Regulation of Digestion

Question 1

Where and how is cellulose broken down?

Answer 1

In the gut, by fermentation by the gut microbiome

Question 2

Important role of the pyloric valve in amylase function

Answer 2

Amylase is pH-sensitive.

Pyloric valve separates the low-pH stomach environment from the neutral duodenum

Question 3

Elements controlling gut

Answer 3

Nervous system (CNS, PNS, enteric)
Endocrine system
Smooth muscle and associated pacemakers

Question 4

Layers of the enteric nervous system

Answer 4

Longitudinal muscle
Myenteric plexus
Circular muscle
Deep muscular plexus
Mucosal plexus
Muscularis mucosae
Mucosa

Question 5

Structures attached to enteric longitudinal muscle

Answer 5

Myenteric plexus

Tertiary plexus

Question 6

Intrinsic neurons in the ENS

Answer 6

Sensory, interneurons, excitatory and inhibitory motor neurons

Question 7

Primary functions of the ENS

Answer 7

Motility, water and salt transport

Question 8

Number of basic ENS motility patterns

Answer 8

Three

Question 9

Basic ENS motility patterns

Answer 9

Fed state
Fasted state
Mass movement contraction

Question 10

Characteristics of fed-state motility pattern

Answer 10

Stomach relaxation (size of fist –> much larger)
Segmentation in small intestine
Peristalsis
Retropulsion/antiperistalsis, in some situations

Question 11

Segmentation

Answer 11

Local stationary constrictions in small intestine.
No net forward movement of chyme
Mixes intestine contents

Question 12

Characteristics of fasted-state motility pattern

Answer 12

Migrating motor complex moves through small intestine

Question 13

Characteristics of migrating motor complex

Answer 13

Slowly moving constriction of intestine
Cleans out debris (bacteria, cell fragments)
Takes ~90 minutes from pylorus to anus

Question 14

Characteristics of mass movement contraction motility pattern

Answer 14

In colon, rectum

Involved in defecation

Question 15

Difference between peristalsis and segmentation

Answer 15

There is no net forward movement in segmentation

Question 16

Where does the ENS regulate motility patterns?

Answer 16

All parts of the gut except upper oesophagus

Question 17

Pacemaker cells in gut

Answer 17

Interstitial cells of Cajal

Question 18

Role of interstitial cells of Cajal

Answer 18

Produce slow wave potentials in smooth muscle

Question 19

Which type of cell is an interstitial cell of Cajal?

Answer 19

Modified smooth muscle cell

Question 20

Role of slow wave potentials

Answer 20

Keep enteric smooth muscle just below threshold

Can be easily depolarised to threshold by CNS

Question 21

Plexi containing neurons in ENS

Answer 21

Submucosal plexus

Myenteric plexus

Question 22

Feed-forward reflexes of ENS

Answer 22

Cephalic reflex

Gastro-colonic reflex

Question 23

Cephalic reflex

Answer 23

Thought of, smell, sight of food can trigger:
Salivation
Relaxation of stomach
Segmentation in intestine

Question 24

Gastro-colonic reflex

Answer 24

Food entering stomach can trigger defecation

Question 25

Feedback reflexes of ENS

Answer 25

Inhibition of gastric emptying

Question 26

Factors inhibiting gastric emptying

Answer 26

Acid in duodenum | Excess material in colon

Question 27

Effects of gastrin

Answer 27

Stimulates gastric acid secretion | Stimulates mucosal growth

Question 28

Target of gastrin

Answer 28

Enterochromaffin-like cells (ECL cells) | Parietal cells

Question 29

Stimuli for gastrin release

Answer 29

Partially digested protein in stomach Stomach distension Neural signals, particularly via vagus nerve

Question 30

Effects of cholecystokinin

Answer 30

``` Stimulates gallbladder contraction Stimulates pancreatic enzyme release Inhibits gastric emptying Inhibits gastric acid secretion Promotes satiety ```

Question 31

Targets of cholecystokinin

Answer 31

Stomach, pancreas, gallbladder

Question 32

Cells secreting cholecystokinin

Answer 32

I-cells in intestine | Segrete into duodenum

Question 33

Stimulus for cholecystokinin release

Answer 33

Presence of fatty acids or some amino acids in chyme CCK-releasing protein (secreted by enterocytes) Parasympathetic stimulation from vagus nerve

Question 34

Effect of secretin

Answer 34

Stimulates bicarbonate secretion Inhibits gastric emptying Inhibits gastric acid secretion

Question 35

Stimulus for secretin release

Answer 35

Acid in small intestine

Question 36

Targets of secretin

Answer 36

Pancreas, stomach

Question 37

Cells releasing gastrin

Answer 37

G-cells in stomach antrum

Question 38

Cells releasing secretin

Answer 38

S-cells in duodenum. | In crypts of Lieberkuhn

Question 39

Effects of motilin

Answer 39

Stimulates migrating motor complex

Question 40

Stimulus for motilin release

Answer 40

Released periodically during fasting period (every 1-2 hours) Release inhibited by eating a meal

Question 41

Targets of motilin

Answer 41

Stomach, intestinal smooth muscle

Question 42

Gastric inhibitory peptide effects

Answer 42

Stimulates insulin release (feedforward) Inhibits gastric emptying Inhibits gastric acid secretion

Question 43

Gastric inhibitory peptide target

Answer 43

Beta-cells of pancreas

Question 44

Gastric inhibitory peptide stimulus

Answer 44

Glucose, fatty acids, amino acids in small intestine

Question 45

Glucagon-like peptide 1 effect

Answer 45

Promotes satiety Stimulates insulin release Inhibits gastric acid secretion, gastric funciton

Question 46

Glucagon-like peptide 1 stimulus

Answer 46

Fats and carbohydrates in gut lumen

Question 47

Glucagon-like peptide 1 target

Answer 47

Endocrine pancreas