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
EPO is triggered by
Hypoxia
Hypotension
Low haematocrit
Where is EPO released from
Secretory cells in the cortex and medullar - peritubullar fibroblasts 85%
15% liver
What does the kidney also produce other than renin that influences arterial tone
PGI2 and PGE2
Renin half life
80 minutes
Renin is found where
◦ stored by the granular cells of the juxtaglomerular apparatus, which lies close to the glomerulus and distal tubule
What gives negative feedback to renin release
AT2
