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Physiology Part 1 > Lec 22 Digestion and Absorption II > Flashcards

Lec 22 Digestion and Absorption II Flashcards

1
Q

Where does digestion occur?

A
  • in lumen or on brush-border membrane

- pre-mucosal

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2
Q

What is definition of digestion?

A
  • breaking down food to small, absorbable components
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3
Q

What is definition of absorption?

A
  • transporting breakdown products of digestion across intestinal epithelium
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4
Q

Where does absorption occur?

A
  • mucosal
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5
Q

What 2 digestive enzymes in salivary glands?

A
  • salivary amylase

- lingual lipase

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6
Q

What 2 digestive enzymes in stomach?

A
  • pepsin [pepsinogen]

- gastric lipase

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7
Q

What 4 types of disaccharides in small intestine?

A
  • maltase
  • isomaltase
  • lactase
  • sucrase
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8
Q

What types of peptidases in small intestine?

A
  • on brush border: aminopeptidase

- intracellular peptidase

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9
Q

What 2 general types of digestive enzymes in small intestine?

A
  • disaccharidases

- peptidases

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10
Q

What general types of digestive enzymes in pancreas?

A
  • proteases
  • lipases
  • glyosidases
  • nucleases
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11
Q

What 4 types of proteases in pancreas?

A
  • trypsin
  • chymotripsin
  • carboxypeptidase [break down polypeptide from C terminus]
  • elastase
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12
Q

Where are disaccharidases and peptidases located?

A

in brush border of small intestine

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13
Q

Where is bulk of lipase made?

A

pancreas

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14
Q

Is lipase made in active or inactive form? why or why not?

A
  • active form
  • doesn’t actually act unless has coenzyme co-lipase
  • co-lipase does get made in inactive form [pro Co-lipase]
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15
Q

What type of macronutrient is most of what we take in every day [carb, protein, or lipid]?

A

carbohydrates

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16
Q

Where is iron primarily absorbed?

A

duodenum

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17
Q

What 3 things are primarily absorbed in duodenum

A

iron, calcium, magnesium

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18
Q

What 2 things are primarily absorbed in ileum?

A
  • vit B12 [cobalamin]

- bile acids

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19
Q

Where are carbohydrates absorbed in small bowel?

A

everywhere - D, J, and I

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20
Q

What does low pH in duodenum trigger?

A

secretin release which tells pancreas to produce bicarbonate

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21
Q

What do fatty acids and amino acids in duodenum trigger?

A

CCK release which tells gallbladder to contract/empty, tells pancreas acinar cells to secrete enzymes

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22
Q

What is breakdown of types of carbohydrates in diet [starch vs sucrose vs lactose]?

A

starch: 50%
sucrose: 30%
lactose: 10%

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23
Q

How is starch digested?

A

amylase

  • primarily from pancreas, some from saliva
  • converts starch –> maltose

maltase

  • from intestine brush border membrane
  • converts maltose –> glucose units
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24
Q

What is starch made of?

A

number of glucose units together

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25
Q

How is sucrose digested?

A

sucrase-isomaltase

  • from intestine brush border membrane
  • converts sucrose –> glucose + fructose
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26
Q

How is lactose digested?

A

lactase

  • from intestine brush border membrane
  • converts lactase –> glucose + galactose
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27
Q

How are carbohydrates absorbed?

A

breakdown products glucose/galactose are actively transported into cell then diffuse into portal vein

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28
Q

What happens to unabsorbed carbohydrate [CHO] in GI tract?

A
  • gets converted to short chain fatty acids [SCFA] in colon
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29
Q

what do scfa do?

A

keep colonic cells healthy

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30
Q

does pancreas make disaccharidases?

A

no, only small intestine brush border does

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31
Q

how does glucose get into cell for absorption usually?

A

Na-glucose cotransporter

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32
Q

What does starch need to break down into for absorption?

A

monosaccharides

33
Q

What does protein breakdown into before absorption?

A

oligopeptides or AA

34
Q

How is protein digested in stomach?

A
  • HCl [acid] denatures protein

- pepsin hydrolyzes protein into polypeptides

35
Q

What is path of pancreatic enzyme activation in duodenum? What 4 proteases does pancreas release that get activated this way?

A
  • pancreas releases 4 proteases [trypsin, chymotrypsin, elastase, carboxypeptidase]
  • enterokinase [enteropeptidase] in duodenal brush border membrane activates trypsin
  • trypsin then activates other pancreatic pro-enzymes
36
Q

How is protein digested in small intestine?

A
  • brush border membrane oligopeptidases hydrolyze polypeptides –> smaller oligopeptides and AA
37
Q

What activates proteases from pancreas?

A
  • enterokinase [enteropeptidase] in duodenal brush border membrane activates trypsinogen –> trypsin
  • trypsin activates other proenzymes
38
Q

What 4 things activate chief cells pepsinogen release?

A
  • gastrin
  • histamine
  • acetylcholine
39
Q

What causes conversion pepsinogen –> pepsin?

A

low pH in stomach

40
Q

How much of protein breakdown occurs in stomach?

A

10-15%

41
Q

What activates chymotrypsinogen?

A
  • active trypsin
42
Q

What happens to di/tripeptides that are absorbed into epithelial cell?

A

they get broken down in cell into AA before being absorbed into capillaries to portal vein

43
Q

What are two ways that protein breakdown products get absorbed

A
  • via di/tripeptide transporter

- via AA transporter

44
Q

Where do absorbed protein breakdown products go?

