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GI Midterm > DSA: Intro To GI Physiology > Flashcards

DSA: Intro To GI Physiology Flashcards

1
Q

What are the 2 surfaces of the GI tract wall?

A

Mucosal Surface - Faces GI Lumen

Serosal Surface - Faces Blood

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2
Q

What are the layers of the GI tract wall from LUMEN to BLOOD?

A 
Mucosal
- Epithelial Cells
- Lamina Propria
- Muscularis Mucosae
Submucosal
Submucosal Plexus
Circular Muscle
Myenteric Plexus
Longitudinal Muscle
Serosal Layer
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3
Q

What are the functions of the 3 Mucosal Layer components?

A

Epithelial Cells - Absorb/Secrete

Lamina Propria - Connective tissue

Muscularis Mucosae - SMOOTH muscle cells that change shape/surface area of epithelial cell layer

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4
Q

Which 2 layers provide motility of the GI Tract? What are their defining characteristics?

A
  1. Circular Muscle - Thick layer and more densely innervated.
  2. Longitudinal Muscle - Thin layer and few nerve fibers.
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5
Q

Which 2 plexuses contain the nervous system of the GI Tract?

A
  1. Submucosal Plexus (Meissner)
    Between Submucosal and Circ. M.
  2. Myenteric Plexus
    Between Circ. And Longitudinal M.
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6
Q

Which components make up the Muscularis Propria?

A
  1. Circular Muscle
  2. Myenteric Plexus
  3. Longitudinal M.
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7
Q

Which 2 nerves supply PARASYMPATHETIC innervation of the GI Tract?

A

Vagus N. (CN X) and Pelvic N.

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8
Q

Which areas are innervated by the Vagus N?

A

Upper GI

Striated Muscle - upper 1/3 esophagus
Stomach Wall
Small Intestine
Ascending Colon
Portion of Transverse Colon
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9
Q

Which areas are innervated by the Pelvic nerve?

A

Lower GI

Walls of Transverse, Sigmoid, and Descending Colon

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10
Q

Where are the PARASYMPATHETIC ganglia located in the GI Tract? SYMPATHETIC Ganglia?

A

Parasympathetic - IN WALLS of organs within Submucosal and Myenteric Plexuses

Sympathetic - OUTSIDE GI Tract Walls

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11
Q

What percent of the Vagus N. Is AFFERENT? EFFERENT?

A

Afferent - 75 Percent
Efferent - 25 Percent

Allows for Vagovagal Reflex

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12
Q

Which 4 SYMPATHETIC ganglia serve the GI Tract?

A

Celiac
Superior Mesenteric
Inferior Mesenteric
Hypogastric

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13
Q

What are the 2 components of the ENTERIC NS?

A

Submucosal Plexus
Myenteric Plexus

Can exert all functions WITHOUT CNS

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14
Q

Which 3 functions are controlled by the ENTERIC NS?

A

Contraction
Secretion
Endocrine

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15
Q

What is the path for HORMONE regulation in the GI Tract?

A

Endrocrine Cell —> Secrete Hormone —> Enter Portal Circ. —> Liver —> Systemic Circ. —> Target Cell

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16
Q

Which 4 GI peptides are classified as HORMONES?

A

Gastrin
Cholecystokinin (CCK)
Secretin
Glucose Dependent Insulinotropic Peptide (GIP)

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17
Q

What is the path for PARACRINE regulation in the GI Tract?

A

Endrocrine Cell —> Secrete Hormone —> Act on local target

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18
Q

Which GI peptide acts via a PARACRINE method?

A

Somatostatin

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19
Q

What is the path of NEUROCRINES within the GI Tract?

A

Neuron of GI Tract —> Action Pot. —> Release of neurocrine on target

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20
Q

Which substances act as NEUROCRINES within the GI Tract?

A 
ACh
NE
VIP
NO
GRP
Enkephalins
Neuropeptide Y
Substance P
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21
Q

What are the 2 forms of Gastrin? When are they secreted?

A

G17 (Little Gastrin) - Secreted in response to a MEAL.

G34 (Big Gastrin) - Secreted during INTERDIGESTIVE period.

Note: Only the C-terminal TETRAPEPTIDE is necessary for biological activity.

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22
Q

Which cells secrete Gastrin?

A

G Cells in antrum of the stomach

23
Q

Which stimuli initiate Gastrin secretion?

A
  1. Products of protein digestion - small peptides and AA; especially phenylalanine and tryptophan
  2. Distention of stomach by food
  3. Vagal Stimulation - such as local vagal response with Gastrin Releasing Peptide (GRP)
24
Q

Which 2 conditions INHIBIT Gastrin secretion?

A
  1. Low pH of gastric content

2. Somatostatin

25
Q

What are 2 major actions of Gastrin?

A
  1. Stimulate increased H+ secretion

2. Stimulate growth of gastric mucosa

26
Q

What is the cause of Zollinger-Ellison Syndrome? Signs/Symptoms? Treatment?

A

Cause: Gastrin secreting tumor usually in the non B-cell pancreas

Sign/Symptom: Increased H+ secretion by parietal cells; hypertrophy gastric mucosa; duodenal ulcers; acidification of intestinal lumen —> deactivated pancreatic lipase —> decreased fat digestion/increased fat excretion (steatorrhea)

Treat: H2 Blocker; Inhibitor of H+ Pump; Remove tumor

27
Q

What are the 2 receptors for CCK? What is their sensitivity for CCK and Gastrin?

A

CCKa - ONLY CCK

CCKb - Equally CCK and Gastrin

Note: C-Terminal Heptapeptide necessary for CCK activity.

