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AIM 2.2 > GI Physiology > Flashcards

GI Physiology Flashcards

1
Q

3 fundamental processes of digestive system

A

1) secretion (enzymes, mucus, ions, hormones)
2) absorption (water, ions, nutrients)
3) motility (crush, mix, propel)

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2
Q

where does the most chemical digestion occur?

A

small intestine

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3
Q

total amount of water secreted

A

9.3 L

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4
Q

total amount of water reabsorbed

A

9.2 L

only lose .1 L

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5
Q

GI sphincters

A

1) upper esophageal
2) lower esophageal
3) pyloric
4) oddi
5) ileocecal
6) internal anal
7) external anal (under voluntary control)

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6
Q

function of GI sphincters

A

keep digestive material moving in one direction

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7
Q

regulation of UES during swallowing

A

by enteric nervous system

Sensory, modulatory, and motor neurons innervate circular and longitudinal layers

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8
Q

basic structure of GI tract

A 
epithelial cells
lamina propria
muscularis mucosa
submucosal plexus
circular muscle
myenteric plexus
longitudinal muscle
serosa
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9
Q

major salivary glands

A

all PAIRED

1) parotid
2) submandibular
3) sublingual

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10
Q

minor salivary glands

A

600 in mouth

Sampled via mucosa when testing for abnormalities

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11
Q

major functions of saliva

A

1) moistens mucosa
2) moistens dry food and cools hot food
3) taste
4) acts as a buffer (high conc of bicarbonate ions)
5) digestion (a-amylase, lingual lipase)
6) controls bacterial flora
7) mineralization of new teeth and repair of enamel lesions (high calcium/phosphate)
8) antibacterial

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12
Q

alpha amylase in saliva

A

Breaks 1-4 glycoside bonds

only works for a short time bc only functional at neutral pH

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13
Q

lingual lipase

A

breaks down fats

only works for a short time bc only functional at neutral pH

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14
Q

How to ductal cells modify saliva as it is secreted?

A

Saliva becomes more isotonic as it passes along duct.

Fewer aquaporins –> force water to stay in saliva.

Low sodium content of saliva aids in detection of salt in diet

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15
Q

causes of increased saliva formation (positive regulators)

A

Conditioning (pavlov).
Food.
Nausea.
Smell.

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16
Q

causes of decreased saliva formation (negative regulators)

A

Dehydration.
Fear.
Sleep.
Anticholinergic drugs.

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17
Q

regulation of saliva formation occurs through ____ branch of the autonomic nervous system

A

Parasympathetic branch.

via ACh

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18
Q

gastrin (source, target, action)

A

Source: antrum of stomach
Target: parietal/chief cells in stomach
Action: increase H+ / intrinsic factor secretion, increase pepsinogen secretion

34aa, 17 aa

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19
Q

CCK (source, target, action)

A

Source: duodenum and jejunum
Target: pancreas and gallbladder
Action: increase enzyme secretion, increase contraction

33 aa

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20
Q

secretin (source, target, action)

A

Source: duodenum
Target: pancreas ducts and bile ducts
Action: increase HCO3/fluid secretion by pancreatic/bile ducts

27 aa

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21
Q

gastrin releasing peptide (GRP)

source, target, action

A

Source: vagal nerve endings
Target: antrum of stomach
Action: increase gastrin release

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22
Q

somatostatin (source, target, action)

A

Source: stomach and duodenum
Target: stomach, pancreas, liver
Action: decrease gastrin release, decrease endocrine/exocrine secretions, decrease bile flow

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23
Q

gastrin inhibitory peptide (GIP)

source, target, action

A

Source: duodenum and jejunum
Target: pancreas
Action: decrease fluid absorption

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24
Q

chemical digestion in stomach

A

Protein digestion begins (main stomach fxn).
Acid denatures protein, activates protein digesting enzyme.
Mucus prevents stomach cells from being digested.

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25
Q

functions of stomach

A

1) reservoir - compliance allows increase in volume with little increase in pressure
2) storage - allows digestion by salivary/lingual enzymes
3) mixing - fluid/food/gastric enzymes
4) kneading of food - to less than 1 mm
5) metered emptying - in response to duodenal feedback
6) vomit - defense against harmful substances ingested

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26
Q

how do we get rid of things that we can’t digest larger than 1 mm from stomach?

