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Bmsc 208 > GI 4 > Flashcards

GI 4 Flashcards

1
Q

Primary process of acid secretion from parietal

A
  1. Free H+ actively transported across apical membrane
  2. Water dissociates to H+ and OH- freeing more H+ to be actively transported out
  3. OH- combines with CO2 via CA to generate HCO3
  4. HCO3 exchanged with Cl at basolateral
  5. Cl diffuses across apical through open channels
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2
Q

What can the primary mechanism of acid secretion create

A

A lot of HCO3 in interstitial which can cause significant shift in pH of blood leading stomach
- short lived because pancreas

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3
Q

What is secondary mechanism of acid secretion

A

CO2 joins H20 to become H2CO3 which dissociates to H+ which is regularly transported across apical and HCO3 transported across basolateral

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4
Q

What happens with endocytosis of apical membrane of parietal cell

A

Channels internalized and cells not very active, cannot secrete a lot of H+

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5
Q

What is the stimuli for acid secretion

A

Insertion of apical H+/K+ ATPase, Cl- and K+ transported stored in vesicles
Stimuli causes exocytosis and insertion of transporters which turns on acid secretion

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6
Q

What is the negative regulator of acid secretion

A

Somatostatin

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7
Q

What is excessive acid treated with

A

H2 receptor antagonists or proton pump inhibitors (H-K ATPase)

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8
Q

What can inhibit acid secretion

A

Somatostatin
Intestinal hormones
Meds

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9
Q

What is the short reflex of gastric acid secretion

A
  • once food enters stomach (further reinforced)
  • luminal distension, AAs and peptides increase gastrin secretion which stimulate parietal cells
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10
Q

What is long reflex of gastric acid secretion

A

Cephalic phase (sight, though,etc)
Brain cause increase ENS activity
Stimulates G cells, ECL cells, parietal cells
Increases HCl

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11
Q

What can increased HCl stimulate

A

D cells to increase somatostatin secretion to affect acid secretion

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12
Q

Gastric digestive enzyme secretion process

A

Chief cells release pepsinogen and gastric lipase
Pepsinogen cleaved to pepsin by HCl
Pepsin breaks down protein to peptides

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13
Q

What is gastric digestive enzymes stimulated by (secretion by chief cells)

A

Acid secretion via short reflex

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14
Q

What does ECL release of histamine activate

A

H2 receptors on parietal cells to stimulate HCl secretion

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15
Q

What does parietal cells release of intrinsic factor form

A

Complex with vit B12 so it can be absorbed

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16
Q

What does D cells activation of somatostatin cause

A

Negative feedback for acid secretion (G cells, parietal cells, and ECL)
Inhibits pepsinogen release (inhibit chief cells)

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17
Q

Food or cephalic reflexes initiate gastric secretion of what

A

Gastrin, histamine, and acid

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18
Q

Gastrin stimulates what

A

Acid secretion by direct action on parietal cells

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19
Q

What is indirect sitmulus of parietal cells

A

Histamine

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20
Q

Acid stimulate what

A

Short reflex secretion of pepsinogen

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21
Q

Mucus and HCO3 secreted from

A

Mucous cells (to prevent breakdown of epithelial cells)

22
Q

What is mucus secretion stimulated by

A

Parasympathetic input and irritation

23
Q

What is HCO3 secretion stimulated by

A

Parasympathetic input and H+

24
Q

What are the 2 mucous cell types

A

Mucous surface cell
Mucous neck cell

25
Q

What is the physical barrier

A

Mucus layer

26
Q

What is the chemical barrier that neutralizes acid

A

Bicarbonate

27
Q

What is a peptic ulcer

A

Sore or break in lining of stomach or duodenum (acid + digestive enzymes break down)

28
Q

What is peptic ulcers caused by

A

Excessive acid production (gastrin secreting tumors)
Nonsteroidal anti-inflammatory drugs (chronic use, aspirin, ibuprofen)
H. Pylori

29
Q

What was believed to cause ulcer

A

Stress, spicy foods, over production of acid

30
Q

What was finally hypothesized to cause ulcers

A

Bacteria

31
Q

How does H.pylori cross mucus layer

A

Urease inside breaks down urea into NH3 and CO2
Creates buffer zone around themselves
Buffer attracted to HCO3 and mucus layer
Mucus layer breaks down and exposes epithelia

32
Q

How much food, fluid, secretions enter small intestine

A

5.5 L and additional 3.5 L added from hepatic, pancreatic, and intestinal

33
Q

Why is motility in small intestine regulated

A

To ensure proper digestion and absorption

34
Q

What type of contraction mix chyme in small intestine

A

Combination of segmental and peristaltic

35
Q

What does contractions in sm int cause

A

Mix chyme with enzymes
Expose nutrients to mucosal epithelium for absorption

36
Q

Where is most absorption in sm int

A

7.5L in duodenum and jejenum (most in jejenu)

37
Q

What promotes and inhibits motility in sm int

A

Parasympathetic innervation, gastrin, and cholecystokinin promotes
Sympathetic innervation inhibits

38
Q

What increase surface area in sm int

A

Plicae (large folds), villi, microvilli

39
Q

What do villi do

A

Increase surface area available for absorption and secrete mucus (goblet cells)

40
Q

What do crypts do

A

Contain hormone and fluid secretory cells and stem cells

41
Q

Where are most nutrients in sm int absorbed into

A

Capillaries in villi

42
Q

What do lateals of lymph vessels transport

A

Most fats to lymph

43
Q

What are brush border enzymes

A

Enzymes stay attached to microvilli

44
Q

Where does venous blood go from GI tract

A

Hepatic portal system
Liver acts as biological filter

45
Q

What does the liver acting as biological filter do

A

Contains variety of enzymes that metabolize drugs and xenobiotics and clear them from the blood stream before it proceeds to systemic circulation

46
Q

Why do drugs given orally have higher dose then IV

A

Absorbed in GI then metabolized in liver then travels through systemic

47
Q

How much secretions enter lumen of sm int

A

3.5 L

48
Q

What 5 types of secretions enter sm it

A

Digestive enzymes (brush border and pancreas)
Bile
Bicarbonate (pancreas)
Mucus (goblet cells)
Isotonic saline (crypt cells)

49
Q

What do mucus and isotonic saline do

A

Lubricate contents of gut

50
Q

How is isotonic saline produced

A
  1. Na, K+, and CL- enter by cotransport
  2. Cl enters lumen through CFTR
  3. Na+ is reabsorbed
  4. Negative CL in lumen attracts Na by paracellular pathway
  5. Water follows

Bmsc 208 (33 decks)

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