A

diffuse into villus capillaries and then into portal vein

45
Q

What is path of 3 main steps of lipid break down for absorption?

A
  • emulsified [get them into solution]
  • cleaved by lipolysis
  • packaged into micelles
46
Q

What happens to lipids in stomach?

A
  • churns fat [mostly triglycerides] into unstable emulsion

- gastric and lingual lipase break down a little [pretty minor]

47
Q

What happens to lipids in duodenum and small intestine?

A
  • fat emulsion stabilized by dietary phospholipids and bile salts from liver
  • dietary fat causes CCK release from duodenal cells –> tells pancreas acinar to release lipase gallbladder to release bile [salts]
  • pancreatic lipase + co-lipase convert: TG –> monoglycerides [MG] + FFA [free fatty acids]
48
Q

What does pancreatic lipase do to triglycerides?

A
  • uses coenzyme co-lipase

- converts TG –> MG [monoglycerides] + FFA [free fatty acids]

49
Q

What 2 things stabilize lipid emulsion?

A
  • phospholipids [from diet]

- bile salts [from liver]

50
Q

What do bile salts do to lipid digestion products?

A
  • package MG and FFA into mixed micelles with bile salts on outside
51
Q

What gets absorbed into intestinal epithelial cell in lipid digestion? Active or passive?

A
  • micelles diffuse passively across brush border membrane
52
Q

What happens to micelles once they enter epithelial cells in intestine?

A
  • get resynthesized as chylomicrons and VLDL
53
Q

Where do lipid breakdown products end up after absorption into epithelial cell?

A
  • get exported into lacteals [lymphatics] as chylomicrons and VLDL
54
Q

What happens to long chain TG vs medium chain TG in digestion?

A
  • long chain TG get digested into micelles and then to chylomicrons and into lacteals/lymphatics
  • medium chain TG absorbed directly into portal vein
55
Q

What is chemical composition of dietary fat [TG vs phospholipids vs cholesterol esters]?

A

95% of fat intake is tryglycerides
phospholipids - 2-8g per day
cholesterol esters - 300-400 mg per day

56
Q

What is structure of triglyceride

A
  • glycerol connected to 3 fatty acids [usually long chain] via ester bonds
57
Q

What bond does lipase hydrolyze?

A

ester bond between glycerol and fatty acid

58
Q

What percentage of lipid digestion is by gastric lipase?

A

20-30%

59
Q

What 3 malabosprtion deficiencies can cause anemia?

A
  • Vit B12
  • Folate
  • Iron
60
Q

What is clinical feature of vit K deficiency?

A

easy bruising

61
Q

What is clinical feature of vit E deficiency?

A

neuropathy

62
Q

What are 2 clinical features of vit D deficiency?

A
  • if vit D deficiency can’t get Ca absorption
  • get tetany [muscle spasm]
  • ostemolacia [bone thinning]
63
Q

What is clinical feature of vit A deficiency?

A
  • night blindness
64
Q

What are clinical features of carb deficiency?

A
  • diarrhea
  • bloating
  • gas
65
Q

What are 2 clinical features of fat deficiency?

A
  • steatorrhea [fatty diarrhea]

- weight loss

66
Q

What is clinical feature of protein deficiency?

A

edema

67
Q

How is heme iron absorbed? vs nonheme iron?

A

heme: can get absorbed into epithelial cell and extracted to Fe2+ in cell
nonheme: converted to Fe2+ in lumen then absorbed via DMT [divalent metal transporter] into cell

68
Q

How does iron get from epithelial cell to blood stream?

A

via ferroportin

69
Q

With what does iron circulate in blood stream?

A

transferrin

70
Q

Where are Ca, Mg, and Fe primarily absorbed in duodenum?

A

duodenum

71
Q

What form do Ca/Mg/Fe need to be in to be absorbed?

A

divalent [+2] form

72
Q

How does Ca get absorbed?

A
  • Ca2+ transported into epithelial cell
  • Ca2+ binds binding protein
  • Ca-ATPase pumps Ca out into blood stream
73
Q

What is role of vit D in Ca absorption?

A
  • Ca binding protein made in response to vit D

- need to have healthy vit D in order to get Ca secretion from epithelial cell into blood stream

74
Q

Path of B12 absorption?

A
  • B12 comes in food to stomach
  • B12 binds R factor [haptocorrin, from saliva] in stomach
  • in duodenum, pancreatic juices break apart B12 and R
  • B12 binds IF in duodenum
  • B12 reabsorbed in ileum
75
Q

4 things that could lead to B12 deficiency

A
  • No R factor [salivary disease]
  • No IF [disease of parietal cell, pernicious anemia, autoimmune gastritis]
  • pancreatic disease [pancreatic juice not available to break up B12 and R]
  • ileal disease or cut out ileum [B12 doesn’t get reabsorbed
76
Q

What vitamins are fat soluble?

A

A, D, E K

77
Q

What is abetalipoproteinemia?

A
  • normal brush border
  • no beta lipoprotein so can’t package fats that enter epithelial cells
  • epithelial cells get packed with FFA and monoglycerides but can’t get out of epithelial cells into lymph
  • have malabsorption of long chain fatty acids
78
Q

What is possible treatment of abetaproteinemia?

A
  • medium chain triglycerides that can get absorbed diretly into portal vein
79
Q

What is role of lipoproteins in fat absorption?

A
  • necessary for packaging fat breakdown products into chylomicrons

Physiology Part 1 (37 decks)

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