Movements of the small intestine 1- Mixing movement (segmentation contraction): When the chyme distends the small intestine wall, many concentric contractions appear, then after these segments relax, other sets of contraction starts at new points.

3-5 hours to pass from the pylorus to the ileocecal valve. 2- Peristalsis: - Each peristaltic wave progress to only 3-5 cm, therefore, the chyme requires about 3-5 hours to pass from the pylorus to the ileocecal valve. - These peristaltic waves greatly increase after meal & they cause progression of the chyme & spread it to be well digested & absorbed. 2-3 times per min.

Peristaltic rush It is strong & powerful waves that wash down the contents of small intestine to the large intestine. It occurs when there is irritant chyme or when there is excessive distention of the small intestine. Rush = ينطلق- يهجم- يهرول

Migrating motor complex These are moderately powerful waves occur in fasting person, starting from the stomach sweeping any excess digestive secretions or other intra intestinal debris into the colon, thereby preventing their accumulation in the upper GIT.

Movements of the muscularis mucosae & muscle fibers of the villi When the mucus membrane contracts it causes folding of the mucosa increasing the absorptive surface area. Contraction of the M. fibers in the villi causes shortening, elongating & shortening again (milking) of the villi helping the lymphatic flow.

Functions of the ileocaecal valve This valve is important to prevent regurgitation of the fecal material from the caecum into the ileum. The ileocecal sphinctor slightly resist the emptying of ileum, so, prolongs the stay of the chyme, thereby facilitates its absorption.

The colon The main function of the colon is to absorb water& electrolytes & to store the fecal material until they can be expelled. The longitudinal M. of the colon is not a complete layer, but they are aggregated in 3 longitudinal strips called the Taenia coli.

Movements of the colon 1- Mixing movements (haustrations): They are segmentation contractions occurring at certain points due to the contraction of the circular Ms & taenia coli, the non stimulated parts of the wall bulge out like sacs called haustrations, which provides a minor amount of forward propulsion of colonic contents.

2- Propulsive movements (mass movement): The content of the caecum & ascending colon is pushed by slow haustral contractions, but from the transverse colon to the sigmoid by mass movements. The mass movements occur about 3 times daily & are specially strong 15 minutes after breakfast. It starts after irritation of the colon, a segment of contraction develops proximal to the irritation, then about 20 cm of the colon distal to the constriction losses the haustration & contracts as one unit forcing the fecal material forward, when the contents reaches the rectum the desire of defecation is felt.

Initiation of mass movement 1- when food enters the stomach or chyme enters the duodenum, mass movement is initiated through gastrocolic & duodenocolic reflexes which are mediated by extrinsic ANS. 2- When there is parasympathetic stimulation or when there is over distention of a segment of colon. 3- when there is irritation of colonic mucosa, mass movement is also initiated

Defecation There is sharp angulation between the sigmoid colon & the rectum, also there is a weak functional sphincter at this site, both these factors prevent the entrance of feces to the rectum. When there is forceful mass movement in the colon, the feces will pushed into the rectum & the desire for defecation is initiated by reflex contraction of the rectum & relaxation of anal sphincter.

Continual dribble of fecal mater through the anus is prevented by tonic constriction of; 1- Internal anal sphincter, which is thickening of circular muscles inside the anus. 2- External anal sphincter, which composes of striated voluntary muscles that surrounds the internal sphincter & extends distal to it. This sphincter is controlled by pudendal N, which is somatic N & therefore, it is under voluntary control.

There are 2 types of defecation reflexes: 1- Intrinsic reflex: When feces distends the rectum, the myenteric plexus are activated & initiates peristaltic waves in the descending colon, sigmoid & rectum forcing the feces to the anus, also there is relaxation of the internal anal sphincter. 2- The parasympathetic defecation reflex: When feces enters the rectum, afferent stimuli travel to the sacral segments, then efferent motor stimuli arise & travel through the pelvic Ns to the descending colon, sigmoid & rectum initiating strong peristaltic waves.