SN7
SHORT NOTE
5M
★ High-yield
Enumerate the non-excretory functions of the kidney.
Non-excretory Functions of the Kidney
Besides excretion, the kidney has important endocrine, metabolic and homeostatic functions.
Endocrine Functions
| Hormone | Source in kidney | Action |
|---|---|---|
| Erythropoietin | Peritubular interstitial cells of the cortex | Stimulates erythropoiesis; released in response to hypoxia |
| Renin | JG cells of the afferent arteriole | Initiates the RAAS → BP and volume control |
| 1,25-dihydroxycholecalciferol | PCT — 1α-hydroxylase | Active vitamin D → ↑ calcium absorption |
| Prostaglandins (PGE2, PGI2) | Medullary interstitial cells | Vasodilatation; protect renal blood flow |
Metabolic Functions
- Gluconeogenesis — the kidney is the second most important site after the liver; contributes up to 20% of glucose in prolonged fasting
- Degradation of hormones — insulin, glucagon, PTH, gastrin
- Metabolism of drugs and of low molecular weight proteins
Homeostatic Functions
- Water balance — via ADH and the counter-current mechanism
- Electrolyte balance — Na+, K+, Ca2+, phosphate, Mg2+
- Acid–base balance — the only route for non-volatile acid
- Long-term blood pressure regulation — pressure natriuresis, with infinite gain
- Excretion of nitrogenous waste — urea, creatinine, uric acid
Consequences of Chronic Renal Failure
| Function lost | Consequence |
|---|---|
| Erythropoietin | Normocytic normochromic anaemia |
| 1α-hydroxylase | ↓ Active vitamin D → hypocalcaemia → secondary hyperparathyroidism → renal osteodystrophy |
| Acid excretion | Metabolic acidosis |
| K+ excretion | Hyperkalaemia → arrhythmia |
| Water and Na+ handling | Oedema, hypertension |
| Waste excretion | Uraemia → encephalopathy, pericarditis, pruritus |
Applied Aspects
- Recombinant erythropoietin corrects the anaemia of chronic renal failure
- Calcitriol (already hydroxylated) must be given, since the kidney can no longer activate vitamin D
- This is why dialysis alone is not enough — it replaces excretion but not the endocrine functions
All questions in Renal System
- Q1Define glomerular filtration rate. Describe the filtration barrier, the forces governing filtration, and the factors affecting GFR. Add a note on autoregulation. ★
- Q2Describe tubular reabsorption in the different parts of the nephron. Explain glucose reabsorption with transport maximum and renal threshold. ★
- Q3Describe the counter-current mechanism of urine concentration. Explain the role of the loop of Henle, vasa recta and ADH. ★
- Q4Describe the role of the kidney in the regulation of acid–base balance. Explain bicarbonate reabsorption, titratable acid and the ammonia mechanism. ★
- Q5Describe the nerve supply of the urinary bladder and the mechanism of micturition. Add a note on the abnormalities of micturition. ★
- SN1Define renal clearance. Describe inulin and creatinine clearance and their significance. ★
- SN2Describe the juxtaglomerular apparatus and the renin–angiotensin system. ★
- SN3Write a short note on antidiuretic hormone. ★
- SN4Classify diuretics according to their site of action and describe their mechanisms. ★
- SN5Enumerate the renal function tests and give their normal values. ★
- SN6Describe the principle and types of dialysis. Give its indications.
- SN7Enumerate the non-excretory functions of the kidney. ★