Gastrointestinal Physiology Irfan Idris Physiology department Medical faculty of UNHAS
GastrointestinalPhysiology
Irfan IdrisPhysiology department
Medical faculty of UNHAS
LEARNING CONCEPT
STRUCTURE
GI TRACT
ORAL CAVITYPHARYNXESOPHAGUSSTOMACHSMALL INTESTINELARGE INTESTINERECTUMANAL CANAL
ACCESSORYORGANS
TONGUETEETHSALIVARY GLANDSPANCREASLIVERGALL 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 AlimentaryTract 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