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FHB Exam 3 > GI: Regulation and Motility > Flashcards

GI: Regulation and Motility Flashcards

1
Q

List GI regulatory mechanisms.

A

endocrine
paracrine
neural

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2
Q

Define enteroendocrine cells (EECs) and distinguish between open, closed, and ECL

A

EECs - gastric sensory cells that respond by secreting a peptide or hormone
open-type - apex is on the lumen and base is connected to a capillary
closed-type - no access to lumen
ECL = enterochromaffin-like cells; receive direct neural inpu

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3
Q

Describe endocrine regulatory mechanisms.

A
  • stimulus activates EEC cell
  • secreted hormone/peptide travels in circulation to a target cell that can be in the same organ, in a different organ, or outside the GI system
  • triggers signal transduction
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4
Q

Describe paracrine regulatory mechanisms.

A 
sensory cells (EECs) secrete a regulatory peptide or chemical messenger that diffuses through the ISF into nearby cells
- no circulation involved
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5
Q

What are target cells for paracrine regulation?

A
  • smooth muscle
  • absorptive enterocytes
  • secretory cells
  • other EECs
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6
Q

Describe paracrine release of histamine.

A

ECLs => histamine => parietal cells => acid secretion

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7
Q

Describe paracrine release of serotonin.

A

enteric neurons/mast cells/ECLs => serotonin => regulates contractility of smooth muscle

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8
Q

Describe Celiac Disease

A
  • allergic response to gliadin, component of gluten
  • leads to inflammation
  • reduces density and length of villi
  • malabsorption
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9
Q

What are the 2 parts of GI neural regulation?

A
  • extrinsic nervous system via the ANS (parasympathetic and sympathetic)
  • enteric nervous system (within the muscularis externa and submucosal layers
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10
Q

Describe parasympathetic extrinsic innervation (which nerves)?

A

through the vagal and pelvic nerves
Vagal
- everything except distal colon and anorectal region
- mostly afferents that deliver sensory information to CNS; efferents carry out vasovagal reflexes
Pelvic
- distal colon and anorectal regions

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11
Q

Describe feature of parasympathetic extrinsic innervation.

A
  • activation of GI
  • acts on smooth muscle, secretory, and endocrine cells
  • postganglionic can be cholinergic or peptidergic
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12
Q

Describe features of sympathetic extrinsic innervation.

A
  • inhibition of GI (activation of sphincters)
  • prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric)
  • postganglionic adrenergic fibers synapse onto ENS or directly
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13
Q

Describe the interplay between extrinsic and intrinsic innervation.

A

extrinsic neurons synapse onto ENS ganglia, delivering information. ENS then carries out the effect and returns sensory information to the ANS

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14
Q

Describe the 2 plexuses of the enteric nervous system.

A
  • myenteric = between muscularis externa
  • submucosal = in submucosal layer
  • linked by interganglionic fibers
  • secretes neurotransmitters or neuromodulators
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15
Q

Which GI muscles are striated?

A

pharynx
upper esophagus
external anal sphincter

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16
Q

Describe the smooth muscle of the GI tract.

A

gap junctions between interstitial cells of Cajal facilitates low resistance and rapid spread of AP

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17
Q

Describe phasic contraction.

A
  • periodic contractions followed by relaxation
  • occurs in esophagus, antrum, and small intestine
  • allows mixing and propulsion
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18
Q

Describe tonic contraction

A
  • constantly contracted

- occurs in upper stomach/lower esophageal, ileocecal, and internal anal sphincter

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19
Q

Differentiate slow wave frequency in different regions of the GI tract.

A 
stomach = 3/min
duodenum = 12/min
20
Q

Describe interstitial cells of Cajal.

A

located in the muscularis externae

pacemaker cells of the GI

21
Q

What are slow waves?

A

oscillations in membrane potential that is not large enough to create an AP

22
Q

What happens if an action potential occurs when a slow wave reaches threshold?

A

creates contraction

23
Q

What contributes to GI tonic contraction?

A

slow waves below threshold create weak contractions

24
Q

What contributes to GI phasic contraction?

