Renal physiology 3

Question 1

What are the main functions of the kidney?

Answer 1

Endocrine functions: cortisol, aldosterone, erythropoetin ( hypoxia)
Removal of waste products e.g urea 
electrolyte balance 
gluconeogenesis
regulate body fluids: ph/osmolarity

Question 2

What are the main functions of calictriol?

Answer 2

Active form of Vitamin D released when [Ca2+] = low

• Increased bone resorption
• Increases gut absorption
• Increases renal Ca2+ reabsorption
• Decreases PTH

Question 3

What are the main functions of PTH?

Answer 3

• Increases Ca2+ rebabsorption ( upregulation of TRPV5 channels)
• Decreases Pi ( internalisation of pi transporters)
• Increases bone resorption

Question 4

How is Ca2+ reabsorbed?

Answer 4

Paracellular transport : solvent drag ( follows Na+)+ transepithelial voltage ( more negative lumen potential allows for secretion/excretion)

• Ca2+ enters epithelial cells via TRP5V channels
• Ca2+ binds to calbidin = buffer
• Transported to the basolateral membrane
• ATPase channels (basolateral membrane) allow exchange for 1 Na+ into the cell for 1 Ca2+ out

Question 5

How does hypertension worsen kidney damage?

Answer 5

• Kidney damage causes GFR to decrease
• Macula densa cells detect a decreased filtered load of Na+ Cl-
• Signal sent via adenosine and Ca2+ to increase GFR by vasodilation of afferent arteriole and vasoconstriction of efferent arteriole
• Renin secretion from granular cells -> RAS system activation
• Hypertension increases glomerular pressure so there is further kidney damage
  Treated with ACE inhibitors e.g ramipril

Question 6

Describe diabetic nephropathy

Answer 6

• Poorly controlled diabetes causes more overspill of glucose into the urine
• More glucose in glomerular capillaries and bowmans space
• glucose reabsorbed in the PCT along with Na+
• More Na+Cl- reabsorbed along with water
• Macula densa cells detect a decreased filtered load of Na+Cl-
• Tubuloglomerular feedback causes vasodilation of afferent arteriole and vasoconstriction of the efferent arteriole to increase GFR and pressure in the glomerular capillaries
• Activates matrix deposition + Hypetrophy + proliferation of mesangial cells which form sclerosis
• Compresses the glomerular capillaries + decreases GFR = kidney damage