The gastrointestinal (GI) tract is the site of nutrient digestion and later absorption. Stretches from mouth to anus

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Department of Physiology School 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

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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

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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

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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

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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 notantagonistic

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)

NBSalivary secretion is the only digestive secretion

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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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Oropharynx 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

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 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

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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

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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

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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 H

₂

receptors and

decrease HCl release

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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

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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 B₁₂and bile salts

Most bile salts are absorbed and recirculated to the liver – important in maintaining bile pool

Brush border enzymes

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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

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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

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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)

CO₂produced 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

& H

₂

O

absorption

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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,