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FHB GI > 45-46 > Flashcards

45-46 Flashcards

1
Q

What are the 4 main functions of the GI tract?

A 
Motility
Secretion 
Digestion 
Absorption
- Also does excretion of some waste
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2
Q

What 3 organs does the celiac a. supply?

A

Liver, spleen, stomach

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3
Q

What 3 organs does the SMA supply?

A

Pancreas, small intestine, proximal colon

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4
Q

What 3 organs does the IMA supply?

A

Distal colon

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5
Q

Where does venous GI blood stop prior to returning to the heart?

A

Liver

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6
Q

What major class of molecules is the lymphatic drainage important for?

A

Lipids and lipid-soluble molecules

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7
Q

What are the 3 layers of the mucosa?

A
  • Epithelium
  • Lamina propria
  • Muscularis mucosae
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8
Q

What types of cells would you encounter in the epithelial layer, and what are their roles?

A
  • Absorptive enterocytes (most abundant) - plays vital role in digestion, absorption.
  • Enteroendocrine cells (EECs) - releases regulatory peptides, amines- regulate GI function.
    Specialized cells:
  • Gastric mucosal cells - produce protons.
  • Mucin-producing cells all throughout - produce mucin (glycoprotein).
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9
Q

What type of epithelium would you find in the esophagus? Intestine?

A
  • Stratified squamous

- Simple columnar

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10
Q

The epithelial lining of the GI tract is continuously renewed. The cells at the villus tip are eventually shed via cell death. Their lifespan about ___ days.

A

3-5 (there are stem cells at bottom of crypts)

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11
Q

What is the intestinal unit of absorption?

A

The villus

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12
Q

What are the names of the tiny extensions from the intestinal villi? What’s the nickname?
What’s their main function?

A

Microvilli (brush border)

- Increase SA

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13
Q

What molecules are common in microvilli membranes?

A

High % of cholesterol and sphingolipids (raft formation)

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14
Q

What does the lamina propria mainly consist of?

What else does it contain?

A
  • Consists of CT: collagen and elastin fibrils.

- Rich in glands, contains lymph vessels and nodes, capillaries, nerve fibers

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15
Q

What’s b/w the lamina propria and submucosa?

A

Muscularis mucosae layer

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16
Q

What does the submucosa mainly consist of?

What else does it contain?

A
  • Consists of CT: collagen and elastin fibrils.

- Glands are present in some regions, as well as large nerve trunks + large blood and lymph vessels

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17
Q

What nervous network is in the submucsa?

What’s its main fcn?

A

Submucosal (Meissner’s) plexus- part of enteric NS

- Helps in the integration of motor and secretory activities

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18
Q

What are the 2 layers/orientations of the muscularis externa/propria?
What’s in b/w these layers?

A

Inner circular muscle layer & outer longitudinal muscle layer
- Myenteric (Auerbach’s) plexus- part of enteric NS

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19
Q

What is the main fcn of the muscularis externa?

A

Mixing and propelling contents of the GI tract

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20
Q

What types of cells make up the serosa?

A

Squamous mesothelial cells

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21
Q

What’s the fcn of the serosa?

A

Viscous secretions lubricate the abdominal organs to reduce friction b/w the abdominal organs during contraction/relaxation of GI tract.

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22
Q

What are the names of the sensor cells of the GI system?

How do they respond to a stimulus?

A 
Enteroendocrine cells (EECs)
- Secreting a regulatory peptide or hormone, which travels via circulation to a target cell at distant location (endocrine)
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23
Q

What’s the difference b/w open and closed EECs?

A

Open are in contact w/GI lumen, closed aren’t

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24
Q

After hormones/peptides released from EECs reach their target, what occurs w/in the target cell?

A

Signal transduction cascade

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25
Q

Hormone/peptide receptors can be found w/in many parts of the GI tract, including glandular structures. Are their receptors ever found outside the GI tract in systems not associated w/GI regulation?

A

Yes

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26
Q

Neuronal input can stimulate EECs during meals. Do nn. ever stimulate them not during a meal?

A

Yes

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27
Q

How do paracrine factors reach their targets?

A

Diffusion through ISF (to near by cells)

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28
Q

What are some e.g.’s of paracrine targets?

A

Smooth muscle, absorptive enterocytes, secretory cells in glands and other EECs.

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29
Q

What’s an e.g. of a paracrine factor released by enterochromaffin-like cells that travels to parietal cells to secrete HCl?

