DIGESTION IN SMALL INTESTINE – MOTILITY, SECRETION & CONTROL
| A | Peristalsis | |
| B |
Peristaltic rush |
|
| C |
Segmentation contraction |
|
| D |
Migrating motor complex |
The following bowel movement is not seen in normal individual:
| A |
Peristalsis |
|
| B |
Peristaltic rush |
|
| C |
Segmentation contraction |
|
| D |
Migrating motor complex |
Peristaltic rush is a very intense peristaltic wave, occurs when intestine is obstructed, thus not seen in normal individuals.
- Peristalsis, segmental contraction, haustrations and migrating motor complex are all normal bowel movements.
Ref: Ganong’s, review of medical physiology, 22nd edition, Page 480, 482
Small intestinal peristalsis is controlled by :
| A |
Myentric plexus |
|
| B |
Meissners plexus |
|
| C |
Vagus nerve |
|
| D |
Para sympathetic system |
A i.e. Myentric plexus
Myenteric (Auerbach’s) plexus is situated b/w and innervates outer longitudinal & middle circular muscular layers and is primarily concerned with motor controlQ. Submucosal (meissner’s) plexus situated between middle circular layer and mucosa is primarly concerned with control of intestinal secretionQ as it innervates glandular epithelium, intestinal endocrine cells & submucosal blood vessels.
| A |
Segmentation |
|
| B |
Haustrations |
|
| C |
Migratory motor complexes (MMC) |
|
| D |
Peristalsis |
D i.e. Peristalsis
- Peristalsis propels the small intestinal content (chyme) toward the large intestine.
- It is a reflex response that is initiated when the gut wall is stretched by the contents of the lumen.
- It occurs in all parts of GIT from the oesophagus to rectum propelling the content forward.
- It can be increased or decreased by autonomic input to gut but its occurrence is independent of extrinsic innervation.
- It is blocked only if the segment is reversed before it is sutured back (not by removed of intestine segment & resuturing in original position).
| A |
Distal colon |
|
| B |
Jejunum |
|
| C |
Proximal Colon |
|
| D |
Ileum |
Ans. is ‘a’ i.e., distal colon
In peristalsis following are involved except ‑
| A |
NO |
|
| B |
Substance P |
|
| C |
Noradrenaline |
|
| D |
VIP |
Ans. is ‘c’ i.e., Noradrenaline
- Peristalsis requires an active myenteric (Auerbach’s) plexus.
- Local stretch by chyme releases serotonin, which activates myenteric plexus.
- Cholinergic neurons of this plexus passing in a retrograde direction release substance P and acetylcholine, causing smooth muscle contraction.
- Cholinergic neurons passing in an antegrade direction activate neurons that secrete NO, VIP, and ATP, produing relaxation ahead of the stimulus.
| A |
Substance P |
|
| B |
Acetylcholine |
|
| C |
VIP (vasoactive intestinal polypeptide) |
|
| D |
Norepinephrine |
Ans. is ‘c’. VIP (vasoactive intestinal polypeptide)
In peristalsis:-
- Acetylcholine & substance P → Causing smooth muscle contraction.
- VIP, NO (Nitric Oxide) & ATP → Producing relaxation ahead of the stimulus.