A

Corn, fiber, etc.

Emptied between meals

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27
Q

stomach secretions

A

1) hydrogen ion
2) pepsinogens
3) mucus
4) intrinsic factor
5) water (2.5L/day)

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28
Q

function of hydrogen ion in stomach

A

Converts pepsinogen into pepsin.
Kills microbes.
Denatures protein

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29
Q

intrinsic factor

A

Produced in stomach.

Aids in absorption of vit B12

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30
Q

D cells

A

Secrete somatostatin (inhibits gastrin release)

Triggered by low stomach pH

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31
Q

G cells

A

Secrete gastrin (stimulate acid secretion, pepsinogen secretion)

32
Q

gastrin release stimulators

A 
Peptides/amino acids.
Stomach stretch (via GRP release).
33
Q

gastrin release inhibitors

A

H+ ions (low pH)

H+ stimulates D cells, which then inhibit G cells

34
Q

gastrin effect chain on other cells

A

Stimulates enterochromaffin-like cell –secretes histamine–> chief cell –secretes pepsinogen

Stimulates chief cells directly to produce pepsinogen.

Stimulates parietal cells directly to secrete H+

35
Q

gastric pit components

A

Parietal cells (acid, intrinsic factor)

ECL cell (histamine secretion)

Chief cell (pepsinogen)

36
Q

resting parietal cell

A

pH 1-2
H+/K+ ATPases are sequestered in tubulovesicles in parietal cells.
Minimal ATPases in cell membrane

37
Q

activated parietal cell

A

Stimulation causes vesicles to fuse with cell membrane, leading to more H+/K+ ATPases inserted into membrane.
Allows increased movement of hydrogen ions into the stomach.

Stimulated by ACh, histamine, gastrin

38
Q

__% of the pancreas is dedicated to producing digestive enzymes

A

80%

39
Q

which pancreatic cells synthesize and secrete the digestive enzymes?

A

acinar cells

40
Q

pancreatic duct cells

A

secrete bicarbonate

41
Q

pancreatic ducts

A

transport enzymes to beginning of small intestine

42
Q

active pancreatic enzymes

A

Lipase.
a-Amylase.
Trypsin inhibitor.
Nucleases.

43
Q

inactive pancreatic enzymes (proenzymes)

A 
[all are proteolytic]
Trypsinogen.
Chymotrypsinogen.
Proelastase.
Procarboxypeptidase A/B

If they were secreted in an active form, they would damage the ducts.

44
Q

major route of pancreas stimulation

A

Partially digested fats/proteins cause CCK release, increasing amount of digestive enzymes. (acts on acinar cells)

Acidity in intestine causes increased sodium bicarbonate release from ductal cells. (acts on ductal cells)

45
Q

minor route of pancreas stimulation

A

seeing/smelling food causes parasympathetic impulses along vagus (CN X) nerves.

46
Q

Which enzyme activates all pancreatic proteases?

A

Trypsin

47
Q

enterokinase

A

cleaves trypsinogen to active form (trypsin)

apical/intrinsic (trapped in brush border)

48
Q

first pass effect

A

Hepatic metabolism of pharmalogical agent when it is absorbed from the gut and delivered to liver via portal circulation.

Greater first pass effect = lower distribution of drug (if administered orally)

49
Q

basolateral side of hepatocytes vs apical side

A

basolateral: blood flows thru cords (portal vein, cords, central vein)
apical: secrete bile (bile flows thru canaliculi to duct)

50
Q

the liver stores:

A 
Glucose in form of glycogen.
Fat soluble vitamins (ADEK).
Folate.
Vitamin B12.
Minerals (copper/iron)
51
Q

bilirubin

A

Only component of bile that is not made/secreted by liver.

From macrophages clearing RBCs.

52
Q

function of water, ions, HCO3 in bile salts

A

Neutralize pH.

Dilute chyme.

53
Q

synthesis of bile acids

A

All start from cholesterol.

Primary: made exclusively in liver

Cholic acid.
chenodeoxycholic acid.

54
Q

secondary bile acids

A

Made by gut bacteria.
Conjugated with taurine or glycine.
Functionally equivalent to primary bile salts.

