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Boards: GI > Guyton Physiology > Flashcards

Guyton Physiology Flashcards

1
Q

What are the layers of the intestinal wall?

A

serosa
muscularis
submucosa
mucosa

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2
Q

What are the two types of electrical waves in the intestinal smooth muscles?

A

slow wave
spike potentials

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3
Q

What is the function of the interstitial cells of Cajal

A

produce the slow waves - electrical pacemakers

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4
Q

What is the threshold potential of intestinal smooth muscle cells?

A
  • 40
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5
Q

List 3 factors that make the intestinal smooth muscle membranes more excitable

A

stretch
ACh
several GI hormones (from food e.g.,)

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6
Q

What protein mediates the intestinal muscle activation caused by IC Ca++ entry

A

calmodulin

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7
Q

What are the two plexuses of the enteric nervous system? What are their main functions?

A

submucosal plexus - Auerbach’s
myenteric plexus - Meissner’s plexus

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8
Q

What is the function of the inhibitory effects of the myenteric plexus?

A

inhibit sphincter muscles

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9
Q

What are the divisions of the intestinal parasympathetic enteric nervous system?

A

cranial and sacral divisions

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10
Q

Explain the gastrocolic reflex

A

food enters the stomach –> stretch –> prevertebral sympathetic ganglia –> colon –> evacuation

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10
Q

Explain the enterogastric reflex

A

duodenum stretched, filled with acid/food –> prevertebral sympathetic ganglia –> stomach emptying inhibited

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10
Q

Explain the colonoileal reflex

A

colon filled –> prevertebral sympathetic ganglia –> inhibit ileal emptying

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11
Q

What are the three types of gastrointestinal reflexed (in terms of how high they travel up and back down the nervous system)

A
  • reflexes that travel just within the enteric nervous system within the gut wall
  • reflexes that travel from the enteric system to the prevertebral ganglia and back to the GI tract
  • reflexes that travel from the GI tract to the spinal cord or brain stem –> back to the GI tract (e.g., defecation reflex)
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12
Q

For gastrin: Where is it produced, what is its stimulus, and what is its effect?

A

G-cells
leads to gastric acid secretions
stimulated by meal ingestion (stomach distention, protein products)

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13
Q

For cholecystokinin (CKK): Where is it produced, what is its stimulus, and what is its effect?

A

produced by I-cells (duodenum, jejunum)
stimulus: food entering the duodenum, fat and fatty acids
effect: gall bladder emptying, inhibits stomach contractions

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14
Q

For secretin: Where is it produced, what is its stimulus, and what is its effect?

A

produced in S-cells
stimulus: gastric acid entering the duodenum
effect: induces pancreatic bicarbonate secretion

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15
Q

For glucose-dependent insulinotropic peptide: Where is it produced, what is its stimulus, and what is its effect?

A

produced by the mucosa of the upper SI
stimulus: fatty acids in the duodenum
effect: slows gastric emptying

16
Q

For motilin: Where is it produced, what is its stimulus, and what is its effect?

A

produced by the stomach and upper duodenum
stimulus: fasting
effect: interdigestive myoelectric complexes

17
Q

What are the two functional movements of the GI tract?

A
  • propulsive
  • mixing
18
Q

What is the main stimulus for peristalsis

A

stretching/distention

19
Q

How far does each peristaltic contraction usually travel?

A

5-10 cm

20
Q

List all organs included in the splanchnic circulation

A

GI tract, pancreas, spleen, liver

21
Q

List mechanisms by which GI gut flow increases after a meal

A
  • vasodilatory substances released after meal (cholecystokinin, vasoactive intestinal peptide, gastrin, secretin)
  • kinins (e.g., bradykinin)
  • decreased O2 from increased metabolism triggering increased blood flow
  • adenosine
22
Q

Why are the intestinal villi especially at risk for ischemic death from decreased local blood flow or circulatory shock?

A

Counter arterial and venous blood flow exchanges O2, I.e., arteriole give O2 to venules, so most O2 doesn’t even reach the tip of the villi
already lower O2 environment –> if circulation drops further –> ischemic injuries

23
Q

How does the musculature of the esophagus differ between dogs and cats?

A

dog: all striated
cat: 2/3 striated, bottom 1/3 smooth

24
Q

What are the triggers that slow stomach emptying

A
  • stretch of duodenum
  • fat, protein products and gastric acid in the duodenum
  • osmolality of the chyme
  • irritants in the duodenum
25
Q

Name 3 hormones, slowing gastric emptying

A
  • cholecystokinin
  • secretin
  • gastric inhibitory peptide (=glucose-dependent insulinotropic polypeptide)
26
Q

How fast do peristaltic waves travel through the intestines, and how far do they typically reach?

A

0.5-2cm/second
3-5 cm, cannot travel further than 10cm

27
Q

Describe the difference between the gastroenteric and the enterogastric reflexes

A

gastroenteric –> full stomach triggers duodenal peristaltic activity
enterogastric –> overfilled duodenum inhibits further gastric emptying

28
Q

Describe the gastroileal reflex

A

ileocecal valve usually blocks chyme from moving forward - opening of the valve is triggered by an additional meal

29
Q

Describe how small intestinal diarrhea develops

A

excessive SI peristaltic movements caused by irritation from infection or chemicals (“peristaltic rush”)

30
Q

What are the 2 reflexes initiating mass reflexes of the colon

A
  • intrinsic reflex - opens the internal anal sphincter when feces reaches the rectum
  • parasympathetic defecation reflex - more powerfully opens the internal anal sphincter

note: external anal sphincter must be opened voluntarily

31
Q

Explain how peritonitis, kidney, or urinary bladder disease may cause ileus

A

inflammation of the peritoneum –> peritoneointestinal reflex –> intestinal paralyzsis

renointestinal and viscerointestinal reflexes also cause inhibition

32
Q

How does the saliva’s electrolyte/ionic composition differ from plasma?

A

high K, high bicarbonate, low Na and Cl

33
Q

Describe the secretory cells of the oxyntic gland and what they secrete

A

peptic cells/chief cells - pepsinogen
parietal cells/oxyntic cells- HCl + intrinsic factor
enterochromaffin-like cells - histamine

34
Q

What is the pH of concentrated hydrochloric acid?

A

0.8

35
Q

Describe how parietal cells secrete hydrochloric acid

A

CO2 and H2O via carbonic anhydrase become H+ and HCO3-

H+ is transported out of the cell with countercurrent with K+ (KHATPase pump)

HCO3- exits on basolateral membrane in exchange for Cl- –> Cl- then enters lumen through Cl- channel –> HCl formed

36
Q

What is intrinsic factor?

A

essential factor for vitamin B12 absorption
secreted also by parietal cells

37
Q

How is pepsinogen activated?

A

in the presence of HCl

38
Q

What do the pyloric glands produce?

A

mucous
gastrin (G cells)

39
Q

How does gastrin affect gastric acid secretion?

A

gastrin stimulates acid secretion

gastrin stimulates histamine release by the enterochromaffin-like cells in the oxyntic glands –> histamine is an important trigger for parietal cells’ HCl production

40
Q

What inhibits gastric secretions?

A
  • distention of the SI
  • acid in the SI
  • food products (protein, fat) in SI
  • hyper or hypoosmolar chyme in SI

–> releases secretin –> opposes acid secretion

Boards: GI (6 decks)

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