Regulation of GI tract Function

Question 1

What are 3 Major control mecahnisms of GI function?

Answer 1

1) neural
2) paracrine
3) endocrine

Question 2

What are EEC’s?

Answer 2

Enteroendocrine cells

Question 3

Where are EEC’s located?

Answer 3

gastric, intestinal, pancreatic, closely associated with secretory cells

Question 4

What do EEC’s contain? What stimulates release of their contents? (generally)

Answer 4

secretory granules

Chemical/mecahnical stimuli

Question 5

EEC’s are a part of what system?

Answer 5

Diffuse neuroendocrine system (DNES)

Question 6

What eefects do EEC’s have on GI? (5 effects)

Answer 6

1) motility
2) absorption
3) appetite and satiety
4) fluid and enzyme secretion

Question 7

5 major hormones of EEC’s?

Answer 7

Gastrin

somatostatin

gastric inhibitory peptide

cholecystokinin

secretin

Question 8

What are the 3 targets of paracrine regulation from EEC’s?

Answer 8

1) smooth muscle
2) absorptive enterocytes
3) glandular secretory cells including other EEC’s

Question 9

What are ECL cells?

Answer 9

gastric enterochromaffin-like cells

Question 10

What do ECL cells secrete?

What effect do these secretions have?

Answer 10

Histamine

Binds to H2 receptors on neiighbouring patietal cells causing ACID PRODUCTION

Question 11

Other than Histamine what are 3 other Paracrine regulatory agents?

Answer 11

1) adenosine
2) nitric oxide
3) prostaglandins

Question 12

Give 3 examples of regulatory molecules in GI tract that have endocrine AND paracrine functions?

Answer 12

1) Cholecystokinin (CCK)
2) Secretin
3) Peptide YY
4) GLP-1/2 (bonus)

Question 13

What causes release of CCK?

Answer 13

partially digested fat/protein in duodenum

Question 14

What effect does Serotonin (5-HT) have?

Answer 14

regulates smooth muscle and water absoprtion

also associated with inflammatory responses of gut (BLESSING AND A CURSE)

Question 15

What is the “little brain of the gut”?

Answer 15

ENS - enteric nervous system

Question 16

4 types of neurons in the ENS?

Answer 16

1) Intrinsic primary afferent neurons
2) Excitatory motor neurons
3) inhibitory motor neurons
4) Interneurons

Question 17

What do intrinsic primary afferent neurons respond to? (4 things)

Answer 17

stretch, muscle tone, pH, food stuf conecntraitons (glucose, lipids, a.a’s)

Question 18

What do the excitatory motor neurons of the ENS promote?

Answer 18

smooth muscle contraction and secretory activity

Question 19

What do inhibitory motor neurons do in the ENS?

Answer 19

Inhibit smooth muscle contraction

Question 20

What are the 2 plexuses that the ENS is organized into?

Answer 20

Inner submocosal plexus (Meissner’s)

Outer myenteric plexus (Auerbach’s) - between longitudinal and circular muscle

Question 21

What do the 2 plexuses of the ENS regulate?

Answer 21

outer myenteric (auerbach’s plexus) - regulates GI tract secretions

Inner muscosal (Meissner’s plexus) - Regulates gut motility

Question 22

Parasympathetic inervation of GI stimulates (3 things)

Answer 22

• glandular secretions
• smooth muscle contraction
• vasvular smooth muscle relaxation, vasodilation, and increased blood flow

Question 23

Nerves that confer sympathetic regulation to GI tract? (3)

Answer 23

1) celiac
2) superior mesenteric
3) inferior mesenteric

Question 24

What does sympathic innervation inhibit in GI tract? (3 things)

Answer 24

1) glandular secretions
2) gut smooth muscle contraction
3) vascular smooth muscle relaxation, vasodilation, and increased blood flow

Question 25

What initiates the BER (basic electrical rhythm) of the GI tract?

Answer 25

INTERSTITIAL CELLS OF CAJAL

Question 26

What effect does acetylcholine and Norepinephrine have on BER of GI tract? (specifically spike potentials)

Answer 26

ach - spike potential frequency increased NE - spike potential frequency decreased

Question 27

What are the 2 basic forms of motility in the gut?

