Kidney function
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The kidney has four main functions: 1. Excretory - forms and excretes urine through glomerular filtration, reabsorption, and secretion 2. Homeostatic - regulates blood volume, pressure, pH and electrolyte concentrations 3. Endocrine - produces hormones like erythropoietin, renin, and prostaglandins 4. Metabolic - performs gluconeogenesis during starvation and metabolizes hormones
Kidney function
- 2. FUNCTIONS OF KIDNEY excretory function homeostatic function endocrine function metabolic function
- 3. EXCRETORY FUNCTION • This include formation and excretion of urine. • The main step involved are – Glomerular filtration – Tubular reabsorption – Tubular secretion
- 4. Filtration • Renal corpuscle • Filtration membrane – Fenestrated endothelium of capillaries – Basement membrane of glomerulus – Slit membrane between pedicels of podocytes 4
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- 6. Forces that influence filtration • Glomerular blood hydrostatic pressure • Opposing forces: – Plasma colloid osmotic pressure – Capsular hydrostatic pressure 6
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- 8. Glomerular Filtration Rate • Volume of plasma filtered / unit time • Approx. 180 L /day • Urine output is about 1- 2 L /day • About 99% of filtrate is reabsorbed 8
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- 10. GFR influenced by: • Blood pressure and blood flow • Obstruction to urine outflow • Loss of protein-free fluid • Hormonal regulation – Renin – angiotensin – Aldosterone – ADH – ANP 10
- 11. Juxtaglomerular apparatus • Juxtaglomerular cells lie in the wall of afferent arteriole • Macula densa in final portion of loop of Henle – monitor Na+ and Cl- conc. and water • Control blood flow into the glomerulus • Control glomerular filtration 11
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- 14. Tubular reabsorption • Water, glucose, amino acids, urea, ions • Sodium diffuses into cell; actively pumped out – drawing water with it 14
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- 17. • In addition to reabsorption, also have tubular secretion – substances move from peritubular capillaries into tubules – a second chance to remove substances from blood. 17
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- 19. • By end of proximal tubule have reabsorbed: • 60- 70% of water and sodium • about 100% of glucose and amino acids • 90 % of K+, bicarb, Ca++, uric acid • Transport maximum – maximum amount of a substance that can be absorbed per unit time • Renal threshold – plasma conc. of a substance at which it exceeds Tm. 19
- 20. Loop of Henle • Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney. • When ADH is present, water is reabsorbed and urine is concentrated. • Counter-current multiplier 20
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- 22. Distal convoluted tubule and collecting ducts • What happens here depends on ADH • Aldosterone affects Na+ and K+ • ADH – facultative water reabsorption • Parathyroid hormone – increases Ca++ reabsorption 22
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- 24. Distal convoluted tubule and collecting ducts • Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs • Secretion of H+ helps maintain blood pH (can also reabsorb bicarb and generate new bicarb) 24
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- 26. Homeostatic Functions of Urinary System 1. Regulate blood volume and blood pressure: – by adjusting volume of water lost in urine – releasing erythropoietin and renin 2. Regulate plasma ion concentrations: – sodium, potassium, and chloride ions (by controlling quantities lost in urine) – calcium ion levels
- 27. 3. Help stabilize blood pH: – by controlling loss of hydrogen ions and bicarbonate ions in urine 4. Conserve valuable nutrients: – by preventing excretion while excreting organic waste products 5. Assist liver to detoxify poisons
- 28. ENDOCRINE FUNCTIONS… Kidneys have primary endocrine function since they produce hormones In addition, the kidneys are site of degradation for hormones such as insulin and aldosterone. In their primary endocrine function, the kidneys produce erythropoietin, renin and prostaglandin. Erythropoietin is secreted in response to a lowered oxygen content in the blood. It acts on bone marrow, stimulating the production of red blood cells.
- 29. Renin -the primary stimuli for renin release include reduction of renal perfusion pressure and hyponatremia. Renin release is also influenced by angiotension II and ADH. It is a key stimulus of aldosterone release. The effect of aldosterone is predominantly on the distal tubular network, effecting an increase in sodium reabsorption in exchange for potassium. The kidneys are primarily responsible for producing vitamin D3 from dihydroxycholecalciferol
- 30. METABOLIC FUNCTION • Kidney perform gluconiogenesis during periods of starvation.