GI Motility

Question 1

What are the four functions of the GI tract?

Answer 1

1. digestion
2. secretion
3. absorption
4. motility

Question 2

What role do the epithelium and mucosa play in the functions of the GI tract?

Answer 2

Secretion and absorption

Question 3

What is the role of smooth muscle in the function of the GI tract?

Answer 3

motility

Question 4

What portions of the GI tract are responsible for motility?

Answer 4

Mouth to rectum

Question 5

What part of the GI tract is responsible for absorption?

Answer 5

Mostly the intestines (specifically the small intestine) although the stomach can absorb some water

Question 6

What portion of the GI tract is responsible for digestion and secretion?

Answer 6

Almost the entire tract

Question 7

What are the two components of the enteric nervous system? What does each component do?

Answer 7

myenteric plexus: smooth muscle activity

submucosal plexus: secretory activity

Question 8

Describe the four layers of the GI tract

Answer 8

1. Mucosa (which contains epithelium)
2. Submucosa (which contains submucosal plexus)
3. Muscularis propria (which contains circular and longitudinal layers, in between which lies the myenteric plexus)
4. serosa

Question 9

Describe parasympathetic innervation in the GI tract

Answer 9

preganglionic parasympathetics release Ach onto nicotinic receptors

Question 10

Describe sympathetic innervation in the GI tract

Answer 10

postganglionics release NE onto alpha one receptors on blood vessels and sphincters. Also onto adrenergic receptors on enteric motor and interneurons

Question 11

Describe the chemical mediators released by each of the following:

1. myenteric plexus
2. submucosal plexus
3. sensory neurons

Answer 11

Mesenteric: Ach and serotonin
Submucosal: Ach and VIP
Sensory neurons: substance P or calcitonin gene-related peptide (CGRP) which excites enteric neurons

Question 12

Where do you find smooth muscle with syncytium gap junctions?

Answer 12

Stomach and intestines. NOT found in esophagus and gall bladder

Question 13

Which has a higher slow wave frequency? Stomach or duodenum?

Answer 13

duodenum (12/min) which stomach only 3/min

Question 14

Can slow waves generate action potentials?

Answer 14

no, which is why external inputs are required

Question 15

Describe sympathetic activity on slow wave depolarization

Answer 15

decreases amplitude or even abolishes wave

Question 16

Describe parasympathetic activity on slow wave depolarization

Answer 16

increases amplitude by enhancing motility

Question 17

Define peristalsis

Answer 17

coordinated contraction and relaxation of circular and longitudinal muscles

Question 18

What produces dilation in GI motility?

Answer 18

contraction of longitudinal muscle and relaxation of circular muscle

Question 19

What decreases lumen size?

Answer 19

contraction of circular muscle upstream

Question 20

What is segmental mixing/moving?

Answer 20

alternating contraction and relaxation of circular muscle in adjacent segments

Question 21

What is it called when lower esophageal sphincter is not fully opening?

Answer 21

achalasia (dysfunction of myenteric ganglia)

Question 22

What happens with prolonged relaxation of lower esophageal sphincter?

Answer 22

GERD

Question 23

What is the job of the proximal stomach?

Answer 23

serves as a reservoir with tonic contractions and slow waves without AP’s

Question 24

What is the job of the distal stomach?

Answer 24

Grind tritutrate (crush, grind and rub food); phasic contractions and slow waves WITH action potentials

Question 25

Where would you find more longitudinal muscles on the stomach

Answer 25

distal stomach with fibers that are continuous with duodenum

Question 26

Where do you find circular muscles on the stomach?

Answer 26

everywhere but the distal portion; does not continue with duodenum

Question 27

What is the function of the pylorus?

Answer 27

to control the size of particles exiting the stomach

Question 28

What initiates gastric relaxation?

Answer 28

swallowing, mechanoreceptorstretch and relaxation supplemented by duodenal mechano- and chemo- receptors via CCK receptors on vagal afferents

Question 29

What increases the amplitude of contraction of slow wave?

Answer 29

parasympathetic increases amplitude and sympathetic decreases amplitude

Question 30

What happens when you increase the amount of the force of contraction?

Answer 30

increase in the amount of gastric emptying per contraction (controlled by neural and hormonal input)

Question 31

What controls the rate of contraction?

Answer 31

intrinsic basic electrical rhythm

Question 32

What controls the size of pyloric opening?

Answer 32

extrinisic (vagal) pathways and intrinsic (myenteric) pathways

Question 33

What is the main job of the large intestine?

Answer 33

to concentrate and store fecal matter before defecation

Question 34

What does the large intestine absorb?

Answer 34

The main function is active sodium absorption which water follows

Question 35

How is the motility of the colon compared to other parts of the GI tract?

Answer 35

slow! 2-4 days

Question 36

How is motility of the colon different than peristalsis?

Answer 36

the muscles remain contracted for some time after a mass movement, there is no MMC but an intense contraction, known as mass movement, forces fecal matter toward the rectum

Question 37

What kind of muscle is on the external anal sphincter?

Answer 37

smooth muscle and skeletal muscle

Question 38

What mediates relaxation of internal spincter?

Answer 38

NO and VIP

Question 39

Describe the defecation reflex

Answer 39

a contraction of the rectum, relaxation of the internal anal sphincter, contraction of the external anal sphincter and increased peristaltic activity in the sigmoid colon; eventually pressure point is reached at which the external anal sphincter relaxes and feces are expelled