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Medical Studies 2B > 5.5 Gastrointestinal Physiology > Flashcards

5.5 Gastrointestinal Physiology Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the two layers of muscle in the muscular layer of the GI tract? What are their actions, and when might these be useful?

A
  • Circular and longitudinal layers
  • Circular lessens diameter (useful primarily in churning)
  • Longitudinal decreases length of entire tract (useful primarily in propulsion)
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2
Q

The two plexuses of nerves in the GI tract are the…

A
  • Submucosal plexus
  • Myenteric plexus
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3
Q

Which areas of the stomach have thicker/thinner muscle layers? Why?

A
  • Fundus: thinner (needs to be able to relax to let food in)
  • Antrum: thicker (grinding and churning of stomach contents)
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4
Q

What are the two overarching motility patterns of the gi tract? Where do we see them?

A
  • Phasic (brief, more frequent spikes): distal stomach and small intestine
  • Tonic (longer, far smaller fluctuations): proximal stomach (why?), gall bladder, and sphincters
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5
Q

True or false: GI smooth muscle cells can control their own motility internally to some degree

A

True (autonomous)

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6
Q

Describe the significance of autonomous GI SMC depolarisation. Does every depolarisation lead to contraction?

A
  • Sets maximum possible contraction rate
  • Not all dep’s are contraction, but all contractions are dep.
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7
Q

Describe the neural circuity of peristalsis (incl. triggers)

A
  • Sensory neurons detect distension, and feed into interneurons
  • Interneurons feed into excitatory motor neurons (oral side of bolus), and inhibitory motor neurons (anal side of bolus)
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8
Q

What are the two GI sphincters in the body that are under voluntary control? What kind of muscle is this?

A
  1. Upper oesophageal sphincter
  2. External anal sphincter
    - This is striated muscle
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9
Q

1° vs 2° peristalsis. Which involves the swallowing centre of medulla?

A

Primary: first wave of muscular contraction (THIS ONE INVOLVES SWALLOWING CENTRE!)

Secondary: clears up any residual food that remains

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10
Q

Oesophageal peristalsis is mediated by the _______ nerves

A

Intrinsic GI nerves. The GI system says “cheers, mate”, and buggers of with full control of the food.

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11
Q

The gastric pacemaker is made of a kind of cell called ___. In this instance, it sets the max rate of contraction to…

A
  • Interstitial cells of Cajal
  • Max rate of 3 contractions per minute
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12
Q

How do nutrients in the small intestine feed back on muscle in the pylorus and antrum?

A
  • Pylorus: contracts, to slow gastric emptying
  • Antrum: slows, to slow churning and pumping across pylorus

(Enterogastric reflex)

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13
Q

Describe the rates of emptying of solids and liquids from the stomach, including the effect of caloric load on liquid emptying

A

Solid: initial lag phase (grinding), then decreases linearly

Liquid: exponential decrease (higher caloric load, slower emptying)

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14
Q

What are the three phases of the migrating motility complex? Does it occur during a fed or fasted state?

A
  • Fasted state
  • Phase 1: nothing
  • Phase 2: isolated contractions
  • Phase 3: 5-10mins of contractions throughout the tract to move things down
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15
Q

How long is an MMC cycle?

A

90mins (Huberman-style)

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16
Q

Describe motility patterns of the small intestine during a fed state. Is this the migrating motility complex?

A
  • No, it’s not the migrating motility complex
  • Isolated contractions throughout the gut
  • Allows segmentation/shuffling of contents, to maximise mixing of enzymes
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17
Q

Describe segmental vs propagative activity of the large intestine

A

Segmental: isolated mixing contractions to maximise salt/water absorption

Propagative: ~6 mass movements per day, may/may not cause defecation

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18
Q

When are colonic mass movements more common?

A
  • More common in day than night
  • More common in morning, and after meals
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19
Q

The four kinds of endocrine signalling from the gut are…

A
  • Endocrine
  • Autocrine
  • Paracrine
  • Synaptic
20
Q

Hormone(s)/action of G cells

A
  • Gastrin
  • Increased stomach motility/acid secretion from parietal cells
21
Q

Hormone(s)/action of S cells

A
  • Secretin
  • Increased bicarbonate and mucus secretion from the pancreas
  • Also increased bile salt secretion
22
Q

Hormone(s)/action of I cells

A
  • Cholecystokinin
  • Satiety, slowed gastric emptying, bile secretion
23
Q

Hormone(s)/action of K cells

A
  • Gastric inhibitory peptide
  • Promote satiety and insulin release
24
Q

Hormone(s)/action of L cells

A
  • GLP-1
  • Promote satiety and insulin release; slow gastric emptying
25
Q

Hormone(s)/action of D cells

A
  • Somatostatin
  • Decreases insulin, glucagon, gastrin

(Where else have you seen D cells?)

