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

1. FUNCTIONS OF KIDNEY

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
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6. Forces that influence filtration
• Glomerular blood hydrostatic pressure
• Opposing forces:
– Plasma colloid osmotic pressure
– Capsular hydrostatic pressure
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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
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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
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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
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14. Tubular reabsorption
• Water, glucose, amino acids, urea, ions
• Sodium diffuses into cell; actively pumped out
– drawing water with it
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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.
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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.
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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
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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
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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)
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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.