Solute Handling

Question 1

describe filtration and reabsorption of Na

Answer 1

• filtration: 100%
• reabsorption:
  
  • PCT: 67%
  • TALoH: 25%
  • DCT: 5%
  • Late distal/collecting duct: 3%
• excretion: <1%

Question 2

describe changes with decreased Na intake

Answer 2

• increased symp. activity
  
  • constriction of afferent arterioles
  • increased Na reabsorption in proximal tubule
• increased capillary oncotic pressure
  
  • increased Na reabsorption in prox. tubule
• increased RAAS
• decreased ANP
  
  • dilation of efferent arterioles

Question 3

name 3 ways symp. stimulation reduces Na excretion

Answer 3

1. decreases GFR and RBF
   
   • decreased filtered Na load and PT cap hydrostatic pressure for excretion
2. direct stimulatory effect on Na reabsorption by renal tubules
3. causes renin release
   
   • increases AGII and aldosterone levels for reabsorp.

Question 4

describe changes with increased Na intake

Answer 4

• increased ANP
  
  • constriction of afferent arterioles (increased GFR)
  • decreased Na reabsorption (collecting ducts)
• decreased symp. activity
  
  • dilation of afferent arterioles (increased GFR)
  • decreased Na reabsorption (prox. tubule)
• decreased capillary oncotic prssure
  
  • decreased Na reabsorption
• decreased RAAS

Question 5

name causes of K shift into cells (hypokalemia)

Answer 5

• insulin
  
  • stimulate Na/K/ATPase
• B2-adrenergic agonists
  
  • • stimulate Na/K/ATPase
• alpha-adrenergic antagonists
  
  • • stimulate Na/K/ATPase
• alkalemia
  
  • H+ is decreased so H+ moves into blood/K+ exchanges into cell
• hyposmolarity

Question 6

name causes of K shift out of cells (hyperkalemia)

Answer 6

• insulin deficiency
  
  • reduce Na/K/ATPase
• B2-adrenergic antagonists
  
  • reduce Na/K/ATPase
• alpha-adrenergic agonists
  
  • reduce Na/K/ATPase
• acidemia
  
  • [H+] is increased so H+ leaves blood/K+ exchanges into blood
• hyperosmolarity
  
  • H2O shifts from ICF to ECF dragging K+
• cell lysis
  
  • releases K+ from ICF into blood
• exercise
  
  • depletion of ATP stores opens K+ channels in muscle cells-shifts into blood

Question 7

describe filtration and reabsorption of K

Answer 7

• filtration: 100%
• reabsorption:
  
  • PCT: 67%
  • TALoH: 20%
  • LD/CD: 4-150%
• excretion: 1-110%

Question 8

describe filtration and reabsorption of phosphate

Answer 8

• filtration: 90% (10% is bound to plasma proteins)
• reabsorption via Na phosphate cotransporter:
  
  • Early PCT: 70%
  • Late PCT: 15%
• excretion: 15% (serves as titratable acid, urinary buffer for H+)

Question 9

describe the effects of PTH

Answer 9

• PTH inhibits Na-phosphate cotransport > inhibits reabsorption = phosphaturia and hypophosphatemia
• PTH binds to the type 1 PTH basolateral receptor in PCT cells which is coupled to adenylyl cyclase via a Gs protein
• Adenylyl cyclase catalyzes conversion of ATP to cAMP to activate PKA and PKC which stimulate the internalization and degradation of sodium-phosphate cotransporters

Question 10

describe the filtration and reabsorption of magnesium

Answer 10

• filtration: 80%
• reabsorption:
  
  • PCT: 30%
  • TALoH: 60%
    
    • furosemide inhibits Mg transport through paracellin channel paracellulary since it ruins positive charge buildup
  • DCT: 5%
• excretion: 5%

Question 11

describe filtration and reabsorption of calcium

Answer 11

• filtration: 60% (40% bound to protein in blood)
• reabsorption:
  
  • PCT: 67%
  • TALoH: 25%
    
    • furosemide inhibits this
  • DCT: 8%
    
    • PTH/thiazide diuretics increase this
• excretion: <1%