GI Motility and Regulation

Question 1

Describe the movement of segmentation.

Answer 1

Segmentation is mixing of the luminal contents.

Question 2

Review the mechanism of smooth-muscle contraction.

Answer 2

Myosin light chain kinase is inside the cell, but is inactive.
Calcium enters the cell during an NMJ depolarization.
Calcium interacts with calmodulin, and the active form of calmodulin activates myosin light chain kinase (MLCK).
MLCK phosphorylates myosin, leading to the actin/myosin interaction and contraction.

Question 3

Smooth muscle cells are held together via _______________ and communicate via ______________.

Answer 3

adherens junctions; gap junctions

Question 4

Auerbach’s plexus is also called ______________.

Answer 4

the myenteric plexus

Question 5

As you go further down the GI tract, the basic electrical rhythm _____________. Why?

Answer 5

increases in frequency; this is important because food material will empty faster than material enters

Question 6

Describe the three phases of digestion in terms of molecular signalling.

Answer 6

(1) Cephalic phase: entirely controlled by the nervous system; occurs when we see/think about food.
(2) Gastric phase: neural and hormonal
(3) Intestinal phase: mostly hormonal

Question 7

Capsaicin activates ___________ in the esophagus.

Answer 7

substance P-sensitive contraction (this is why spicy food stimulates digestion)

Question 8

Failure of the lower esophageal sphincter to relax is called _____________; it can make swallowing difficult.

Answer 8

achalasia

Question 9

The pyloric sphincter prevents passage of particles greater than _________.

Answer 9

2 mm in diameter

Question 10

The stomach can store up to ______________.

Answer 10

4 liters of food

Question 11

Hydrochloric acid in the stomach does what?

Answer 11

Denatures proteins

Kills bacteria

Question 12

Gastric motility contractions begin in the _____________.

Answer 12

distal stomach (in the antrum) and proceed to the proximal stomach

Question 13

Compare emptying rates for carbohydrates, fat, and protein.

Answer 13

Carbohydrates: fastest
Fat: slowest
Protein: intermediate

Question 14

Describe the steps of vomiting.

Answer 14

(1) Increased salivation of bicarb-rich secretions
(2) Reverse peristalsis from small intestine to stomach
(3) Abdominal muscles contract
(4) Relaxation of the UES and LES
(5) Gastric emptying

Question 15

Explain the gastroileal and gastrocolic reflexes.

Answer 15

Gastroileal: food arrival in the stomach stimulates movement through ileocecal sphincter

Gastrocolic: food arrival in the stomach stimulates movement through the colon

Both are mediated by the enteric nerve.

Question 16

Explain the migrating motor complex phases.

Answer 16

Every 90-100 minutes, the stomach and small intestine contract to clean out the gut.

Phase I: quiescence
Phase II: irregular contractions mix up the food, but do not cause peristalsis
Phase III: pushes food to ileocecal valve

Question 17

True or false: the large intestine also has regular contractions in the absence of feeding.

Answer 17

False. The MMC phases stop at the ileocecal valve.

Question 18

The sections of large intestine are called ___________.

Answer 18

haustra

Question 19

Haustrations serve to _________________.

Answer 19

compact food

Question 20

The basal electric rhythm is ______ derived.

Answer 20

myogenically

Question 21

Gastrin is induced by ____________ and stimulates increased ___________ and decreased _____________.

Answer 21

gastric distension; peristalsis; pyloric tone

Question 22

Arrival of ____________ leads to secretion of cholecystokinin by the enteric endocrine cells.

Answer 22

fats in the duodenum

Question 23

Transit of the intestine takes about ________ hours.

Answer 23

3-5