Pancreas and it's information 1 mbbs and other Sciences

It's about pancreas

1. Pancreas An elongated, accessory digestive gland lies transversely across the posterior abdominal wall, posterior to the stomach between duodenum on the right and spleen on the left. Anatomically, it is divided into 4 parts: head, neck, body and tail. Physiologically, exocrine part and endocrine part .

2. Structural Characteristics (Exocrine Part) Acinar cells – Contains numerous zymogen granules in the cytoplasm Produce thick secretion containing numerous enzymes

3. Pancreatic ducts Main Pancreatic duct begins in the tail and runs throughout the length of gland, receiving numerous tributaries on the way. Joins the common bile duct to form ampulla of Vater , which opens into 2 nd part of duodenum. b) Accessory pancreatic duct Drains upper part of head and then opens into duodenum about 2 mm above main duct on the minor duodenal papilla.

4. Properties of Pancreatic Juice Volume – 1200 - 1500 ml/day Reaction – Alkaline (pH – 7.8 - 8.4) due to very high concentration of HCO 3 - Specific gravity – 1.010 -1.018 Composition of Pancreatic Juice It contains 99.5% of water and 0.5% of solids . The solids are organic and inorganic substances . Organic constituents are certain enzymes amylase, lipase, protease and trypsin inhibitor and traces of albumin & globulin .

5. Inorganic substances are cations like Na + , K + , Ca 2+ , Mg 2+ & Zn 2+ ; and anions such as HCO 3 - , Cl and traces of SO4 2- and HPO 4 2 - . Pancreatic enzymes Pancreas secretes 4 major types of enzymes Pancreatic α amylase Its action on CHO is like salivary amylase Hydrolyses glycogen , starch and most other complex CHO except cellulose to form disaccharides.

6. 2. Pancreatic lipases Pancreatic lipase is a powerful lipolytic enzyme, hydrolyses neutral fats to glycerol esters and fatty acids. Cholesterol ester hydrolase converts cholesterol esters to cholesterol. Phospholipase A2 (inactive form) , gets converted to active form by the action of trypsin . - acts on lysolecithin & lysocephalin and converts them into phosphoryl choline .

7. 3. Pancreatic proteases includes 3 endopeptidases ( trypsin , chymotrypsin & elastase ) and 2 exopeptidases ( cardoxypeptidase A & B) . Trypsin is most powerful proteolytic enzyme secreted in an inactive form of trypsinogen . Trypsin hydrolyses proteins into proteoses and to polypeptides.

8. Chymotrypsin is also secreted in an inactive form chymotrypsinogen and is activated by trypsin . It hydrolyses proteins into small polypeptides. Elastase is secreted as pro- elastase , which is activated by trypsin . It digests elastin .

9. Carboxypeptidase A cleaves carboxyl-terminal amino acids that have aromatic or branched aliphatic side chains . Carboxypeptidase B cleaves carboxyl-terminal amino acids that have basic side chains . Nucleases splits nucleic acids of ribose and deoxyribose type into nucleotides . Collagenase digests collagen.

10. Mechanism of Pancreatic Secretion Secretion of Pancreatic Enzymes Synthesized in ribosomes , which are attached to ER of acinar cells Precursor for pancreatic enzymes are amino acids After synthesis, enzymes are packed into different zymogen granules by golgi apparatus and stored in the cytoplasm.

11. B. Secretion of HCO 3 - HCO 3 - are secreted from cells of pancreatic ductules and released into pancreatic duct . CO 2 + H 2 O → H 2 CO 3 H 2 CO 3 → H + + HCO 3 -

12. Regulation of Pancreatic Secretion Regulation of cephalic phase By conditioned reflexes , initiated by sight, smell and thought of food . Unconditioned reflexes initiated by stimulation of taste buds by food in the mouth cavity, act of chewing and swallowing.

13. 2. Regulation of gastric phase Occurs when stomach is distended by food . This phase is regulated by neural control exerted through vagus and hormonal control executed through hormone gastrin . 3. Regulation of intestinal phase Intestinal phase of pancreatic secretion begins when chyme enters the duodenum and jejunum. This phase is regulated by hormones secretin and CCK.

14. Role of secretin Secreted from S-cells located among mucous membrane of duodenum and jejunum. Stimulant for release is low pH (<4.5) of chyme . Secretin enters blood circulation and acts on pancreatic duct cells and produces large amount of watery juice with high concentration of HCO 3 - .

15. b) Role of cholecystokinin Secreted from I-cells located among mucous membrane of duodenum and jejunum. Stimulant for release are amino acids, fatty acids and monoglycerides present in the chyme . CCK passes via blood to the pancreas and causes secretion of pancreatic juice rich in enzymes.

16. Functions of Pancreatic Juice Plays important role in the digestion of proteins and lipids. Mild digestive action on carbohydrates. Major proteolytic enzymes are trypsin and chymotrypsin . Others are carboxypeptidases , nuclease, elastase and collagenase . Trypsin converts proteins into proteoses and polypeptides . Chymotrypsin converts proteins into polypeptides.

17. Nucleases convert RNA and DNA into mononucleotides . Elastase digests elastic fibers. Collagenase digests collagen fibers. Lipolytic enzymes are pancreatic lipase, cholesterol ester hydrolase , phospholipase A , phospholipase B , collipase and bile salt activated lipase. Pancreatic lipase is a strong lipolytic enzyme . It digests triglycerides into monoglycerides and fatty acids .

18. C holesterol ester hydrolase converts cholesterol ester into free cholesterol and fatty acids by hydrolysis. Phospholipase A digests phospholipids into lysophospholipids . Phospholipase B converts lysophospholipids to phosphoryl choline and free fatty acids. Pancreatic amylase converts starch into dextrin and maltose.

19. Applied Physiology A. Pancreatitis – It is the inflammation of pancreatic acini . It is of 2 types : Acute pancreatitis It is an acute inflammatory disease , thought to result from auto digestion of pancreatic tissue by proteolytic enzymes, which leak out the acini and are activated within the pancreas. Feature are severe upper abdominal pain, nausea & vomiting, loss of appetite & weight , fever and shock .

20. 2. Chronic pancreatitis Chronic inflammation of pancreas, which results in a slow destruction of tissue resulting in the deficiency of pancreatic secretions. Patients with an excessive destruction of pancreas may develop - Diabetes mellitus due to pancreatic endocrine deficienct of insulin - Digestive disturbances due to deficiency of pancreatic enzymes mainly affect fat metabolism resulting in steatorrhoea .

21. Steatorrhea – It is formation of bulky, foul smelling , frothy and clay colored stools with large undigested fat because of impaired digestion and absorption of fat. Main cause of steatorrhea is lack of pancreatic lipase enzyme .