GI I & II: General Principles of GI Regulation Flashcards

1
Q

What is the importance of reducing the size of food particles during the motility phase of digestion?

A

It allows for an increased surface area for chemical digestion by enzymes.

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2
Q

The rate at which food is propelled is regulated to optimize ____________.

A

the time for digestion and absorption

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3
Q

What are the associated glands of the GI system, and what are they responsible for?

A
  • salivary glands, pancreas, liver, and gallbladder
  • they are responsible for producing mucous and secretions and emptying them into the GI tract to aid digestion and absorption
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4
Q

The GI tract excretes which products from the liver?

A

cholesterol, steroids, drug metabolites

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5
Q

What represents the largest immune organ of the body?

A

GI tract

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6
Q

Are GI sphincters smooth muscle or skeletal muscle?

A

they are circular muscle structures, either smooth or skeletal

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7
Q

What is the blood supply of the GI tract? How much blood flow does the GI tract receive?

A

The blood vessels that supply the GI tract comprise the splanchnic circulation, which receives 25% of our total cardiac output.

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8
Q

What are the 3 major arteries that supply the abdominal organs?

A
  • celiac artery (liver, spleen, stomach)
  • SMA (pancreas, small intestine, proximal colon)
  • IMA (distal colon)
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9
Q

Does the venous drainage from the GI tract return directly to the heart?

A

No! The venous blood from the abdominal organs flows to the liver first via the portal vein (portal circulation). Blood from the liver is then transported via hepatic veins to the IVC.

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10
Q

Why is lymphatic drainage important for in the GI tract?

A

transport of lipids and lipid-soluble molecules (including certain vitamins and drugs), which are too large to enter capillaries and pass into lymph vessels; they are then drained via thoracic duct into systemic circulation

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11
Q

The nature of mucosal epithelium varies according to ________.

A

function

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12
Q

What is the lifespan of the epithelial lining of the GI tract?

A

3-5 days (epithelial lining is continuously renewed w/ cells at the villus tip shedding every 3-5 days)

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13
Q

Where are proliferative cells located that help to replenish the epithelial lining?

A

they are localized in crypts

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14
Q

Describe the epithelium of the mucosal layer.

A

It is a single, continuous layer of specialized cells lining the lumen of the entire GI tract (innermost layer) and interconnected via tight junctions.

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15
Q

What is the most abundant cell type of the mucosal epithelium?

A

absorptive enterocytes (play a vital role in digestion and absorption)

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16
Q

The surface of small intestinal epithelium consists of which structures, and what is their purpose?

A

villi and crypts, which are fingerlike projections that help to increase surface area for absorption and also harbor the intestinal stem cells, which help replenish the epithelial lining

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17
Q

What is the difference between esophageal and intestinal epithelium?

A

Esophageal epithelium helps in transportation of swallowed food (squamous type), while intestinal epithelium helps in absorption or selective uptake of nutrients, ions, and water (columnar type)

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18
Q

The unit of absorption of intestinal cells:

A

villus

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19
Q

Epithelial cells on the surface of a villus have numerous cytoplasmic extensions at the luminal surface, called _______.

A

microvilli, or brush border

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20
Q

The mucosal folds, villi, and microvilli increase the SA of the small intestine by how much?

A

~600 fold

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21
Q

What is the implication of reduced surface area in the small intestine?

A

malabsorption, which is implicated in celiac disease

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22
Q

What is the main thing to note about the lamina propria (and in which layer is it located?)

A
  • It is rich in glands, as well as lymph vessels and nodes, capillaries, and nerve fibers
  • It is part of the mucosa
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23
Q

What is the “little brain” in the gut composed of?

A
  • Meissner’s plexus (submucosal plexus)

- Auerbach’s plexus (myenteric plexus)

24
Q

What is the innermost vs. outermost layer of the GI tract?

A
  • innermost: epithelial lining of the mucosa

- outermost: serosa

25
Q

The GI tract undergoes periods of _________ vs. _________.

A

relative quiescence (intermeal period); intense activity (postprandial period)

26
Q

What are some of the significant examples of paracrine regulation?

A
  • histamine: released by ECLs in stomach; binds to neighboring parietal cells that secrete HCl in response
  • serotonin: released from enteric neurons, mucosal mast cells, and ECLs; regulates contractile activity of smooth muscle cells
  • cholecystokinin: paracrine AND/OR endocrine regulator released from duodenum in response to dietary protein or lipid; acts locally on nerve terminals (paracrine) and pancreas (endocrine)
27
Q

True or false: 75% of the mass of the immune system in the human body is present in the GI tract.

A

False- half of the mass of the immune system is found in the GI tract.

28
Q

What is an example of pathology associated with paracrine regulation?

A

celiac disease (gluten enteropathy) - due to an allergic response to gliadin, a component in gluten of wheat flour, rye, and barley; causes an inflammatory rxn in small intestine, resulting in reduction of density/length of microvilli; causes red. absorpt. of nutrients

29
Q

The gut is innervated by 2 sets of nerves:

A

extrinsic (ANS) and intrinsic (enteric) nervous system

30
Q

Describe the parasympathetic innervation of the gut.

