Kidney Endocrine Functions - Renal

Introduction
- The kidneys are also involved in promoting erythropoiesis and producing activated vitamin D
  - erythropoiesis (red blood cell production)
    
    the kidneys produce a glycoprotein growth factor called erythropoietin (EPO)
    
    in hypoxia, there is less O₂being delivered to the kidneys
    
    this in turn causes the production of hypoxia-inducible factor-1α (HIF-1α) which acts on the fibroblasts in the renal cortex to transcribe EPO (increased EPO mRNA)
    
    EPO promotes the differentiation of proerythroblasts to eventually form into erythrocytes (red blood cells)
    
    note that one can commonly see anemia in patients with chronic renal failure since the functioning renal mass is decreased
    
    this is why recombinant human EPO is a treatment for anemia of chronic renal failure
  - vitamin D production
    
    the kidneys contain an enzyme called 1α-hydroxylase
    
    1α-hydroxylase catalyzes the hydroxylation (at the C1 position) of 25-hydroxycholecalciferol into 1,25-dihydroxycholecalciferol
    
    1,25-dihydroxycholecalciferol is a physiologically active form of vitamin D
    
    in the kidney, 25-hydroxycholecalciferol can also be hydroxylated (at the C24 position) into 24,25-hydroxycholecalciferol, an inactive form of vitamin D
    
    1α-hydroxylase is regulated by a number of factors such as
    
    plasma Ca²⁺ concentration
    
    a decrease in plasma Ca²⁺ increases 1α-hydroxylase activity
    
    parathyroid hormone
    
    increases 1α-hydroxylase activity
    
    plasma phosphate concentration
    
    a decrease in plasma phosphate increases 1α-hydroxylase activity
- Prostaglandins
  - the kidneys locally produce prostaglandins (e.g., PGE2) that result in vasodilation of the afferent arteriole
    
    this in turn increases renal blood flow
    
    nonsteroidal antiinflammatory drugs (NSAIDs) impair prostaglandin synthesis
    
    the renoprotective effects of prostaglandins are loss in low blood volume states (e.g., hemorrhage)
- Dopamine
  - low levels of dopamine dilates the renal arterioles and thus increases renal blood flow
    
    secreted by proximal tubular cells to promote natriuresis

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T