Peristalsis in fasting -Migrating Motor Complex1.A type of peristalsis which occurs in stomach & small intestine during long periods of fasting for several hours aftre meals.2. It is different from normal peristalsis as a large portion of stomach and intestine is involved in contraction. The contraction extend to 40 cm of the stomach in the intestine. & movement occurs once in every 1.5 -2 hrs.3. Starting from stomach and it goes to entire length of intestine at a velocity of 6-12 cm/minute. So, it takes only 10 min to reach colon after originating from stomach. 4.It sweeps & pushes the excess digestive secretions into the colon & prevents accumulation of the secretions in stomach and intestine,

Control of Peristalsis in Small Intestine by Nervous and Hormonal Signals

1.Peristaltic activity of the small intestine is greatly increased after a meal due to entry of chyme into the duodenum causing stretch of the duodenal wall.2. Hormones: (i) gastrin, CCK, insulin, motilin, and serotonin: all

enhance intestinal motility (ii) secretin and glucagon inhibit small intestinal motility. 3. Gastroileul Reflex: On taking meal, a gastroileal reflex increases peristalsis in the ileum and forces the chyme lying at ileocecal valve into the cecum of the large intestine.

Movements of the Colon

The principal functions of the colon are (1) absorption of water and electrolytes(2) storage of fecal matter until it can be expelled. The proximal half of the colon is concerned principally with absorption, and the distal half with storage. The movements of the colon are normally very sluggish. Types: a. mixing movements b. propulsive movements.

MOVEMENTS OF LARGE INTESTINE

Two types of movements:1. Mixing Movements- Haustrations, Segmental

contractions2. Propulsive Movements- Mass Peristalsis

3. Antipropulsion (reverse peristalsis)

Mixing Movements of Colon-"Haustrations."

1. At the point of circular constrictions in the large intestine, the circular muscle contracts and at the same time, the teniae coli ( longitudinal muscle of colon) also contracts & un-contracted portion of colon bulge outward forming haustrations.

2. They also move slowly toward the anus and provide a minor forward propulsion of the contents of colon

Propulsive Movements of Colon-"Mass MovementsIt is main propulsive movement of colon. Steps: A constrictive ring occurs at a distended point in the colon. Then, colon distal to the constrictive ring lose its haustra and contract as a unit, pushing the faecal matter in this segment en masse further down the colon. Duration of mass movement is 10 minutes

Initiation of Mass Movements by Gastrocolic and Duodenocolic Reflexes. Mass movements after meals occur due to gastrocolic and duodenocolic reflexes due to distention of the stomach and duodenum.

Defecation

1. Voiding of faeces is called defaecation. 2. Faeces is formed in large intestine & stored in Sigmoid

colon. 3. When faeces enters rectum due to mass movement of

colon, it raises intrarectal pressure to 20-25 cm of water & stimulates defaecation reflex.

4. In defaecation the rectum contracts & the internal & external anal sphincters relax.

5. The internal sphincter is made of smooth muscle & is innervated by parasympathetic nerve fibres via pelvic nerve.

6. The external sphincter is made of skeletal muscle & is supplied by somatic nerve fibres through pudendal nerve.

DEFAECATION REFLEX1. Stimulus: When faeces enters rectum from sigmoid colon due to mass movement of colon, the sensory nerve endings in wall of rectum get stimulated.2. Sensory Afferent Fibres: Sensory Impulses from rectum are carried via afferent fibres of pelvic nerves to the defaecation centre.3. The defaecation centre: it is located in sacral segments of spinal cord. The defaecation centre sends motor impulses via 4. Motor Efferent Fibres which are present in the efferent fibres of pelvic nerve and cary impulses to the descending colon, sigmoid colon and rectum.5. Effector: The motor impulses cause strog contractions of the descending colon, sigmoid colon and rectum and relaxaes the internal anal sphincter.6. At the same time, the external anal sphincter which is under somatic nervous system (spinal nerve-pudendal nerve) also relaxes due to signals from cerebral cortex to inhibit the pudendal nerve’s action of keeping the external sphincter always contracted. See diagm book page 252- practice)

APPLIED PHYSIOLOGY1. Constipation- failure of voiding feces2. Evacuation of gases from GIT- a. Exogenous 90% gas- swallowed while eating or

drinking carbonated beveragesb. Endogenous-10% gas- produced by bacteria action

on foodc. Gas is evacuated by flatus (through anus) or

through mouth by belching d. Composititon of flatus- N2, O2, Methane,CO2,

Odorous material -fatty acids& H2S

APPLIED PHYSIOLOGYGastrocolic ReflexDefecation may also occur by gastro colic reflex mediated by enteric nervous system, the distention of stomach (after eating) leads to contraction of rectum and thus defaecation.

Role of Hormones in GASTRIC EMPTYING

Hormonal Feedback from the Duodenum Inhibits Gastric Emptying-Role of Fats and the Hormone Cholecystokinin. (i) Hormones cholecystokinin (CCK), released from mucosa

of the jejunum by stimulus of fats entering the duodenum: This hormone acts as an inhibitor to stomach motility

(ii) Secretin is released mainly from the duodenal mucosa in response to gastric acid passed from the stomach through the pylorus. It inhibits stomach emptying.

(iii) Gastric inhibitory peptide GIP has a weak effect of decreasing gastrointestinal motility. GIP is released from the upper small intestine in response mainly to fat in the chyme.