A
  • vagus nerve innervates the esophagus, stomach, gallbladder, pancreas, first part of intestine, cecum, proximal part of colon
  • pelvic nerves innervates the distal part of the colon and anorectal region
31
Q

What is meant by the fact that the vagus nerve is mixed?

A

75% of fibers are afferent and 25% are efferent

32
Q

What is the vagovagal reflex?

A
  • refers to GI tract reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain
  • active during receptive relaxation of the stomach in response to swallowing food (vagovagal reflex goes from stomach to brain, then back to stomach)
33
Q

In general, sympathetic innervation inhibits GI function. What is the exception?

A

GI sphincter muscles, which are activated by sympathetic innervation (sphincter muscles are tonically contracted and relax only briefly to allow for passage of bolus)

34
Q

What are the sympathetic ganglia serving the GI tract?

A

celiac, superior mesenteric, inferior mesenteric

35
Q

Are sympathetic nerve fibers afferent or efferent?

A

50% afferent, 50% efferent (thus, sensory and motor info is relayed back and forth between GI tract and CNS, coordinated by submucosal and myenteric plexuses)

36
Q

Can the enteric nervous system act autonomously from extrinsic innervation?

A

Yes, even despite receiving input from extrinsic neurons that modulate its activity.

37
Q

Almost all contractile tissues of GI tract are ________.

A

smooth muscles

38
Q

Where does striated muscle exist in the GI system?

A

pharynx, upper 1/3rd of esophagus, and external anal sphincter

39
Q

What is the role of interstitial cells of Cajal (ICCs) in GI motility?

A

Smooth muscle of GI tract forms gap junctions with ICCs in order to permit rapid cell-to-cell spread of APs (essentially, ICCs transfer NT signal to muscle cells for faster motility)

40
Q

What is a unique feature of GI smooth muscle electrical activity?

A

slow waves, which represent oscillating depolarization and repolarization of the membrane potential and are not large enough to elicit APs and/or contractions

41
Q

Where do slow waves originate?

A

interstitial cells of Cajal, located b/t longitudinal and circular layers of muscularis externa (known as “pacemaker cells” for GI smooth muscle)

42
Q

What happens if the membrane potential is depolarized up to the threshold at the plateau/peak of the slow wave?

A

the AP occurs “on top of” the slow wave, followed by much stronger contractions (phasic contractions)

43
Q

In the smooth muscle of the GI tract, are individual APs followed by separate twitches?

A

no, they summate into one long contraction

44
Q

How does smooth muscle exhibit basal, tonic contractions?

A

even sub-threshold waves produce weak contraction, so APs are not necessarily needed to contract smooth muscle

45
Q

Where do segmentation vs. peristaltic contractions occur?

A
  • segmentation: predominantly in small and large intestine

- peristaltic: pharynx, esophagus, gastric antrum, intestines

46
Q

What is the function of segmentation vs. peristaltic contractions?

A
  • segmentation: allow mixing of luminal contents w/ GI tract secretions but produce no forward movement
  • peristaltic: help propel chyme along GI tract (contraction occurs at a point orad to the bolus and, simultaneously, the portion caudad to the bolus relaxes)
47
Q

How can CCK be both paracrine and endocrine?

A

It can act locally on nerve terminals (paracrine) and on the pancreas (endocrine).

48
Q

What is the action of peptide YY?

A

-decreases gastric emptying and acid secretion
-decreases pancreatic secretion
-decreases intestinal motility
-decreases food intake
(in essence, helps to reduce appetite and limit food intake)

49
Q

What is the stimulus for secretin secretion?

A

H+ in the duodenum (secretin is released by S cells once luminal pH drops below 4.5)

50
Q

What is the action of CCK?

A

It slows digestion by decreasing gastric emptying and H+ secretion, as well as food intake. It also increases pancreatic enzyme secretion and contraction of the gallbladder to allow for fat to be adequately digested.

51
Q

Post-ganglionic neurons of parasympathetic system are either _______ or ________.

A

cholinergic (release ACh at nicotinic synapse) or peptidergic (release various peptides, like substance P or VIP)

52
Q

What is the effect of sympathetics vs. parasympathetics on GI sphincter muscles?

A

they are activated by sympathetic fibers, meaning they are in a state of tonic contraction most of the time; parasympathetics inhibit this tonic contraction during digestion when it is important for food to pass through

53
Q

Post-ganglionic neurons of sympathetic system are ______.

A

adrenergic (release NE)

54
Q

The pre-ganglionic neurons of both the sympathetic and parasympathetic systems are ______.

A

cholinergic (release ACh)

55
Q

Are the gap junctions in the smooth muscle of the GI tract high or low resistance?

A

low resistance

56
Q

Where are phasic vs. tonic contractions found in the GI tract?

A
  • phasic: esophagus, gastric antrum, small intestine

- tonic: orad of stomach and sphincters (lower esophageal, ileocecal, internal anal, and external anal)