Fisiologi Gastrointestinal PDF

Learning Objectives  Identify structure of small intestine that enhance the digestive process  Describe the function of local intestinal hormone  State the role of bile & of pancreatic juice in digestion  Describe how entry of pancreatic juice & bile into the small intestine...

Learning Objectives  Identify structure of small intestine that enhance the digestive process  Describe the function of local intestinal hormone  State the role of bile & of pancreatic juice in digestion  Describe how entry of pancreatic juice & bile into the small intestine is regulated  List the enzymes involved in chemical digestion  Describe the process of absorption of digested foodstuffs that occurs in the small intestine  List major functions of the large intestine & describe the regulation of defecation Nurfitri Bustamam 2 Small intestine Structure  Long tube (about 6 m) extending from pyloric sphincter in stomach and joins large intestine at the ileocecal sphincter  duodenum (20 cm), jejunum (2.5 m) and ileum (3.5 m)  Surface area greatly increased by intestinal mucosal foldings, villi and microvilli  Structure of a villus (see figure) Nurfitri Bustamam 3  Usus Halus Panjang: duodenum 25 cm, jejenum 2,5 m, ileum 3,6 m dg diameter 2,5 - 4 cm. Struktur permukaan absorpsi: Nurfitri Bustamam 4  Motilitas  Segmentasi paling sering, frekuensi sesuai slow wave mencampur kimus dg liur pencernaan mendekatkan kimus ke permukaan absorpsi  Peristaltik mendorong kimus ke arah usus besar obstruksi usus  peristaltik rush Migrating motility complex (MMC) dorong kimus dari gaster ke ileum (siklus 90-120 menit)  kimus diusus 3-5 jam Nurfitri Bustamam 5 Sfingter Ileosekal  Biasanya tertutup  Regangan ileum terminal relaksasi sfingter  Regangan sekum kontraksi sfingter (dikoordinasi oleh pleksus)  Refleks gastroileal: peningkatan sekresi & motorik lambung akan meningkatkan motilitas ileum terminal Nurfitri Bustamam 6 Liur pencernaan yang disekresi ke dalam usus halus:  liur pankreas  empedu  liur usus halus (succus entericus) Nurfitri Bustamam 7 Anatomi Pancreas Nurfitri Bustamam 8  Fig. kel endokrin & eksokrin pankreas Note: pulau2 Langerhans hanya 1%, 99% sel asinus Nurfitri Bustamam 9 Liur Pankreas  1200-1500 ml/hari  pH 7,1-8,2  menetralisir asam lambung, stop kerja pepsin & agar kerja enzim di duodenum optimal  Komponen cair alkali: disekresi oleh sel duktus kelenjar dirangsang oleh sekretin mengandung banyak NaHCO3  Komponen enzim: disekresi oleh sel asinus kelenjar (99%) dirangsang oleh CCK Nurfitri Bustamam 10  Protease dlm bentuk proenzim: tripsinogen, kimotripsinogen, prokarboksipeptidase. Diaktifkan oleh tripsin di dlm lumen duodenum. Pankreas mengandung inhibitor tripsin. Why? Mukus melindungi dinding usus halus dari enzim proteolitik tsb.  Amilase pankreas: mencerna polisakarida mjd oligosakarida, dilanjutkan oleh oligosakaridase pada brush border usus halus.  Lipase pankreas: trisilgliserol hidrolase, ester kolestero hidrolase, profosfolipase A2  Ribonuklease & deoksiribonuklease Pancreatic Inssufisiensi  Steatorrhea Nurfitri Bustamam 11 12 Pancreatitis  Heavy alcohol intake or biliary tract obstruction  Insufficient amount of tripsin inhibitor  Pancreatic cells release tripsin  Tripsin  digest pancreatic cells Nurfitri Bustamam 13  Regulation of pancreatic secretion Mainly hormonal:  Secretin: acid chyme in duodenum stimulates secretions rich in water and HCO3- but poor in enzymes  CCK: digestive products of proteins and fat in duodenum stimulates secretions of pancreatic juice rich in enzymes. Both hormones are secreted by upper intestinal cells. Nervous control of pancreatic secretion  Parasympathetic impulses along vagus nerves stimulate secretion