Urine Formation

1
Urine Formation

• Glomerular filtrate is the plasma like fluid
  that is squeezed from the glomerulus and is
  collected by the bowmans capsule
• Glomerular filtration rate (GFR) can be auto
  regulated using BP in vessels, flow of tubular
  fluid, the enzyme renin

2
Urine Formation

• Renin an enzyme that is produced when BP is low,
  changes a protein into the hormone angiotensin II
• angiotensin II slows GFR to reduce water loss,
  promotes Na and water retention

3
Urine Formation

• PCT reabsorbs 65 of filtrate through passive
  and active transport
• Na is key b/c of osmotic gradient
• Cl-, HCO3, glucose, are also reabsorbed
• The nephron reabsorbs 40-60 of urea but due to
  the reabsorption of 99 water the concentration
  of urea is much higher
• Of 180L filtrate only 2-3L voided

4
Formation Hormones

• Aldosterone the salt hormone increases the
  nephron loop uptake of Na which in turn
  increases K and Cl- uptake
• Atrial natriuretic peptide (ANP) is secreted
  when BP is high causes a decrease in water and
  Na uptake reducing B volume
• Antiduretic hormone (ADH) dehydration trigger,
  causes increase in water uptake in PCT
• Parathyroid (PTH) restores Ca2 levels

5
Water conservation

• Countercurrent multiplier occurs in the loop.
  The thin descending part diffuses water out to
  ECF based on osmolarity, the thick ascending part
  actively transports salt and K in response to
  increased levels of salt and K
• Countercurrent exchange B vessels loose water
  due to osmolarity and then on the way up gain
  more water then they lost