika tulang leher dan panggul terlalu bengkok kedepan.
2) Kifosis
Adalah jika tulang punggung dan tungging terlalu bengkok kebelakang. Kelainan ini dapat terjadi karena kebiasaan menulis yang terlalu membungkuk yang dilakukan selama bertahun – tahun.
3) Skoliosis
Skoliosis adalah jika ruas-ruas tulang belakang bengkok ke samping. Kelainan ini dapat terjadi jika seseorang sering membebani
salah satu sisi tulang belakang, dan kebiasaan ini dilakukan selama bertahun-tahun.
d) Nekrosa
Nekrosa terjadi bila selaput tulang (periosteum) rusak sehingga bagian tulang tidak memperoleh makanan, lalu mati dan mengering.
e) Gangguan persendian
Macam gangguan pada persendian antara lain dislokasi, ankilosis, artritis, dan terkilir.
i. Dislokasi
Dislokasi disebabkan bergesernya sendi dari kedudukan semula karena jaringan gantungnya (ligamentum) sobek.
ii. Ankilosis
Ankilosis adalah suatu keadaan persendian yang tidak dapat digerakkan karena seolah - olah menyatu.
iii. Terkilir
Terkilir adalah tertariknya ligamentum ke posisi yang tidak sesuai, tetapi sendi tidak bergeser. Terkilir dapat terjadi karena gerakan tiba-tiba atau gerakan yang jarang dan sulit dilakukan.
iv. Artritis
Artrisis adalah peradangan yang_terjadi pada sendi. Artrisis dapat dibedakan menjadi empat sebagai berikut:
a. Artritis Gout
Gout terjadi karena adanya timbunan asam urat pada sendi-sendi kecil terutama jari - jari tangan. Sebagai akibatnya ruas jari-jari membesar.
b. Osteoartritis
Osteoartritis adalah menipisnya tulang rawan sehingga mengalami degenerasi. Akibatnya, terjadi gangguan pada saat sendi digerakkan.
c. Artritis eskudatif
Artrisis eskudatif adalah terisinya rongga sendi oleh cairan yang disebut getah radang. Penyakit ini terjadi karena serangan kuman.
d. Artritis sika
Artrisis sika adalah berkurangnya minyak sendi yang menyebabkan rasa nyeri saat tulang digerakkan.
f) Serangan Kuman pada Sendi
Ø Infeksi gonorhoe dan sifilis dapat menyerang persendian sehingga sendi menjadi kaku. Layuh sendi adalah keadaan tidak bertenaga pada sendi yang disebabkan layuhnya tulang akibat infeksi sifilis ketika bayi dalam kandungan.
Otot merupakan alat gerak aktif yang mampu menggerakkan tulang, kulit dan rambut setelah mendapat rangsangan. Otot memiliki tiga kemampuan khusus yaitu :
- kontraktibilitas : kemampuan untuk berkontraksi / memendek
- Ekstensibilitas : kemampuan untuk melakukan gerakan kebalikan dari gerakan yang ditimbulkan saat kontraksi
- Elastisitas : kemampuan otot untuk kembali pada ukuran semula setelah berkontraksi. Saat kembali pada ukuran semula otot disebut dalam keadaan relaksasi
JENIS OTOT
1. otot lurik
- Nama lain: otot rangka, otot serat lintang (musculus striated) atau otot involunter
- Struktur : serabut panjang, berwarna/lurik dengan garis terang dan gelap, memiliki inti dalam jumlah banyak dan terletak dipinggir
- Kontraksi: menurut kehendak kita (dibawah kendali sistem syaraf pusat), gerakan cepat, kuat, mudah lelah dan tidak beraturan
- Struktur anatomi dari otot rangka seperti gambar dibawah ini!
2. Otot Polos
- Nama lain : otot alat-alat dalam / visceral / musculus nonstriated / otot involunter
- Struktur : bentuk serabut panjang seperti kumparan, dengan ujung runcing, dengan inti berjumlah satu terletak dibagiann tengah.
- Kontraksi : tidak menurut kehendaK atau diluar kendali sistem saraf pusat, gerakan lambat, ritmis dan tidak mudah lelah.
3. otot jantung
- Nama lain: Myocardium atau musculus cardiata atau otot involunter
- struktur : Bentuk serabutnya memanjang, silindris, bercabang. Tampak adanya garis terang dan gelap. memiliki satu inti yang terletak di tengah
- Kontraksi: tidak menurut kehendak, gerakan lambat, ritmis dan tidak mudah lelah
1. KOORDINASI BADAN
Koordinasi badan menyelaras aktiviti sistem-sistem dan organ-organ Koordinasi badan terdiri dari koordinasi saraf dan koordinasi kimia. Koordinasi badan penting supaya setiap anggota badan dapat berfungsi secara bersepadu.
2. SISTEM SARAF KITA
Sistem saraf kita berbahagi kepada 2 bahagian iaitu sistem saraf pusat dan sistem saraf periferi.
| | KOMPONEN DAN FUNGSINYA |
| SISTEM SARAF PUSAT | 1. OTAK - berfungsi sebagai pusat mentafsir maklumat.
2. SARAF TUNJANG - menyambungkan otak dengan saraf periferi dan juga sebagai pusat kawalan tindakan refleks. |
| SISTEM SARAF PERIFERI | 1. SARAF KRANIUM - menyambungkan otak dengan anggota di kepala seperti mata.
2. SARAF SPINA - menyambungkan bahagian lain dalam badan dengan saraf tunjang. |
Sistem saraf kita terbentuk dari rangkaian neuron-neuron. Neuron ialah sel saraf yang merupakan asas kepada sistem saraf yang berfungsi membawa impuls. Terdapat 3 jenis neuron. Neuron deria, neuron perantaraan dan neuron motor.
Fungsi setiap neuron adalah seperti berikut :-
| NEURON | FUNGSINYA |
| DERIA | Menerima ransangan, menjana impuls dan seterusnya menghantar impuls itu ke neuron perantaraan. |
| PERANTARAAN | Menerima impuls dari neuron deria dan menghantarnya ke neuron motor |
| MOTOR | Menerima impuls dari neuron perantaraan dan menghantar ke otot untuk gerak balas. |
Bahagian-bahagian dalam neuron pula mempunyai fungsi seperti dibawah :-
| BAHAGIAN NEURON | FUNGSI |
| BADAN SEL | Bahagian yang menempatkan nukleus dan berfungsi sebagai pusat aktiviti sel |
| AKSON | Membawa impuls keluar dari badan sel |
| DENDRON | Membawa impuls masuk ke dalam badan sel |
| SALUT MEILIN | Melindungi akson dan Dendron |
| SINAPS | Ruang khas diantara neuron-neuron yang membenarkan impuls mengalir dalam satu arah sahaja |
| RESEPTOR | Struktur khas pada neuron deria ini menjana impuls apabila ia menerima ransangan |
| EFEKTOR | Struktur khas pada neuron motor ini menerima impuls dari sistem saraf pusat dan melakukan gerak balas |
Sistem saraf manusia adalah istimewa. Kadang-kadang kita boleh bergerak balas dengan cepat dan otomatik apabila kita menerima ransangan yang mungkin memudaratkan kita. Gerak balas yang berlaku dengan cepat dan tanpa berfikir ini disebut sebagai "tindakan refleks". Tindakan refleks tidak melibatkan otak tetapi pergerakan impuls hanya melalui saraf tunjang sahaja. Contohnya apabila kita tersentuh sterika panas, gerak balas menarik tangan dengan cepat merupakan tindakan refleks. Tindakan ini memastikan badan kita tidak tercedera dengan teruk. Pergerakan impuls(maklumat) semasa tindakan refleks disebut "arka refleks" ialah :
Reseptor-->Neuron deria-->sinaps-->Neuron perantaraan-->Sinaps-->Neuron Motor-->Efektor
Ada sejenis tindakan refleks istimewa iaitu "Sentakan Lutut", arka refleknya TIDAK melibatkan neuron perantaraan.
Selain daripada reseptor biasa yang ditemui pada organ deria kita, para saintis telah mengenal pasti sejenis reseptor pada otot-otot dan tendon yang terlibat dengan pergerakan badan apabila kita melakukan aktiviti tanpa penglihatan. Reseptor ini disebur "reseptor regang". Reseptor regang terlibat secara langsung dalam Deria Kinestesis yang juga berfungsi mengimbangkan badan dan membolehkan seseorang mengkoordinasikan badan dalam keadaan gelap.
3. OTAK
Selain dari neuron-neuron, otak adalah bahagian yang terpenting dalam sistem saraf kita. Otak merupakan pusat kawalan semua aktiviti badan. Mari kita belajar mengenali otak.
Otak terdiri daripada 3 bahagian :-
a. SEREBRUM - mengawal deria dan tindakan terkawal.
b. SEREBELUM - mengawal keseimbangan badan.
c. MEDULA OBLONGATA - mengawal tindakan luar kawal seperti pergerakan jantung.
Tindakan terkawal dikawal oleh serebrum. Contoh tindakan terkawal ialah membaca, menunggang basikal dan menyanyi.
Tindakan luar kawal pula dikawal oleh medula oblongata. contoh tindakan luar kawal ialah degupan jantung, pergerakan usus ["peristalsis"] dan kadar pernafasan.