of pancreatic enzymes. Nurfitri Bustamam 14 Nurfitri Bustamam 15  (Constanzo 5th ed) Nurfitri Bustamam 16  The biliary system includes: The liver The gall bladder Associated ducts: – Hepatic ducts (right, left and common) – Cystic duct – Common bile duct Nurfitri Bustamam 17 Functions of liver Synthesis & secretion of bile Metabolic processes (e.g. gluconeogenesis, glycogenolysis) Detoxification and degradation (e.g. drugs & hormones) Synthesis of plasma proteins (e.g. albumin & clotting factors) Storage (e.g. iron & Vit B12) Activation of vitamin D Removal of bacteria and old RBC Excretion of cholesterol and bilirubin Nurfitri Bustamam 18 Bile secretion Bile is secreted by hepatocytes About 500 ml (250-1200 ml) is secreted per day pH 7.6-8.6 Enters duodenum during digestion of meals Stored in gall bladder and concentrated between meals Nurfitri Bustamam 19 Nurfitri Bustamam 20  Empedu Empedu duktus hepatis vesica fellea Persen zat 2 -4 10 -12 padat Garam 10 - 20 50 – 200 empedu (mmol/l) pH 7,8 – 8,6 7,0 – 7,4 Nurfitri Bustamam 21 Composition of human bile (g/dl) Hepatic Gall bladder Water 98% 89% Bile salts 1.1 6 Bilirubin 0.04 0.3 Cholesterol 0.1 0.3-0.9 Fatty acids 0.12 0.3-1.2 Lecithin 0.04 0.3 Nurfitri Bustamam 22  Bile salts Most important component of the bile Bile salts: cholic acid, chenodeoxycholic acid, cholesterol They are Na+ and K + salts of bile acids They are derivatives of cholesterol Recycled through the enterohepatic circulation Nurfitri Bustamam 23  (Constanzo 5th ed) Nurfitri Bustamam 24  Sirkulasi Enterohepatik Garam Empedu  Pada saat antarmakan, empedu tidak masuk duodenum, tetapi disimpan di kantung empedu, dipekatkan (absorpsi air), & diasamkan.  Garam empedu didaur ulang via sirkulasi enterohepatik, hanya 5% sekresi empedu yg terbuang bersama feses.  Pigmen empedu (bilirubin) oleh bakteri diubah mjd urobilinogen (mewarnai feses).  Dietary fiber sequesters bile  lowering cholesterol in the blood. This occurs because the sequestered bile salts escape the enterohepatic circulation. Therefore, the liver must either synthesize new cholesterol, or remove it from the blood, or both to produce more bile salts. 25 Nurfitri Bustamam 26 Nurfitri Bustamam 27 Function of bile salts Emulsify large fat particles into smaller ones that can be attacked by lipase (detergent action) – fat digestion Help in the transport and absorption of fat (micellar formation) & fat soluble vitamin Prevent precipitation of cholesterol by keeping them in solution (prevent gall stones) Stimulate bile secretion by liver cells (choleretic action) & contraction of gall bladder (cholagogue action) Excretion of cholesterol, drugs, toxin, bile pigments, inorganic substrate Bicarbonate in bile neutralizes acid in duodenum Nurfitri Bustamam 28 Fungsi Garam Empedu  Mengemulsikan lemak: droplet lemak yg besar menjadi droplet kecil (1mm) shg memperluas permukaan  Efek hidrotropik (membentuk misel dg lemak) shg larut air  Efek koleretik: meningkatkan sekresi empedu oleh hati  Mengaktifkan lipase Nurfitri Bustamam 29 Nurfitri Bustamam 30  Garam empedu melarutkan kolesterol; terlalu byk kolesterol/sedikit garam empedu kristalisasi kolesterol batu empedu saat kontraksi nyeri.  