Gastrointestinal
Physiology
Irfan Idris
Physiology department
Medical faculty of UNHAS
LEARNING CONCEPT
GI TRACT
STRUCTURE
ACCESSORY
ORGANS
ORAL CAVITY
PHARYNX
ESOPHAGUS
STOMACH
SMALL INTESTINE
LARGE INTESTINE
RECTUM
ANAL CANAL
TONGUE
TEETH
SALIVARY GLANDS
PANCREAS
LIVER
GALL BLADDER
INGESTION
SECRETION
FUNCTION
DIGESTION
MOVEMENT
ABSORPTION
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 :
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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

Lieberkühn
Deep tubular glands


epithelium into the sub mucosa. In the small
intestine, these pits, called crypts of
Complex glands—the salivary glands,
pancreas, and liver
Secretion of Water and
Electrolyte
1.
2.
3.
4.
Nerve stimulation on basal portion of the cell
membrane, causing active transport of Cl- ions to
the inside the cell
The resulting increase in electronegativity inside
the cell the causes positive ions also move to the
interior of the cell
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
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
Basic Regulatory Mechanism of
Glandular Cells

Effect of Local Contact


Effect of enteric nervous system

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Tactile stimulation
Chemical irritation
Distention of the gut wall
Autonomic stimulation



The mechanical present of food causes the glands
to secrete moderate to large quantities of
digestive juice
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



Absorption of Proteins

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sodium co-transport mechanism
Absorption of Fats

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Glucose is transported by a Sodium Co-Transport Mechanism
Fructose is transported by facilitated diffusion
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