Dr/Nahla Yacout 2016/2017

1. Gastro-intestinal tract 2 Physiology 232 BMS Dr/Nahla Yacout 2016/2017

2. Objectives • Identify the three parts of the small intestine • Enumerate functions of small intestine, liver, bile • Explain the hemolysis of Hb & the fate of bilirubin • Explain the functions of pancreas, the enzymes present in the pancreatic juice & their functions • Enumerate the functions of large intestine & what happens in defecation • Summary of digestion • Define jaundice & its types

3. Small intestine • The small intestine is the body’s major digestive organ, where digestion is completed & all absorption occurs • It consists of 3 subdivisions: Duodenum – Jejunum – Ileum Intestinal juice • Is secreted by intestinal glands • It contains no enzymes

4. Liver • Liver, gall bladder & pancreas are accessory organs associated with the small intestine • Liver has essential digestive function which is bile secretion • Bile passes from liver to reach the duodenum in order to digest fats there Bile leaves the liver through: Right & Left hepatic ducts Right & Left hepatic ducts fuse to form: Common hepatic duct Common hepatic duct + Cystic duct (That comes from the gall bladder) = Common bile duct ….. That passes to the duodenum to digest fats there

6. Functions of liver: 1. Bile secretion 2. Carbohydrate metabolism Conversion of glucose to glycogen in presence of insulin Conversion of glycogen to glucose in presence of glucagon (After a meal, blood will have high glucose level …. Insulin will convert some of this glucose into glycogen to be stored) 3. Fat metabolism 4. Protein metabolism 5. Detoxification of drugs 6. Vitamin A synthesis 7. Storage of fat soluble vitamins & some water soluble vitamins 8. Purify the blood from ammonia by converting it into urea

7. Bile Function of bile: Fat digestion Composition of bile: • Bile salts • Bile pigments • Cholesterol • Triglycerides • Phospholipids • Electrolytes Only Bile salts & Phospholipids have digestive functions

8. The chief bile pigment is: Bilirubin (A waste product of the heme of Hb, formed during the breakdown of erythrocytes) In Spleen … Hb Globin ….. Amino acid synthesis Heme ….. Biliverdin ….. Unconjugated bilirubin Unconjugated bilirubin enters the liver ….. Inside liver, conjugation will occur, & so Unconjugated bilirubin is converted into Conjugated bilirubin Conjugated bilirubin passes through hepatic ducts to reach duodenum …. Converted into Urobilinogen Part passes to large intestine Other part passes to kidney & get out in the form of Stercobilin & get out in the form of Urobilin

10. Gall bladder Is a muscular sac which stores the bile hat is not immediately required for digestion When bile is required for digestion, its wall contracts, & bile is expelled into cystic duct & then into common bile duct to reach the duodenum

11. Pancreas • Is a gland which is important in digestive process, because it produces enzymes that digest all categories of food • It produces a juice called (Pancreatic juice) which passes from the pancreas to the duodenum (1st part of the small intestine) through the Pancreatic duct Functions of pancreas:

12. Types of enzymes present in pancreatic juice: 1. Pancreatic proteases (Protein – digesting enzymes) They are released in inactive form & then activated in the duodenum where they will work Examples: • Trypsinogen …… Trypsin • Chymotrypsinogen ….. Chymotrypsin • Procarboxypeptidase …. Carboxypeptidase 2. Carbohydrases (Digest carbohydrates) They are released in active form Example:Amylase 3. Lipases: (Digest lipids) They are released in active form Example:Pancreatic lipase

13. Functions of small intestine:1. Digestion • Food that reaches the small intestine is: Carbohydrates …. Partially digested in mouth Proteins ….. Partially digested in stomach Fats ….. Not digested • Pancreatic enzymes … Reach the small intestine from pancreas to digest all categories of food • Bile …. Reaches the small intestine from the liver to digest fats 2. Absorption

14. Large intestine (Colon) Large intestine begins at the caecum & ends at the rectum & anal canal • Colon is divided into: Caecum – Ascending colon – Transverse colon – Descending colon – Sigmoid colon – Rectum – Anal canal (The anal canal has two sphincters … Involuntary internal anal sphincter & Voluntary external anal sphincter) Functions of large intestine: The main function is forcing the fecal material towards the anus & then eliminate it from the body …. Defecation Defecation: The rectum is usually empty, but when feces are forced into it … Stretching of rectal wall occurs causing: • Sigmoid colon & rectum to contract • Internal anal sphincter to relax • External anal sphincter to contract

16. Summary of digestion

17. Summary of digestion

19. Jaundice Is yellow discoloration of skin & mucous membranes due to increase in concentration of bilirubin in blood It is not a disease in itself, it is a sign of abnormal bilirubin metabolism & excretion Normally, In spleen, Hb …. Heme …. Biliverdin …… Unconjugated bilirubin (Fat soluble) In liver, Conjugation occurs & so Unconjugated bilirubin is converted into Conjugated bilirubin (Water soluble & easily excreted) Conjugated bilirubin passes through the hepatic ducts to reach the duodenum In duodenum, Conjugated bilirubin …. Urobilinogen (Part passes to large intestine & goes out with feces as Stercobilin ……… Another part goes to the kidneys & goes out as Urobilin)

20. Types of jaundice: Hemolytic jaundice: Due to increased hemolysis of RBCs ….. High amount of Hb …… High amount of biliverdin & unconjugated bilirubin Obstructive jaundice: Due to obstruction of one or more of the hepatic ducts ……. Leading to high amount of conjugated bilirubin Hepatocellular jaundice: Due to damage of liver by viral infection or cirrhosis Damaged liver will be unable to conjugate all bilirubin & also unable to remove conjugated bilirubin through ducts, So, Unconjugated & conjugated bilirubin will increase