Regulation of Intestinal FunctionThe GI has its own nervous system (enteric nervous system), it cansense and form reflex actions due to the presence of food.In the intestine the enteric plexus is very extensive and this is involved inseveral 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 emptyingof the stomach.3- Intestino-intestinal reflex = over-distension of one part of the intestine causes reflex relaxation of the rest of the intestine.
Regulation of Pancreatic SecretionHORMONES : a) Secretin = released from intestinal mucosa in response to presence of acidic chyme in small intestine. Acidic Sodium Chyme Bicarbonate Intestinal Neutralization Glandular Mucosal Cells of Cell Pancreas Secretin Blood Disfunction of the above may cause duodenal ulcer.
Regulation of Pancreatic SecretionHORMONES : b) CCK = released mainly in response to presence of fat, proteins and carbohydrates in small intestine. Fatty Digestive Chyme enzymes Intestinal Digestion Glandular Mucosal Cells of Cell Pancreas CCK Blood
Gallbladder EmptyingThe bile is secreted by the liver and stored in the gallbladder. Both secretin and CCKstimulate 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 + Pancreas CCK FAT Duodenum ... CCK Blood
Digestion and AbsorptionFood mainly contains: Carbohydrates – mainly polysaccharides (starches) and disaccharides. Lipids (fat) – mainly triglycerids Proteins – polymers of amino acidsAlso 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.
DigestionDigestion = breaking down of large compounds in food into smaller and simplersubstances that can be absorbed and used by the cells of the body.
= glucose Carbohydrates in Food = fructoseMost common carbohydrates ingested are: = galactose - Starch – long chain of glucose (polysaccharides) with occasional branching. - Sucrose (table sugar) – a disaccharide consist of glucose and fructose. - Lactose (milk sugar) – a disaccharide consist of glucose and galactose.
Lactose Intolerance Deficiency in enzyme lactase Inadequate lactose digestion (Lactose in milk) High level of lactose in intestine (Colon)Osmotic effect (water moves Bacterial action onfrom blood to lumen) undigested lactose. Intraluminal volume and gas DIARRHEOA & GAS
Digestion of Carbohydrates- The digestion of carbohydrates occur in mouth and it continues in the duodenum.
Digestion & Absorption of Carbohydrates- Short oligosaccharids (α-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 bysecondary active transport and fructose is transported by facilitated diffusion. Fructose Na+ Glucose Intestinal Lumen Fructose K+ Glucose Na+ Blood
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. pepsinogen Chief cells Pepsin in the stomach Protein Polypeptides + amino acids - Most protein digestion occurs in duodenum and jejunum. Pancreatic enzymes Food from the stomach Duodenum (small intestine)
- Pancreatic enzymes are activated in the duodenum by the action of enterokinase. Enterokinase
- Final Products of protein digestion are: Amino acids, Dipeptides and Tripeptides.
Absorption of Proteins- There are five different transport systems for protein digestionproducts: Neutral amino acids Acidic amino acids Secondary active transport IMINO acids Basic amino acids Facilitated diffusion Di- and Tri-peptides Tertiary active transport
Digestion of Lipids- 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.