A

Histamine

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30
Q

What’s an e.g. of a paracrine factor released by enteric neurons, mucosal mast cells and specialized EECs called enterochromaffin cells that act on near by smooth m?

A

Serotonin (5-HT)

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31
Q

Half of the mass of the immune system in the human body is present in the GI tract. Would these cells be categorized as paracrine or endocrine?

A

Paracrine

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32
Q

What’s another name for Celiac disease?

What causes the allergic rxn?

A
  • Gluten enteropathy

- A component in gluten of wheat flour, rye and barley called gliadin

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33
Q

What happens to the GI tract when a Celiac pt eats gluten?

Tx?

A
  • Small intestine inflammation leads to reduction in density and length of microvilli and reduced absorption of nutrients
  • GF diet
34
Q

GASTRIN

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Endocrine

- Gastric antrum (G cells)

35
Q

GASTRIN

  • Stimuli for secretion?
  • Action
A
  • Small peptides, AAs

- Increases parietal cells’ H+ secretion; increases ECL cells’ histamine secretion; growth of gastric mucosa.

36
Q

CCK

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Both

- Duodenum (I cells)

37
Q

CCK

  • Stimuli for secretion?
  • Action
A
  • FAs, hydrolyzed ptn
  • Decreased gastric emptying and H+ secretion; decreased food intake; increased pancreatic enzyme secretion; increased contraction of GB

(eating fatty/ptn-rich meal takes longer to digest)

38
Q

SECRETIN

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Both

- Duodenum (S cells)

39
Q

SECRETIN

  • Stimuli for secretion?
  • Action
A
  • H+ in duodenum

- Increased pancreatic ductal secretions (HCO3- and water)

40
Q

Glucoinsulotropic peptide (GIP)

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Endocrine

- Duodenum and Jejunum (K cells)

41
Q

Glucoinsulotropic peptide (GIP)

  • Stimuli for secretion?
  • Action
A
  • FAs, glucose

- Increased insulin secretion from pancreatic beta cells

42
Q

Peptide YY (PYY)

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Both

- Intestine (L cells)

43
Q

Peptide YY (PYY)

  • Stimuli for secretion?
  • Action
A
  • FAs, glucose, hydrolyzed protein
  • Decreased gastric emptying and acid secretion; decreased pancreatic secretion; decreased intestinal motility; decreased food intake
44
Q

Proglucagon-derived peptides 1/2 (GLP-1/2)

  • Paracrine or endocrine or both?
  • Secretion site (+ cells)?
A
  • Both

- Intestine (L cells)

45
Q

Proglucagon-derived peptides 1/2 (GLP-1/2)

  • Stimuli for secretion?
  • Action
A
  • FAs, glucose, hydrolyzed protein

- Glucose homeostasis; increased epithelial cell proliferation

46
Q

What 2 major parasympathetic nn. innervate the gut?

A
  • Vagal nerves (from medulla)

- Pelvic nerves (from sacral cord)

47
Q

What organs do the vagal and pelvic nerves each innervate?

A
  • Vagal: esophagus, stomach, gallbladder, pancreas, 1st part of intestine, cecum, proximal colon
  • Pelvic: Distal colon, anorectal region
48
Q

How does parasympathetic (generally) affect the GI system?

Symp?

A
  • Activates it

- Inhibits it (exception: sphincters activated)

49
Q

Regarding the parasymp NS, are the preganglionic or postganglionic fibers long?
What are the 2 types of neurons it can have?

A
  • Preganglionic

- Cholinergic or peptidergic

50
Q

Cholinergic neurons release ___________ (and what type of synapse?)
Peptidergic neurons release _________________________.

A
  • Acetylcholine (nicotinic synapse)

- Various peptides: substance P, vasoactive intestinal peptide (VIP)

51
Q

What % of the vagal nerve fibers are efferent vs. afferent?

A

75% afferent, 25% efferent fibers

- Vagovagal reflexes–both efferent and afferent in the vagus nerve.

52
Q

Regarding the symp NS, are the preganglionic or postganglionic fibers long?
What types of neurons does it have?

A

Postganglionic

- Adrenergic (release NE)

53
Q

The 3 sympathetic ganglia that serve the GI tract are:

Which region of the cord do they stem from?

A

Celiac, superior mesenteric and inferior mesenteric (each w/their own plexus)
- Thoracolumbar region

54
Q

Where can postganglionic symp fibers synapse?

*How is this different from parasymp?