A

when APs occur on top of a slow wave

25
Q

What is unique about GI action potentials?

A
  • slow waves

- APs are summed up to create longer contractions, instead of separate contractions

26
Q

What controls amplitude and frequency of slow waves?

A

normal GI regulation

27
Q

Describe segmentation contraction

A
  • mixes the food up, NO MOVEMENT
  • contraction occurs through the chyme (separating it)
  • relaxation brings the chyme back together (mixing it)
28
Q

Describe peristaltic contraction.

A
  • movement of food

- orad contraction with simultaneous caudad relaxation pushes the food forward

29
Q

Which neurotransmitters are involved in peristaltic contraction?

A
  • orad contraction = ACh and Substance P

- caudad relaxation = VIP and NO

30
Q

What is the difference between parasympathetic and sympathetic innervation?

A
  • sympathetics synapse on ENS ganglia or directly on cells

- parasympathetics synapse onto the ENS ganglia

31
Q

Describe gastrin as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: small peptides and AAs
  • secreted by: G cells of gastric antrum epithelium
  • action: increased parietal acid secretion, increased ECL histamine secretion, increased growth of gastric mucosa
32
Q

Describe CCK (cholecystokinin) as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: fatty acids, hydrolyzed proteins
  • secreted by: I cells of duodenum
  • action: decreased gastric emptying and acid secretion, decreased food intake, increased pancreatic enzyme secretion, increased contraction of gallbladder
33
Q

Describe secretin as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: protons in duodenum
  • secreted by: S cells of duodenum
  • action: increase pancreatic secretion of water and bicarb
34
Q

Describe GIP (gluco-insulinotropic-peptide) as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: fatty acids and glucose
  • secreted by: K cells of upper intestines
  • action: increased insulin secretion from pancreatic B cells
35
Q

Describe peptide YY as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: fatty acids, glucose, hydrolyzed protein
  • secreted by: L cells of intestine
  • action: decrease gastric emptying and acid secretion, decrease pancreatic secretion, decrease intestinal motility, decrease food intake
36
Q

For the most part, what is the relationship between CCK and PYY?

A

opposite effects
CCK increases acid secretion
PYY decreases

37
Q

Describe GLP1/GLP2 (proglucagon-derived peptide) as a hormone mediator (cells, stimulus, action)?

A
  • stimulus: fatty acids, glucose, hydrolyzed protein
  • secreted by: L cells of intestine
  • action: glucose homeostasis, increased epithelial proliferation
38
Q

Which 2 hormones are secreted by L cells?

A

PYY and GLP

39
Q

Which hormones are only endocrine?

A
  • gastrin

- GIP

40
Q

Which hormones have both endocrine and paracrine functions?

A
  • CCK
  • secretin
  • PYY
  • GLP
41
Q

Describe ACH neuromodulation.

A
  • source: cholinergic neurons
  • contraction of smooth muscle
  • relaxation of sphincters
  • increased salivary, gastric, and pancreatic secretions
    ==> pushes food forward
42
Q

Describe NE neuromodulation.

A
  • source: adrenergic neurons
  • relaxation of smooth muscle
  • contraction of sphincters
  • increased salivary secretions
    ===> helps in peristalsis
43
Q

Describe VIP (Vasoactive Intestinal Peptide) neuromodulation

A
  • source: neurons
  • relaxation of smooth muscle
  • increased intestinal and pancreatic secretion
    ==> helps in peristalsis
44
Q

Describe GRP/Bombesin (Gastrin-releasing peptide) neuromodulation.

A
  • increased gastric secretion
45
Q

Describe enkephalin neuromodulation

A
  • contraction of smooth muscle

- decreased intestinal secretion

46
Q

Describe neuropeptide Y neuromodulation

A
  • relaxation of smooth muscle

- decreases intestinal secretion

47
Q

Describe substance P neuromodulation

A
  • co-secreted with ACh
  • contraction of smooth muscle
  • increased salivary secretion
    ==> helps with peristalsis

FHB Exam 3 (23 decks)

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