26
Q

Hormone(s)/action of Mo cells

A
  • Motilin
  • Promotes migrating motility complex
27
Q

True or false: gastric pacemaker ICCs can be modulated by enteric AND extrinsic nerves

A

True. Maximum degrees of freedom.

28
Q

True or false: colonic contractions are primarily generated with minimal input from the CNS

A

This is true. The CNS doesn’t wanna deal with that shit

29
Q

Describe the wave-like contractions that allow mixing in the stomach

A
  • Pylorus remains closed, keeping the system contained
  • Contraction propagates from the mid-stomach (corpus) to the antrum
30
Q

List 2 excitatory/inhibitory neurotransmitters used during peristalsis

A

Exc: substance P and Ach

Inh: nitric oxide and ATP

31
Q

Where are the cell bodies of vagal sensory GI neurons? Where do they carry their input to.

A
  • Cell bodies in nodose ganlgia in the neck. (No dose of drug required to feel full)
  • Carry info then to nTs
32
Q

Which kind of afferent GI neurons are involved in physiological vs noxious stimuli

A

Vagal: just physiological

Spinal: physiological and noxious (lateral spinothalamic tract)

33
Q

List two vago-vagal reflexes involved in stomach function

A
  1. Mixing of contents + pumping through Pylorus
  2. Adjust volume (relaxation) in response to feeding
34
Q

Where does the nTs output motor information from sensory GI fibres to? How does this modulate gastric activity?

A
  • Dorsal motor nucleus of the CN X.
  • Resulting parasympa fibres then synapse in myenteric plexus, modulating intrinsic GI nervous system
35
Q

What are 3 reasons why it’s advantageous to have a connection between the gut and the brain

A
  1. Allows for coordination of different parts of the GI tract (e.g. chewing increased pancreatic activity); like a sales manager
  2. Allows for regulation of food intake (gut speaks to brain)
  3. Allows for external stressors to influence digestion (brain speaks to food)
36
Q

Which parts/plexuses of the GI tract does the sympathetic nervous system innervate?

A
  • Myenteric and submucosal plexuses
  • Blood vessels (constrict to divert flow elsewhere)
37
Q

The parasympa nerves that innervate the distal colon and rectum arise from…

A

The sacral spinal cord

38
Q

How much more fluid is secreted than absorbed by the GI tract every day. Where is it secreted from, and what happens to it?

A
  • 200mL excess, lost during defecation
  • Comes from salivary glands, liver, pancreas, gall bladder, stomach
39
Q

Hormone(s)/action of Enterochromaffin-like cells

A
  • Histamine
  • Smooth muscle contraction
40
Q

How much fluid is ingested vs secreted in the GI tract each day?

A

Ingested: 2L
Excreted: 200mL

41
Q

What region of the stomach are oxyntic vs pyloric glands found? What do they secrete?

A
  • Corpus: oxyntic glands (acid and pepsin)
  • Antrum: pyloric (gastrin)
42
Q

Parietal cell acid secretion is stimulated by… and inhibited by… (multiple)

A

Stimulated by histamine, gastrin, nerves.

Inhibited by PGE2, and somatostatin.

43
Q

Outline the enterogastric reflex. Which hormones drive it?

A
  • When acid and nutrients are detected in the duodenum, gastric secretion and motility is inhibited by CCK, secretin, and incretins.
44
Q

It takes _ to _ days for GI mucosa cells to be regenerated from stem cells

A

4 to 6 days.

45
Q

What are the functions of acinar vs ductal pancreatic exocrine cells

A

Acinar: Release enzymes
Ductal: Release bicarbonate

46
Q

Describe the ionic mechanics of GI absorption vs secretion

A
  • Absorption: active Na+ transport, water and Cl- follow
  • Secretion: active Cl- transport, water and Na+ follow

Medical Studies 2B (88 decks)

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