excretion

the kidneys

• Main function: water balance

• Renal artery = main artery

• Vasa recta: network of BVs surrounding the loop of Henle

• Using the flat kidney diagram on the practical

• contains macula densa

macula densa

• Macula densa: sense sodium chloride (salt) and pressure

  • Draws water to it when salt concentration is high

  • Decreases resistance to blood flow in afferent arterioles

    • Forces more blood to flow through the arterioles → raises BP

  • Increases renin release → will increase water reabsorption

  • Juxtaglomerular cells: cells that line the macula densa

filtration barrier of kidneys

• Filtration barrier: negatively charged that repels proteins → want proteins to be reabsorbed (you could die)

podocytes

Inside filtration barrier

• Podocytes: cell bodies form foot processes that wrap around the glomerular capillaries

  • Form the barrier

• Things that are filtered out of the filtrate (stuff you want) go back into the bloodstream

pressure

• Pressure is positive if water flows from the capillaries to the Bowman's capsule

• Pressure is pushing against the wall of the capillary

• Glomerular colloid osmotic pressure: pressure of large proteins

  • Albumins → set up colloid osmotic pressure to prevent protein loss from blood

  • Can’t get out but they have pressure acting on them

• Pressure from Bowman’s capsule is pushing on the capsule

• Net filtration pressure (10 mmHg) = glomerular hydrostatic pressure (60 mmHg) -  [ Bowman’s capsule pressure (18 mmHg) + glomerular osmotic pressure (32 mmHg) ]

  • If it's negative then you’re in kidney failure

  • Easier to add up Bowman’s capsule and osmotic pressure before subtracting because they act in the same direction

renal tubules

Filtration + secretion - reabsorption = excretion

tubule epithelium

simple cuboidal

ureter epithelium

transitional epithelium

• holds volume

bladder epithelium

smooth muscle and skeletal muscle