Lec 5 Small Intestine Diarrhea

Question 1

How is water absorbed in small intestine?

Answer 1

passively following active absorption of solute

Question 2

What is main ion of absorption?

Answer 2

Na

Question 3

What is main ion of secretion?

Answer 3

Cl

Question 4

What percent of water in gut lumen is normally absorbed?

Answer 4

95%

Question 5

What are folds of kerkring?

Answer 5

folds in small intestine

Question 6

Where are stem cells located in small bowel epithelium?

Answer 6

crypts contain stem cell compartment

Question 7

What is role of paneth cells?

Answer 7

secrete lysosymes and defensins to protect stem cell compartment

located at base of crypts

Question 8

Where are paneth cells located?

Answer 8

only in small intestine – not stomach or colon

Question 9

What 3 factors of small intestine increase its surface area?

Answer 9

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

Question 10

What is surface area of small intestine?

Answer 10

200 m^2

Question 11

How much water do we intake every day?

Answer 11

2 L

Question 12

How much fluid presented to small intestine each day?

Answer 12

8 L (7-9) to small intestine

Question 13

How much fluid presented to colon each day?

Answer 13

1.5 L (1.5-2)

Question 14

How much feces excreted each day?

Answer 14

100-200 mL

Question 15

What is absorption efficiency of small intestine?

Answer 15

75-80%

Question 16

What is absorption efficiency of colon?

Answer 16

> 90%

Question 17

What is max absorption capacity of small intestine?

Answer 17

12 L/day

Question 18

What is max absorption of colon?

Answer 18

5 L/day

Question 19

Is paracellular transport active or passive?

Answer 19

always passive = due to electrochemical gradient

Question 20

Which part of bowel has highest passive paracellular permeability?

Answer 20

highest permeability in jejunum = very leaky

lower in ileum, lowest in colon

more distal = pores are smaller and tighter

Question 21

What are the 3 mechs by which Na is transported?

Answer 21

• 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

Question 22

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

Answer 22

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

Question 23

Is potassium secreted or absorbed in gut?

Answer 23

secretion more than absorption

Question 24

How is K secreted in small intestine?

Answer 24

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

Question 25

How is Cl primarily absorbed in gut?

Answer 25

follows electrochemical gradient created by Na transport

Question 26

What are 2 main ways to stimulate absorption?

Answer 26

- enhance Na absorption directly | - slow intestinal transit

Question 27

What are 4 things that increase Na absorption?

Answer 27

- mineralocorticoirds (colon more than small intestine) - glucocorticoids - somatostain [octreotide] - adrenergic agonists [epinephrine, clonidine]

Question 28

What is effect of somatostatin on gut?

Answer 28

can act as hormone - enhances Na absorption - slows intestinal transit --> decrease diarrhea

Question 29

What is effect of clonidine on gut?

Answer 29

a2 agonist --> increases Na absorption --> decrease diarrhea

Question 30

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

Answer 30

- opiates | - somatostatin [octreotide]

Question 31

Mech of Cl secretion?

Answer 31

- enters basolaterally via Na:K:2Cl transporter and exits apical membrane via Cl channel {CFTR] theres is a basal rate of Cl secretion

Question 32

What things increase Cl secretion?

Answer 32

anything that activates cAMP, cGMP, or intracellular Ca

Question 33

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

Answer 33

by increasing cAMP --> increase secretions

Question 34

What is effect of bile acids in colon?

Answer 34

increase cAMP and Ca and cause secretory diarrhea

Question 35

What is normal transit time through small bowel?

Answer 35

2-6 hours

Question 36

What are some factors that increase colonic transit?

Answer 36

- cholinergics - anxiety - feeding - laxative - distension

Question 37

What are some factors that slow colonic transit?

Answer 37

- anti cholinergics - depression - opiates

Question 38

What is stool weight/water for definitive diarrhea?

Answer 38

> 150-200 g stool/24 hr | > 150-200 mL stool/24 hr

Question 39

What defines acute vs chronic diarrhea?

Answer 39

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

Question 40

What type of motility in small bowel in fed state?

Answer 40

2 types: segmental non-propulsive contractions: mix food, retard passage peristalsis: short waves with proximal contraction and distal relaxation

Question 41

What type of motility in small bowel in fasting state?

Answer 41

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

Question 42

What are characteristics of small bowel diarrhea?

Answer 42

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

Question 43

What are characteristics of colonic diarrhea?

Answer 43

- low volume [b/c normal volume entering colon] - frequency - urgency - tenesmus - mucus - blood

Question 44

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

Answer 44

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

Question 45

What is pathogenesis behind osmotic diarrhea?

Answer 45

- non-absorbable solute in bowel lumen --> draws water in | - mucosal transport processes usually intact

Question 46

What are some solutes that commonly cause osmotic diarrhea?

Answer 46

- lactose [if lactase deficient] - sorbitol [in chewing gum] - minerals like magnesium

Question 47

What are charateristics of osmotic diarrhea?

Answer 47

- 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]

Question 48

What is mech of secretory diarrhea?

Answer 48

excess stimulation of normal secretory processes

Question 49

What are some examples of things that cause secretory diarrhea?

Answer 49

- bacterial toxins [cholera] - hormones [VIP - bile acids - drugs [caffeine] - inflammatory mediators [histamine, bradykinin, eiconsanoids, 5HT]

Question 50

What is mech of cholera?

Answer 50

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

Question 51

What are characteristics of secretory diarrhea?

Answer 51

- salt and water depletion --> may be life threatening - stool volume persists despite fasting - no osmotic gap - stool pH neutral

Question 52

What causes hypermotility diarrhea?

Answer 52

due to insufficient absorption time - hyperthyroidism, cholinergics, laxatives, anxiety

Question 53

What causes hypomotility diarrhea?

Answer 53

altered peristalsis and stasis leading to bacterial overgrowth due to impaired innervation as in DM or any other cause of stasis or bacterial overgrowth