Control Of Alimentary Tract

Question 1

How does the innervation of the parasympathetic nervous system affect the gut?

Answer 1

Stimulates digestive activity
Stimulates gall bladder
Relaxes the rectum

Question 2

How does innervation of sympathetic nervous system affect the gut?

Answer 2

Inhibits digestive activity
Stimulates glucose release from the liver 
Inhibits salivation 
Relaxes bladder
Contracts the rectum

Question 3

Gut has its own “brain”

It’s called…

Answer 3

Enteric nervous system

Question 4

Where are 2 muscles involved in peristalsis?

Answer 4

circular and longitudinal muscles

Question 5

Where are circular muscles found?

Answer 5

found close to lumen

Question 6

Where are longitudinal muscles found?

Answer 6

on outer surface

Question 7

What are innervates GI tract?

Answer 7

innervated by intrinsic neurons of the enteric nervous system and by axons of extrinsic parasympathetic, sympathetic and visceral afferent neurons

Question 8

Relaxation of fundus (reservoir) is mediated by reflexes and can be differentiated into 3 stages

Answer 8

1. Receptive
2. Adaptive
3. Feedback

Question 9

What is mechanism of fundus relaxation/storage?

Answer 9

relaxation is mediated by NANC
also controlled by reflex chains involving release of NA
when stomach is ready to receive food, NA is released from sympathetic nerve fibres which helps stomach to relax

Question 10

Is pyloric sphincter often contracted or relaxed?

Answer 10

often relaxed but closes upon arrival of peristaltic wave

Question 11

What is function of pyloric sphincter?

Answer 11

acts as sieve, larger particles are pushed back to antrum to be further digested
sieving effect: viscous + solid matter are retained in stomach

Question 12

What causes opening of pyloric sphincter?

Answer 12

repulsion of chyme causes the opening -> small partially digested material is squirted through pyloric sphincter into duodenum

Question 13

What are types of control in GI?

Answer 13

Endocrine, paracrine, neural (vago-vagal reflex, enteric or local reflex) and metabolic (type of food eaten)

Question 14

Describe the difference in the structure of fundus + antrum? how do these differences help with their function?

Answer 14

Fundus -> has thinner muscle layer so it is able able to expand to allow accommodation to occur
Antrum -> large, thick muscle layer so is able to provide grinding action

Question 15

When is gastrin secreted?

Answer 15

can be secrete because there’s distension of stomach or we have seen food

Question 16

What does distension of stomach initiate?

Answer 16

neuronal stimulation that promotes gastrin releasing peptide which acts on G cells that release hormone gastrin

Question 17

What are the effects of gastrin? (gastrin mediated effects)

Answer 17

gastrin travels in circulation
it can promote histamine secretion from enterochromaffin like cell (ECL) -> histamine binds to its receptors on surface of parietal cells. Parietal cells then secrete HCl
gastrin can also promote ACH release

Question 18

What is difference between endocrine and paracrine?

Answer 18

hormones (endocrine) go to target tissues via BLOOD + paracrine agents go via interstitial fluid

Question 19

What is paracrine control?

Answer 19

Gastrin can cause hypersecretion of acid

Somatostatin is only released when there is hypersecretion of acid

Question 20

What is vago-vagal reflex?

Answer 20

describes type of reflex in which both afferent (sensory) + efferent (motor) axons are in vagus nerve trunk
describes reflex control of responses to gut stimuli via NTS + DMVN

Question 21

the pathway of vago-vagal reflex is via…..

Answer 21

brainstem (medulla)

Question 22

When is vago-vagal reflex active?

Answer 22

Active during receptive relaxation of stomach in response to swallowing -> reflex goes from stomach to brain + back to stomach -> active relaxation of smooth muscles of stomach. it promotes motility + acid secretion

Question 23

What is NTS?

Answer 23

main site of termination of vagal afferents

Question 24

What is DMVN?

Answer 24

main site of origin of vagal efferents (motor) supplying the gut

Question 25

Describe the vago-vagal reflex pathway?

Answer 25

vagal afferents get sent to NTS -> vagal efferents will send motor reflexes down
Ach is released pre-ganglionically and post-ganglionically -> causes motility + acid secretion

Question 26

What are 2 nerve fibres intrinsic to gut? What are their functions?

Answer 26

Myenteric plexus (auerbach's plexus) -> motor function for motility 
Submucosal plexus (Meissner's plexus) -> intestinal secretions

Question 27

What are the neurotransmitters involved of enteric nervous system?

Answer 27

Ach, NO, NA, 5-HT, GABA + ATP

Question 28

Where are myenteric plexus and submucosal plexus found?

Answer 28

found in wall of colon

Question 29

What do the 2 plexuses receive?

Answer 29

receive inputs from both SNS + PNS
Parasympathetic activity ->increase contraction of proximal colon
Sympathetic activity -> decrease colonic movement

Question 30

What is colo-colonic reflex?

Answer 30

is when you taken in food + its in stomach, food starts to get digested, food particles tend to promote movement aborally (lower end of gut) -> food starts to move down

Question 31

What is myenteric plexus?

Answer 31

most prominent plexus
cholinergic innervation -> increases gastric motility + secretion
adrenergic stimulation -> decreases gastric motility + secretion

Question 32

What is metabolic control?

Answer 32

types of food eaten
rate of emptying is dependant upon material’s ability to be absorbed:
- carbohydrates emptied quickly into duodenum
-proteins - slow emptying
-fatty foods - even slower
-fatty acids in duodenum -> decrease in gastric emptying by increasing contractility of pyloric sphincter

Question 33

What is peristalsis?

Answer 33

• wave of propulsive contractions that move contents of gut towards anus

Question 34

What is difference in peristalsis in large intestine and small intestine?

Answer 34

slower in large intestine compared to small intestine