Otak juga membolehkan kita berupaya menaakul dan berfikir dengan baik. Ini menyebabkan seseorang manusia mempunyai minda. Minda yang baik dipengaruhi oleh faktor pemakanan, penyakit otak dan kecederaan otak semasa kemalangan.
Saintis telah mengenalpasti bahagian-bahagian serebrum yang mengawal aktiviti badan. Contohnya bahagian penghujung belakang serebrum terlibat dengan penglihatan dan tengah atasnya mengawal pergerakan anggota badan.
4. KOORDINASI KIMIA
Bergandingan dengan koordinasi saraf, koordinasi kimia dikawal oleh hormon dan kelenjar endokrin. Hormon adalah bahan kimia dalam badan yang mengawal aktiviti badan. Hormon dihasilkan oleh bahagian badan yang disebut sebagai kelenjar endokrin. Kelenjar endokrin juga digelar "kelenjar tanpa duktus" kerana ia membebaskan hormon terus ke dalam aliran darah kita.
Manusia mempunyai 6 jenis kelenjar endokrin utama iaitu :-
a. Pituitari - terletak dalam otak ia mengawal kelenjar lain serta berfungsi dalam pertumbuhan.
b. Tiroid - terletak di tepi leher ia mengawal metabolisme, perkembangan otak.
c. Adrenal - terletak di atas ginjal ia menolong seseorang menghadapi kecemasan.
d. Pankreas - terletak di pankreas ia mengawal aras gula dalam darah.
e. Ovari (perempuan) - terletak dalam ovari ia mengawal perkembangan seks.
f. Testis (lelaki) - terletak dalam testis ia mengawal perkembangan seks.
Jika kuantiti hormon ini tidak seimbang ia akan mencacatkan aktiviti badan. contohnya jika hormon yang dikeluarkan dari pankreas tidak mencukupi, seseorang akan menghidap penyakit kencing manis.
5. PERBANDINGAN KOORDINASI SARAF DAN KOORDINASI KIMIA
Walaupun kedua-dua koordinasi saraf dan koordinasi kimia berfungsi mengkoordinasikan aktiviti badan, namun kita boleh membandingkan dan membezakan kedua-duanya.
| KOORDINASI SARAF | KOORDINASI KIMIA |
| Dikawal oleh sistem saraf | Dikawal oleh sistem endokrin |
| Maklumat dihantar dalam bentuk IMPULS | Maklumat dihantar dalam bentuk HORMON |
| Gerak balasnya boleh dipercepat atau diperlambatkan | Gerak balas adalah lambat |
| Pusat kawalan adalah otak dan saraf tunjang | Pusat kawalan adalah kelenjar-kelenjar |
6. DADAH MENGGANGGU KOORDINASI !!!
Walaupun kita telah dikurniakan dengan badan yang mampu mengkoordinasikan aktivitinya terdapat 2 bahan yang boleh mengganggunya. Bahan itu ialah dadah dan alkohol.
Dadah merupakan bahan kimia yang boleh mengubah fungsi badan. Contoh dadah ialah heroin. Dadah dikenali sebagai "bahan psikoaktif" kerana ia mampu mengubah perlakuan seseorang setelah menyerang sistem saraf kita.
Pengambilan dadah boleh mendatangkan kesan buruk kepada badan kita.
Kesan dadah secara :-
a. Fizikal - mata merah, hidung berair.
b. Mental - gila, tidak boleh menumpukan perhatian.
c. Psikologi - tidak waras, marah-marah.
d. Fisiologi - gerakbalas lambat, imuniti lemah.
e. Sosial - tidak mahu bergaul dan menimbulkan masaalah seperti mencuri dan menghisap gam.
f. Ekonomi - hilang sumber pendapatan dan menghabiskan duit kerajaan.
7. ALKOHOL JUGA MERBAHAYA !!
Alkohol menjejaskan fungsi otak dan koordinasi badan. Keadaan ini mengakibatkan peningkatan kadar kemalangan serta masaalah rumah tangga. Pengambilan alkohol juga boleh mencacatkan bayi dalam kandungan.
8. JAGALAH BADAN ANDA
Setelah mempelajari koordinasi badan, kita seharusnya menghargai fungsi koordinasi saraf dan koordinasi kimia. Dengan adanya kedua-dua koordinasi ini badan kita boleh melakukan aktiviti dengan sempurna. Penjagaan kesihatan mental juga penting supaya kita hidup dalam harmoni dan bahagia. Kita hendaklah menjauhkan diri dari gejala penyalahgunaan dadah serta ketagihan alkohol.
Disediakan oleh Johnny Lim
| 1. Terdapat 3 jenis bendalir di dalam badan manusia, iaitu: (a) Darah (b) Limfa (c) Bendalir tisu 2. Jantung merupakan organ berotot yang berfungsi untuk mengepam dan
mengedarkan darah ke seluruh tubuh badan. Rajah 1: Struktur keratan membujur jantung 3. Bahagian utama jantung ialah: 4. Injap-injap di jantung seperti injap bikuspid, trikuspid dan injap sabit
memastikan darah mengalir dalam satu arah sahaja. 5. Peredaran darah manusia melibatkan dua sistem peredaran: (a) sistem peredaran sistemik (b) sistem peredaran pulmonari 6. Sistem peredaran pulmonari melibatkan peredaran darah terdeoksigen dari
ventrikel ke peparu dan darah beroksigen dari peparu ke aurikel kiri. 7. Sistem peredaran sistemik melibatkan peredaran darah beroksigen dari
ventrikel kiri ke seluruh badan dan darah terdeoksigen dari seluruh badan ke aurikel kanan jantung. Rajah 2: Sistem peredaran darah manusia
8. Terdapat dua sistem utama peredaran darah di kalangan organisma, iaitu: Sistem peredaran darah
Tertutup Terbuka 9. Rumusan (Peta Minda) SISTEM PEREDARAN DARAH MANUSIA Struktur Alat Peredaran Darah Pada Manusia Sistem peredaran darah pada manusia tersusun atas jantung sebagai pusat peredaran darah, pembuluh-pembuluh darah dan darah itu sendiri. 1. Jantung Jantung mempunyai empat ruang yang terbagi sempurna yaitu dua serambi (atrium) dan dua bilik (ventrikel) dan terletak di dalam rongga dada sebelah kiri di atas diafragma. Jantung terbungkus oleh kantong perikardium yang terdiri dari 2 lembar :
a. lamina panistalis di sebelah luar
b. lamina viseralis yang menempel pada dinding jantung Jantung memiliki katup atrioventikuler (valvula bikuspidal) yang terdapat di antara serambi dan bilik jantung yang berfungsi mencegah aliran dari bilik keserambi selama sistol dan katup semilunaris (katup aorta dan pulmonalis) yang berfungsi mencegah aliran balik dari aorta dan arteri pulmonalis kiri ke bilik selama diastole.
2. Pembuluh Darah Pembuluh darah terdiri atas arteri dan vena. Arteri berhubungan langsung dengan vena pada bagian kapiler dan venula yang dihubungkan oleh bagian endotheliumnya. Arteri dan vena terletak bersebelahan. Dinding arteri lebih tebal dari pada dinding vena. Dinding arteri dan vena mempunyai tiga lapisan yaitu lapisan bagian dalam yang terdiri dari endothelium, lapisan tengah yang terdiri atas otot polos dengan serat elastis dan lapisan paling luar yang terdiri atas jaringan ikat ditambah dengan serat elastis. Cabang terkecil dari arteri dan vena disebut kapiler. Pembuluh kapiler memiliki diameter yang sangat kecil dan hanya memiliki satu lapisan tunggal endothelium dan sebuah membran basal. Perbedaan struktur masing-masing pembuluh darah berhubungan dengan perbedaan fungsional masing-masing pembuluh darah tersebut. |
The Human Respiratory System
- Air enters the nostrils
- passes through the nasopharynx,
- the oral pharynx
- through the glottis
- into the trachea
- into the right and left bronchi, which branches and rebranches into
- bronchioles, each of which terminates in a cluster of
- alveoli
Only in the alveoli does actual gas exchange takes place. There are some 300 million alveoli in two adult lungs. These provide a surface area of some 160 m2 (almost equal to the singles area of a tennis court and 80 times the area of our skin!).
Breathing
In mammals, the diaphragm divides the body cavity into the
- abdominal cavity, which contains the viscera (e.g., stomach and intestines) and the
- thoracic cavity, which contains the heart and lungs.
The inner surface of the thoracic cavity and the outer surface of the lungs are lined with pleural membranes which adhere to each other. If air is introduced between them, the adhesion is broken and the natural elasticity of the lung causes it to collapse. This can occur from trauma. And it is sometimes induced deliberately to allow the lung to rest. In either case, reinflation occurs as the air is gradually absorbed by the tissues.
Because of this adhesion, any action that increases the volume of the thoracic cavity causes the lungs to expand, drawing air into them.
- During inspiration (inhaling),
- The external intercostal muscles contract, lifting the ribs up and out.
- The diaphragm contracts, drawing it down .
- During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breath 15-18 times a minute exchanging about 500 ml of air.
- In more vigorous expiration,
- The internal intercostal muscles draw the ribs down and inward
- The wall of the abdomen contracts pushing the stomach and liver upward.
Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. This is called the vital capacity. Even with maximum expiration, about 1200 ml of residual air remain.
The table shows what happens to the composition of air when it reaches the alveoli. Some of the oxygen dissolves in the film of moisture covering the epithelium of the alveoli. From here it diffuses into the blood in a nearby capillary. It enters a red blood cell and combines with the hemoglobin therein.
At the same time, some of the carbon dioxide in the blood diffuses into the alveoli from which it can be exhaled.
| Composition of atmospheric air and expired air in a typical subject.
Note that only a fraction of the oxygen inhaled is taken up by the lungs. |
| Component | Atmospheric Air (%) | Expired Air (%) |
| N2 (plus inert gases) | 78.62 | 74.9 |
| O2 | 20.85 | 15.3 |
| CO2 | 0.03 | 3.6 |
| H2O | 0.5 | 6.2 |
|
| 100.0% | 100.0% |
The ease with which oxygen and carbon dioxide can pass between air and blood is clear from this electron micrograph of two alveoli (Air) and an adjacent capillary from the lung of a laboratory mouse. Note the thinness of the epithelial cells (EP) that line the alveoli and capillary (except where the nucleus is located). At the closest point, the surface of the red blood cell is only 0.7 µm away from the air in the alveolus. (Reproduced with permission from Keith R. Porter and Mary A. Bonneville, An Introduction to the Fine Structure of Cells and Tissues, 4th. ed., Lea & Febiger, 1973.)
The rate of cellular respiration (and hence oxygen consumption and carbon dioxide production) varies with level of activity. Vigorous exercise can increase by 20-25 times the demand of the tissues for oxygen. This is met by increasing the rate and depth of breathing.
It is a rising concentration of carbon dioxide — not a declining concentration of oxygen — that plays the major role in regulating the ventilation of the lungs. The concentration of CO2 is monitored by cells in the medulla oblongata. If the level rises, the medulla responds by increasing the activity of the motor nerves that control the intercostal muscles and diaphragm.
However, the carotid body in the carotid arteries does have receptors that respond to a drop in oxygen. Their activation is important in situations (e.g., at high altitude in the unpressurized cabin of an aircraft) where oxygen supply is inadequate but there has been no increase in the production of CO2.
The smooth muscle in the walls of the bronchioles is very sensitive to the concentration of carbon dioxide. A rising level of CO2 causes the bronchioles to dilate. This lowers the resistance in the airways and thus increases the flow of air in and out.
SYRUCTURE OF THE HUMAN RESPIRATORY SYSTEM
Usually air will enter the respiratory system through the nostrils. The nostrils then lead to open spaces in the nose called the nasal passages. The nasal passages serve as a moistener, a filter, and to warm up the air before it reaches the lungs. The hairs existing within the nostrils prevents various foreign particles from entering. Different air passageways and the nasal passages are covered with a mucous membrane. Many of the cells which produce the cells that make up the membrane contain cilia. Others secrete a type a sticky fluid called mucus. The mucus and cilia collect dust, bacteria, and other particles in the air. The mucus also helps in moistening the air. Under the mucous membrane there are a large number of capillaries. The blood within these capillaries helps to warm the air as it passes through the nose. The nose serves three purposes. It warms, filters, and moistens the air before it reaches the lungs. You will obviously lose these special advantages if you breath through your mouth.
Air travels from the nasal passages to the pharynx, or more commonly known as the throat. When the air leaves the pharynx it passes into the larynx, or the voice box. The voice box is constructed mainly of crtilage, which is a flexible connective tissue. The vocal chords are two pairs of membranes that are stretched across the inside of the larynx. As the air is exspired, the vocal chords vibrate. Humans can control the vibrations of the vocal chords, which enables us to make sounds. Food and liquids are blocked from entering the opening of the larynx by the epiglottis to prvent people from choking during swallowing.
Trachea –
The larynx goes directly into the trachea or the windpipe. The trachea is a tube approximately 12 centimeters in length and 2.5 centimeters wide. The trachea is kept open by rings of cartilage within its walls. Similar to the nasal passages, the trachea is covered with a ciliated mucous membrane. Usually the cilia move mucus and trapped foreign matter to the pharynx. After that, they leave the air passages and are normally swallowed. The respiratory system cannot deal with tabacco smoke very keenly. Smoking stops the cilia from moving. Just one cigarette slows their motion for about 20 minutes. The tabacco smoke increases the amount of mucus in the air passages. When smokers cough, their body is attempting to dispose of the extra mucus.
- Around the center of the chest, the trachea divides into two cartilage-ringed tubes called bronchi. Also, this section of the respiratory system is lined with ciliated cells. The bronchi enter the lungs and spread into a treelike fashion into smaller tubes calle bronchial tubes.
The bronchial tubes divide and then subdivide. By doing this their walls become thinner and have less and less cartilage. Eventually, they become a tiny group of tubes called bronchioles.
Each bronchiole ends in a tiny air chamber that looks like a bunch of grapes. Each chamber contains many cup-shaped cavities known as alveoli. The walls of the alveoli, which are only about one cell thick, are the respiratory surface. They are thin, moist, and are surrounded by several numbers of capillaries. The exchange of oxygen and carbon dioxide between blood and air occurs through these walls. The estimation is that lungs contain about 300 million alveoli. Their total surface area would be about 70 square meters. That is 40 times the surface area of the skin. Smoking makes it difficult for oxygen to be taken through the alveoli. When the cigarette smoke is inhaled, about one-third of the particles will remain within the alveoli. There are too many particles from smoking or from other sources of air pollution which can damage the walls in the alveoli. This causes a certain tissue to form. This tissue reduces the working area of the respiratory surface and leads to the disease called emphysema.
Diseases of the Lungs
Pneumonia is an infection of the alveoli. It can be caused by many kinds of both bacteria (e.g., Streptococcus pneumoniae) and viruses. Tissue fluids accumulate in the alveoli reducing the surface area exposed to air. If enough alveoli are affected, the patient may need supplemental oxygen.
In asthma, periodic constriction of the bronchi and bronchioles makes it more difficult to breathe in and, especially, out. Attacks of asthma can be
- triggered by airborne irritants such as chemical fumes and cigarette smoke
- airborne particles to which the patient is allergic.
Pandangan anterior keratan rentas jantung. Anak panah putih menunjukkan arah darah bergerak
Setiap degupan jantung melibatkan turutan yang dikenali sebagai "kitar kardiak". Ia terbahagi kepada tiga bahagian: "sistol atrium" (atrial systole), "sistol ventrikel" (ventricular systole) dan "diastol kardiak sepenuhnya" (complete cardiac diastole). Sistol atrium adalah pengecutan kedua-dua atrium, sistol ventrikel adalah pengecutan kedua-dua ventrikel, manakala diastol kardiak pula merupakan pengenduran keseluruhan otot-otot jantung.
Apabila sistol atrium berlaku, injap atrioventrikular (atrioventricular valves) akan terbuka. Darah dipam masuk ke dalam ventrikel. Apabila sistol atrium berakhir, sistol ventrikel pula bermula. Tekanan tinggi dalam ventrikel menyebabkan injap atrioventrikular tertutup, dan injap sabit (semilunar valves) terbuka. Ini menyebabkan darah hanya dipam ke dalam aorta dan arteri pulmonari tetapi tidak ke dalam atrium.
Diastol kardiak berlaku setelah darah dipam keluar dari jantung. Pada masa ini, darah di dalam aorta akan mengalir balik ke dalam jantung, tetapi ini tidak berlaku kerana penutupan injap sabit.
Bunyi jantung yang kita dengari adalah disebabkan oleh penutupan injap atrioventrikular (bunyi pertama) dan penutupan injap sabit (bunyi kedua).
Aturan kitar kardiak
Otot kardiak adalah myogenik. Ini bererti bahawa berbeza dengan otot rangka yang memerlukan rangsangan (sama ada sedar atau reflex), rangsangan otot jantung adalah secara automatik. Pengecutan berirama berlaku sendiri, walaupun frekuensi boleh berubah disebabkan keresahan, kesan hormon, senaman atau berasa terancam.
Irama pengecutan diselaraskan oleh node sinoatrial dan node atrioventrikular. Node sinoatrial, sering dikenali sebagai perentak jantung, terletak di bahagian atas dinding atrium kanan dan bertanggungjawab menghasilkan impuls eletrik yang memulakan pengecutan atrium. Apabila impuls ini tiba di node atrioventrikular yang terletak di dinding antara ruang ventrikel, ia akan dilambatkan sedikit. Ini bertujuan memastikan atrium telah mengecut sepenuhnya. Selepas itu, impuls ini dialirkan melalui berkas His (bundle of His) di dalam septum dan dialirkan ke dalam dinding-dinding ventrikel. Impuls ini menyebabkan pengecutan ventrikel berlaku.
Jantung mampu terus berdegup walaupun setelah dikeluarkan dari tubuh manusia yang hidup. Perkara ini terus menakjubkan manusia sepanjang zaman. Malah kaum Aztec yang tinggal di Amerika Selatan telah begitu kagum dengan keupayaan jantung berdegup di luar tubuh ini, sehinggakan mereka mengamalkan pengorbanan manusia dengan meragut keluar jantung dari mangsa pengorbanan hidup-hidup sebagai bahan persembahan kepada dewa matahari.
