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
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
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
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
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
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
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