55
Q

bile acid structure

A

Ampipathic.
Hydrophobic side is attracted to fat.
Hydrophilic side binds to water.

Allows emulsification of fat, micelle formation.

56
Q

gall bladder when there’s no food

A

Gall bladder expands.
Sphincter of Oddi is closed.

Gallbladder pumps out ions, so water follows, concentrating the bile.

57
Q

gallbladder after ingestion of food

A

Gallbladder contracts.
Sphincter of Oddi relaxes.

via CCK and neural stimulation.

58
Q

emulsification of fat

A

1) bile acids emulsify fat droplets.
2) hydrolysis of triglycerides to FAs and monoglycerides
3) dissolve FAs/MAGs into micelles (mixed micelles)

59
Q

why form micelles?

A

Micelle solubilization of polar lipids greatly increases their rate of diffusion to epithelial surface of small intestine.

Essential for absorption of lipids.

60
Q

micelle structure

A

Hydrophobic core:
Cholesterol,
TAGs,
Phospholipid tails.

Hydrophilic external:
Bile salts,
Phospholipid heads,
MAG heads.

61
Q

major regulation of bile secretion

A

FAs and AAs in chyme entering duodenum stimulate secretion of CCK into blood. CCK: opens sphincter of Oddi, contraction of gallbladder.

Acidic chyme stimulates secretion of Secretin into blood. Secretin: secretion of bicarbonate from liver bile ducts.

62
Q

minor regulation of bile secretion

A

Parasympathetic impulses from vagus nerve (CN X) stimulate bile production by liver.

63
Q

mechanisms to increase surface area of small intestine

A

Cylinder.
Folds.
Villi.
Microvilli.

Amplified 20x

64
Q

small intestine epithelial cells

A

1) absorptive cell: AAs, glucose, monoglycerides, membrane enzymes
2) goblet cell - mucin
3) enteric endocrine cell: gastrin, CCK, secretin
4) stem/progenitor cell: cell renewal
5) paneth cell: lysozyme to kill bacteria

65
Q

absorptive cell of small intestine

A

Absorbs AAs, glucose, monoglycerides

contains membrane enzymes

66
Q

enteric endocrine cells

A

Small intestine.

Secrete gastrin, CCK, secretin.

67
Q

secreted digestive enzymes

A 
Amylase.
Lipase.
Pepsin.
Trypsin.
Other proteases.

All enter small intestine, mix with chyme.

68
Q

cell membrane bound digestive enzymes

A

Enterokinase.
Disachharidases.
Peptidases.

Final products of digestion.
Close to cell transporters for easy/quick uptake into cell.

NOT secreted. Digestion occurs at cell surface.

69
Q

main digestive enzymes: carbohydrates

A

Amylase (salivary glands, pancreas). [secreted] - break sugars down to disaccharides

Disaccharidases (small intestine) [cell membrane bound] - break disaccharides to monosaccharides

70
Q

transport of glucose into enterocytes

A

Uses glucose/Na+ co-transporter

71
Q

main digestive enzymes: protein

A

Pepsin (stomach) [secreted]

Acid (stomach) [secreted} - denatures protein.

Proteases: trypsin, chymotrypsin, carboxypeptidase, elastase (pancreas, secreted) - each cleave at a different AA to form different smaller pieces

Peptidases (small intestine, membrane bound) - cleave to individual AAs

72
Q

transportation of amino acids

A

through bloodstream

73
Q

transportation of fats

A

through lymph.

eventually to bloodstream

74
Q

main digestive enzymes: fat

A

Lingual lipase (mouth, secreted).

Pancreatic lipase, phospholipase, cholesterol esterase (pancreas, secreted)

75
Q

process of fat digestion and absorption

A

1) bile salts coat fat droplets.
2) pancreatic lipase breaks fats down into MAGs and FAs stored in micelles.

3) MAGs/FAs move out of micelles and enter cells by diffusion.
[cholesterol is transported into cells]

4) absorbed fats combine with cholesterol/proteins in enterocytes to form chylomicrons.
5) chylomicrons removed by lymphatic system

76
Q

transport of protein components into enterocytes

A

amino acids transported by Na+ co-transporter

small peptides (2-3 aa) have separate transporter - must be further digested by peptidases in cytoplasm before transport in capillaries

AIM 2.2 (26 decks)

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