Answer 27

1) propulsive waves - propel and mix food 2) mixing waves - "chop" chyme

Question 28

What is segmentation (GI motility)?

Answer 28

pattern of rhythmic contractions driven by the superimposition of programmed ENS on BER (basic electrical rhythm)

Question 29

What initiates peristalsis?

Answer 29

peristalsis is initiated in response to stretching of the gut wall by a bolus of food

Question 30

what is the speed range (in cm/s) of peristalsis in the gut?

Answer 30

2-25 cm/s

Question 31

Does peristalsis require extrinsic innervation?

Answer 31

NO

Question 32

What is the main thing responsible for peristalsis?

Answer 32

internal myenteric (Auerbach's plexus)

Question 33

How does sympathetic and parasympathetic innervation affect peristalsis?

Answer 33

sympathetic innervation - inhibits peristalsis force and contraction Parasympathetic - increases rate and force of peristalsis contraction

Question 34

What are MMCs?

Answer 34

peristalsis-like motor patterns that are present during fasting

Question 35

What are the 4 phsaes of MMC?

Answer 35

D1, D2, J1,J2,J3

Question 36

What is the role of MMC?

Answer 36

"house cleaning" of undigested food remnants through GI tract

Question 37

What well known sign does MMC produce?

Answer 37

audible borborygmous - stomach growling

Question 38

What is the function of Haustrations? (segmented appeareance of Large intestine?)

Answer 38

functions to turn over feces to maximize water absorption

Question 39

What are the 5 LONG RANGE reflexes of the gut?

Answer 39

1) gastro-enteric reflex 2) Gastro-ileal reflex 3) gastro- and duodeno- colic reflexes 4) ileo-gastric reflex 5) Intestino-intestinal reflex

Question 40

What are the 4 activatory reflexes (long range reflexes)?

Answer 40

1 - gastro enteric 2- gastro-illeal 3) gastro-colic 4) duodeno-colic

Question 41

What are the 2 inhibitory reflexes?

Answer 41

1- illeo-gastric 2 - intestino - intestinal

Question 42

4 Main mucosal and pancreatic secretions

Answer 42

1 - mucus 2- water 3- enzymes and factors 4- electrolytes

Question 43

What activates gastric acid production (3 things)?

Answer 43

1) gastrin (from G-cells) 2) histamine (secreted by ECL cells) 3) Acetylcholine (from stretch-sensitive neurons and parasympathetic nerves)

Question 44

What is gastric acid production inhibited by? (2 things)

Answer 44

1. somatostatin (from D cells) 2. prostaglandins

Question 45

What cell releases Gastrin? WHere it is located?

Answer 45

G cells; located in pyloric region of stomach

Question 46

What are 4 things that activate gastrin secretion?

Answer 46

1. vagal stimulation 2. stretch or distention of stomach 3. amino acids from partial protein digestion 4. stimulants

Question 47

What inhibits gastrin secretion?

Answer 47

excess acid which stimualtes D cells to produce somatostain

Question 48

What are the 2 non-hormonal functions of the pancreas?

Answer 48

1. alkaline mucus production 2. enzymes for digestion of carbs, protein, and lipids

Question 49

What are the 2 hormones that control the pancreas?

Answer 49

1. secretin (from S cells) 2. CCK (from I cells)

Question 50

Where is Secretin secreted from?

Answer 50

S-cells of intestinal mucosa

Question 51

What stimulates production of secretin?

Answer 51

Presence of fats and acid in intestine

Question 52

What does secretin do to pancreas?

Answer 52

STimulates the release and production of bicarbonate ion

Question 53

What effect does secretin ahve on the stomach? (2 things)

Answer 53

inhibits acid secretion in stomach; causes contraction of pyloric sphincter

Question 54

What is CCK secreted in response to?

Answer 54

H+ ions, amino acids, small peptides

Question 55

What does CCK promote the secretion of ? (2 things)

Answer 55

1. alkaline pancreatic juice 2. enzymes from exocrine cells