A
  • At ganglia in ENS or directly innervate *smooth muscle, endocrine or secretory cells.
  • Parasymp synapse directly in ENS plexuses (*no DIRECT innervation)
55
Q

What general types of receptors would give afferent feedback via parasymp?

A

Mechanoreceptors, chemoreceptors

56
Q

Are the submucosal and myenteric plexi linked?

A

Yes (via interganglionic strands)

57
Q

What 2 major/general types of neurochemicals (neurocrines) does the ENS release?

A

NTs + neuromodulators (modulate activity of NTs)

58
Q

ACh

  • Source
  • Actions
A
  • Cholinergic neurons

- Contraction of smooth m. in wall; relaxation of sphincters; increased salivary, pancreatic, and gastric secretions

59
Q

NE

  • Source
  • Actions
A
  • Adrenergic neurons

- Relaxation of smooth m. in wall; contraction of sphincters; increased salivary secretions

60
Q

Vasoactive intestinal peptide (VIP)

  • Source
  • Actions
A
  • Neurons of mucosa and smooth m.

- Relaxation of smooth m; increased intestinal and pancreatic secretions

61
Q

Enkephalins (opiates)

  • Source
  • Actions
A
  • Neurons of mucosa and smooth m.

- Contraction of smooth m; decreased intestinal secretions

62
Q

Neuropeptide Y

  • Source
  • Actions
A
  • Neurons of mucosa and smooth m.

- Relaxation of smooth m; decreased intestinal secretions

63
Q

Gastrin-releasing peptide (GRP) AKA Bombesin

  • Source
  • Actions
A
  • Neurons of gastric mucosa

- Increased gastric secretions

64
Q

Substance P

  • Source
  • Actions
A
  • Co-secreted w/ACh

- Contraction of smooth m; increased salivary secretions

65
Q

Almost all contractile tissues of GI tract are smooth muscles, except these 3 places, which contain striated muscle.

A

What are the pharynx, the upper 1/3rd of esophagus, and the external anal sphincter?

66
Q

What types of cells do GI smooth m. cells form gap junctions w/, and why?

A
  • Interstitial cells of Cajal

- Permits rapid cell-to-cell spread of action potentials

67
Q

Define what an interstitial cell of Cajal is.

Where are they located?

A

Specialized group of cells that are involved in the transmission of information from enteric neurons to smooth muscle cells.

  • Also pacemaker cells where “slow waves” originate
  • Located b/w the 2 layers of the muscularis externa
68
Q

Is GI smooth m. contraction phasic, tonic, or both?

A

Both (organ specification on slide 57)

69
Q

What are “slow waves” of the GI system?

A

Oscillating depolarization and repolarization of the membrane potential that are not large enough to elicit APs and/or contractions

70
Q

Would a contraction be produced if the slow waves don’t reach threshold?

A

Weak, basal, *tonic contractions occur even w/o APs

71
Q

How could slow waves reach threshold, and what type of contraction would be produced?

A

If at the plateau or peak of the slow wave, the membrane potential is depolarized up to threshold, then AP occurs “on top of” the slow wave
- Produces stronger, *phasic contraction

72
Q

What is the approx wave freq in the stomach vs. duodenum? (varies throughout GI tract)

A

3/min in stomach, 12/min in duodenum

73
Q

Do GI smooth mm. have twitch summation (separate twitches)?

A

No, 1 long contraction

74
Q

What 3 general ways could the body influence the slow wave amplitude, and to a lesser extent the freq?

A

Neurally, hormonally, and paracrine

75
Q

Explain the segmentation process.

A

A small section contracts, splitting the chyme, sending it in both orad and caudad directions. This section then relaxes allowing chyme to merge- this serves to mix chyme but produces no forward movement.

76
Q

What is the purpose of segmentation?

A

Mixing of the luminal contents with GI tract secretions and increase exposure to the mucosal surfaces where absorption occurs

77
Q

Where does segmentation predominantly occur?

A

Small and large intestines

78
Q

Where do peristaltic contractions predominantly occur?

A

Pharynx, esophagus, gastric antrum, small and large intestine

79
Q

What is the purpose of peristaltic contractions?

A

To propel the chyme along the GI tract

80
Q

Explain the process of peristaltic contractions.

A

A contraction occurs at a point orad to the bolus, simultaneously, the portion caudad to the bolus relaxes; the chyme is thus propelled in the caudad direction.

81
Q

During peristaltic contractions, what NTs are involved w/orad contraction? What about caudad relaxation?

A
  • ACh and substance P: orad contraction

- VIP and nitric oxide: caudad relaxation

FHB GI (10 decks)

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