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GI/Liver > Lec 5 Small Intestine Diarrhea > Flashcards

Lec 5 Small Intestine Diarrhea Flashcards

1
Q

How is water absorbed in small intestine?

A

passively following active absorption of solute

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2
Q

What is main ion of absorption?

A

Na

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3
Q

What is main ion of secretion?

A

Cl

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4
Q

What percent of water in gut lumen is normally absorbed?

A

95%

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5
Q

What are folds of kerkring?

A

folds in small intestine

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6
Q

Where are stem cells located in small bowel epithelium?

A

crypts contain stem cell compartment

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7
Q

What is role of paneth cells?

A

secrete lysosymes and defensins to protect stem cell compartment

located at base of crypts

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8
Q

Where are paneth cells located?

A

only in small intestine – not stomach or colon

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9
Q

What 3 factors of small intestine increase its surface area?

A
  • folds of kerkring [3x]
  • villi [10x]
  • microvilli [20x]
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10
Q

What is surface area of small intestine?

A

200 m^2

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11
Q

How much water do we intake every day?

A

2 L

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12
Q

How much fluid presented to small intestine each day?

A

8 L (7-9) to small intestine

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13
Q

How much fluid presented to colon each day?

A

1.5 L (1.5-2)

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14
Q

How much feces excreted each day?

A

100-200 mL

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15
Q

What is absorption efficiency of small intestine?

A

75-80%

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16
Q

What is absorption efficiency of colon?

A

> 90%

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17
Q

What is max absorption capacity of small intestine?

A

12 L/day

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18
Q

What is max absorption of colon?

A

5 L/day

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19
Q

Is paracellular transport active or passive?

A

always passive = due to electrochemical gradient

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20
Q

Which part of bowel has highest passive paracellular permeability?

A

highest permeability in jejunum = very leaky

lower in ileum, lowest in colon

more distal = pores are smaller and tighter

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21
Q

What are the 3 mechs by which Na is transported?

A
  • Na channel: passive transport into cell down electrochemical gradient
  • Glucose or AA coupled Na co-transport into cell
  • Na-H exchanger: Na into cell in exchange for H

Na once in cell exits basolaterally by Na-K ATPase

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22
Q

How is electric neutrality kept in the Na-H exchange path?

A

Na into cell in exchange for H out of cell

driving force for HCO3-Cl exhcnager: Cl into cell in exchange for HCO3 secretion to maintain neutrality

23
Q

Is potassium secreted or absorbed in gut?

A

secretion more than absorption

24
Q

How is K secreted in small intestine?

A

secreted passively secondary to lumen-negative potential created by Na absoprtion

25
Q

How is Cl primarily absorbed in gut?

A

follows electrochemical gradient created by Na transport

26
Q

What are 2 main ways to stimulate absorption?

A
  • enhance Na absorption directly

- slow intestinal transit

27
Q

What are 4 things that increase Na absorption?

A
  • mineralocorticoirds (colon more than small intestine)
  • glucocorticoids
  • somatostain [octreotide]
  • adrenergic agonists [epinephrine, clonidine]
28
Q

What is effect of somatostatin on gut?

A

can act as hormone

  • enhances Na absorption
  • slows intestinal transit

–> decrease diarrhea

29
Q

What is effect of clonidine on gut?

A

a2 agonist –> increases Na absorption –> decrease diarrhea

30
Q

What are 2 drugs [or types] that slow intestinal transit?

A
  • opiates

- somatostatin [octreotide]

31
Q

Mech of Cl secretion?

A
  • enters basolaterally via Na:K:2Cl transporter and exits apical membrane via Cl channel {CFTR]

theres is a basal rate of Cl secretion

32
Q

What things increase Cl secretion?

A

anything that activates cAMP, cGMP, or intracellular Ca

33
Q

What is mech by which yersinia, Campylobacter, some types of E Coli, and cholera cause diarrhea?

A

by increasing cAMP –> increase secretions

34
Q

What is effect of bile acids in colon?

A

increase cAMP and Ca and cause secretory diarrhea

35
Q

What is normal transit time through small bowel?

A

2-6 hours

36
Q

What are some factors that increase colonic transit?

A
  • cholinergics
  • anxiety
  • feeding
  • laxative
  • distension
37
Q

What are some factors that slow colonic transit?

A
  • anti cholinergics
  • depression
  • opiates
38
Q

What is stool weight/water for definitive diarrhea?

A

> 150-200 g stool/24 hr

> 150-200 mL stool/24 hr

39
Q

What defines acute vs chronic diarrhea?

A

acute < 2-3 wks; usually self limited infectious cause

chronic > 3 wks

40
Q

What type of motility in small bowel in fed state?

A

2 types:
segmental non-propulsive contractions: mix food, retard passage

peristalsis: short waves with proximal contraction and distal relaxation

41
Q

What type of motility in small bowel in fasting state?

A

cyclic stripping waves to clear contents and prevent bacterial overgrowth = MMC

42
Q

What are characteristics of small bowel diarrhea?

A
  • high volume [b/c more volume overwhelming colon]
  • moderate increase in number of bowel movements
  • minimal urgency
  • no tenesmus
  • little mucus
43
Q

What are characteristics of colonic diarrhea?

A
  • low volume [b/c normal volume entering colon]
  • frequency
  • urgency
  • tenesmus
  • mucus
  • blood
44
Q

A problem with which part of bowel will cause bile acid induced diarrhea?

A

ileal dysfunction – b/c ileum is where bile acids normally absorbed

45
Q

What is pathogenesis behind osmotic diarrhea?

A
  • non-absorbable solute in bowel lumen –> draws water in

- mucosal transport processes usually intact

46
Q

What are some solutes that commonly cause osmotic diarrhea?

A
  • lactose [if lactase deficient]
  • sorbitol [in chewing gum]
  • minerals like magnesium
47
Q

What are charateristics of osmotic diarrhea?

A
  • water (not Na) depletion –> not life threatening
  • stool volume decreases with fasting
  • osmotic gap in fecal fluid
  • acidic stool pH [b/c bacteria ferment the solute]
48
Q

What is mech of secretory diarrhea?

A

excess stimulation of normal secretory processes

49
Q

What are some examples of things that cause secretory diarrhea?

A
  • bacterial toxins [cholera]
  • hormones [VIP
  • bile acids
  • drugs [caffeine]
  • inflammatory mediators [histamine, bradykinin, eiconsanoids, 5HT]
50
Q

What is mech of cholera?

A

cholera toxin enters enterocyte and causes increase in cAMP –> drives Cl out of cell –> secretory diarrhea

51
Q

What are characteristics of secretory diarrhea?

A
  • salt and water depletion –> may be life threatening
  • stool volume persists despite fasting
  • no osmotic gap
  • stool pH neutral
52
Q

What causes hypermotility diarrhea?

A

due to insufficient absorption time

  • hyperthyroidism, cholinergics, laxatives, anxiety
53
Q

What causes hypomotility diarrhea?

A

altered peristalsis and stasis leading to bacterial overgrowth

due to impaired innervation as in DM or any other cause of stasis or bacterial overgrowth

GI/Liver (36 decks)

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