Gastrointestinal Physiology Irfan Idris Physiology department Medical faculty of UNHAS

LEARNING CONCEPT STRUCTURE GI TRACT ORAL CAVITY PHARYNX ESOPHAGUS STOMACH SMALL INTESTINE LARGE INTESTINE RECTUM ANAL CANAL ACCESSORY ORGANS TONGUE TEETH SALIVARY GLANDS PANCREAS LIVER GALL BLADDER FUNCTION INGESTION DIGESTION ABSORPTION SECRETION MOVEMENT

The alimentary tract provides the body with a continual supply of water, electrolytes, and nutrients : (1) movement of food through the alimentary tract; (2) secretion of digestive juices and digestion of the food; (3) absorption of water, various electrolytes, and digestive products; (4) circulation of blood through the gastrointestinal organs to carry away the absorbed substances; and (5) control of all these functions by local, nervous, and hormonal systems

Functional Types of Movements in the Gastrointestinal Tract Propulsive movement : Peristalsis : a contractile ring appears around the gut and then moves forward; this is analogous to putting one’s fingers around a thin distended tube, then constricting the fingers and sliding them forward along the tube Mixing movement In some areas, the peristaltic contractions themselves cause most of the mixing. This is especially true when forward progression of the intestinal contents is blocked by a sphincter, so that a peristaltic wave can then only churn the intestinal contents, rather than propelling them forward

law of the gut

Stimulus for intestinal peristalsis Distention of the gut Chemical or physical irritation of the epithelial gut Parasympathetic nervous signals

General Principles of Alimentary Tract Secretion Single-cell mucous glands called simply mucous cells (goblet cells) Pits that represent invaginations of the epithelium into the sub mucosa. In the small intestine, these pits, called crypts of Lieberkühn Deep tubular glands Complex glands—the salivary glands, pancreas, and liver

Secretion of Water and Electrolyte 1. Nerve stimulation on basal portion of the cell membrane, causing active transport of Cl - ions to the inside the cell 2. The resulting increase in electronegativity inside the cell the causes positive ions also move to the interior of the cell 3. The excess of both these ions inside the cell creates an osmotic force that pulls water to the interior, thereby increasing the hydrostatic pressure inside the cell and causing the cell to swell 4. The pressure in the cell then results initiates minute opening of secretory border of the cell causes flushing of water, electrolyte, and organic materials out of the glandular cell into the lumen of the gland

Basic Regulatory Mechanism of Glandular Cells Effect of Local Contact The mechanical present of food causes the glands to secrete moderate to large quantities of digestive juice Effect of enteric nervous system Tactile stimulation Chemical irritation Distention of the gut wall Autonomic stimulation Parasympathetic increase the rate of secretion Sympathetic can have dual effect; increase or decrease the secretion depend on the rate of stimulation Hormonal

DIGESTION PROCESS

Absorption of water and ion

Absorption of Nutrients Absorption of Carbohydrates Glucose is transported by a Sodium Co-Transport Mechanism Fructose is transported by facilitated diffusion Absorption of Proteins sodium co-transport mechanism Absorption of Fats monoglycerides and free fatty  bile micelles Diffusion Absorption in the Large Intestine: Formation of Feces active absorption of sodium electrical potential gradient created by absorption of the sodium causes chloride absorption as well