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Physiology III > Lecture 30: Intestinal Transport of Electrolytes and Water > Flashcards

Lecture 30: Intestinal Transport of Electrolytes and Water Flashcards

1
Q

What are the 3 ways for water intake

A

Food, drink and metabolic water

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2
Q

What are the 5 ways to lose water

A

Skin, lungs, GI tract, kidneys and milk

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3
Q

What are the enterosystemic sources of fluid

A
  1. Oral intake
  2. Saliva
  3. Secretion form stomach, pancreas, liver, SI and LI
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4
Q

What is insensible evaporation

A

Humidification of breathing

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5
Q

What is a normal fluid balance important for intestinal function

A

Creates an appropriate environment for digestion, fermentation, and absorption, stabilizes pH

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6
Q

What % of fluid is recovered in small and large intestine

A

98%

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7
Q

In dogs and cats, what % of fluid is reabsorbed in small intestine

A

80%

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8
Q

In dogs and cats, what % of fluid is reabsorbed in large intestine

A

18%

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9
Q

Colonic fluid provides __

A

Reserve capacity

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10
Q

What portion of the LI has a high absorptive capacity

A

Colon

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11
Q

___is the site for control of enterosystemic fluid balance

A

Epithelium

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12
Q

At what area of the epithelium does secretion occur

A

Crypts of small and large intestine

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13
Q

At what area of the epithelium does absorption occur

A

Villi of small intestine

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14
Q

What activates secretory mechanisms

A

Meals/food

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15
Q

What compensatory mechanism occur in order to increase uptake or excrete solutes and water

A

Expression of intestinal/epithelial transporters which can match the need

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16
Q

What does the SI absorbed

A

Water, Na+, Cl-, K+

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17
Q

What does the SI secrete

A

HCO3-

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18
Q

What does the LI absorb

A

Water, Na+, Cl-

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19
Q

What does LI secrete

A

K+ and HCO3-

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20
Q

T or F: SI fluid absorption is isomolar

A

True

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21
Q

What causes an increase in water absorption in GI

A

Increase in luminal osmotic pressure resulting from an influx and digestion of food

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22
Q

What ion facilitates the absorption of Na+ and water in the GI

A

Cl-

23
Q

__stimulation of the luminal surface triggers chloride secretion

A

Mechanical

24
Q

___plexus is involved in mediating the secretory response

A

Submucosal

25
Q

Stroking of the luminal surface releases ___ from unknown sources and causes __ secretion

A

Prostaglandins, and Cl-

26
Q

Stroking of the musical surface also causes ___ release from enterochromaffin cells

A

Serotonin

27
Q

Serotonin activates 5-HT1P/5-HT4 receptors containing substance P, ACh, glutamate. Release of these neurotransmitters activates release of ACh or VIP and cause __secretion

A

Cl-

28
Q

What receptor is Cl- secretion linked to

A

CFTR

29
Q

What are the two mechanisms in which CFTR can be activated

A
  1. Food binds receptors on apical membrane
  2. Receptors on basolateral membrane activated and increase Ca2+ and cAMP and pKA which phosphorylates CFTR channel and transport Cl- into intestinal lumen
30
Q

What are some agonists that can activate basolateral K channel and CFTR

A

ACh, histamine, bile acids

31
Q

What channel on basolateral membrane supplies cell with Cl-

A

NKCC1

32
Q

How does V. Cholera toxin activate CFTR channel

A
  1. Toxin is released from bacteria
  2. Toxin activates G-protein and then AC
  3. CAMP increase and opens CFTR
33
Q

How does V. Cholera cause diarrhea

A

When it activates CFTR channel and increase Cl- secretion into lumen it draws Na+ and water into lumen resulting in diarrhea

34
Q

How does the chyme remain isosmotic throughout passage throughout SI and LI

A

Balance between water secretion and absorption

35
Q

How does water cross epithelium in GI

A

Passes through tight junctions

36
Q

What two secondary active co-transporters are most important for fluid reuptake in GI

A
  1. Na+/glucose
  2. Na+/Amino acids
37
Q

How does oral rehydration therapy work

A

Utilizes SGLT1 channel to drive H20 reabsorption

38
Q

How do you activate the colonic reserve capacity

A

Stimulate ENaC channel in CD

39
Q

How is ENaC activated

A
  1. Aldosterone activates Na/K pump
  2. Triggers insertion of preformed Na+ channels
  3. Triggers expression of new channel proteins
40
Q

__ is responsible for Na+ uptake from luminal fluid

A

ENaC

41
Q

___ alters the rate of insertion, degradation and recycling of ENaC

A

Aldosterone

42
Q

Describe the pathway of activating the RAAS system

A
  1. Decrease pressure/blood loss
  2. Angiotensinogen
  3. AI
  4. AII
  5. Aldosterone
  6. Kidney reabsorb Na+ and water
  7. Colon reabsorbs Na+ and Cl- via ENac
43
Q

How does amiloride work

A

Potassium sparing diuretic that blocks ENaC and inhibits Na+ absorption in distal colon of GI, promotes loss of Na+ and H20

44
Q

Describe K+ absorption in the small intestine

A

Passive via solvent drag, uptake H20 take K+ with it

45
Q

Describe K+ absorption in distal colon

A

Active K+ absorption based on pH. Increase H+ ions, decrease pH causes active K+ uptake

46
Q

What transporter recovers K+ in the distal colon if diet K+ is low

A

H/K+ ATPase

47
Q

What happens to K+ absorption if water is lost (ex: diarrhea)

A

Can’t build up gradient and can lead to hypokalemia

48
Q

what are the 2 mechanisms Cl- is absorbed in GI tract

A
  1. Voltage gated dependent- passive paracellular and transcellular Cl- absorption drive by SGLT or ENac
  2. Electroneutral Cl-HCO3- exchanger
49
Q

Where is the Cl-HCO3- present in GI

A

Epithelial cells of villi and surface cells of ileum and proximal colon

50
Q

Why is the Cl/HCO3- exchanger important for hindgut

A

Net movement of bicarbonate into the gut elevates the pH which is important for hindgut fermentation

Tightly linked to acid base homeostasis

51
Q

What triggers Na+/H+ exchanger

A

High luminal pH

52
Q

What causes the luminal pH to be high and then trigger Na/H+ exchanger

A

Secretin is stimulated in the SI from the arrival of acidic material from stomach, increase secretion of HCO3- in ductal cells, increasing pH and triggering Na/H+ exchanger

53
Q

Describe the electroneutral absorption of Na and Cl-

A

The Cl-/HCO3- exchanger stimulated ton combat low pH from stomach acid by releasing bicarb into lumen and in response Na/H exchanger is activated to combat high luminal pH

54
Q

Why can diarrhea occur after surgical resection of large part of the ileum

A
  1. Bile salts and acids spill over into the colon because transporters in ileum reduced and maxed out.
  2. Bile acid build up stimulate CFTR in colon which stimulates motility
  3. Isosmotic absorption of h20 is compromised and decreased NACl- is decreased so resulting in diarrhea

Physiology III (34 decks)

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