Exam #5: Fluid & Electrolytes Flashcards Preview

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Flashcards in Exam #5: Fluid & Electrolytes Deck (21):
1

Where is Na+ absorbed?

Generally, Na+ is absorbed in BOTH the small & large intestine

2

What are the mechanisms of Na+ absorption? Where are these transporters located? When are they primarily functioning?

There are four key transport proteins involved in the uptake of Na+:
Jejunum= following a meal
1) SGTL1 (glucose)
2) Amino Acid Transporter B

Jejunum, Ileum, & Proximal Colon= interdigestive period
3) Na+/H+ Exchanger

Colon
4) Na+ channel


*****Note that the basolateral membrane has Na+/K+ ATPase, which keeps Na+ flowing DOWN its concentration gradient

3

Where is Cl- absorbed?

Cl- is absorbed in BOTH the small & large intestine

4

What are the mechanisms of Cl- absorption?

There are two mechanisms for Cl- absorption:
1) Passive diffusion of Cl- following Na+ & water via a paracellular pathway
2) Cl-/bicarbonate Exchanger i.e. Cl- IN & HCO3- OUT

5

Where is Cl- secreted?

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6

What is the mechanism of Cl- secretion?

CFTR that is located in the apical membrane of the enterocyte.

*****Note that Na+ follows and causes water to stay in the lumen

7

What regulates the CFTR?

Intracellular signaling & accumulation of 2nd messengers result in secretion of Cl- (Na+ follows & water stays in the lumen). Specifically,
1) cAMP opens the CFTR
2) Ca++ opens the CFTR

8

Where is K+ absorbed? Where is K+ secreted?

Small intestine= absorption
Large intestine= secretion

9

What are the mechanisms of K+ absorption? What is the mechanism for K+ secretion?

Small intestine= "solvent drag"
- NaCl are absorbed from the gut lumen
- Water follows & DRAGS K+ with it

Colon= lumen is negative
- K+ is attracted to the negative lumen & goes the opposite direction
- result is net secretion

10

What are the signals that regulate electrolyte absorption & secretion?

Intracellular signaling & 2nd messenger accumulation i.e. cAMP & Ca++
- Secretion of Cl- via CFTR opening
- Inhibit Na+ absorption via Na/H+
- NET RESULT= NaCl IN LUMEN

Steroids= increase transcription of proteins that generally facilitate Na+ & water uptake
- Na+/K+ ATPase
- Na+ Channels
- Na+/H+ exchanger

Thus,
Intracellular messengers= less water retention
Steroids= retention

11

What are the neuronal pathway & agents that lead to fluid secretion?

ACh
VIP
5-HT

****All increase 2nd messengers that stimulate the CFTR & Na+/H+ exchanger

12

What are the paracrine/immune pathway & agents that lead to fluid secretion?

Prostalgandin
Histamine

*****Both increase 2nd messengers that stimulate the CFTR & Na+/H+ exchanger

13

What are the bacterial agents that lead to fluid secretion?

Cholera toxin
E. coli toxins

*****Both increase 2nd messengers that stimulate the CFTR & Na+/H+ exchanger

14

What are the endocrine mechanisms that promote fluid absorption?

Mineralcorticoids
Glucocorticoids

****Both upregulate the transcription of Na+ channels & Na+/K+ ATPase

15

What is the role of somatostatin in fluid absorption?

Increased Na+/H+ exchanger leading to fluid absorption

16

What is the difference between osmotic diarrhea and secretory diarrhea?

Osmotic= diarrhea caused by a nonabsorbable nutrient

Secretory= diarrhea caused by intestinal secretion of fluid and electrolytes

17

List the causes of osmotic diarrhea.

Disaccharide deficieicny
Pancreatic enzyme def.
Nutrient binding sub.
Loss of enterocytes
Bacterial overgrwoth
Antacids

18

What are the causes of secretory diarrhea?

Enterotoxins
Inflammatory cytokines
Tumor

19

What are the causes of both osmotic and secretory diarrhea?

Inflammatory conditions
Infectious disease

20

What are the different causes of constipation?

1) Diet/ Lifestyle
2) GI
3) Pharmacological
4) Endocrine
5) Neurogenic

21

How do the small & large intestine compare in net absorption & secretion?

Small intestine=
- Absorb: Na+, Cl-, K+ & H2O
- Secrete: Bicarbonate

Large intestine=
- Absorb: Na+, Cl-, & H2O
- Secrete: K+ & Bicarbonate

Thus, the MAIN difference is that K+ is ABSORBED in the small intestine & SECRETED in the large intestine

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