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Physiology > Exam #3 (GI) > Flashcards

Exam #3 (GI) Flashcards

1
Q

3 major activities of the GI tract

A
  1. Motility
  2. Secretions: of juices & enzymes. digestion
  3. Absorption
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2
Q

Submucosal Plexus

A

Aka Meissner’s plexus
Lies between the submucosa & the circular muscle
Primarily controls SECRETION & blood flow

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3
Q

Myenteric Plexus

A

Aka Auerbach’s plexus
Lies between the circular muscle & the longitudinal muscle
Primarily controls MOTILITY of the smooth muscles

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4
Q

Parasympathetic NS in GI tract

A

Usually excitatory
Increases GI motility & secretion
Decreases activity of sphincters
Innervation is supplied by Vagus & pelvic nerves

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5
Q

Vagus nerve innervates

A

Upper 1/3 esophagus (striated), stomach, pancreas, small & upper large intestines (ascending colon). Stops at splenic flexure.

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6
Q

Pelvic nerve innervates

A

Lower large intestines, rectum, & anus

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7
Q

What is the vasovagal reflex?

A

It is the contraction of the gastrointestinal muscle layers in response to distension of the tract by food

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8
Q

The vagus nerve is __% afferent & __% efferent

A

75% afferent: from mechano & chemo receptors to CNS

25% efferent: from CNS to smooth muscles, secretory & endocrine cells

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9
Q

Sympathetic NS in the GI tract is usually

A

Inhibitory
Increases sphincter tone
Reduces blood flow to GI tract

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10
Q

Hirschsprung’s Disease

A

Aka congenital aganglionic megacolon
Resulting from an aganglionic section of bowel (absent ganglion cells). It’s missing myenteric plexus
Begins at the anus & progresses upwards, more common in males

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11
Q

Signs & Symptoms of Hirschsprung’s Disease

A

Delayed passage of meconium
Abdominal distension
Constipation

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12
Q

Hormones in the GI tract

A

gastrin
cholecystokinin (CCK)
secretin
gastric inhibitory peptide (GIP)

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13
Q

Paracrines in the GI tract

A

somatostatin

histamine

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14
Q

Neurocrines in the GI tract

A 
ACh
norepi
vasoactive intestinal peptide (VIP)
gastrin-releasing peptide (GRP) or bombesin
enkephalins
neuropeptide Y
substance P
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15
Q

Official hormones

A

Those which meet the following criteria:

  1. substance must be secreted in response to a physiologic stimulus & can be carried in the bloodstream to a distant site, where it produces a physiologic action
  2. its function must be independent of any neural activity
  3. it must be isolated, purified, chemically identified, and synthesized
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16
Q

Candidate hormones

A

Those that do not meet the criteria of a GI hormone

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17
Q

Gastrin, cholecystikinin (CCK), secretin, & GIP are all

A

Official hormones

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18
Q

Substance P, VIP, enteroglucagon, bombesin, & motilin are all

A

Candidate hormones

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19
Q

Gastrin secreted by

A

G (gastrin) cells in the antrum of the stomach

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20
Q

Litte vs Big gastrin

A

“Little gastrin”/G17 = Secreted in response to a meal

“Big gastrin”/G34 = Secreted during the inter-digestive period (between meals)

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21
Q

Stimuli for the secretion of gastrin

A
  • small peptides & AA in stomach lumen (*Phenylalanine & tryptophan: most important stimuli)
  • distention of stomach
  • vagal stimuli, mediated by GRP
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22
Q

Stimuli for the inhibition of gastrin

A
  • stomach lumen H (low pH) via negative feedback
23
Q

Actions of Gastrin

A
  • Increases H secretion by gastric parietal cells (increases HCL)
  • Increases motility
  • Increases pancreatic secretions
  • Stimulates growth of gastric, small intestine, & colon mucosa by stimulating RNA & protein synthesis
24
Q

Cause of Zollinger-Ellison syndrome

A

Due to a gastrin-secreting tumor or gastrinoma. Ectopic secretion of gastrin

25
Q

Signs & Symptoms of Zollinger-Ellison syndrome

A
  • Hypertrophy of the gastric mucosa
  • Duodenal ulcers caused by the unrelenting secretion of H
  • Acidification of the intestinal lumen -> inactivates pancreatic lipase, an enzyme necessary for fat digestion ==> Fat is excreted in the stool***** (STEATORRHEA)
26
Q

Cholecystokinin (CCK) is coordinate to do what? It is secreted by what?

