Gastrointestinal Physiology

Question 1

Migrating Myoelectric Complex (MMC)

Answer 1

A four phased, interdigestive state that usually runs between 1-2 hours. Functionally, it serves as a house keeping mechanism of the GI tract from the mid-stomach to the terminal ileum. Stage 3 is triggered by motilin secreted by M cells of the digestive track and is a 10 minute period of serial contractions.

Question 2

Contrast primary and secondary propulsion involved in swallowing.

Answer 2

Primary: a voluntary contract contraction caused by swallowing centers in the medulla. Secondary: an involuntary contraction caused by autonomic and enteric innervation.

Question 3

Myenteric plexus

Answer 3

Question?

Question 4

Achalasia

Answer 4

Caused by the inability lower esophageal smooth muscles to relax causing pain with swallowing and dilation of the superior esophagus. You can treat this by cutting the lower esophageal sphincter; however, this also results in GERD.

Question 5

Ileosis

Answer 5

Tumor that obstructs the ileum. This area of the tract needs to be resected.

Question 6

Gastric accommodation

Answer 6

When food enters the stomach, the vagus nerve sends signals for the stomach to expand. Feelings of pressure will not occur until roughly a liter of food enters to fill the stomach.

Question 7

What is the effect of a vagotomy on gastric accommodation?

Answer 7

Without the vagus, there is no gastric accommodation and people experience pain when eating small amounts of food.

Question 8

Describe the order in which things leave the stomach?

Answer 8

Carbohydrates, proteins, and finally fats

Question 9

What is the first pass effect?

Answer 9

When things are digested, they pass first through the liver before they reach systemic circulation.

Question 10

Where are the three places in the GI tract that do not have smooth muscle?

Answer 10

esophagus, external anal sphincter, and mouth

Question 11

What are the functions of the GI tract?

Answer 11

Remember: DEEP MASS Digestion Endocrine Elimination Protection Motility Absorption Secretion Storage

Question 12

Describe the pH throughout the GI tract.

Answer 12

Stomach 1-2 Jejenum 5 enters 7 exists

Question 13

Describe the enteric nervous system.

Answer 13

Myenteric (muscle movement) and submucosal (secretions)

Question 14

Describe action potential in the GI tract.

Answer 14

The resting membrane potential is not a flatline, but rather resting membrane potential (RMP) that are slow waves. Once it reaches threshold at -40 mV, there are action potentials that can be reached called spike potentials (SP). The amount of SP that are reached correlates to the strength of the contraction.

Question 15

How do calcium levels change contraction in smooth muscle?

Answer 15

Increased Calcium levels intracellularly leads to increased binding to calmodulin and more crossbridges increasing the strength of the contraction.

Question 16

Contrast the rate of contractions in the stomach v. the jejunum.

Answer 16

In the stomach, the rate is 3 waves/min in order to promote mixing; whereas in the jejunum the rate is 12 waves/min to promote movement to the colon.

Question 17

Facts that can help depolarization of smooth muscles

Answer 17

Stretch, acetylcholine, parasympathetics, gastrin, serotonin, substance P (tachykinin)

Question 18

Factors that can help in hyperpolarization of smooth muscle

Answer 18

Sympathetics, VIP (vagoactive intestinal peptide), NO

Question 19

What sets the timing for action potentials in the GI tract?

Answer 19

RMPs, slow waves

Question 20

Describe motility in the small intestines.

Answer 20

Peristalsis - contraction of the circular muscle behind and relaxation of the circular muscle in front of the bolus. Cholinergic leads to contraction and VIP leads to relaxation. This is mainly under vagal/extrinsic control.

Segmentation - There is contraction behind and ahead of the bolus to promote mixing as well as motion down the GI tract. This is predominantly under enteric control/ intrinsic control.

Question 21

Describe contractions in the gall bladder.

Answer 21

CCK or cholescystokinin causes contraction of the gallbladder that induces the release of bile. Vagal stimulation is also involved.

The sphincter of Oddi is opened by vagal relaxation.

Question 22

Describe motion in the colon.

Answer 22

1. Segementation caused by the contraction of tenai coli and is very slow.
2. Mass movements: peristaltic contractions in the ascending and transverse colon under vagal control. Note that the distal colon is not under vagal control.

Question 23

Gastrocolic reflex

Answer 23

When you eat, the fullness of the stomach causes vagal activation leading to mass movement in the colon leading often to the rectospincteric reflex in which you feel the need to defecate.

Question 24

Valsalva maneuver

Answer 24

increase in abdominal pressure to move feces out of the colon