Non filtration functions of the kidney Flashcards
What are 3 hormones that the kidney is key in producing
Vitamin D
EPO
Renin
How is the kidney involved in vitamin D production
- Vitamin D3 may be absorbed fron the diet or produced in the skin in reaction of UV to 7-dehydrocholesterol
- Vitamin D3 is then hydrolysed in the liver (CYP450) to form 25-hydroxycholecalciferol
- 25-OHD3 is then converted in the proximal tubule to calcitriol (active)
Where is EPO released from
Peritubular capillary fibroblasts 85%
15% from the liver
Why is EPO released
HYpoxia
Hypotension
Low HCT
What inhibits EPO release
High red cell bolume
renal failure
What are the 6 functions of the kidney
Water balance
Electrolyte balance
Acid base
Waste product removal
Non filtraiton functions
BP
Explain how water balance is achieved by the kidney
◦ Renal blood flow accounts for 20% of cardiac output, with 180L a day of ultrafiltrate from plasma produced in renal corpuscles. Resorption of water to maintain homeostasis is carefully managed whereby urine volume is ~1.5L/day and can reduce down to obligatory losses of minimum ~430mLs
◦ Water reabsorption occurs along the length of the nephron
‣ 65% in proximal convoluted tubule following solute reabsorption
‣ 10% in the loop of Henle
‣ 24-25% reabsorbed in collecting ducts regulated by ADH insertion of aquaporins in apical membrane in combination with the countercurrent multiplier mechanism
* This is the principle mechanism of regulation of water balance
What wastes are eliminated by the kidney?
◦ Active secretion and filtration of creatinine from muscle
◦ Active secretion and filtration of urea from protein metabolism
◦ Active secretion of organic acids and drugs (proximal tubule)
◦ Elimination of ammonia
How is BP controlled by the kidney
◦ Control of sodium reabsorption (regulated by aldosterone)
◦ Control of water reabsorption (regulated by vasopressin/ADH)
◦ Release of renin from macula densa cells (thus, regulation of angiotensin II synthesis)
◦ Thus, control of extracellular fluid volume (influencing preload) and peripheral vascular resistance (influencing afterload)
What non filtrations of the kidney are there 3
Secretion of hromones
- Renin
- EPO
- Prostacyclin
- Thrombopoetin
Biotransformation
- INsulin clearance
- Calcitriol
Gluconeogenesis
What are the two precursers of vitamin D
◦ Vitamin D2 (ergocalciferol) only in diet
◦ Vitamin D3 (cholecalciferol) absorbed in diet or produced in skin by the action of UV light
‣ 7-dehydrocholesterol → 7-dehydroxycholecalciferol → cholecalciferol
What is the first step in activation of vitamin D
◦ Liver: Cholecalciferol hydrolysed → 25-hydroxycholecalciferol (25-OHD3)
‣ Enzyme: Vitamin D25-hydroxylase (CYP450 enzyme)
‣ Alpha 1 hydrolase
How is vitamin D activated in the kidney
◦ Kidney: 25-OHD3 hydrolysed → 1,25-dihydroxycholecalciferol (calcitriol – active form)
‣ in the proximal tubule, Enzyme: 1alpha hydroxylase
‣ Released into circulation
‣ Transported by Vitamin D binding enzyme to intestine, kidney, bone
What increases vitamin D activation in the kidney
HYpocalcaemia
PTh
EPO is what type of hormone
glycoprotein
