Digestive System Week 13 Dr. Walid Daoud A. Professor

The Pancreas Pancreas is a soft oblong gland. It lies posterior to the greater curvature of the stomach and is connected by pancreatic duct to the duodenum. Pancreas has a head, body and tail. Pancreatic juice: 1-2 L / day. Alkaline pH ( ). Water and enzymes 98.5%. Sodium bicarbonate 1.5%

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Functions of Pancreatic Juice 1- Sod. bicarbonate: Neutralizes acidity in duodenum. 2- Pancreatic amylase: Digests starch into maltose. 3- Proteolytic enzymes: Trypsin, chemotrypsin, carboxypeptidase. 4- Pancreatic lipase: Digests fat into glycerol and fatty acids.

The Bile Hepatic cells secrete 1-2 L of bile daily. Alkaline pH ( ) due to sod. bicarbonate which is absorbed during storage of bile in the gall bladder and bile becomes acidic. Composition of bile: 1- Bile salts. 2- Cholesterol. 3- Bile pigments: bilirubin and biliverdin.

Steps of Bile Pigment Formation 1- Old red blood cells are broken releasing iron + globin + bilirubin. 2- bilirubin binds to plasma proteins forming hemobilirubin which is taken by the liver. 3- Bilirubin conjugates with glucoronic acid or SO4 forming cholebilirubin excreted by hepatic cells with bile. 4- In the intestine cholebilirubin is reduced by intestinal bacteria to stercobilinogen.

Fate of Stercobilinogen A- 2/3 lost in feces. B- 1/3 absorbed in the portal blood to the liver cells and oxidized again into bilirubin or excreted in bile (enterohepatic circulation of stercobilinogen). C- Small amount passes in circulation and excreted in urine as urobilinogen which is oxidized by air into urobilin..

Functions of Gall Bladder 1- Storage of bile. 2- Concentration of bile. 3- Secretion of mucus (white bile). 4- Acidification of liver bile. 5- Biliary pressure buffer. 6- Emptying of its contents.

Small Intestine Small intestine (21 feet in length) is divided into 3 segments: 1- Duodenum 2- Jejunum 3- Ileum. Functions: 1- Digestion mainly in upper half. 2- Absorption mainly in lower half. 3- Movement of chyme into the colon. 4- Secretion of hormones regulating digestion

Succus Entericus Digestive juice of small intestine, 2-3 L /day, alkaline pH 7.6, contains sod. bicarbonate & Enzymes: 1- Peptidases group. 2- Disaccharidases group. 3- Intestinal lipase. 4- Nucleases. 5- Enterokinase.

Mechanism of Intestinal Secretion 1- Local axon reflex. 2- Hormonal mechanism. 3- Extrinsic nerves.

Movements of Small Intestine 1- Peristaltic movement: A wave of contraction preceded by a wave of relaxation. A wave of contraction preceded by a wave of relaxation. 2- Mass peristalsis: A rapid wave of peristalsis along the whole length of intestine in less than 1 minute. A rapid wave of peristalsis along the whole length of intestine in less than 1 minute. 3- Antiperistalsis. 4- Segmenting movements.

Absorption It is the passage of digested nutrients (glucose, amino acids and fatty acids) from alimentary canal into blood or lymph. 90% of absorption occurs through the villi in small intestine and depends on: 1- Diffusion. 2- Facilitated diffusion. 3- Osmosis. 4- Active transport.

Large Intestine It extends from the end of ileum to anus. 4 regions: cecum, colon, rectum & anal canal Functional Anatomy: 1- Proximal colon: for absorption. From cecum to middle of transverse colon. From cecum to middle of transverse colon. 2- Distal colon: for storage. From middle of transverse colon to the junction of pelvic colon with rectum. From middle of transverse colon to the junction of pelvic colon with rectum. 3- Rectum and anal canal: for defecation.

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Functions of Large Intestine 1- Digestion: No digestion in human but in animals. No digestion in human but in animals. 2- Absorption. 3- Excretion. 4- Secretion of mucin. 5- Storage of feces. 6- Synthesis of vitamin K and B complex. 7- Defecation.

- Defecation Reflex - Gastrocolic Reflex - Gastrocolic Reflex