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Biochemistry of kidney.pptx
- 1. Biochemistry of kidney BCH415(Tissue Biochemistry) BIOCHEMISTRY DEPT, FACULTY OF SCIENCE FEDERAL UNIVERSITY DUTSE
- 3. Functions of theKidney • Regulation of the water and electrolyte content of the body. • Retention of substances vital to the body • Maintenance of acid/base balance. • Excretion of waste products, water soluble toxic substances and drugs. • Endocrine functions
- 4. Urine is formedas a result of a three phase process • Glomerular filtration • Selective (active) and passive reabsorption • Secretion
- 5. Glomerular filtration • Filtrationtakes place through the semipermeable walls of the glomerular capillaries • The driving hydrostatic pressure is provided by arterial pressure • About 20% of renal plasma flow is filtered each minute (~ 125 ml/min) GFR • Result is glomerular filtrate GF (primary urine) (~ 150 l).
- 6. Reabsorption • In theproximal and distal tubule, the GF becomes highly concentrated as the result of the removal of water. • At the same time, many other low molecular weight constituents are reabsorbed by active transport – glucose, AA and organic and inorganic ions
- 7. Proximal Tubule • Reabsorbs60% of all solute (100% of glucose and AA, 90% of bicarbonate, 80-90% of inorganic phosphate and water.
- 8. Loop of Henle •Next reabsorption of NaCl • In descending loop of Henle - resorption of water by osmosis - increasing of osmolarity (hypertonic) • In ascending loop of Henle - active transport of NaCl out of the tubule - decreasing of osmolarity (hypotonic)
- 9. Distal Tubule andCollecting Ducts • Aldosterone promotes Na+ ions and water reabsorption • Excretion of H+ ions • The final concentration of urine depends upon antidiuretic hormone (ADH).
- 11. Secretion • Some ofthe substances that have to be excreted from the body are released into urine in the kidney by active transport – H+ and K+ ions, urea, creatinine and drugs.
- 12. Energy for thetransport • ATP is derived from the oxidative metabolism of glucose, lactate, pyruvate, fatty acids, glycerol, citrate and AA absorbed from the blood.
- 14. Maintenance of acidbase balance Proton secretion • The tubule cells absorb CO2 from the blood and then hydrate it to carbonic acid (carbonate dehydratase). • Carbonic acid then dissociates to HCO3- and H+. • H+ is exported to the urine by an ATP-driven membrane-localised transport system, while HCO3- returns to the blood.
- 16. Maintenance of acidbase balance
- 17. Endocrine function ofkidney Hormones of the kidney • Erythropoietin • Calcitriol • Angiotensin
- 19. Erythropoietin • Polypeptide hormonethat is formed predominantly by the kidney (also by the liver) • It controls the differentiation of the bone marrow stem cells • The release is stimulated by hypoxia (low pO2) • The hormon ensures that the bone marrow cells are converted to erythrocytes, so that their concentration in the blood increases
- 20. Calcitriol • 1-alpha,25-dihydroxycholecalciferol isa steroid-related hormone involved in calcium homeostasis. • It is formed in the liver from calcidiol by hydroxylation at C-1 • The activity of hydroxylase (calcidiol-1-monooxygenase) is regulated by the hormone parathyrin (parathormone).
- 21. Renin – angiotensinsystem • Renin is an enzyme which converts the plasma protein angiotensinogen to angiotensin I. • Angiotensin converting enzyme (ACE) which is formed in the lungs converts angiotensin I to angiotensin II which causes vasoconstriction and an increase in blood pressure. • Angiotensin II also stimulates the aldosterone production (water and sodium retention which together increase blood volume).
- 22. Renin increases theproduction of angiotensin II which is released when there is fall in intravascular volume and dehydration. This leads to: • Constriction of the efferent arteriole to maintain GFR, by increasing the filtration pressure in the glomerules. • Release of aldosterone. • Increased release of ADH. • Thirst • The opposite occurs when fluid overload occurs.
- 24.