Function of large intestine (dental) 0910

8/7/2019 Function of large intestine (dental) 0910

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FUNCTION OFLARGE INTESTINEDR. MOHD.HEIKAL MY

PHYSIOLOGY DEPARTMENT

Faculty of Medicine [email protected]


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OBJECTIVES

1. To explain the function of large intestine in

term of secretion, motility and absorption

2. To describe the role of colonic normal flora GItract

3. To explain the mechanism of defecation


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LARGE INTESTINE

Primary function: to store and concentrate fecal

material before defecation

Secretion consists of mucus and fluid containingHCO-3 and K+

i) protection to the mucosa

ii) lubrication to facilitate passage of feces

iii) neutralized acid produced by bacterial fermentation


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MOTILITY

i) Haustral contractions

Similar to segmentation but slow and non

propulsive; BER (1/30min)

Initiated by distension

Controlled by local reflexes through intrinsic

plexuses

Fx : facilitate mixing & absorption, storageCommon in proximal colon


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ii) Mass action contraction(Mass movement)

Simultaneous, intense and prolonged contraction

of colonic smooth muscle over large confluent

areas

Triggered by gastrocolic reflex

Move colonic contents from one portion of large

intestine to another in few secondsCommon in central and distal colon


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Intestinal & colon reflex

Reflex mediated from the stomach to the smallintestine & colon by:

i) Hormones : Gastrin

ii) Local Distension in stomach PNS

Ileum & Colonic Motility and Mass movement

movement of material through ileocecal sphinc.

pushes colonic contents to rectum

+ defecation reflex Gastroileal & gastrocolic reflexes

initiated to move the existing contents father down

the tract to prepare for the incoming food


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ABSORPTION

Function : absorption of water and Na+

90% of fluid semisolid feces

Na+ is actively absorbed and H2O follows the

osmotic gradient Absorption of vitamin K (synthesized by colonic

bacteria)

Absorption of fatty acids ( undigested fiber

metabolized by bacteria) through passive diffusion


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COLONIC NORMAL FLORA

500 different species bacteria reside in colon

Slow colonic movement : bacterial growth &accumulation

Harmless & provide beneficial functions: Nutritional contributions

Vit K, B complex, Folic acid

Short chain fatty acids

Enhance intestinal immunity :

Competitive supress the growth of pathogenic microbes Promote colonic motility

Maintain colonic mucosal integrity


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DEFECATIONAccomplished by series of

voluntary & involuntary acts

Initiated by movement of fecesinto rectum (*1).

The resultant in intra-rectalpressure produces an urge todefecate.

Stimulation of stretch receptorENS & PNS activity (*3a, *3b)

Signals sent to mass movement& local peristalsis in large intestine(*4a, *4b)

At the same time reflex relaxationof internal anal sphincter occurs.

External anal sphincter can becontrolled voluntarily

Defecation occurs if external

sphinter relax


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thank


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TUTORIAL

1. Describe the neural reflexes leading to increase salivary

secretion.

2. List and explain the cephalic, gastric and intestinal phase stimuli

that stimulate or inhibit gastric acid secretion.

3. Describe the factors that control gastric emptying

4. Identify the enzymes involved in carbohydrate digestion and the

mechanism of carbohydrate absorption in the small intestine.

5. List three ways in which protein or their digestion products can

be absorbed from intestinal lumen into interstitial space/blood

circulation. 6. Explain the role of bile salt in fat digestion and absorption.

7. Describe the hormonal regulation of pancreatic juice secretion.

8. Describe the sequence of events that occur during defecation.

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Function of large intestine (dental) 0910