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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
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?
Yes
26
Neuronal input can stimulate EECs during meals. Do nn. ever stimulate them not during a meal?
Yes
27
How do paracrine factors reach their targets?
Diffusion through ISF (to near by cells)
28
What are some e.g.'s of paracrine targets?
Smooth muscle, absorptive enterocytes, secretory cells in glands and other EECs.
29
What's an e.g. of a paracrine factor released by enterochromaffin-like cells that travels to parietal cells to secrete HCl?
Histamine
30
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?
Serotonin (5-HT)
31
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?
Paracrine
32
What's another name for Celiac disease? | What causes the allergic rxn?
- Gluten enteropathy | - A component in gluten of wheat flour, rye and barley called gliadin
33
What happens to the GI tract when a Celiac pt eats gluten? | Tx?
- Small intestine inflammation leads to reduction in density and length of microvilli and reduced absorption of nutrients - GF diet
34
GASTRIN - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Endocrine | - Gastric antrum (G cells)
35
GASTRIN - Stimuli for secretion? - Action
- Small peptides, AAs | - Increases parietal cells' H+ secretion; increases ECL cells' histamine secretion; growth of gastric mucosa.
36
CCK - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Both | - Duodenum (I cells)
37
CCK - Stimuli for secretion? - Action
- 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
SECRETIN - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Both | - Duodenum (S cells)
39
SECRETIN - Stimuli for secretion? - Action
- H+ in duodenum | - Increased pancreatic ductal secretions (HCO3- and water)
40
Glucoinsulotropic peptide (GIP) - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Endocrine | - Duodenum and Jejunum (K cells)
41
Glucoinsulotropic peptide (GIP) - Stimuli for secretion? - Action
- FAs, glucose | - Increased insulin secretion from pancreatic beta cells
42
Peptide YY (PYY) - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Both | - Intestine (L cells)
43
Peptide YY (PYY) - Stimuli for secretion? - Action
- FAs, glucose, hydrolyzed protein - Decreased gastric emptying and acid secretion; decreased pancreatic secretion; decreased intestinal motility; decreased food intake
44
Proglucagon-derived peptides 1/2 (GLP-1/2) - Paracrine or endocrine or both? - Secretion site (+ cells)?
- Both | - Intestine (L cells)
45
Proglucagon-derived peptides 1/2 (GLP-1/2) - Stimuli for secretion? - Action
- FAs, glucose, hydrolyzed protein | - Glucose homeostasis; increased epithelial cell proliferation
46
What 2 major parasympathetic nn. innervate the gut?
- Vagal nerves (from medulla) | - Pelvic nerves (from sacral cord)
47
What organs do the vagal and pelvic nerves each innervate?
- Vagal: esophagus, stomach, gallbladder, pancreas, 1st part of intestine, cecum, proximal colon - Pelvic: Distal colon, anorectal region
48
How does parasympathetic (generally) affect the GI system? | Symp?
- Activates it | - Inhibits it (exception: sphincters activated)
49
Regarding the parasymp NS, are the preganglionic or postganglionic fibers long? What are the 2 types of neurons it can have?
- Preganglionic | - Cholinergic or peptidergic
50
Cholinergic neurons release ___________ (and what type of synapse?) Peptidergic neurons release _________________________.
- Acetylcholine (nicotinic synapse) | - Various peptides: substance P, vasoactive intestinal peptide (VIP)
51
What % of the vagal nerve fibers are efferent vs. afferent?
75% afferent, 25% efferent fibers | - Vagovagal reflexes–both efferent and afferent in the vagus nerve.
52
Regarding the symp NS, are the preganglionic or postganglionic fibers long? What types of neurons does it have?
Postganglionic | - Adrenergic (release NE)
53
The 3 sympathetic ganglia that serve the GI tract are: | Which region of the cord do they stem from?
Celiac, superior mesenteric and inferior mesenteric (each w/their own plexus) - Thoracolumbar region
54
Where can postganglionic symp fibers synapse? | *How is this different from parasymp?
- At ganglia in ENS or directly innervate *smooth muscle, endocrine or secretory cells. - Parasymp synapse directly in ENS plexuses (*no DIRECT innervation)
55
What general types of receptors would give afferent feedback via parasymp?
Mechanoreceptors, chemoreceptors
56
Are the submucosal and myenteric plexi linked?
Yes (via interganglionic strands)
57
What 2 major/general types of neurochemicals (neurocrines) does the ENS release?
NTs + neuromodulators (modulate activity of NTs)
58
ACh - Source - Actions
- Cholinergic neurons | - Contraction of smooth m. in wall; relaxation of sphincters; increased salivary, pancreatic, and gastric secretions
59
NE - Source - Actions
- Adrenergic neurons | - Relaxation of smooth m. in wall; contraction of sphincters; increased salivary secretions
60
Vasoactive intestinal peptide (VIP) - Source - Actions
- Neurons of mucosa and smooth m. | - Relaxation of smooth m; increased intestinal and pancreatic secretions
61
Enkephalins (opiates) - Source - Actions
- Neurons of mucosa and smooth m. | - Contraction of smooth m; decreased intestinal secretions
62
Neuropeptide Y - Source - Actions
- Neurons of mucosa and smooth m. | - Relaxation of smooth m; decreased intestinal secretions
63
Gastrin-releasing peptide (GRP) AKA Bombesin - Source - Actions
- Neurons of gastric mucosa | - Increased gastric secretions
64
Substance P - Source - Actions
- Co-secreted w/ACh | - Contraction of smooth m; increased salivary secretions
65
Almost all contractile tissues of GI tract are smooth muscles, except these 3 places, which contain striated muscle.
What are the pharynx, the upper 1/3rd of esophagus, and the external anal sphincter?
66
What types of cells do GI smooth m. cells form gap junctions w/, and why?
- Interstitial cells of Cajal | - Permits rapid cell-to-cell spread of action potentials
67
Define what an interstitial cell of Cajal is. | Where are they located?
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
Is GI smooth m. contraction phasic, tonic, or both?
Both (organ specification on slide 57)
69
What are "slow waves" of the GI system?
Oscillating depolarization and repolarization of the membrane potential that are not large enough to elicit APs and/or contractions
70
Would a contraction be produced if the slow waves don't reach threshold?
Weak, basal, *tonic contractions occur even w/o APs
71
How could slow waves reach threshold, and what type of contraction would be produced?
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
What is the approx wave freq in the stomach vs. duodenum? (varies throughout GI tract)
3/min in stomach, 12/min in duodenum
73
Do GI smooth mm. have twitch summation (separate twitches)?
No, 1 long contraction
74
What 3 general ways could the body influence the slow wave amplitude, and to a lesser extent the freq?
Neurally, hormonally, and paracrine
75
Explain the segmentation process.
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
What is the purpose of segmentation?
Mixing of the luminal contents with GI tract secretions and increase exposure to the mucosal surfaces where absorption occurs
77
Where does segmentation predominantly occur?
Small and large intestines
78
Where do peristaltic contractions predominantly occur?
Pharynx, esophagus, gastric antrum, small and large intestine
79
What is the purpose of peristaltic contractions?
To propel the chyme along the GI tract
80
Explain the process of peristaltic contractions.
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
During peristaltic contractions, what NTs are involved w/orad contraction? What about caudad relaxation?
- ACh and substance P: orad contraction | - VIP and nitric oxide: caudad relaxation

FHB GI (10 decks)

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