Pancreas

1. Pancreas Weighs about 100g, and produces about 1L of juice/day. Secretions are both endocrine and exocrine. Digestive function Metabolic function Islets of Langerhans Secret insulin and glucagon Acini: secret pancreatic juice

2. Sodium Bicarbonate For neutralization of acid Enzymes for digestion of food Pacreatic Juice • Pancreatic juice contains: • Water and electrolytes (Na+, K+, Cl+, Ca++) • Bicarbonate (HCO3-) • Digestive enzymes: • Amylase • Trypsin • Lipase • Ribonuclease • Deoxyribonuclease • Etc.

3. From stomach From small intestine Regulation of the Digestive System • The activities of the G.I. Tract is regulated by: • Neural mechanisms: • Automomic nervous system • Sympathetic • Parasympathetic • Enteric nervous system • myenteric • Submucosal • Action of hormones (endocrine): • Hormones secreted from the glands located in the G.I. Tract act on effector cells of the G.I. Itself. Examples of such hormones are: secretin, gastrin, CCK (cholecystokinin)

4. Regulation of Gastric Secretion • Contractions and secretions of the stomach to some extent are automatic. For example: the presence of food causes distension in the stomach wall and this will lead to contractions. Presence of some food materials in the stomach stimulate its glands to secret gastric juice. • However, when ANS or hormones are active their effects dominate the function of the stomach. • There are 3 phases in the control of gastric secretion: 1- Cephalic phase: sight, smell, taste, even thoughts of food can initiate this phase. 2- Gastric phase: when food enters the stomach this phase becomes active. 3- Intestinal phase: when food enters samll intestine this phase becomes active.

5. Exocrine Endocrine Cephalic Phase Sight Smell Sound Thoughts Taste Touch Temp. Etc. Vagal nuclei Mouth Vagus Parietal cells HCl Chief cells Enzyme Mucus cells Mucus G cells Gastrin ACh Gastric Gland - Cephalic phase is abolished by cutting vagus (vagotomy).

6. Gastric Phase Vagal nuclei CENTRAL Vagus Food entering stomach Distension, protein digestion products ACh ACh LOCAL Parietal cells HCl Chief cells Enzyme Mucus cells Mucus G cells Gastrin Enteric Plexus Gastric Gland - Gastric secretion is abolished after administration of atropine Atropine is blocker of ACh

7. 2- Inhibition (strong): Food entering small intestine HCl CCK - CCK is released in response to fat and - secretin is released in response to low pH. Secretin Blood Intestinal Phase 1- Stimulation (weak): Food entering small intestine HCl G cell Gastrin Blood QUESTION

8. Regulation of Intestinal Function The GI has its own nervous system (enteric nervous system), it can sense and form reflex actions due to the presence of food. In the intestine the enteric plexus is very extensive and this is involved in several reflexes: 1- Gastroilial reflex = increase gastric activity causes increased motility of ileum and movement of chyme (food mixed with digestive juice) through the ileocecal valve. 2- Ileogastric reflex = when ileum is distended this decreases the motility and emptying of the stomach. 3- Intestino-intestinal reflex = over-distension of one part of the intestine causes reflex relaxation of the rest of the intestine. QUESTION

9. Sodium Bicarbonate Intestinal Mucosal Cell Neutralization Glandular Cells of Pancreas Secretin Blood Regulation of Pancreatic Secretion 1- HORMONES : a) Secretin = released from intestinal mucosa in response to presence of acidic chyme in small intestine. Acidic Chyme Disfunction of the above may cause duodenal ulcer.

10. Digestive enzymes Intestinal Mucosal Cell Digestion Glandular Cells of Pancreas CCK Blood Regulation of Pancreatic Secretion 1- HORMONES : b) CCK = released mainly in response to presence of fat, proteins and carbohydrates in small intestine. Fatty Chyme QUESTION

11. Gallbladder Emptying The bile is secreted by theliver and stored in the gallbladder. Both secretin and CCK stimulate secretion of bile by the liver. CCK is major stimulator of gallbladder contraction. Neural reflexes also help with gallbladder contraction and bile release into duodenum. Vagus Liver ACh + CCK Gallbladder + Sphincter of Oddi Pancreas _ CCK QUESTION Duodenum . . FAT . CCK Blood

12. Digestion and Absorption Food mainly contains: Carbohydrates – mainly polysaccharides (starches) and disaccharides. Lipids (fat) – mainly triglycerids Proteins – polymers of amino acids Also in small amounts food contains: - Nucleic acids, DNA and RNA - Salts and minerals, Na, Cl, Ca, Fe, PO4, Cu, etc. - Vitamins, C, D, Thiamin (B1), Riboflavin (B2), B12 etc.

13. Digestion = breaking down of large compounds in food into smaller and simpler substances that can be absorbed and used by the cells of the body. Digestion Hydrolysis

14. - Sucrose (table sugar) – a disaccharide consist of glucose and fructose. - Lactose (milk sugar) – a disaccharide consist of glucose and galactose. Carbohydrates in Food Most common carbohydrates ingested are: - Starch – long chain of glucose (polysaccharides) with occasional branching.

15. Digestion of Carbohydrates - The digestion of carbohydrates occur in mouth and it continues in the duodenum.

16. Final products of CarbohydratesDigestion Fructose Fructose Digestion & Absorption of Carbohydrates • Short oligosaccharids (a-limit dextrins), maltotrios and maltose are broken down to • single sugars (monosaccharides) by the brush border enzymes. • The resulted monosaccharides are : Glucose (80%) • Fructose (10%) • Galactose (10%) • The monosaccharides (glucose & galactose) are transported into epithelial cells by: • “secondary active transport” QUESTION Intestinal Lumen Na+ Glucose Facilitated Diffusion K+ Glucose Blood Na+

17. - Most protein digestion occurs in duodenum and jejunum. Pancreatic enzymes Food from the stomach Duodenum (small intestine) Digestion of Proteins • Proteins are polymeres of amino acids, they can be formed from less than 100 amino • acids up to thousands. • There is no digestion of proteins in mouth, the digestion starts in the stomach by the • action of pepsin. Pepsin in the stomach Protein Polypeptides + amino acids

18. Enterokinase - Pancreatic enzymes are activated in the duodenum by the action of enterokinase. QUESTION

19. - Final Products of protein digestion are: Amino acids, Dipeptides and Tripeptides.

20. Absorption of Proteins - There are five different transport systems for protein digestion products: Neutral amino acids Acidic amino acids IMINO acids Basic amino acids Di- and Tri-peptides Secondary active transport Facilitated diffusion Passive diffusion

21. Digestion of Lipids QUESTION - For their digestion, lipids must be first emulsified. - The bile secreted into duodenum combines with lipids and reduces their surface tension breaking the lipids into small droplets.

22. Digestion of Lipids QUESTION

23. Chylomicrons Absorption of Lipids