Th/ obat utk melarutkan kristal, laser, or buang kantung empedu Nurfitri Bustamam 31 Guyton 32 Nurfitri Bustamam 33  Bilirubin Nurfitri Bustamam 34 Guyton 35 Gall Bladder No digestive role Stores bile Concentrates bile Empties during meals Secretes mucus Nurfitri Bustamam 36  Regulation of bile secretion & gall bladder emptying  Chemical – Bile salts: most important stimulant of bile secretion by liver cells  Hormonal – Secretin: secreted in response to acid chyme, causes secretion of bile rich in water and HCO3- – CCK: secreted in response to fatty acids, amino acid & kolagogue/ kolesistagogue in duodenum, causes gall bladder to contract and sphincter of Oddi to relax  Neural Vagal stimulation:  Increases bile secretion  Weak contraction of gall bladder Nurfitri Bustamam 37 Nurfitri Bustamam 38 Nurfitri Bustamam 39 Nurfitri Bustamam 40 Sekresi Usus Halus  Kelenjar Brunner Menghasilkan mukus dg larutan NaHCO3- Melindungi mukosa duodenum dari asam lambung Dirangsang oleh n. vagus  Kelenjar intestinal/crypte Lieberkuhn menghasilkan air & elektrolit; alkali (7,4-7,8 & isotonik); sekresi dirangsang oleh Vasoactive Intestinal Peptide (VIP)  Paneth cell: lysozyme  Goblet cell: mucus Pada Brush border tdpt enteropeptidase, disakaridase (maltase, sukrose, laktase), & aminopeptidase Nurfitri Bustamam 41 Nurfitri Bustamam 42 Nurfitri Bustamam 43 Nurfitri Bustamam 44  Plicae circulares + villi + microvili permukaan usus halus  Absorpsi terutama di bag proksimal usus halus; semakin ke distal permukaan absorpsi  Malabsorption: berkurangnya permukaan absorpsi, contoh: gluten enteropathy (celiac disease) Nurfitri Bustamam 45 Nurfitri Bustamam 46 Absorpsi di Usus Halus  Karbohidrat Glukosa & galaktosa: transpor aktif sekunder bersama natrium (simport) Fruktosa: difusi terfasilitasi Pentosa: difusi biasa  Protein Asam amino: transpor aktif sekunder bersama natrium dipeptida & tripeptida dpt masuk ke sel dg carrier, dicerna oleh enzim intrasel mjd asam amino, lalu berdifusi ke darah. Protein dpt diserap utuh secara pinositosis Nurfitri Bustamam 47  Sumber protein di GI: makanan, liur pencernaan, sel mukosa yg dilepaskan. Hanya 2-5% protein yg tdk tercerna & diabsorpsi di usus halus.  Lemak Hasil akhir pencernaan lemak: asam lemak bebas, gliserol, monosakarida Garam empedu bersama lesitin & monogliserida mengemulsifikasi lemak Membentuk misel (agregat garam empedu dg asam lemak bebas & monogliserida) yg larut air Nurfitri Bustamam 48  Monogliserida, asam lemak, kolesterol dari misel berdifusi ke sel mukosa; selanjutnya misel tsb dpt mengangkut monogliserida & asam lemak lainnya Asam lemak dg C < 10-12 dari sel mukosa langsung masuk vena porta As lemak dg C > 10-12 & kolesterol diesterkan di sel mukosa menjadi ester trigliserida & ester kolesterol, lalu dibungkus oleh lapisan lipoprotein, kolesterol & fosfolipid membentuk chylomicron Chylomicron dieksositosis, masuk ke sistem limfatik Nurfitri Bustamam 49 Nurfitri Bustamam 50 Nurfitri Bustamam 51  (Constanzo 5th ed) Nurfitri Bustamam 52  Absorpsi air & elektrolit  Air di usus halus berasal dari: 2000 ml makanan/minuman & 7000 ml liur pencernaan 95% air diserap, di feses hanya 200 ml Di usus halus & besar berdifusi sesuai gradien osmotik  Natrium dg pompa, glukosa meningkatkan absorpsi natrium (dasar terapi diare)  Zat besi diserap dlm btk fero. Sekret lambung mereduksi feri dlm makanan mjd fero. Nurfitri Bustamam 53 Nurfitri Bustamam 54 Na+ Diffusion, cotransport, Stimulated by or active transport aldosteron Ca2+ Active transport Stimulated by calcitriol & PTH K+ diffusion Mg2+ Fe2+ Active transport PO43- SO42- Cl-, I- HCO3- Diffusion or carrier mediated transport Water soluble diffusion vit Vit B12 Active transport Must be bound to intrinsic factor Fat soluble Vit. diffusion Absorbed from micelles Nurfitri Bustamam 55 Nurfitri Bustamam 56 Nurfitri Bustamam 57  Muntah/Emesis/Vomitus  Muntah: pengeluaran isi lambung (+ duodenum) melalui mulut  Rangsang: tactile stimulation of the back of throat irritation or distension of stomach & duodenum elevated intracranial pressure rotation/acceleration chemical agent chemoreceptor triger zone psychogenic  Diawali dg nausea, palpitasi, pusing, pucat, keringat dingin, pupil dilatasi, dan bersendawa Nurfitri Bustamam 58  Proses Muntah impuls pusat muntah (medula oblongata) kontraksi ddg abdomen & diafragma tek intra abdominal uvula tutupi sal nasal + glotis tertutup + epiglotis menutupi trachea UOS & LOS relaksasi + gel anti-peristaltik mulut Nurfitri Bustamam 59  Bulimia nervosa  A 27-year-old woman came to the emergency department in April 1999.  