PENGENALAN
Penghadaman ialah satu proses penghancuran atau pengisaran makanan secara fizikal, kemudiannya diikuti dengan beberapa proses kimia bagi memecahkan molekul makanan yang kompleks menjadi molekul atau elemen yang lebih halus dan terasing bagi memudahkan proses penyerapan. Bahan yang tidak dapat dimanfaatkan atau dipecahkan akan dibuang menerusi proses seterusnya yang dikenali sebagai penyingkiran.
PENGHADAMAN
Penghadaman bermula apabila makanan memasuki tubuh menerusi mulut. Poses ini juga turut melibatkan organ-organ lain seperti kelenjar liur, hati, pundi hempedu dan pankerias.
Mulut
Dalam mulut, makanan dipotong serta dikunyah oleh gigi dengan bantuan air liur yang melembutkan makanan dan memecahkan beberapa karbohidrat tertentu. Selepas kunyahan ditelan, gumpalan makanan yang dipanggil bolus memasuki kerongkong.
Kerongkong
Makanan dalam bentuk bolus dibawa ke perut melalui kerongkong menerusi gerakan peristalsis.
Perut
Cecair gastrik yang dibebaskan oleh dinding perut terus menguraikan secara pengisaran terutamanya ke atas bahan-bahan protein dalam makanan dengan tindakbalas asid hidroklorik serta enzim penghadaman pepsin kepada peptid. Makanan kekal di dalam perut sehingga ia berubah menjadi elemen separa cair yang dikenali sebagai chyme sebelum ia memasuki duodenam.
Usus kecil (Duodenum)
Sepanjang duodenum yang panjangnya 30 cm, makanan terus diuraikan lagi oleh enzim penghadaman daripada pundi hempedu dan pankerias, juga cecair dari dalam usus kecil itu sendiri kepada bentuk makanan yang lebih halus lagi.
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| Kelenjar | Fungsi Enzim | Hasil |
| 1 | Hempedu | Menyerap dan menguraikan lemak | Lemak halus (droplet) |
| 2 | Pankerias | amylase bertindak ke atas kanji. lipase bertindak ke atas lemak. trypsin betindak ke atas protein. | Dextrin dan maltose Fatty acid dan gliserol Acid amino |
| 3 |
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Usus kecil (illium)
Di dalam illium sepanjang 6 meter ini, enzim-enzim tambahan yang dirembeskan oleh kelenjar-kelenjar di sepanjang usus kecil melengkapkan proses penghadaman. Nutrien-nutrien diserap menerusi dinding usus dan dihantar ke rangkaian pembuluh darah dan pembuluh limfa yang terdapat di sekitar usus. Manakala bahan-bahan yang tidak terhadam dibawa ke usus besar.
Usus besar
Air di dalam bahan-bahan yang tidak terhadam akan diserap di sepanjang usus besar, manakala bakinya akan memasuki rektum.
Rektum
Bahan-bahan sisa yang tidak terhadam akan dihantar bahagian akhir usus besar dan seterusnya dibuang keluar sebagai najis menerusi dubur.
PENYERAPAN
Penyerapan ialah satu proses apabila air, garam dan hasil pencernaan unsur makanan dari lumen usus diserap melalui membran ke dalam sel mukosa usus dan seterusnya ke dalam sistem peredaran darah untuk diedarkan kepada tisu sasaran di dalam tubuh. Sekiranya sistem yang terlibat dalam proses penyerapan ini rosak, maka nutrien tidak akan dapat disalurkan kepada sel-sel secara berkesan.
Pada tubuh manusia, kebanyakan penyerapan berlaku di dalam usus kecil. Secara umumnya, usus tidak boleh menyerap molekul yang lebih kompleks daripada gula heksosa (glukosa, fruktosa dan galaktosa), asid amino, asid lemak dan gliserol. Untuk memudahkan penyerapan hasil pencernaan, dinding usus telah dijadikan oleh Allah S.W.T. mempunyai permukaan yang luas bagi membolehkan penyerapan berlaku dengan lebih berkesan. Ciri-ciri dinding usus yang diperlukan termasuk:
| | usus yang panjang |
| | mempunyai beribi-ribu vilus pada permukaan dinding dalam usus kecil dan duodenum |
| | mempunyai beribu-ribu mikrovilus pada setiap sel mukosa dinding usus. |
Tambahan pula, usus kecil mempunyai sistem kapilari darah yang luas supaya hasil pencernaan boleh diangkut dengan cepat dari tapak serapan ke hati melalui venal portal hati.
Nutrien yang diserap ke dalam sistem peredaran darah, sebahagian besarnya akan dibawa ke hati melalui vena portal dan dari situ nutrien akan diedarkan ke tisu-tisu lain. Lemak yang masuk ke dalam sistem limfa akan dibawa masuk ke dalam duktus toraks dan kemudian ke dalam peredaran vena.
Sebaik sahaja nutrien-nutrien masuk ke dalam tisu, satu proses osmosis berlaku dimana nutrien di dalam salur darah yang berada pada kepekatan tinggi akan diserap oleh sel-sel yang berada pada kepekatan rendah. Begitu juga akan berlaku perpindahan oksigen daripada salur darah kepada sel mengikut cara yang sama walaupun mekanismanya agak rumit.
Nutrien dan kegunaan
| Bil | Nutrien | Keterangan |
| 1 | Karbohidrat | Diserap dalam bentuk glukosa, galaktosa dan fruktosa. Glukosa dan galaktosa diserap 2kali lebih cepat daripada fruktosa. Sumber tenaga. |
| 2 | Gula monosakarida | Diserap secara pengangkutan aktif bertentangan dengan cerun kepekatan. |
| 3 | Protein | Diserap dalam bentuk asid amino dan dipeptida melalu pengangkutan aktif. Untuk pembinaan enzim dan komponen struktural bagi sel. |
| 4 | Lemak | Diserap dalam bentuk asid lemak dan gliserol dan juga sebagai titisan lemak. Digunakan untuk sumber tenaga dan pembinaan molekul biologikal. |
| 5 | Vitamin dan garam mineral | Diserap dalam bentuk asal, iaitu tidak dicernakan. Digunakan untuk proses metabolisme. |
| 6 | Antioksidan | Melawan oksidasi dan radikal bebas, anti kanser. |
| 7 | Fitokimia | Memelihara kesihatan |
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ASIMILASI
Asimilasi ialah proses menggabungkan hasil pencernaan atau nutrien yang mudah kepada juzuk-juzuk kompleks dalam hidupan. Proses asimilasi tidak semestinya berlaku selepas penyerapan kerana bahan yang diserap ke dalam kapilari darah usus dibawa oleh vena portal hepar ke hati untuk diproses dan disediakan bagi kegunaan metabolisme atau asimilasi.
Kebanyakan gula ringkas ditukarkan kepada glikogen untuk disimpan di dalam hati dan otot, dan yang lain diedarkan ke seluruh tubuh untuk respirasi sel. Glikogen yang berlebihan ditukar kepada lipid yang disimpan dalam pelbagai tapak simpanan lipid (lemak).
Gliserol dan asid lemak diangkut ke tapak simpanan lipid dalam bentuk titisan lipid dan sebahagiannya sebagai fospolipid. Ia disimpan di bawah kulit, disekeliling jantung dan ginjal serta mesenteri. Lipid yang diperlukan oleh sel dikeluarkan dari simpanan dan dibawa ke hati untuk pembinaan komponen sel atau penghasilan tenaga.
Asid amino yang diperlukan oleh tubuh untuk pertumbuhan, pembaikan tisu dan aktiviti rembesan diedarkan dari hati ke seluruh tubuh melalui sistem peredaran darah; sementara yang berlebihan digunakan untuk menghasilkan kumpulan amino dan bahan kumuh bernitrogen. Ada juga yang ditukarkan kepada asid keto yang kebanyakannya digunakan dalam metabolisme karbohidrat.
Sebahagian vitamin seperti vitamin A, D, K dan B2 boleh disimpan dalam hati; sementara yang lain jika berlebihan akan diproses oleh hati dan ditapis keluar dari darah oleh ginjal.
Metabolisme adalah merujuk kepada satu istilah kolektif bagi segala proses kimiawi yang berlaku di dalam tubuh nmanusia. Metabolisme terbahagi kepada 2 :
| | katabolik - bahan yang bersifat kompleks diuraikan menjadi unit ringkas; selalunya disertai dengan pembebasan tenaga. Contohnya pembakaran glukosa dalam sel tubuh bagi menghasilkan tenaga dan produk sampingan iaiatu karbon dioksida dan air. |
| | anabolik - bahan yang bersifat komplek dibina daripada juzuk-juzuk yang ringkas; juga biasanya disertakan dengan pembebasan tenaga.Contohnya sintesis protein kompleks daripada asid amino. |
PERGERAKAN DAN KORDINASI SISTEM ENDOKRIN
| 1. | Sistem endokrin terdiri daripada beberapa kelenjar tanpa duktus yang merembeskan hormon terus ke dalam sistem peredaran darah. Rajah 1 menunjukkan kedudukan kelenjar endokrin dalam manusia.
