12/2/2010
dr. Yudi Herlambang dr Nuraiza Meutia Department of Physiology School of Medicine University of Sumatera Utara
The gastrointestinal (GI) tract is the site of nutrient digestion and later absorption. Stretches from mouth to anus
The GI tract moves and mixes food (motility) while also secreting chemicals to breakdown food.
GI tract also eliminates waste.
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Alimentary canal : mulut, pharynx, esophagus, lambung, usus halus dan usus besar. Accessory digestive organs : gigi geligi, lidah, kantung empedu, kelenjar liur, hati, dan pankreas
6 aktivitas dalam proses digestif :
memasukkan, memindahkan, dan pencernaan secara mekanis, + pencernaan secara kimia, absorpsi, dan defekasi
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Ingestion (memasukkan) : taking food into the digestive tract
Propulsion (memindahkan) : swallowing, peristalsis, segmentas
GI tract propulsion: peristalsis Caused by circular and lengthwise muscle contraction Occurs in esophagus, stomach, small intestine
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Mass movements
Peristaltik haustra
GI tract control valves: sphincters Located throughout the intestinal tract Respond to inputs from nerves, hormones, hormone-like compounds and pressure around them Upper and lower esophageal sphincters Pyloric sphincter Base of the stomach Allows stomach contents to enter intestine a few milliliters (1 tsp) at a time
Ileocecal sphincter End of small intestine Prevents contents of large intestine from re-entering small intestine
Two anal sphincters
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Mechanical digestion (pencernaan secara mekanis) : mengunyah, mencampur, dan mengaduk makanan.
Chemical digestion (pencernaan secara kimia) : catabolic breakdown of food
Absorption : movement of nutrients from the GI tract to the blood or lymph
Defecation : elimination of indigestible solid wastes
3 hal yang mengatur kerja sistem pencernaan : 1. Persarafan Saraf otonom (ekstrinsik) dan enterik (intrinsik) 2. Hormonal 3. Mekanisme lokal Local messenger yang berespon thd perubahan pH atau stimulus kimia dan fisik.
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Intrinsic controls Pleksus submukosa (plexus of Meissner) dan pleksus mienterik (plexus of Auerbach) Persarafan enterik lokal ini (local enteric plexuses / gut brain) menghasilkan Short reflexes
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Extrinsic controls Bagian dari simpatis dan parasimpatis yang bersinap dengan neuron di dalam pleksus. Menghasilkan Long reflexes, within or outside the GI tract Juga melibatkan CNS.
Figure 23.6
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Mechano- and chemoreceptors respond to: Stretch, osmolarity, and pH Presence of substrate, and end products of digestion
They initiate reflexes that: Activate or inhibit digestive glands Mix lumen contents and move them along
Figure 23.4
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Fungsi rongga mulut (oral/buccal cavity) :
Analisa bahan yang ada di rongga mulut sebelum ditelan Proses mekanis oleh gigi, lidah dan palatum Lubrikasi Membatasi digesti
Mencakup berbagai proses, yaitu menempatkan makanan yang belum dikunyah ke permukaan gigi, mengunyah, menghaluskan, dan mencampurkan saliva. Aksi volunter, tapi sebagian besar merupakan refleks akibat adanya makanan di rongga mulut.
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Otot-otot pengunyahan : utama : temporalis, masseter, pterigoid lateral & medial. Tambahan : milohioid & geniohioid Persarafan : n. Trigeminus (n. V)
Terdiri dari 97-99,5 % air. Dihasilkan : 1-2 ltr/hari, pH:6,0-7,4. • Kelenjar parotis, sekresi serus • Kelenjar sublingualis, sekresi serus & mukus • Kelenjar submandibularis, sekresi serus & mukus • Kelenjar bukalis, sekresi mukus
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Fungsi : 1. Amilase : mencerna polisakarida 2. Mukus : melicinkan makanan agar mudah ditelan 3. Lisozim : antibakteri 4. Stimulasi taste buds oleh makanan terlarut 5. Melumas bibir & lidah untuk bicara 6. Membantu membersihkan gigi & mulut 7. Sebagai buffer makanan yg asam.