She had no pain, disphagia or dypnoea While trying to induce vomiting with handle of the toothbrush, she accidentally swallowed the toothbrush.  Removed by endoscopy without complication. (Lancet 2001;357:1012) Nurfitri Bustamam 60 Nurfitri Bustamam 61  Sekresi di Usus Besar  Mukosa mempunyai crypti Lieberkuhn tetapi tidak mengandung enzim  Sekresi dirangsang oleh refleks mienterikum lokal  Fungsi mukus: pelindung dinding, perekat feses, pelicin jalan feses, melindungi usus dari keaktifan bakteri yg terdapat dlm feses.  Bila ada iritasi kuat krn infeksi, mukosa akan mensekresi sejumlah air & elektrolit yg ditambahkan ke dalam mukus sehingga dapat mengencerkan bahan penyebab iritasi. Nurfitri Bustamam 62 Absorpsi di Usus Besar   500 cc kimus masuk ke usus besar melalui katup ileosekal setiap hari.  Air & elektrolit akan di serap sehingga hanya 200 cc cairan di feses.  Mukosa usus besar mampu menyerap aktif natrium  Proksimal colon = absorbing colon  Distal colon = storage colon Nurfitri Bustamam 63 Bakteri usus besar  Meningkatkan imunitas  Merangsang motilitas kolon  Berkontribusi dlm memberi nutrisi: mensintesis vit. K & B kompleks, & meningkatkan keasaman kolon sehingga meningkatkan absorpsi kalsium, magnesium, & zinc  Memfermentasi KH yg tidak tercerna, misal selulosa menghasilkan gas (dimethyl sulfide, H2, N2, CH4, & CO2) Nurfitri Bustamam 64 Motilitas Usus Besar  Gerakan mencampur: kontraksi otot sirkuler & longitudinal menyebabkan bagian lainnya menggembung keluar membentuk kantung (haustration)  Gerakan mendorong (mass movement): terutama di kolon transfersum & desendens, timbul sesudah makan (refleks duodenokolik & gastrokolik), refleks melalui pl. mienterikus  Iritasi kolon menimbulkan refleks mass movement yg kuat Nurfitri Bustamam 65  Defekasi  Mass movement yg kuat dpt mendorong bahan feses melalui rektum & anus keluar, tetapi jarang karena ada kontraksi sfingter ani internum & eksternum.  Regangan rektum oleh bahan feses menimbulkan impuls aferen melalui pl. mienterikum & menimbulkan gel. peristaltik di kolon desenden, kolon sigmoid yg mendorong feses. Bila sampai di anus sfingter ani internus dihambat & sfingter ani eksternus relaksasi.  Refleks tsb sangat lemah, diperkuat refleks lain melalui segmen sakral medula spinalis, kemudian dikembalikan ke kolon desendens, kolon sigmoid, rektum & anus melalui serat parasimptis.  + valsava manuever (kontraksi diafragma, otot abdomen + glottis tertutup) Nurfitri Bustamam 66 Nurfitri Bustamam 67 Masalah defekasi  Diarrhea  Constipation Motilitas intestinal Lack of fiber in diet Osmotically active Improper bowel particle habit Small intestine Lack of exercise secretion Emotional upset Laxative abuse Feses:  Jml sesuai dg diet  Komposisi: sisa makanan, empedu, liur pencernaan, mukus, lekosit, epitel yg lepas, bakteri Nurfitri Bustamam 68 Gastrocolic Reflex  Distention of the stomach by food increases the motility of the colon and increases the frequency of mass movements in the large intestine.  This long arc reflex, called the gastrocolic reflex, has its afferent limb in the stomach, which is mediated by the parasympathetic nervous system. The efferent limb of the reflex, which produces increased motility of the colon, is mediated by the hormones CCK and gastrin. Nurfitri Bustamam 69 Nurfitri Bustamam 70  (Vander, 2019) Nurfitri Bustamam 71 72