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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 to neutralise acid
  • 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
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)
  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 (57 decks)

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