SALIVARY GLANDS Sympathetic and parasympathetic responses are not antagonistic 1. Parasympathetic system has the dominant role - continuous 2. Increased parasympathetic stimulation produces a watery saliva rich in enzymes 3. Increased sympathetic stimulation produces a smaller volume of thick saliva rich in mucus inhibits secretion (dry mouth when nervous) NB Salivary secretion is the only digestive secretion completely under neural control
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CONTROL OF SALIVARY SECRETION cerebral cortex
salivary centre in medulla
pressure receptors and chemoreceptors in the mouth
simple reflex
other inputs Conditioned reflex
autonomic nerves
salivary glands ↑ salivary secretion
The mouth and stomach are connected by a tube called the esophagus.
Epiglottis is a flap of tissue at the top of esophagus which prevents food from entering the trachea (windpipe).
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Oropharynx To convey food into the esophagus. Important role in swallowing.
Anatomi Esofagus : Esofagus dimulai dari tingkat kartilago cricoid (C6) sampai ke bagian kardia lambung, sepanjang ± 25 cm pada pria dan 23 cm pada wanita. Diameter 2 cm.
5 % bagian atas – otot rangka ½ bagian bawah – otot polos di antaranya : campuran otot rangka & otot polos
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Four-cup holding tank Secretes acid and enzymes Only proteins are significantly digested in the stomach Churns and mixes food Chyme is formed Holds food for two to four hours Releases food “a little bit at a time” to the small intestine. Solid take longer than liquids and fat meal takes longer that CHO or protein
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Pada Epitel terdapat Goblet cells yang manghasilkan lapisan mukus alkalin .
Pada Gastric pits terdapat gastric glands yang mensekresi gastric juice, mukus, dan gastrin
Variety of secretory cells : Mucous neck cells : alkaline mucus Parietal cells : HCl dan intrinsic factor Chief cells : pepsinogen Enteroendocrine cells : gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), dan somatostatin ke lamina propria
HCl Gastrin Histamine Pepsinogen
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Stomach pressure remains constant until about 1L of food is ingested
Relative unchanging pressure results from reflexmediated relaxation and plasticity
Reflex-mediated events include:
Receptive relaxation – as food travels in the esophagus, stomach muscles relax Adaptive relaxation – the stomach dilates in response to gastric filling
Plasticity – intrinsic ability of smooth muscle to exhibit the stress-relaxation response
Peristaltic waves move toward the pylorus at the rate of 3 per minute This basic electrical rhythm (BER) is initiated by pacemaker cells (cells of Cajal)
Most vigorous peristalsis and mixing occurs near the pylorus Chyme is either:
Delivered in small amounts to the duodenum or Forced backward into the stomach for further mixing
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Figure 23.18
Pengeluaran cairan lambung diatur oleh
mekanisme neural dan hormonal . Proses stimulasi atau inhibisi berlangsung dalam 3 fase : Cephalic (reflex) phase: sebelum makanan masuk Gastric phase: ketika makanan masuk ke lambung Intestinal phase: ketika sebagian dari makanan yang sudah dicerna masuk ke duodenum
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Hal yang dapat merangsang :
Melihat atau memikirkan makanan Stimulasi reseptor pengecap atau penghidu Hal yang dapat menghambat :
Depresi atau hilang nafsu makan Penurunan stimulasi parasimpatetik
Figure 24.15a
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Hal yang dapat merangsang : Stomach distension Activation of stretch receptors (neural activation) Activation of chemoreceptors by peptides, caffeine, and rising pH Release of gastrin to the blood Hal yang dapat menghambat : A pH lower than 2 Emotional upset that overrides the parasympathetic division
Figure 24.15b
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Excitatory phase : makanan yg sebagian telah dicerna memasuki duodenum.
