GI Motility Of Small Intestine

Question 1

Functions of small intestine

Answer 1

absorption

Regulating gastric secretion

Emptying process

Question 2

3 types of motility processes occurring in small intestines

Answer 2

-segmentation
-peristalsis
-migrating motility complex

Question 3

Segmentation

Answer 3

Small short-lived contractions

Question 4

Small intestines’ function in mixing chyme

Answer 4

Mixing chyme with:

-fluid from the intestine
-(e.g. bile from the liver and biliary tree)
-Bile facilitates the digestion of fats

-pancreatic enzymes (e.g., lipases, proteases)
-These enzymes facilitate the breakdown of proteins, lipids, and carbohydrates

-intestinal and pancreatic fluid
-(e.g., bicarbonate, mucus)

Question 5

Small intestine function in Moving chyme anterograde (towards anal side) or retrograde (toward oral side)

Answer 5

This “to-and-fro” movement helps in the mixing of chyme

This movement also increases the contact time between chyme and the mucosal surface, which supports the overall goal of enhancing absorption

Question 6

Segmentation process of small intestine

Answer 6

When a food bolus enters the small intestine, it causes distension

➡️distension actitivates stretch receptors and consequently trigger myenteric plexus to stimulate smooth muscles to constrict

➡️the smooth muscles of the small intestine constrict at different points, forming sausage-like appearance

➡️when smooth muscles contract, 1/2 of the bolus goes up (oral side) while the other 1/2 is pushed down (anal side)

➡️as a result, the chyme is mixed with other points of chyme along the length of small intestine

➡️this also propels the bolus towards the large intestine

Question 7

Peristalsis of small intestine

Answer 7

-The main function of peristalsis is propulsion.
-It propels food from the small intestines to the large
intestines

-Peristalsis occurs whenever food bolus enters the
small intestines

Question 8

The process of peristalsis of small intestine

Answer 8

-When a food bolus enters the small intestines, it results in distension, stretching the intestinal walls

-This activates the receptors on the submucosa, which send signals to the myenteric/Auerbach’s plexus
-This plexus is located in between the circular and outer longitudinal layers of the external muscularis layer

-The myenteric plexus then sends efferent signals to the smooth muscle layers of the small intestine
-To stimulate contraction, it releases
-acetylcholine
-substance P
-To inhibit contraction/stimulate relaxation, it releases VIP or nitric oxide

Question 9

Peristalsis (of small intestine) process along the oral side (above the food bolus)

Answer 9

The circular layer contracts, forming a constriction ring around the food bolus

The longitudinal layer relaxes, keeping the lumen tight

Question 10

Peristalsis (of the small intestine) process on the anal side (below the bolus)

Answer 10

-The circular layer relaxes, so the constriction ring does not form
-it sends signals down a descending plexus
-this will release acetylcholine or substance P

-The longitudinal layer contracts, opening up the lumen o It sends signals down a descending plexus
-this will release VIP or nitric oxide

Question 11

Migrating motility complex (MMC) of small intestine

Answer 11

-The migrating motility complex is a type of peristaltic wave (primarily propulsion) which occurs only between meals, during the fasting state

-it starts at the stomach (pylorus)/duodenum and travels al the way to the ileum
-It takes about 2 hours for the MMC to arrive at the ileum from the duodenum

Question 12

Function of MMC of small intestine

Answer 12

These contractions pull food residue, dead cells, bacteria, and any undigested substances

Question 13

What stimulates MMC?

Answer 13

Motilin which is released by small intestine

Question 14

Ileo-cecal valve/sphincter

Answer 14

-When the food bolus arrives at the end of the small intestine, it needs to pass through the ileo-cecal valve/sphincter before reaching the colon/large intestines

-The ileo-cecal valve/sphincter is a tightly-constricted rim of smooth muscle

Question 15

Ileo-cecal valve only opens when stimulated by

Answer 15

1) elevated gastric levels

2)gastro-ileal reflex

Question 16

Elevated gastrin levels and gastro-ileal reflex help with:

Answer 16

-Relaxing the valve
-Constricting the distal ileum, which propels the bolus/feces to move

Question 17

Gastrin as a stimulus for the opening of ileo-cecal sphincter

Answer 17

-When food enters the stomach, the stretch response stimulates the enteroendocrine G cells to release gastrin

-Gastrin functions to:
-Stimulate gastric contraction
-Stimulate parietal cells to produce hydrochloric acid (HCl)
-Stimulate chief cells to produce pepsinogen
-Regulate gastric emptying
-Gastrin also travels through the blood to reach the ileum,
where it propels fecal matter through:
1) Relaxation of the ileo-cecal valve
2)Contraction of the distal ileum

Question 18

Gastro-ileal reflex as a stimulus of opening of ileo-cecal valve:

Answer 18

-When there is acidic or fatty chyme in the stomach
➡️these stimulate the sensory receptors
➡️the sensory receptors send signals to the CNS through the vagus nerve

-The efferent fibers of the vagus nerve send signals to the ileum, where it also stimulates:
-Relaxation of the ileo-cecal valve
-Contraction of the distal ileum