renal phy - countercurrent exchange, osmotic gradient of the kidney

Question 1

what are some characteristics of intercalated cells

reabsorption of K+

Answer 1

• large numbers of mitochondria and intracytoplasmic vesicles
• located in the outer part of medullary collecting ducts
• reabsorb K+ from the tubular fluid
• K+ is actively transported into the cell form the lumen by a H+,K+-ATPase
• play a major role in renal regulation of the acid-base balance

Question 2

what are some characteristics of principal cells

secretion of K+

Answer 2

• contain fewer mitochondria but extensive basolateral membrane, which contains Na+, K+-ATPase
• located in the early part of the outer medullary collecting duct
• high intracellular K+ generated by Na+,K+ - ATPase couple with the negative electrochemical portential in the tubular lumen favors the passive movement of K+ out of the cell into the tubular lumen
• Na+ is efficiently reabsorbed in these cells
• tightly regulated by aldosterone

Question 3

where does regulation of solute excretion occur

Answer 3

in the distal tubular segments and in collecting ducts

Question 4

reabsorption and secretion in the distal tubule and collecting ducts ultimately controls what

Answer 4

the level of solute excretion

Question 5

the reabsorption and secretion in the distal tubule and collecting ducts is tightly regulated by:

Answer 5

a number of humoral mechanisms

Question 6

humoral mechanisms regulating reabsorption and secretion in the DCT and CD are mediated by:

Answer 6

• atrial natriutetic peptide (ANP)
• third factors
• aldosterone
• vasopressin (ADH)
• parathyroid hormone, VD3, and calcitonin

Question 7

what is atrial natriuretic peptide (ANP)

Answer 7

• short peptide hormone that is produced and secreted by the cardiac atrial myocytes in response to stretch (high blood volume)
• this hormone both increases GFR and inhibits Na+ reabsorption in the CD
• net result is an increase in Na+ and water excretion and decrease in circulating blood volume

Question 8

what are third factors

Answer 8

• ANP-like natriuretic factors and some non-peptide hormone
• inhibit the Na+,K+-ATPAse and increase Na+ excretion

Question 9

what is aldosterone

Answer 9

• steroid mineralocorticoid hormone that is secreted by the adrenal cortex
• acts to increase the body fluid volume and regulate the levels of K+

Question 10

secretion and release of aldosterone is stimulated by

Answer 10

• systemic hypotension (through angiotensin II) - percieved volume depletion
• high plasma levels of K+ (hyperkaliemia)

Question 11

aldosterone acts on the ____ of the collecting dycts by a number of mechanisms

Answer 11

principal cells

Question 12

what are the mechanisms of how aldosterone acts on the principal cells

Answer 12

• increase the permeability of the apical membrane Na+ channels
• increase the numbers of Na+,K+-ATPases in the basolateral membrane and stimulating their activity
• increasing apical K+ channels
• decreasing K+ back leak through basolateral K+ channels

Question 13

what is the net results of aldosterone actions

Answer 13

• increase in Na+ reabsorption - decrease in Na+ excretion - increase in body fluid volume
• increase in K+ secretion - increase in K+ excretion - decrease in extracellular K+ levels actions

Question 14

Na+ is freely filtered in the

Answer 14

glomerulus

Question 15

what percent of filtered Na+ is reabsorbed

Answer 15

99.5%

Question 16

what does angiotensin II do to Na+

Answer 16

stimulates Na+ reabsorption and decreases Na+ excretion

Question 17

what does ANP and third factors do to Na+

Answer 17

inhibits Na+ reabsorption and increases Na+ excretion

Question 18

Na+ is the major ____ cation

Answer 18

extracellular

Question 19

K+ is the major ____ cation

Answer 19

intracellular

Question 20

what are factors affecting the extracellular K+

Answer 20

• diet intake
• internal K+ balance
• excretion of K+

Question 21

to maintain the extracellular K+ contant:

Answer 21

rate of K+ entry (ingestion + cell damage) = rate of K+ exit (cellular uptake + renal/external excretion)