Chapter 62 - Guyton

Question 1

Layers of intestinal wall from outer to inner layer.

Answer 1

serosa–>longitudinal muscle layer–>circular muscle layer–>submucosa–>mucosa

Question 2

syncytium

Answer 2

when an action potential is elicited anywhere within the muscle mass, it generally travels in all directions in the muscle

Question 3

Most GI contractions occur rhythmically, as a result of which types of waves?

Answer 3

slow waves (these waves will initiate spike potentials which are the true action potentials that cause smooth muscle contraction)

Question 4

The slowness of opening and closing of the __________ channels accounts for the long duration of the action potentials.

Answer 4

calcium-sodium

Question 5

Factors that depolarize the membrane (make it more excitable).

Answer 5

stretching of the muscle, Ach, stimulation parasympathetic nerves that secrete Ach
at their endings, and stimulation by several specific gastrointestinal hormones

Question 6

Important factors that make the membrane potential hyperpolarized (less excitable).

Answer 6

effect of NE or EPI on the fiber membrane and stimulation of the sympathetic nerves that secrete mainly NE at their endings

Question 7

During which type of waves does a significant amount of calcium enter the fibers and cause contraction?

Answer 7

spike potentials

Question 8

Two plexuses of the enteric nervous system.

Answer 8

myenteric - GI movements; submucosal - GI secretion and blood flow

Question 9

Why might the myenteric plexus inhibit some muscles?

Answer 9

it inhibits the pyloric sphincter and ileocecal valve to allow emptying

Question 10

_____________ most often excites gastrointestinal

activity.

Answer 10

Acetylcholine

Question 11

_____________ almost always inhibits gastrointestinal activity.

Answer 11

Norepinephrine

Question 12

Stimulation of parasympathetic nerves causes general ________ in activity of the entire enteric nervous system.

Answer 12

increase

Question 13

The sympathetic fibers to the gastrointestinal tract originate in the spinal cord between segments?

Answer 13

T5-L2

Question 14

The parasympathetic fibers to the gastrointestinal tract originate?

Answer 14

cranial (mainly vagus) and sacral (S2-S4) nerves

Question 15

Strong sympathetic stimulation of the gut results in?

Answer 15

little to no movement of food through the GI tract

Question 16

Primarily stimulates gastric acid secretion.

Answer 16

gastrin

Question 17

At the same time that this hormone causes emptying of the gallbladder, it also slows the emptying of food from the stomach to give adequate time for digestion of the fats in the upper intestinal tract.

Answer 17

CCK

Question 18

In response to gastric juice emptying into the duodenum from the stomach, this hormone has a mild effect on motility of the gastrointestinal tract and acts to promote pancreatic secretion of bicarbonate which in turn helps to neutralize the acid in the small intestine.

Answer 18

secretin

Question 19

Functional types of movement in the digestive tract.

Answer 19

propulsive (peristalsis) and mixed movements

Question 20

Effectual peristalsis requires an active ________ plexus.

Answer 20

myenteric

Question 21

Splanchnic Circulation

Answer 21

blood flow through the gut itself plus blood flows through the spleen, pancreas, and liver

Question 22

Fats absorbed from the intestinal tract are not carried in the portal blood to the liver, as with the other nutrients. What occurs with fat?

Answer 22

absorbed by intestinal lymphatics and then conducted to the systemic circulating blood by way of the thoracic duct, bypassing the liver

Question 23

What is a major value of sympathetic vasoconstriction of the gut and splanchnic blood supply?

Answer 23

to provide muscles and the heart with blood during exercise, or to send blood to other tissues where it is needed during circulatory or hemorrhagic shock