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    GastrointestinalPhysiology

    Irfan Idris

    Physiology departmentMedical faculty of UNHAS

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    LEARNING CONCEPT

    STRUCTURE

    GI TRACT

    ORAL CAVITY

    PHARYNX

    ESOPHAGUSSTOMACH

    SMALL INTESTINE

    LARGE INTESTINE

    RECTUM

    ANAL CANAL

    ACCESSORY

    ORGANS

    TONGUE

    TEETH

    SALIVARY GLANDS

    PANCREAS

    LIVER

    GALL BLADDER

    FUNCTION

    INGESTION

    DIGESTION

    ABSORPTION

    SECRETION

    MOVEMENT

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    The alimentary tract provides the body with acontinual 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

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    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 ones fingers around a thindistended tube, then constricting the fingers and slidingthem 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 aperistaltic wave can then only churn the intestinal contents,rather than propelling them forward

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    law of the gut

    (usus)

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    Stimulus for intestinal

    peristalsis Distention of the gut

    Chemical or physical irritation of theepithelial gut

    Parasympathetic nervous signals

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    General Principles of Alimentary

    Tract Secretion Single-cell mucous glands called simply

    mucous cells (goblet cells)

    Pits that represent invaginations of theepithelium into the sub mucosa. In the smallintestine, these pits, called crypts ofLieberkhn

    Deep tubular glands Complex glandsthe salivary glands,

    pancreas, and liver

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    Secretion of Water andElectrolyte

    1. Nerve stimulation on basal portion of the cellmembrane, causing active transport of Cl- ions tothe inside the cell

    2. The resulting increase in electronegativity insidethe cell the causes positive ions also move to theinterior of the cell

    3. The excess of both these ions inside the cellcreates an osmotic force that pulls water to theinterior, thereby increasing the hydrostatic

    pressure inside the cell and causing the cell toswell

    4. The pressure in the cell then results in ruptures ofsecretory border of the cell causes flushing ofwater, electrolyte, and organic materials out of

    the glandular cell into the lumen of the gland

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    Basic Regulatory Mechanism ofGlandular Cells Effect of Local Contact

    The mechanical present of food causes the glandsto secrete moderate to large quantities ofdigestive 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 ofstimulation

    Hormonal

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    DIGESTION PROCESS

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    Absorption of water and ion

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    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

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