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| 2. | Hormon ialah bahan kimia yang disintesiskan oleh kelenjar endokrin yang merembeskannya terus ke dalam sistem peredaran darah. |
| 3. | Jadual 1 menunjukkan kelenjar endokrin yang utama, hormon yang dirembeskan dan fungsi hormon berkenaan. |
| Kelenjar | Hormon yang dirembeskan | Fungsi |
| Pituitari (Kelenjar agung) | a. Hormon pertumbuhan (GH) | Merangsang pertumbuhan badan |
| b. Hormon perangsang tiroid (TSH) | Merangsang kelenjar tiroid merembeskan hormon tiroksina. |
| c. Hormon antidiuresis (ADH) | Merangsang penyerapan semula air dari tubul ginjal. |
| d. Hormon perangsang folikel (FSH) | Merangsang perkembangan folikel Graaf dan tubul semen. |
| e. Hormon peluteinan (LH) | Menyebabkan pembebasan ovum daripada ovari dan perkembangan folikel menjadi korpus luteum.
Merangsang perembesan hormon seks oleh ovari dan testis. |
| f. Hormon adrenokortikotrof (ACTH) | Merangsang korteks adrenal menghasilkan hormon. |
| g. Hormon prolaktin | Merangsang perembesan susu oleh kelenjar susu. |
| h. Hormon oksitosin | Merangsang pengecutan otot uterus semasa bersalin. |
| Tiroid | Tiroksina | Mengawal kadar metabolisme sel badan, khususnya respirasi dalam mitokondria.
Mengawal aras aktiviti, menggalakkan pertumbuhan yang normal bagi rangka dan perkembangan mental. |
| Kelompok sel Langerhans dalam pankreas | Insulin Glukagon | Menyebabkan penukaran glikosa kepada glikogen.
Menyebabkan penukaran glikogen kepada glukosa. |
| Adrenal | Adrenalina Aldosteron | Menyediakan badan untuk menentang atau lari dalam keadaan kecemasan dengan merangsang peningkatan aras glukosa dalam darah. Mengawal tekanan osmosis darah melalu penyerapan semula ion natrium. |
| Ovari | Estrogen Progesteron | Merangsang perkembangan organ seks perempuan dan ciri seks sekunder seperti perkembangan kelenjar susu dan pembesaran buah dada. Menyebabkan dinding uterus menebal untuk penempelan uterus. |
| Testis | Testosteron | Merangsang perkembangan organ seks lelaki dan ciri seks sekunder seperti pertumbuhan misai dan suara menjadi kasar.
Merangsang spermatogenensis. |
Jadual 1
| 4. | Hormon juga digunakan di dalam bidang perubatan dan penternakan: |
| | (a) | Perubatan |
| | | i. | Kanak-kanak yang mengalami kretinisme diberi suntikan hormon tiroksina dan hormon pertumbuhan. |
| | | ii | Pesakit diabetes mellitus diberikan suntikan insulin. |
| | | iii | Penyakit lain yang disebabkan kekurangan hormon adalah seperti diabetes insipidus (kekurangan hormon ADH) dan miksodema (kekurangan tiroksina) |
| | | iv. | Estrogen diberikan kepada wanita untuk mencegah osteoporosis. |
| | | v. | Rawatan hormon kortisol untuk pesakit asma. |
| | (b) | Penternakan |
| | | i. | Estrogen sintetik iaitu dietilstilbestrol(DES) digunakan untuk merangsang pertumbuhan lembu. |
| | | ii. | Bovine Somatotrophine (BST) untuk meningkatan penghasilan susu dalam lembu. |
TIP
Pelajar perlu ada penguasaan secara masteri untuk kedudukan kelenjar dalam sistem endokrin, hormon yang dirembeskan, fungsi hormon dan kesan keurangan serta kelebihan hormon berkenaan.
The principal function of the urinary system is to maintain the volume and composition of body fluids within normal limits. One aspect of this function is to rid the body of waste products that accumulate as a result of cellular metabolism. Other aspects of its function include regulating the concentrations of various electrolytes in the body fluids and maintaining normal pH of the blood.
In addition to maintaining fluid homeostasis in the body, the urinary system controls red blood cell production by secreting the hormone erythropoietin. The urinary system also plays a role in maintaining normal blood pressure by secreting the enzyme renin.
The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys form the urine and account for the other functions attributed to the urinary system. The ureters carry the urine away from kidneys to the urinary bladder, which is a temporary reservoir for the urine. The urethra is a tubular structure that carries the urine from the urinary bladder to the outside.
Kidneys
The kidneys are the primary organs of the urinary system. The kidneys are the organs that filter the blood, remove the wastes, and excrete the wastes in the urine. They are the organs that perform the functions of the urinary system. The other components are accessory structures to eliminate the urine from the body.
The paired kidneys are located between the twelfth thoracic and third lumbar vertebrae, one on each side of the vertebral column. The right kidney usually is slightly lower than the left because the liver displaces it downward. The kidneys protected by the lower ribs, lie in shallow depressions against the posterior abdominal wall and behind the parietal peritoneum. This means they are retroperitoneal. Each kidney is held in place by connective tissue, called renal fascia, and is surrounded by a thick layer of adipose tissue, called perirenal fat, which helps to protect it. A tough, fibrous, connective tissue renal capsule closely envelopes each kidney and provides support for the soft tissue that is inside.
In the adult, each kidney is approximately 3 cm thick, 6 cm wide, and 12 cm long. It is roughly bean-shaped with an indentation, called the hilum, on the medial side. The hilum leads to a large cavity, called the renal sinus, within the kidney. The ureter and renal vein leave the kidney, and the renal artery enters the kidney at the hilum.
The outer, reddish region, next to the capsule, is the renal cortex. This surrounds a darker reddish-brown region called the renal medulla. The renal medulla consists of a series of renal pyramids, which appear striated because they contain straight tubular structures and blood vessels. The wide bases of the pyramids are adjacent to the cortex and the pointed ends, called renal papillae, are directed toward the center of the kidney. Portions of the renal cortex extend into the spaces between adjacent pyramids to form renal columns. The cortex and medulla make up the parenchyma, or functional tissue, of the kidney.
The central region of the kidney contains the renal pelvis, which is located in the renal sinus and is continuous with the ureter. The renal pelvis is a large cavity that collects the urine as it is produced. The periphery of the renal pelvis is interrupted by cuplike projections called calyces. A minor calyx surrounds the renal papillae of each pyramid and collects urine from that pyramid. Several minor calyces converge to form a major calyx. From the major calyces the urine flows into the renal pelvis and from there into the ureter.
Each kidney contains over a million functional units, called nephrons, in the parenchyma (cortex and medulla). A nephron has two parts: a renal corpuscle and a renal tubule. The renal corpuscle consists of a cluster of capillaries, called the glomerulus, surrounded by a double-layered epithelial cup, called the glomerular capsule. An afferent arteriole leads into the renal corpuscle and an efferent arteriole leaves the renal corpuscle. Urine passes from the nephrons into collecting ducts then into the minor calyces. The juxtaglomerular apparatus, which monitors blood pressure and secretes renin, is formed from modified cells in the afferent arteriole and the ascending limb of the nephron loop.
Ureter
Each ureter is a small tube, about 25 cm long, that carries urine from the renal pelvis to the urinary bladder. It descends from the renal pelvis, along the posterior abdominal wall, behind the parietal peritoneum, and enters the urinary bladder on the posterior inferior surface.
The wall of the ureter consists of three layers. The outer layer, the fibrous coat, is a supporting layer of fibrous connective tissue. The middle layer, the muscular coat, consists of inner circular and outer longitudinal smooth muscle. The main function of this layer is peristalsis to propel the urine. The inner layer, the mucosa, is transitional epithelium that is continuous with the lining of the renal pelvis and the urinary bladder. This layer secretes mucus which coats and protects the surface of the cells.
The urinary bladder is a temporary storage reservoir for urine. It is located in the pelvic cavity, posterior to the symphysis pubis, and below the parietal peritoneum. The size and shape of the urinary bladder varies with the amount of urine it contains and with pressure it receives from surrounding organs.
The inner lining of the urinary bladder is a mucous membrane of transitional epithelium that is continuous with that in the ureters. When the bladder is empty, the mucosa has numerous folds called rugae. The rugae and transitional epithelium allow the bladder to expand as it fills.
The second layer in the walls is the submucosa that supports the mucous membrane. It is composed of connective tissue with elastic fibers.
The next layer is the muscularis, which is composed of smooth muscle. The smooth muscle fibers are interwoven in all directions and collectively these are called the detrusor muscle. Contraction of this muscle expels urine from the bladder. On the superior surface, the outer layer of the bladder wall is parietal peritoneum. In all other regions, the outer layer is fibrous connective tissue.
There is a triangular area, called the trigone, formed by three openings in the floor of the urinary bladder. Two of the openings are from the ureters and form the base of the trigone. Small flaps of mucosa cover these openings and act as valves that allow urine to enter the bladder but prevent it from backing up from the bladder into the ureters. The third opening, at the apex of the trigone, is the opening into the urethra. A band of the detrusor muscle encircles this opening to form the internal urethral sphincter.
