Digestion in intestine Role of liver and pancreas

Digestion in intestine. Role of liver and pancreas.

Small intestine The Small Intestine plays key role in digestion and absorption of nutrient, 90% of nutrient absorption occurs in the small intestine Three subdivisions: 1. Duodenum – 25 cm in length, Contains Brunner glands “Mixing bowl” that receives: chyme from stomach digestive secretions from pancreas and liver 2. Jejunum – 2. 5 m in length, Is the location of most: chemical digestion nutrient absorption 3. Ileum – 3. 6 m in length Contains Peyer patches

Small intestine PHYSIOLOCIAL EVENTS: 1. 2. 3. 4. Mechanical digestion Chemical digestion Absorption Propulsion

Small intestine 1. MECHANICAL DIGESTION In segmentation, nonadjacent segments of the intestine alternately contract and relax, moving the chyme forward and then backward resulting through mixing. This results in the chyme being well mixed with the enzymes from the liver and the pancreas.

Small intestine In addition, segmentation ensures that the chyme well move to the plasma membrane of the lining cells of the small intestine. These simple columnar epithelial cells have brush border enzymes within their plasma membrane which complete the chemical digestion of the chyme.

Small intestine 2. CHEMICAL DIGESTION Chemical digestion in the small intestines, is the result of the intestinal brush border enzymes.

Small intestine 3. PROPULSION Propulsion is the result of peristalsis. This causes adjacent segments to alternately contract and relax. Peristalsis occurs only after most nutrients have been absorbed. It requires about 2 hours for undigested material to reach the ileocecal valve.

Small intestines neurological control MECHANICAL DIGESTION: Segmentation is initiated by intrinsic pacemaker cells in longitudinal smooth muscle layer. The rate of segmentation in the duodenum is 12 -14 contractions/minute. Segmentation moves intestinal contents slowly and steadily toward the ileocecal valve at a rate which allows time to complete digestion and absorption. The stomach initiates the gastroileal reflex, which enhances the force of segmentation.

Small intestines neurological control CHEMICAL DIGESTION and ABSORPTION: There is no neurological control within the small intestines, this is due to the natural of the brush border enzymes. PROPULSION: Peristalsis occurs only after most nutrients have been absorbed. Peristaltic waves initiated in the duodenum begin to sweep slowly along the small intestines, moving 10 -70 cm before dying out. Each successive wave is initiated a bit more distally, and this pattern of peristaltic activity, migrating mobility complex, continues until the undigested food is moved to the ileum a 2 hour trip. The gastroileal reflex causes the ileocecal sphincter to relax. Peristalsis is regulated extrinsically by the autonomic nervous system. The parasympathetic division is excitatory and the sympathetic is inhibitory.

Small intestines hormonal control MECHANICAL DIGESTION: Gastrin stimulates contraction of the smooth muscle of the small intestines. This results in an increase in segmentation. ABSORPTION is inhibited by Somatostatin. PROPULSION: Perstalsis is stimulated by gastrin. Also, gastrin relaxes the ileocecal valve, which allow chyme into the large intestines.

Large intestine PHYSIOLOGICAL EVENTS: 1. Absorption - vitamins, electrolytes, and water. Mass movements occur within the large intestines. They are long slow-moving contractile waves that occur 3 or 4 times per day. Typically mass movements occur during or after eating. • use ~9 liters of water every day in digestive juices • > 90% of water reabsorbed l not enough water absorbed – diarrhea l too much water absorbed – constipation 2. Propulsion - The presence of food in the stomach activates the gastroileal reflex in the small intestines. It, in turn, stimulates the gastrocolic reflex of the large intestines.

Liver functions: Ø Secterion of bile Ø Detoxication of blood (drugs, alcohols) Ø Carbohydrate metabolism Ø Lipid metabolism Ø Protein synthesis Ø Fetal RBC production Ø Phagocytosis Ø Stores • • Ø Ø Gycolgen Vitamins (A, D, E, K) Fe and other minerals Cholesterol Activates vitamin D Endocrine function

Bile is a yellowish-green liquid that hepatic cells secrete Ø The liver produces and secretes 250 to 1500 ml of bile per day. Ø The major constituents of bile are - water; - bile pigment (bilirubin); - bile salts; - phospholipids (mainly lecithin); - cholesterol; Ø inorganic ions (Na, K, Ca, Mg, Cl, SO 4, PO 4, ( H 2 CO 3. Ø

Gallbladder Ø The gallbladder is a saclike organ attached to the inferior surface of the liver. This organ stores and concentrates bile, which drains to it from the liver by way of the bile ducts, hepatic ducts, and cystic duct, respectively.

Liver and gallblader control Ø NEUROLOGICAL CONTROL The gallbladder is regulated by the autonomic nervous system. The parasympathetic division, using the vagus nerve, is excitatory and the sympathetic division inhibits the gallbladder.

Liver and gallblader control Ø HORMONAL CONTROL The liver is stimulated by secretin to produce bile more rapidly. Cholecystokinin stimulates the gallbladder to contract and hepatopancreatic sphincter to relax, so that bile can enter the duodenum.

Pancreas The pancreas is a large gland lying across the posterior abdominal wall. It has 2 secretions: - A digestive secretion (exocrine) poured into the duodenum (secretes pancreatic juice), and - Hormonal (endocrine) passed into the blood stream. (The pancreatic islets, or islets of Langerhans secrete hormones, insulin and glucagon. ) Ø

Pancreatic juice Ø Ø 1) 2) 3) 4) Exocrine secretion of about 1500 ml per day. Contains water, bicarbonate, and wide variety of digestive enzymes. These enzymes include amylase, which digest starch; trypsin, which digest protein; lipase, which digest triglycerides. pancreatic ribonuclease & deoxyribonuclease

PANCREAS CHEMICAL DIGESTION

PANCREAS CHEMICAL DIGESTION

PANCREAS CHEMICAL DIGESTION

PANCREAS CONTROL Ø NEUROLOGICAL CONTROL The pancreas is regulated by the autonomic nervous system. The parasympathetic Division, using the vagus nerve, is excitatory and the sympathetic division inhibits the pancreas.

PANCREAS CONTROL Ø HORMONAL CONTROL The pancreas is regulated hormonally by secretin and cholecystokinin (CCK). CCK induces the acinar cells to secrete the enzymes found in pancreatic juice. Secretin causes bicarbonate ions to form.