A

Coordinated to promote fat digestion & absorption

Secreted by the I cells of the duodenal & jejunal mucosa

27
Q

CCK is secreted in response to

A
  • Monoglycerides & FA (but not triglycerides: glycerol + 3 FAs)
  • Small peptides & amino acids
28
Q

Actions of CCK

A
  • Contraction of the gallbladder w/ simultaneous relaxation of the sphincter of Oddi. Ejects bile from the gallbladder into the lumen of the small intestine
  • Secretion of pancreatic enzymes (Lipase =lipids, Amylase=carbs, Pancreatic proteases = protein)
  • Secretion of HCO3 from the pancreas
  • Growth of the exocrine pancreas & gallbladder
  • Inhibition of gastric emptying (allows more time for digestion & absorption)
29
Q

Secretin

A
  • structurally homologous to glucagon
  • secreted by the S cells (secretin cells) of the duodenum in response to H+ & FA
  • all 27 of it’s AA are required for it’s biologic activity
30
Q

Actions of Secretin

A
  • To reduce H+ in lumen of small intestine
31
Q

Glucose-Dependent Insulinotropic Peptide (GIP) are secreted by

A
  • K cells of the duodenal & jejunal mucosa

- it is the only GI hormone that is secreted in response to all 3 types of nutrients: Glucose, AA & FA

32
Q

Actions of GIP

A
  • stimulation of insulin secretion

- inhibition of gastric H secretion

33
Q

Somatostatin secreted by

A

D cells of GI mucosa. Also secreted by the hypothalamus & by the delta cells of the endocrine pancreas
It is a paracrine

34
Q

Somatostatin is secreted in response to

A

Decreased luminal pH. Thus inhibits gastric H secretion & increases pH

35
Q

Histamine stimulates

A

Stimulates gastric H+ secretion

36
Q

Actions of VIP

A
  • Induce smooth muscle relaxation (LES, stomach, gallbladder)
  • Stimulate secretin of water into pancreatic juice & bile
  • Inhibition of gastric acid secretion & absorption from the intestinal lumen
37
Q

Phasic vs Tonic contractions

A 
Phasic = periodic contraction & relaxation: esophagus, gastric antrum, small intestines
Tonic = sustained contraction: LES, orad stomach (upper region of stomach), ileocecal, internal anal sphincter)
38
Q

Gastroesophageal reflux disease (GERD)

A

Due to weakness or decreased tone of LES, gastric contents reflux into esophagus

39
Q

Alchalasia

A

Due to sustained contraction or increased tone of the LES, not allowing food to enter stomach. “Bird beak appearance”

40
Q

Parietal cells secrete what?

A

HCl & Intrinsic factor. Found in the body of the stomach

41
Q

Chief cells secrete what?

A

Pepsinogen. Found in the body of the stomach

42
Q

G cells secrete what?

A

Gastrin. Found in the antrum of the stomach

43
Q

Mucous cells secrete what?

A

Mucus & Pepsinogen. Found in the antrum of the stomach

44
Q

Required for the absorption of vitamin B12 in the terminal ileum

A

Intrinsic factor

45
Q

Gastric ulcers

A
  • Mucosal barrier is defective, which allows H+ & pepsin to digest a portion of the mucosa
  • H+ secretion is decreased, not increased as expected, b/c some of the H leaks into the damaged mucosa
  • Gastrin levels are increased by negative feed back mechanism from low H
46
Q

Duodenal ulcers

A
  • more common than gastric ulcers
  • most common cause: H. pylori
  • H secretion is higher than normal & is responsible along w/ pepsin for damaging mucosa
  • gastrin levels in response to a meal is higher than normal b/c somatostatin which normally inhibits gastrin is also inhibited
47
Q

Drugs which block H secretion & are used for the treatment of ulcers

A

Atropine: muscarine receptor blocker
Cimetidine: H2 receptor blocker
Omeprazole: inhibits H-K-ATPase

48
Q

The absence of Intrinsic factor causes

A

Pernicious anemia

49
Q

The only essential secretion of the stomach

A

Intrinsic Factor

50
Q

Following gastrectomy (removal of the stomach), patients must receive IV vitamin B12 to bypass the absorption due to

A

Loss of intrinsic factor

51
Q

Secretin & CCK are the major stimulants of

A

Pancreatic secretion

52
Q

What carbohydrates are absorbed?

A

Only monosaccharides are absorbed: Glucose, Galactose, Fructose

53
Q

Fat soluble vitamins

A

A, D, E, K. These have to be taken in fat form in order to be absorbed

Physiology (13 decks)

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