Urethra
The final passageway for the flow of urine is the urethra, a thin-walled tube that conveys urine from the floor of the urinary bladder to the outside. The opening to the outside is the external urethral orifice. The mucosal lining of the urethra is transitional epithelium. The wall also contains smooth muscle fibers and is supported by connective tissue.
The internal urethral sphincter surrounds the beginning of the urethra, where it leaves the urinary bladder. This sphincter is smooth (involuntary) muscle. Another sphincter, the external urethral sphincter, is skeletal (voluntary) muscle and encircles the urethra where it goes through the pelvic floor. These two sphincters control the flow of urine through the urethra.
In females, the urethra is short, only 3 to 4 cm (about 1.5 inches) long. The external urethral orifice opens to the outside just anterior to the opening for the vagina.
In males, the urethra is much longer, about 20 cm (7 to 8 inches) in length, and transports both urine and semen. The first part, next to the urinary bladder, passes through the prostate gland and is called the prostatic urethra. The second part, a short region that penetrates the pelvic floor and enters the penis, is called the membranous urethra. The third part, the spongy urethra, is the longest region. This portion of the urethra extends the entire length of the penis, and the external urethral orifice opens to the outside at the tip of the penis.
The integumentary system includes the largest organ in the human body the skin. The system also includes the projections from the skin, the hair and nails, and the receptors that allow the skin to be a sensory organ. The purpose of the integument is to protect the underlying tissue from foreign particles, damage, and water loss. In humans, the skin is also responsible for producing Vitamin D.
LAYERS OF THE SKIN
The outer layer of the skin is the epidermis. It is made of epithelial cells, with dead cells on the outermost layer, creating a protective and watertight sheath. Below the epidermis is the dermis. In this second layer are the secretion glands, blood vessels, hair follicles, and most of the receptors. Below this is the subcutaneous tissue, a fatty cushion below the skin separating the dermal layers from the underlying tissues.
Receptors of the Integumentary System
The cutaneous sense, the sense of touch, is "felt" by nerve endings in the skin and provides information about the body's external environment and the skin itself. There are two types of nerve endings in the skin: free nerve endings and encapsulated nerve endings.
The free nerve endings sense pain, heat, cold, and intense stimuli depending on their location in the skin. In the epidermis, the nerves sense pain; in the dermis, the nerves sense temperature. A combination of their activation signals intense stimuli, which is why extreme temperatures are both hot/cold and painful.
The encapsulated nerve endings sense touch and pressure and are located in the dermis. The encapsulation is a connective tissue around the nerve ending. There are different types of encapsulated nerves: Merkel disc and Meissner corpuscles that sense touch, and the Ruffini corpuscle and Pacinian corpuscle that sense pressure. The Pacinian corpuscle also senses vibration and is more in the subcutaneous tissue, deeper than the dermis receptors.
The number of receptors in an area directly correlates to the sensitivity of that area. The highest receptor density occurs in the hands and face.
OTHER FUNCTIONS
The hair and nails are formed by keratinizing epithelial cells that release the protein as they die. The hair grows out of follicles that have keratinizing cells at their base. A small muscle attached to the base of the hair follicle is responsible for the hair "standing on end" in cases of fright or cold. There are also secretion glands alongside the follicles that release oils that keep the skin and hair moist. Different parts of the body have different densities of follicles with different activities of growth, which differs also between men and women.
Hair is thought to have originally been a protective feature for temperature regulation. Similarly, nails occur at the end of the fingers and toes to protect them against damage. Nails are grown from a nailbed as keratin is deposited.
Another feature of skin is the ability of melanin, a chemical produced by melanocytes, to convert sunlight to Vitamin D. Melanocytes are also responsible for skin tone and freckles.
Sistem limfatik merupakan satu system pengangkutan yang membantu peredaran darah, ia membawa cecair yang keluar dari salur darah kembali semula ke dalam salur darah.
FUNGSI
1. Memusnahkan toxin dan menghalang perebakkan penyakit/jangkitan keseluruh badan (Immunity)
2. Membantu mengekalkan keseimbanganVcecair antara tisu dan peredaran darah
3. Mengangkut lemak tercerna daripada usus ke dalam peredaran darah
PENGENALAN
Terbahagi kepada 2 komponen
1. Organ Primer (primary organs)
• Thymus
• Bone marrow
(Mengawal pengeluaran lymphocyte,sel yang bertindak sebagai sistem imun)
2. Organ sekunder (Secondary organs)
• Salur/kapilari Limfatik
• Nodus limfa
• Spleen
(Terlibat secara langsung dalam menjalankan ketiga-tiga fungsi sistem limfatik)
THYMUS
• Sepasang kelenjar yang terletak pada ventral trakea dan atas sedikit dari jantung.
• Berlaku pembentukkan limfosit
KAPILARI LIMFATIK (Lymphatic capillaries)
• Ia merupakan salur-salur halus yang saling bersambungan dan membentuk struktur seperti jaring.
• Terletak dibawah kulit dan selaras dengan kapilari darah.
• Ia nipis dan mempunyai sistem injap untuk mengelakkan berlakunya ‘backflow’.
SALUR LIMFATIK (Lymphatic Vessel)
• Merupakan salur limfatik yang lebih besar dan terletak di bahagian dalam badan.
• Kapilari limfatik bersambung dengan salur limfatik.
• Ia juga mempunyai injap
• Terdapat bintilan pelbagai saiz berbentuk biji kacang yang di panggil nodus limfa.
NODUS LIMFA
• Adalah bintilan tisu yang berbentuk seperti biji kacang. Berdiameter 2 hingga 35 mm, berwarna Kelabu-merah jambu (greyish-pink).
• Terdapat di sepanjang salur limfatik
• Mengandungi ‘leukocyte’ (sel darah putih) yang mempunyai fungsi phagositosis’
• Cecair limfa mesti melalui nodus ini sebelum kembali kedalam sistem peredaran darah.
An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens can evolve rapidly, producing adaptations that avoid the immune system and allow the pathogens to successfully infect their hosts.
To survive this challenge, multiple mechanisms evolved that recognize and neutralize pathogens. Even simple unicellular organisms such as bacteria possess enzyme systems that protect against viral infections. Other basic immune mechanisms evolved in ancient eukaryotes and remain in their modern descendants, such as plants, fish reptiles, and insects. These mechanisms include antimicrobial peptides called defensins, phagocytosis, and the complement system. Vertebrates such as humans have even more sophisticated defense mechanisms. The immune systems of vertebrates consist of many types of proteins cells, organs, and tissues, which interact in an elaborate and dynamic network. As part of this more complex immune response, the human immune system adapts over time to recognise specific pathogens more efficiently. This adaptation process is referred to as "adaptive immunity" or "acquired immunity" and creates immunological memory. Immunological memory created from a primary response to a specific pathogen, provides an enhanced response to secondary encounters with that same, specific pathogen. This process of acquired immunity is the basis of vaccination.
Disorders in the imune system can result in disease. Immunodeficiency occurs when the immune system is less active than normal, resulting in recurring and life-threatening infections. Immunodeficiency can either be the result of a genetic disease, such as severe combined immunodeficiency, or be produced by pharmaceuticals or an infection, such as the acquired immune deficiency syndrome (AIDS) that is caused by the retrovirus HIV. In contrast, autoimmune diseases result from a hyperactive immune system attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's Thyroiditis, rheumatoid arthritis, diabetes mellitus type 1 and lupus erythematosus. Immunology covers the study of all aspects of the immune system which has significant relevance to human health and diseases. Further investigation in this field is expected to play a serious role in promotion of health and treatment of diseases.
Layered defense
The immune system protects organisms from infection with layered defenses of increasing specificity. Most simply, physical barriers prevent pathogens such as bacteria and viruses from entering the organism. If a pathogen breaches these barriers, the innate immune system provides an immediate, but non-specific response. Innate immune systems are found in all plants and animals. However, if pathogens successfully evade the innate response, vertebrates possess a third layer of protection, the adaptive immune system, which is activated by the innate response. Here the immune system adapts its response during an infection to improve its recognition of the pathogen. This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory, and allows the adaptive immune system to mount faster and stronger attacks each time this pathogen is encountered.
| Components of the immune system |
| Innate immune system | Adaptive immune system |
| Response is non-specific | Pathogen and antigen specific response |
| Exposure leads to immediate maximal response | Lag time between exposure and maximal response |
| Cell-mediated and humoral components | Cell-mediated and humoral components |
| No immunological memory | Exposure leads to immunological memory |
| Found in nearly all forms of life | Found only in jawed vertebrates |
Both innate and adaptive immunity depend on the ability of the immune system to distinguish between self and non-self molecules. In immunology, self molecules are those components of an organism's body that can be distinguished from foreign substances by the immune system. Conversely, non-self molecules are those recognized as foreign molecules. One class of non-self molecules are called antigens (short for antibody generators) and are defined as substances that bind to specific immune receptors and elicit an immune response.
Surface barriers
Several barriers protect organisms from infection, including mechanical, chemical and biological barriers. The waxy cuticle of many leaves, the exoskeleton of insects, the shells and membranes of externally deposited eggs, and skin are examples of the mechanical barriers that are the first line of defense against infection.However, as organisms cannot be completely sealed against their environments, other systems act to protect body openings such as the lungs, intestines and the genitourinary tract. In the lungs, coughing and sneezing mechanically eject pathogens and other irritants from the respiratory tract. The flushing action of tears and urine also mechanically expels pathogens, while mucus secreted by the respiratory and gastrointestinal tract serves to trap and entangle microorganisms.
