Question

how does segmental propulsion movement differ from direct, fast peristalasis??

digenstion small intestine

Answer 1

Difference between segmental propulsion movement and fast peristalsis-

SEGMENTAL PROPULSION MOVEMENTS -

It is also known as rhythmic segmental contractions or pendular movements.

These are ring like contractions that appear at fairly regular intervals (rhythmic) along the small intestine involving a localised segment of 1-2 cm by increases in calcium influx.

They are 2 types - eccentric and concentric contractions.

ECCENTRIC CONTRACTIONS-

-Eccentric contractions are mainly due to contraction of outer longitudinal smooth muscle layer.

They are mainly concerned with mixing function i.e food is thoroughly mixed with digestive juices.

-These are localised contractions which occur in several regions at once or sequentially.

-They initially produce a segment shortening and consequently dilates it.

CONCENTRIC CONTRACTIONS-

-Concentric contractions are mainly due to inner circular smooth muscle layer.

-These contractions are mainly concerned with churning action i.e food is divided(segmented) and is propelled towards the large intestine.

-These contractions occur over a segment longer than eccentric contraction segment.

-These contractions cause narrowing of lumen and push the contents away from the constricted segment.

Therefore, by segmental contractions, the food is divided(segmented) and mixed together with digestive juices thoroughly and finally chyme is formed.

FAST PERISTALSIS -

features of peristalsis -

-When intestinal Wall is stretched or distended by food(chyme), a circular constriction forms above it due to contraction of circular muscle layer while the lumen below it is dilated due to contraction of longitudinal muscle layer.

Therefore, intestinal contents move towards the dilated part;then contraction of circular muscles spread to this dilated part which in turn constricted, while the segment below it is dilated by contraction of longitudinal muscle layer.

Several of these wave-like contractions occur simultaneously along the length of the intestine, so that its movement is vermiform(like a worm), therefore, they are called vermicular or peristaltic movements.

Peristalsis is a coordinated reaction in which a wave of contraction preceded by a wave of relaxation passes down a hollow viscus. The contents of viscus as they are propelled along would always enter a segment which had actively relaxed and enlarged to receive them.

Function-These waves propel the intestinal contents towards the ileo-caecal valve. Each peristaltic wave lasts for 1-2 seconds and propels the chyme a few centimetres.

PERISTALIS FOOD - Ring like Peristalic contractions sweep food along the Small intestine SEGMENTATION chyme is mixed with circular Muscles contract, breaking chyme into smaller Pieces thoroughly digestive juices