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Department of PhysiologySchool of Medicine

University of Sumatera Utara

dr. Yudi Herlambang

dr Nuraiza Meutia

� 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 perubahanpH 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, sekresiserus

• Kelenjar sublingualis, sekresi serus & mukus

• Kelenjarsubmandibularis, sekresiserus & mukus

• Kelenjar bukalis, sekresimukus

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Fungsi :1. Amilase : mencerna polisakarida2. Mukus : melicinkan makanan agar mudah ditelan3. Lisozim : antibakteri4. Stimulasi taste buds oleh makanan terlarut5. Melumas bibir & lidah untuk bicara6. Membantu membersihkan gigi & mulut7. 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

autonomic nerves

salivary glands

↑ salivary secretion

pressure receptors

and chemoreceptors

in the mouth

other inputs

Conditioned reflex

simple

reflex

� 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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OropharynxOropharynx

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 rangka½ bagian bawah – otot polosdi 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

Pepsinogen

HCl

Gastrin

Histamine

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� Stomach pressure remains constant until about 1L of food is ingested

� Relative unchanging pressure results from reflex-mediated 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 olehmekanisme neural dan hormonal .� Proses stimulasi atau inhibisi berlangsung dalam3 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 telahdicerna memasuki duodenum.

� Inhibitory phase : distensi duodenum, adanya lipid, acidic, atau kimus hipertonik, dan bahan iritan diduodenum

(Initiates inhibition of local reflexes and vagalnuclei)

(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

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