Chemical barriers also protect against infection. The skin and respiratory tract secrete antimicrobial peptides such as the β-defensins. Enzymes such as lysozyme and phospholipase A2 in saliva, tears, and breast milk are also antibacterials. Vaginal secretions serve as a chemical barrier following menarche, when they become slightly acidic, while semen contains defensins and zinc to kill pathogens.In the stomach, gastric acid and proteases serve as powerful chemical defenses against ingested pathogens.
Within the genitourinary and gastrointestinal tracts, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space and, in some cases, by changing the conditions in their environment, such as pH or available iron. This reduces the probability that pathogens will be able to reach sufficient numbers to cause illness. However, since most antibiotics non-specifically target bacteria and do not affect fungi, oral antibiotics can lead to an “overgrowth” of fungi and cause conditions such as a vaginal candidiasis (a yeast infection). There is good evidence that re-introduction of probiotic flora, such as pure cultures of the lactobacilli normally found in unpasteurized yoghurt, helps restore a healthy balance of microbial populations in intestinal infections in children and encouraging preliminary data in studies on bacterial gastroenteritis, inflammatory bowel diseases, urinary tract infection and post-surgical infections. Innate
For more details on this topic, see Innate immune system.
Microorganisms or toxins that successfully enter an organism will encounter the cells and mechanisms of the innate immune system. The innate response is usually triggered when microbes are identified by pattern recognition receptors, which recognize components that are conserved among broad groups of microorganisms, or when damaged, injured or stressed cells send out alarm signals, many of which (but not all) are recognized by the same receptors as those that recognize pathogens. Innate immune defenses are non-specific, meaning these systems respond to pathogens in a generic way. This system does not confer long-lasting immunity against a pathogen. The innate immune system is the dominant system of host defense in most organisms.
Humoral and chemical barriers
Inflammation
For more details on this topic, see Inflammation.
Inflammation is one of the first responses of the immune system to infection. The symptoms of inflammation are redness and swelling, which are caused by increased blood flow into a tissue. Inflammation is produced by eicosanoids and cytokines, which are released by injured or infected cells. Eicosanoids include prostaglandins that produce fever and the dilation of blood vessels associated with inflammation, and leukotrienes that attract certain white blood cells (leukocytes). Common cytokines include interleukins that are responsible for communication between white blood cells; chemokines that promote chemotaxis; and interferons that have anti-viral effects, such as shutting down protein synthesis in the host cell. Growth factors and cytotoxic factors may also be released. These cytokines and other chemicals recruit immune cells to the site of infection and promote healing of any damaged tissue following the removal of pathogens.
Complement system
For more details on this topic, see Complement system.
The complement system is a biochemical cascade that attacks the surfaces of foreign cells. It contains over 20 different proteins and is named for its ability to “complement” the killing of pathogens by antibodies. Complement is the major humoral component of the innate immune response. Many species have complement systems, including non-mammals like plants, fish, and some invertebrates
In humans, this response is activated by complement binding to antibodies that have attached to these microbes or the binding of complement proteins to carbohydrates on the surfaces of microbes. This recognition signal triggers a rapid killing response. The speed of the response is a result of signal amplification that occurs following sequential proteolytic activation of complement molecules, which are also proteases. After complement proteins initially bind to the microbe, they activate their protease activity, which in turn activates other complement proteases, and so on. This produces a catalytic cascade that amplifies the initial signal by controlled positive feedback. The cascade results in the production of peptides that attract immune cells, increase vascular permeability, and opsonize (coat) the surface of a pathogen, marking it for destruction. This deposition of complement can also kill cells directly by disrupting their plasma membrane.
Cellular barriers
A scanning electron microscope image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.
Leukocytes (white blood cells) act like independent, single-celled organisms and are the second arm of the innate immune system. The innate leukocytes include the phagocytes (macrophages, neutrophils, and dendritic cells), mast cells, eosinophils, basophils, and natural killer cells. These cells identify and eliminate pathogens, either by attacking larger pathogens through contact or by engulfing and then killing microorganisms.Innate cells are also important mediators in the activation of the adaptive immune system.
Phagocytosis is an important feature of cellular innate immunity performed by cells called 'phagocytes' that engulf, or eat, pathogens or particles. Phagocytes generally patrol the body searching for pathogens, but can be called to specific locations by cytokines. Once a pathogen has been engulfed by a phagocyte, it becomes trapped in an intracellular vesicle called a phagosome, which subsequently fuses with another vesicle called a lysosome to form a phagolysosome. The pathogen is killed by the activity of digestive enzymes or following a respiratory burst that releases free radicals into the phagolysosome.Phagocytosis evolved as a means of acquiring nutrients, but this role was extended in phagocytes to include engulfment of pathogens as a defense mechanism. Phagocytosis probably represents the oldest form of host defense, as phagocytes have been identified in both vertebrate and invertebrate animals.
Neutrophils and macrophages are phagocytes that travel throughout the body in pursuit of invading pathogens. Neutrophils are normally found in the bloodstream and are the most abundant type of phagocyte, normally representing 50% to 60% of the total circulating leukocytes. During the acute phase of inflammation, particularly as a result of bacterial infection, neutrophils migrate toward the site of inflammation in a process called chemotaxis, and are usually the first cells to arrive at the scene of infection. Macrophages are versatile cells that reside within tissues and produce a wide array of chemicals including enzymes, complement proteins, and regulatory factors such as interleukin 1.Macrophages also act as scavengers, ridding the body of worn-out cells and other debris, and as antigen-presenting cells that activate the adaptive immune system
Dendritic cells (DC) are phagocytes in tissues that are in contact with the external environment; therefore, they are located mainly in the skin, nose, lungs, stomach, and intestines. They are named for their resemblance to neuronal dendrites, as both have many spine-like projections, but dendritic cells are in no way connected to the nervous system. Dendritic cells serve as a link between the bodily tissues and the innate and adaptive immune systems, as they present antigen to T cells, one of the key cell types of the adaptive immune system.
Mast cells reside in connective tissues and mucous membranes, and regulate the inflammatory response. They are most often associated with allergy and anaphylaxis.Basophils and eosinophils are related to neutrophils. They secrete chemical mediators that are involved in defending against parasites and play a role in allergic reactions, such as asthma. Natural killer (NK cells) cells are leukocytes that attack and destroy tumor cells, or cells that have been infected by viruses.
Adaptive
For more details on this topic, see Adaptive immune system.
The adaptive immune system evolved in early vertebrates and allows for a stronger immune response as well as immunological memory, where each pathogen is "remembered" by a signature antigen. The adaptive immune response is antigen-specific and requires the recognition of specific “non-self” antigens during a process called antigen presentation. Antigen specificity allows for the generation of responses that are tailored to specific pathogens or pathogen-infected cells. The ability to mount these tailored responses is maintained in the body by "memory cells". Should a pathogen infect the body more than once, these specific memory cells are used to quickly eliminate it.
Lymphocytes
The cells of the adaptive immune system are special types of leukocytes, called lymphocytes. B cells and T cells are the major types of lymphocytes and are derived from hematopoietic stem cells in the bone marrow.B cells are involved in the humoral immune response, whereas T cells are involved in cell-mediated immune response.
Association of a T cell with MHC class I or MHC class II, and antigen (in red)
Both B cells and T cells carry receptor molecules that recognize specific targets. T cells recognize a “non-self” target, such as a pathogen, only after antigens (small fragments of the pathogen) have been processed and presented in combination with a “self” receptor called a major histocompatibility complex (MHC) molecule. There are two major subtypes of T cells: the killer T cell and the helper T cell. Killer T cells only recognize antigens coupled to Class I MHC molecules, while helper T cells only recognize antigens coupled to Class II MHC molecules. These two mechanisms of antigen presentation reflect the different roles of the two types of T cell. A third, minor subtype are the γδ T cells that recognize intact antigens that are not bound to MHC receptors.
In contrast, the B cell antigen-specific receptor is an antibody molecule on the B cell surface, and recognizes whole pathogens without any need for antigen processing. Each lineage of B cell expresses a different antibody, so the complete set of B cell antigen receptors represent all the antibodies that the body can manufacture.
Killer T cells
Killer T cells directly attack other cells carrying foreign or abnormal antigens on their surfaces.
Killer T cell are a sub-group of T cells that kill cells infected with viruses (and other pathogens), or are otherwise damaged or dysfunctional.As with B cells, each type of T cell recognises a different antigen. Killer T cells are activated when their T cell receptor(TCR) binds to this specific antigen in a complex with the MHC Class I receptor of another cell. Recognition of this MHC:antigen complex is aided by a co-receptor on the T cell, called CD8. The T cell then travels throughout the body in search of cells where the MHC I receptors bear this antigen. When an activated T cell contacts such cells, it releases cytotoxins, such as perforin, which form pores in the target cell's plasma membrane, allowing ions, water and toxins to enter. The entry of another toxin called granulysin (a protease) induces the target cell to undergo apoptosis.T cell killing of host cells is particularly important in preventing the replication of viruses. T cell activation is tightly controlled and generally requires a very strong MHC/antigen activation signal, or additional activation signals provided by "helper" T cells (see below).
