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Physio - GI > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

what anchors mucosal secretion to the intestinal microvilli?

A

glycocalyx

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2
Q

what are the diffusion barriers to absorption? (4)

A
  • unstirred water layer (UWL)
  • luminal (apical) cell membrane
  • basal cell membrane
  • ECF
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3
Q

what pump accounts for 33% of the total resting cell energy budget of the GI tract?

A

Na-K ATPase

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4
Q

how is secondary active transport typically done?

A

couple movement of Na with a sugar or amino acid

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5
Q

example of uniport, symport, and antiport?

A

uniport: Ca-ATPase
symport: Na-glucose, Na-amino acid
antiport: Na-K ATPase, H-K ATPase

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6
Q

pepsin:
- what secretes it
- what activates it
- action

A
  • from stomach
  • activated by low pH
  • acts on aromatic aa’s and some others
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7
Q

trypsinogen:
- what secretes it
- what activates it
- action

A
  • from pancreas
  • activated by mucosal enteropeptidase (enterokinase)
  • cleaves peptide bonds nest to characteristic aa’s
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8
Q

procarboxypeptidase:
- what secretes it
- what activates it
- action

A
  • from pancreas
  • activated by trypsin
  • cleaves C-terminal aa’s
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9
Q

what types of nutrients are absorbed via secondary active symport?

A
  • free aa’s
  • dipeptides
  • tripeptides
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10
Q

what nutrients are absorbed via facilitated diffusion?

A
  • Glu

- Asp

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11
Q

how do nutrients get through the basal membrane and into the blood/lymph?

A

basal membrane -> facilitated diffusion -> then simple diffusion to blood/lymph

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12
Q

describe the breakdown of total digested protein in small intestine in terms of where it is from

A

50% - food
25% digestive juices
25% sloughed mucosal cells

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13
Q

how much total protein escapes digestion and absorption?

A

2-5%

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14
Q

principal carb sources

A
  • polysaccharides (starches)
  • disaccharides (sucrose, lactose)
  • monosaccharides (glucose, fructose)
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15
Q

animal starch vs. plant starches

A
  • glycogen (animal): 1,4a-linkages, 1,6a-branches
  • amylopectin (plant): similar but less 1,6a-branches
  • amylose (plant): only 1,4a-linkages
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16
Q

action of salivary and pancreatic alpha-amylases

A

dk

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17
Q

action of salivary and pancreatic alpha-amylases

A
  • attack straight chain 1,4a-linkages

- spare 1,6a-links, terminal 1,4a-links, and 1,4a-links next to branch points

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18
Q

products of salivary and pancreatic alpha-amylases

A
  • maltose (disaccharide)
  • maltotriose (trisaccharide)
  • a-limit dextrins
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19
Q

where does the final digestion of carbs occur?

A

ileum via membrane-bound oligosaccharidases in microvilli

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20
Q

what causes lactose intolerance?

A

deficiency of lactase and/or sucrase -> retain disaccharides -> retain water -> diarrhea, bloating, gas

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21
Q

describe levels of lactase throughout lifetime

A

highest in infants, declines during childhood and adulthood

22
Q

what are the principal absorbed monosaccharides and how is each absorbed through apical then basal membrane?

A
  • glucose (Na-dependent symport ->facilitated diffusion)
  • galactose (Na-dependent symport ->facilitated diffusion)
  • fructose (facilitated diffusion -> facilitated diffusion)
23
Q

what are non-digestible carb components of food?

A
  • cellulose
  • pectins
  • lignins
24
Q

impact of non-digestible carb components of food

A

add bulk, retain water -> enhance stood transit time by distention related events (natural laxative)

25
Q

what emulsifies lipids and where?

A

small intestine - bile salts (glycocholate), lecithin, monoglycerides

26
Q

what is the major lipid digestive enzyme?

A

pancreatic lipase - hydrolyzes fatty acid ester linkages

27
Q

what is required for lipase to function?

A

colipase - binds TG surface, displacing emulsifier molecule and anchoring lipase

28
Q

what is required for lipase to function?

A

colipase - binds TG surface, displacing emulsifier molecule and anchoring lipase

29
Q

describe structure of micelles

A
  • outer layer of emulsifier

- inner layer of cholesterol, lysolecithin, MG, fa’s

30
Q

describe intracellular fate of absorbed lipids of different sizes

A

directly pass to portal blood

>10-12 C -> re-esterified

31
Q

how much fat is normally in stool?

A
32
Q

how much cholesterol is absorbed from lumen and why?

A

almost insoluble in water -> only 50% absorbed

33
Q

describe formation of chylomicrons and how they help absorption of fat

A

glycophospholipids + free TGs -> Golgi -> lipid droplets -> add lipoproteins, phospholipids -> chylomicron -> secretory vesicle into extracellular space -> lymph -> thoracic duct -> circulation

34
Q

describe absorption of water-soluble vitamins

A
  • B’s, niacin, folate, ascorbate

- diffusion, cotransport, and active transport

35
Q

which water-soluble vitamin has different absorption?

A

B12 - needs intrinsic factor, absorbed in ileum

36
Q

describe absorption of fat-soluble vitamins

A
  • A,D,E,K

- like water-soluble but in proximal small intestine primarily

37
Q

how much of Na entering each portion of gut is absorbed?

A

duodenum and jejunum - 55%
ileum - 25%
large intestine - 20%

38
Q

describe Na absorption in jejunum

A

-passively absorbed at tight junctions and lateral spaces in response to osmotic forces

39
Q

describe Na absorption in ileum

A
  • mainly electrogenic - diffusion down gradient via specific membrane protein channels
  • also some by neutral Na/Cl exchange
  • indirectly dependent on Na/K ATPase
40
Q

describe Na absorption in colon

A

purely electrogenic

41
Q

describe Na absorption in colon

A

purely electrogenic

42
Q

how much of the Ca ingested is absorbed and where?

A

50% - mostly in upper small intestine

43
Q

describe Ca absorption

A

needs Ca-binding protein (upregulated by vit D), then basal Ca ATPase (2 Ca: 1 ATP)

44
Q

how is iron transported in blood?

A

bound to transferrin

45
Q

how is iron stored?

A

complexed with ferritin

46
Q

describe iron absorption

A
  • as free iron: combines w/ DMT-1 in duodenum

- as iron heme complex: directly into intestinal mucosal cells

47
Q

what iron carrier releases iron to the plasma?

A

ferroportin

48
Q

what regulates iron uptake into mucosal cells?

A

intracellular [ferritin]

49
Q

where does water absorption primarily occur?

A

lower small intestine and large intestine - net water movement occurs in small intestine until osmolality of lumen equals that of cytoplasm-interstitium-plasma

50
Q

describe water absorption in colon

A

solely follows electrogneic movement of Na - largely through tight junctions between epithelial cells

Physio - GI (5 decks)

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