GIT Physio Pt 1/4 (GIT Regulation)

Question 1

What are the intrinsic and extrinsic components that regulate GIT functions and secretions?

Answer 1

Intrinsic = (Enteric Nervous System)
Extrinsic = (Autonomic Nervous System)
- symp NS decreases GIT activity
- psymp NS increases GIT activity

The ENS is (smtimes) regulated by psymp. n symp. NS, but it can function independently without influence from either.

Question 2

Function of the Enteric NS?

Answer 2

• regulates local secremotor fxns while monitoring local changes in luminal activities & chemical/mechanical stimuli in gut (= local sensory + motor (secretions, blood flow, GIT motility)

Question 3

What does the ENS (anatomically) comprise of?

Answer 3

Myenteric (Auerbach’s) plexus
Submucosal (Meisnner’s) plexus

Question 4

Where does the ENS lie in the GIT wall? (Hint: GIT wall!)

Answer 4

context:
GIT wall made of: MSMA (mucosa, submucosa, muscularis propria - inner, outer, innermost (stomach), adventitia/serosa)

Myenteric lies within muscularis propria (between the inner circular, outer longitudinal layer)

Meissner’s plexus lies within the submucosa of the wall.

Note: this is also why “ANS terminates at submucosa-muscularis propria layer of GIT wall”

Question 5

Function of Myenteric and Submucosal plexus specifically?

Answer 5

Myenteric: controls GIT motility (eg. contractions aka. peristalsis)

Submucosal: controls GIT Secretions and Local blood flow

Question 6

What do afferent (viscerosensory) fibres of GIT sense? (note: a part of ENS! - draw the diagram of nervous systems - this is separate entity)

Answer 6

• distension
• chemical stimuli (eg. pH, osmolarity, nutrients, etc)
• mechanical stimuli

Question 7

Note on GIT reflexes:

Answer 7

Types:
1. within ENS [Intrinsic reflexes] - include controlling GIT secretions, peristalsis, blood flow LOCALLY

2. w help of ANS [Short Extrinsic reflexes] (eg. enterogastric, gastrocolic reflexes) - between parts of GIT; reflex travels from gut –> prevertebral sympathetic ganglia (splanchnic) and back
3. w more help from ANS [Long Extrinsic reflexes] - involving WHOLE GIT (eg. vasovagal reflex, pain reflexes, defecation reflexes, vomitation reflex); reflex travels from gut –> spinal cord/ brainstem and back

Question 8

What does enterogastric reflex and gastrocolic reflex do? (for fun)

Note: there are ~3 extrinsic reflexes:
1. enterogastric
2. gastrocolic
3. gastroileal
(apparently some got 4 but wtv)

Answer 8

Enterogastric: when got food in duodenum (after chyme goes there), distension of duodenum –> decreases stomach motility and secretions (let duodenum cope w the new load first)

Gastrocolic: when got food in stomach, stimulates evacuation of feces through colon to ‘make space’ for more

Gastroileal

Question 9

(KIV: Hypothalamic regulation of GIT in notes - Lateral nuclei = hunger/feeding centre; Ventromedial Lateral Nuclei = satiety centre)

Question 10

Name 2 anorexigenic (satiety) signals.

Answer 10

Leptin (released by adipose tissue)
CCK (released by I cells of duodenum/jejunum)

Question 11

Name 3 orexigenic (hunger) signals.

Answer 11

Ghrelin (released by stomach n pancreas)

Glucagon (released by pancreas alpha cells in islets of Langerhans)

Neuropeptide Y

Question 12

(not v related to nervous systems but:)
List the pH in:
1. oral cavity
2. stomach
3. gall bladder (bile)
4. pancreas, small int, large int

Answer 12

1. 6.5
2. 1.5
3. 7-8
4. 7-8

Question 13

note: GIT REGULATED by what?

Answer 13

• endocrine hormones (travel via blood to act on further places)
• paracrine hormones (act locally to nearby structures)
• pH
• chemical/ food stimuli
• mechanical stimuli
• etc