Helper T cells
Function of T helper cells: Antigen presenting cells (APCs) present antigen on their Class II MHC molecules (MHC2). Helper T cells recognize these, with the help of their expression of CD4 co-receptor (CD4+). The activation of a resting helper T cell causes it to release cytokines and other stimulatory signals (green arrows) that stimulate the activity of macrophages, killer T cells and B cells, the latter producing antibodies. The stimulation of B cells and macrophages succeeds a proliferation of T helper cells.
Helper T cells regulate both the innate and adaptive immune responses and help determine which types of immune responses the body will make to a particular pathogen.These cells have no cytotoxic activity and do not kill infected cells or clear pathogens directly. They instead control the immune response by directing other cells to perform these tasks.
Helper T cells express T cell receptors (TCR) that recognize antigen bound to Class II MHC molecules. The MHC:antigen complex is also recognized by the helper cell's CD4 co-receptor, which recruits molecules inside the T cell (e.g. Lck) that are responsible for T cell's activation. Helper T cells have a weaker association with the MHC:antigen complex than observed for killer T cells, meaning many receptors (around 200–300) on the helper T cell must be bound by an MHC:antigen in order to activate the helper cell, while killer T cells can be activated by engagement of a single MHC:antigen molecule. Helper T cell activation also requires longer duration of engagement with an antigen-presenting cell.The activation of a resting helper T cell causes it to release cytokines that influence the activity of many cell types. Cytokine signals produced by helper T cells enhance the microbicidal function of macrophages and the activity of killer T cells. In addition, helper T cell activation causes an upregulation of molecules expressed on the T cell's surface, such as CD40 ligand (also called CD154), which provide extra stimulatory signals typically required to activate antibody-producing B cells.
γδ T cells
γδ T cells possess an alternative T cell receptor (TCR) as opposed to CD4+ and CD8+ (αβ) T cells and share the characteristics of helper T cells, cytotoxic T cells and NK cells. The conditions that produce responses from γδ T cells are not fully understood. Like other 'unconventional' T cell subsets bearing invariant TCRs, such as CD1d-restricted Natural Killer T cells, γδ T cells straddle the border between innate and adaptive immunity.On one hand, γδ T cells are a component of adaptive immunity as they rearrange TCR genes to produce receptor diversity and can also develop a memory phenotype. On the other hand, the various subsets are also part of the innate immune system, as restricted TCR or NK receptors may be used as pattern recognition receptors. For example, large numbers of human Vγ9/Vδ2 T cells respond within hours to common molecules produced by microbes, and highly restricted Vδ1+ T cells in epithelia will respond to stressed epithelial cells.
An antibody is made up of two heavy chains and two light chains. The unique variable region allows an antibody to recognize its matching antigen.
B lymphocytes and antibodies
A B cell identifies pathogens when antibodies on its surface bind to a specific foreign antigen.This antigen/antibody complex is taken up by the B cell and processed by proteolysis into peptides. The B cell then displays these antigenic peptides on its surface MHC class II molecules. This combination of MHC and antigen attracts a matching helper T cell, which releases lymphokines and activates the B cell. As the activated B cell then begins to divide, its offspring (plasma cells) secrete millions of copies of the antibody that recognizes this antigen. These antibodies circulate in blood plasma and lymph, bind to pathogens expressing the antigen and mark them for destruction by complement activation or for uptake and destruction by phagocytes. Antibodies can also neutralize challenges directly, by binding to bacterial toxins or by interfering with the receptors that viruses and bacteria use to infect cells.
Alternative adaptive immune system
Although the classical molecules of the adaptive immune system (e.g. antibodies and T cell receptors) exist only in jawed vertebrates, a distinct lymphocyte-derived molecule has been discovered in primitive jawless vertebrates, such as the lamprey and hagfish. These animals possess a large array of molecules called variable lymphocyte receptors (VLRs) that, like the antigen receptors of jawed vertebrates, are produced from only a small number (one or two) of genes. These molecules are believed to bind pathogenic antigens in a similar way to antibodies, and with the same degree of specificity.
Immunological memory
For more details on this topic, see Immunity (medical).
When B cells and T cells are activated and begin to replicate, some of their offspring will become long-lived memory cells. Throughout the lifetime of an animal, these memory cells will remember each specific pathogen encountered and can mount a strong response if the pathogen is detected again. This is "adaptive" because it occurs during the lifetime of an individual as an adaptation to infection with that pathogen and prepares the immune system for future challenges. Immunological memory can either be in the form of passive short-term memory or active long-term memory.
Passive memory
Newborn infants have no prior exposure to microbes and are particularly vulnerable to infection. Several layers of passive protection are provided by the mother. During pregnancy, a particular type of antibody, called IgG, is transported from mother to baby directly across the placenta, so human babies have high levels of antibodies even at birth, with the same range of antigen specificities as their mother. Breast milk also contains antibodies that are transferred to the gut of the infant and protect against bacterial infections until the newborn can synthesize its own antibodies.This is passive immunity because the fetus does not actually make any memory cells or antibodies—it only borrows them. This passive immunity is usually short-term, lasting from a few days up to several months. In medicine, protective passive immunity can also be transferred artificially from one individual to another via antibody-rich serum
The time-course of an immune response begins with the initial pathogen encounter, (or initial vaccination) and leads to the formation and maintenance of active immunological memory.
Active memory and immunization
Long-term active memory is acquired following infection by activation of B and T cells. Active immunity can also be generated artificially, through vaccination. The principle behind vaccination (also called immunization) is to introduce an antigen from a pathogen in order to stimulate the immune system and develop specific immunity against that particular pathogen without causing disease associated with that organism. This deliberate induction of an immune response is successful because it exploits the natural specificity of the immune system, as well as its inducibility. With infectious disease remaining one of the leading causes of death in the human population, vaccination represents the most effective manipulation of the immune system mankind has developed.
Most viral vaccines are based on live attenuated viruses, while many bacterial vaccines are based on acellular components of micro-organisms, including harmless toxin components. Since many antigens derived from acellular vaccines do not strongly induce the adaptive response, most bacterial vaccines are provided with additional adjuvants that activate the antigen-presenting cells of the innate immune system and maximize immunogenicity.
Disorders of human immunity
The immune system is a remarkably effective structure that incorporates specificity, inducibility and adaptation. Failures of host defense do occur, however, and fall into three broad categories: immunodeficiencies, autoimmunity, and hypersensitivities.Immunodeficiencies For more details on this topic, see Immunodeficiency.
Immunodeficiencies occur when one or more of the components of the immune system are inactive. The ability of the immune system to respond to pathogens is diminished in both the young and the elderly, with immune responses beginning to decline at around 50 years of age due to immunosenescence. In developed countries, obesity, alcoholism and drug use are common causes of poor immune function.However, malnutrition is the most common cause of immunodeficiency in developing countries. Diets lacking sufficient protein are associated with impaired cell-mediated immunity, complement activity, phagocyte function, IgA antibody concentrations, and cytokine production. Deficiency of single nutrients such as iron; copper; zinc; selenium; vitamins A, C, E, and B6; and folic acid (vitamin B9) also reduces immune responses. Additionally, the loss of the thymus at an early age through genetic mutation or surgical removal results in severe immunodeficiency and a high susceptibility to infection
Immunodeficiencies can also be inherited or 'acquired'.Chronic granulomatous disease, where phagocytes have a reduced ability to destroy pathogens, is an example of an inherited, or congenital, immunodeficiency. AIDS and some types of cancer cause acquired immunodeficiency Autoimmunity
For more details on this topic, see Autoimmunity.
Overactive immune responses comprise the other end of immune dysfunction, particularly the autoimmune disorders. Here, the immune system fails to properly distinguish between self and non-self, and attacks part of the body. Under normal circumstances, many T cells and antibodies react with “self” peptides One of the functions of specialized cells (located in the thymus and bone marrow) is to present young lymphocytes with self antigens produced throughout the body and to eliminate those cells that recognize self-antigens, preventing autoimmunity.
Hypersensitivity
For more details on this topic, see Hypersensitivity.
Hypersensitivity is an immune response that damages the body's own tissues. They are divided into four classes (Type I – IV) based on the mechanisms involved and the time course of the hypersensitive reaction. Type I hypersensitivity is an immediate or anaphylactic reaction, often associated with allergy. Symptoms can range from mild discomfort to death. Type I hypersensitivity is mediated by IgE released from mast cells and basophils. Type II hypersensitivity occurs when antibodies bind to antigens on the patient's own cells, marking them for destruction. This is also called antibody-dependent (or cytotoxic) hypersensitivity, and is mediated by IgG and IgM antibodiesImmunecomplexes (aggregations of antigens, complement proteins, and IgG and IgM antibodies) deposited in various tissues trigger Type III hypersensitivity reactions. Type IV hypersensitivity (also known as cell-mediated or delayed type hypersensitivity) usually takes between two and three days to develop. Type IV reactions are involved in many autoimmune and infectious diseases, but may also involve contact dermatitis (poison ivy). These reactions are mediated by T cells, monocytes, and macrophages.
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