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Physiology Part 1 > Lec 21 Digestion and Absorption I > Flashcards

Lec 21 Digestion and Absorption I Flashcards

1
Q

What is surface area of intestine?

A

200 m squared

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2
Q

What are amplification factors of folds of kerkring, villi, microvilli respectively?

A

folds of kerkring: 3

villi: 10
microvilli: 20

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3
Q

Where are epithelial cells born? where do they migrate up [crypt vs villus]? How long does differentiation/migration take?

A
  • cells born near bottom of crypt
  • differentiate and mature as migrate up villus
  • process = 5-6 days
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4
Q

What is function of villus?

A

absorption

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5
Q

What is function of crypt?

A

secretion

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6
Q

Difference betweeen villi/crypts in intestine?

A

small intestine: villi and crypts

colon: just crypts

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7
Q

What is total oral intake h2o per day?

A

2 L/day

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8
Q

What is total salivary secretion per day?

A

1 L/day

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9
Q

What is total gastric secretion per day?

A

2 L/day

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10
Q

What is total bile secretion per day?

A

1 L/day

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11
Q

What is total pancreatic secretion per day?

A

2 L/day

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12
Q

What is total fluid presented to SI?

A

8 L/day

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13
Q

What is total jejunal secretion per day?

A

4 L/day

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14
Q

What is total ileal secretion per day?

A

2 L/day

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15
Q

What is total H2O presented to colon per day?

A

1.5 L/day

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16
Q

What is total H20 in fecal excretion per day?

A

0.1-0.2 L/day

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17
Q

Is daily net effect secretion or absorption h2o?

A

absorption

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18
Q

What is total fluid presented to small intestine per day? absorption efficiency? max absorption capacity?

A

total fluid presented: 7-9 L/day
Absorption Efficiency: 75-80%
Max absorption: 12 L/day

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19
Q

What is total fluid presented to colon per day? absorption efficiency? max absorption capacity?

A

total fluid presented: 1.5-2 L/day
Absorption Efficiency: 90%
Max absorption: 5 L/day

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20
Q

How does space between cells change in fasting vs absorptive state?

A

fasting: cells packed closer together

absorptive/when eating: more space between cells so water can transport in

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21
Q

What is mech of H2O absorption?

A
  • solute [Na] transported into cell or between cells
  • creates osmotic gradient
  • water flows into space to equalized osmolality
  • hydrostatic pressure develops relative to capillary
  • water flows into capillary to equalize hydrostatic
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22
Q

How does passive permeability change along intestine?

A
  • passive permeability decreases from proximal to distal
  • jejunum > Ileum > colon
  • means more volume H2O absorbed in proximal
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23
Q

Does small bowel or large bowel disease produce higher volume of diarrhea? why?

A
  • small bowel disease produces higher volume diarrhea

- due to higher volume h2o absorption and higher passive permeability in small intestine

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24
Q

Which parts of intestine have highest net h2o movement over time?

A

proximal > distal

duodenum > jejunum > ileum > colon

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25
Q

What is major ion that drives fluid absorption?

A

sodium

26
Q

What 3 ways sodium transported?

A
  • solute-coupled Na transport
  • Na hydrogen exchanger
  • electrogenic Na transport
27
Q

What is mech solute-coupled Na tranpsort?

A

Na transported from lumen along with glucose or amino acids

28
Q

What type of Na exchange is basis of oral rehydration therapy in diarrhea?

A

solute coupled Na transport

29
Q

What is mech of Na hydrogen exchanger?

A

allows Na and Cl entry, HCO3 secretion

30
Q

What is mech of electrogenic Na transport?

A
  • Na exits basolateral membrane via Na-K ATPase

- luminal Na enters cell via apical membrane channel, down electrochemical gradient

31
Q

What is effect of Na-K atpase? what does it set up?

A
  • sets up Na gradient for Na-H antiporter and electrogenic Na absorption via Na channel
32
Q

Mech of Cl absorption?

A
  • follows electrochecmical gradient generated by Na transport and via Cl-HCO3 exchange
33
Q

What is major ion that drives fluid secretion?

A

Cl

34
Q

Where does Cl enter [and how]? Where does it exit??