Inhibitory phase : distensi duodenum, adanya lipid, acidic, atau kimus hipertonik, dan bahan iritan di duodenum (Initiates inhibition of local reflexes and vagal nuclei) (Closes the pyloric sphincter) (Releases enterogastrones that inhibit gastric secretion
Figure 24.15c
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Sekresi HCl distimulasi oleh ACh, histamine,
dan gastrin melalui sistem second-messenger Release of hydrochloric acid: Is low if only one ligand binds to parietal cells Is high if all three ligands bind to parietal cells Antihistamines block H2 receptors and
decrease HCl release
Figure 23.17
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Small intestine (about 10 feet) Duodenum, first 10 inches Jejunum, next four feet Ileum, last five feet Most digestion is completed in the jejunum Most digestive enzymes from intestine cells and pancreas Muscular contraction move and mix food Meal remains 3 to 10 hours with about 95% of the meal digested by the time it leaves
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Features that increase surface area Circular folds Project into lumen 3-10 mm Prominent in duodenum and jejunum and disappear near mid ileum Villi 4-5 million in entire length 0.5-1.5 mm long
Two primary function Digestion Absorption of nutrients and water Digestion Mainly in duodenum – small intestine and pancreatic enzymes Digestive enzymes Pancreatic enzymes:
Trypsin,Chymotrypsin,Carboxypeptida se,Nucleases, Pancreatic lipase, Pancreatic amylase
Intestinal enzymes:
Peptidases, Disaccharidases, Lipase, Nucleotidases
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Absorption Nutrients broken down into simple sugars, fatty acids and amino acids Principle sites of absorption Duodenum: iron, calcium, vitamins, fats, sugars, amino acids, vitamins Jejunum: fat, sugar, amino acid (largely complete by mid jejunum), vitamins Ileum: vitamin B12 and bile salts Most bile salts are absorbed and recirculated to the liver – important in maintaining bile pool
Brush border enzymes
reassembly
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S cells secrete secretin secretin target tissue = pancreatic ducts and liver induces release of water and HCO3- from pancreatic duct cells and secretion of HCO3- into bile by liver HCO3- neutralizes acidic chyme
Stimuli for secretin secretion acid (pH less than 4.5 stimulates secretion) secretin = nature’s antacid
I cells secrete cholecystokinin (CCK) CCK target tissues = pancreatic acinar cells and gall bladder induces secretion of digestive enzymes from pancreatic acinar cells induces contraction of gall bladder, which releases bile into small intestine
Stimuli for CCK secretion presence of protein and/or fat in chyme
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Largest organ in body Blood supply hepatic artery delivers oxygenated blood hepatic portal vein products absorbed into capillaries in the intestines do not directly enter general circulation this blood is delivered first to the liver by the hepatic portal vein, and then passed on to the general circulation
Digestive functions secretes bile - essential for digestion and absorption of fats Function - overall is to filter and process nutrient-rich blood, not just a digestive function regulates carbohydrate metabolism through glycogen storage and release regulates many aspects of lipid metabolism, eg., cholesterol synthesis and release of ketones detoxifies blood urea and bile synthesis
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Figure 24.21a, b
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Functions (converts chyme to feces) Absorption of water and electrolytes (mainly on right side) Absorbs 800 ml water/day Sigmoid colon reservoir for dehydrated fecal mass ~200 g feces/day Water – 80-90% Food residue Bacteria Cells Unabsorbed minerals
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Secretes mucus (no enzymes) Mass Peristaltic Movements (2-3x day) Bacteria produce vitamin K and several B’s Flatus (NH3, CO2, H2, H2S, CH4) CO2 produced when fatty acids and HCl are neutralized by bicarbonate Bacterial fermentation of carbohydrates produces CO2, H2, CH4 Excess occurs with aerophagia and diets high in indigestible carbohydrates Rectum and anus sites of some of most common disorders known to humans Constipation Hemorrhoids Abscesses and fistulas Colon and rectal cancer
Secretion & H2O absorption 2000 ml – 150 ml = ?
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Rectum
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Reflex relaxation of internal sphincter Valsalva maneouvre raising intraabdominal pressure Relaxation of puborectalis (anorectal angle) Voluntary relaxation of external sphincter
TERIMA KASIH, TOLONG DIBACA KEMBALI DARI BUKU TEKS
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