28
Q

Which cells secrete CCK?

A

J Cells of the duodenal and jejunal mucosa

29
Q

What are the 2 main stimuli for CCK secretion?

A
  1. Monoglycerides / FA (Not Triglyc.)

2. Small peptides / AA

30
Q

What is the OVERALL function of CCK?

A

Ensure pancreatic enzymes & bile salts secreted to aid in digestion/absorption.

31
Q

What are the 5 ACTIONS of CCK?

A
  1. Stimulate contraction of gallbladder & relax Sphincter of Oddi —> bile enters lumen —> emulsify/solubilize dietary lipids.
  2. INCREASE Pancreatic enzyme release
    - Lipase, Amylase, Protease
  3. INCREASE Pancreatic HCO3- secretion
    - Potentiate effect of Secretin
  4. Growth of exocrine pancreas and gallbladder
  5. Inhibition of gastric emptying
32
Q

Which cells secrete Secretin?

A

S Cells of Duodenum

33
Q

What stimulates secretion of Secretin?

A

H+ and Fatty Acid in lumen of Small Intestine

34
Q

What are the 2 main functions of Secretin?

A
  1. INCREASE Pancreatic and Biliary HCO3-

2. DECREASE Gastric H+ secretion and inhibit trophic effects of Gastrin on gastric mucosa

35
Q

Which HORMONE is the only one secreted in response to ALL 3 NUTRIENTS?

A

Glucose Dependent Insulinotropic Peptide (GIP)

36
Q

Which cells secrete GIP?

A

K Cells of the Duodenal and Jejunal mucosa

37
Q

What are the 3 stimuli for GIP secretion?

A

Fatty Acids
Amino Acids
ORAL Glucose

38
Q

What are the 3 main actions of GIP?

A
  1. INCREASED Insulin secretion from pancreatic B-cells (Incretin Effect)
  2. DECREASED Gastric H+ Secretion
  3. DECREASED Gastric Emptying
39
Q

What defines a Candidate GI Hormone?

A

Failure to meet one or more of the following criteria:

  1. Function independent of neural activity
  2. Isolated, purified, chemically identified and synthesized
  3. Secreted in response to physiological stimulus —> Carried in blood —> Produce physiologic action at site
40
Q

What are the 4 candidate GI Hormones?

A

Motilin
Pancreatic Polypeptide
Enteroglucagon
Glucagon-like Peptide 1 (GLP-1)

41
Q

Where is Motilin secreted? What is the function of Motilin?

A

Secretion: Upper duodenum during FASTING state

Function: INCREASE gastrointestinal motility; initiate interdigestive myoelectric complexes that occur at 90 min interval

42
Q

What stimulates secretion and is the function of Pancreatic Polypeptide?

A

Stimulation: Secreted by Pancreas in response to ingestion of Carbs, Protein, and Lipids

Function: INHIBIT Pancreatic HCO3- secretion; Not fully understood.

43
Q

What stimulates and is the function of GLP-1?

A

Stimulation: Synthesized/secreted by L Cells of Small Intestine

Function: Incretin - binds to pancreatic Beta cell receptors & stimulates insulin secretion; Inhibits glucagon secretion; inhibits appetite

44
Q

Somatostation:

Secreted By?
Stimuli?
Function?

A

Secreted by D Cells (both endocrine/paracrine) of GI Mucosa; Hypothalamus; Delta Cells of Endocrine Pancreas

Stimuli: DECREASED luminal pH

Function: Inhibit secretion of GI hormones; Inhibit gastric H+ secretion

45
Q

Histamine:

Secreted by?
Function?

A

Secreted by Enterochromaffin-like (ECL) cells in gastric glands

Function: Along with Gastrin and ACh, Histamine stimulates H+ secretion

46
Q

Where are the centers located that control appetite & feeding behavior?

A

Hypothalamus

Satiety Center - Ventral Posterior Nucleus (VPN)

Feeding Center - Lateral Hypothalamic Area (LHA)

47
Q

What are the 2 types of neurons within the Arcuate Nucleus that impact satiety and feeding centers?

A
  1. Anorexigenic Neurons
    - Release pro-opiomelanocortin (POMC)
    - Cause DECREASED appetite
  2. Orexigenic Neurons
    - Release Neuropeptide Y
    - Cause INCREASED appetite
48
Q

Which 5 substances affect satiety/feeding centers by influencing anorexigenic and orexigenic neurons?

A

Leptin, Insulin, GLP-1, Ghrelin, and Peptide YY (PYY)

49
Q

What effect does Leptin have on satiety/feeding centers?

A

Stimulate Anorexigenic Neurons
Inhibit Orexigenic Neurons

DECREASE APPETITE (Long Term) - Secreted by fat cells in proportion to body fat.

50
Q

What effect does Insulin have on satiety/feeding centers?

A

Stimulate Anorexigenic Neurons
Inhibit Orexigenic Neurons

DECREASE APPETITE - Short Term

51
Q

What effect does GLP-1 have one satiety/feeding centers?

A

Synthesized/secreted by Intestinal L Cells

DECREASE APPETITE

52
Q

What effect does Ghrelin have on feeding/satiety centers?

A

Secreted by Gastric Cells BEFORE meal ingestion.

Stimulate Orexigenic Neurons
Inhibit Anorexigenic Neurons

INCREASE APPETITE

53
Q

What effect does Peptide YY (PYY) have on feeding/satiety centers?

A

Secreted by L Cells following meal

DECREASE APPETITE

  • Directly act on hypothalamus
  • Inhibit Ghrelin secretion

GI Midterm (2 decks)

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