A
  • enters basolaterally [Na:K:2Cl transporter]
  • exceeds electrochemical equilibrium
  • exits apical membrane [CFTR Cl channel]
35
Q

When is Cl secreted? What increases Cl secretion?

A
  • Cl is secreted always at basal rate
  • secretion increased by: hormonal, neural, inflammatory factors that activate
  • – cAMP, cGMP, intracellular Ca
36
Q

What is basis of secretory diarrhea?

A

increased Cl secretion

37
Q

What are 7 hormones that promote intestinal secretion?

A
  • VIP
  • secretin
  • PGE1
  • bradykinin
  • ACh
  • serotonin
  • histamine
38
Q

How does VIP affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via cAMP

39
Q

How does secretin affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via cAMP

40
Q

How does PGE1 affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via cAMP

41
Q

How does bradykinin affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via cAMP

42
Q

How does ACh affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via Ca

43
Q

How does seretonin affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via Ca

44
Q

How does histamine affect intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via Ca

45
Q

What are 4 neurotransmitters than promote intestinal secretion via cAMP?

A

VIP
Secretin
PGE1
Bradykinin

46
Q

What are 3 neurotransmitters than promote intestinal secretion via Ca?

A

ACh
Serotonin
Histamine

47
Q

What are 5 bacterial toxins that promote intestinal secretion via cAMP/GMP?

A
  • cholera [V. cholera] [cAMP]
  • heat labile toxin [E. coli] [cAMP/GMP]
  • campylobacter [cAMP]
  • salmonella [cholera-like] [cAMP]
  • yersinia enterocolitica [cGMP]
48
Q

What do laxatives do to intestinal secretion?

A

promote intestinal secretion

49
Q

What do dihydroxy bile acids and long chain fatty acids do to intestinal secretion? via what secondary messengers?

A
  • promote intestinal secretion

- via cAMP and Ca

50
Q

What does ricinoleic acid [castor oil] do to intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via cAMP

51
Q

What does senokot do to intestinal secretion? via what secondary messenger?

A

promotes intestinal secretion via Ca

52
Q

What is mech of osmotic diarrhea?

A
  • non-absorbable solute in bowel lumen
  • water enters lumen
  • solute and water load exceeds colonic absorptive capacity
  • mucosal transport processes usually intact – no underlying problem with transporters
53
Q

2 examples of things that commonly can cause osmotic diarrhea?

A

failure to absorb dietary solute
- lactose in lactase deficiency

ingestion non-absorbable solute
- sorbitol, aspartame, etc artificial sugar

54
Q

2 consequences of osmotic diarrhea? is it life threatening?

A
  • water depletion [not Na depletion] –> not life-threatening
  • stool volume decreases with fasting
55
Q

Mech of secretory diarrhea?

A
  • stimulation of normal secretory process

- absorptive process intact but overwhelmed

56
Q

2 consequences of secretory diarrhea? is it life threatening?

A
  • salt and water depletion –> may be life-threatening

- stool volume persists despite fasting = very large volume

57
Q

What examples of things that cause secretory diarrhea?

A

secretagogues that increase cAMP/cGMP/Ca

  • bacterial toxins [cholera]
  • hormones [VIP]
  • bile acids [ileal resection, bacterial overgrowth]
  • drugs
  • inflammatory mediators [histamine, bradykinin, serotonin, IL-1]
58
Q

Mech of cholera induced diarrhea?

A
  • secretory diarrhea
  • cholera toxin increases cAMP
  • — increases Cl channel into lumen
  • — inhibits Na/H exchanger [which reabsorbs Na]
59
Q

What are two types of motility diarrhea?

A

hypermotility, hypomotility

60
Q

What is cause of hypermotility diarrhea? 4 examples?

A
  • insufficient contact time for absorption

- hyperthyroidism, cholinergics, laxatives, anxiety

61
Q

What is cause of hypomotility diarrhea?

A
  • altered peristalsis, stasis, bacterial overgrowth

- impaired innervation [diabetes, IBS, vagotomy], any cause of stasis or bacterial overgrowth

Physiology Part 1 (37 decks)

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