B. Osmoregulation

• What is excretion 


  filtration of the blood to remove urea
• What is osmoregulation 


  Maintaining the water potential of blood
• Where do kidneys receive blood from

  Renal arteries
• What is the cortex

  Outer layer of kidney
• What is the medulla

  Region in the middle of the kidney organised into renal pyramids
• What is the pelvis

  Region of kidney that drains the urine into the ureter
• What is the bowman’s capsule

  Beginning of a nephron and it holds the glomerulus
• What is a glomerulus


  Bundle of capillaries that sits inside bowman’s capsule
• What are the proximal convoluted tubules

  Branches off the bowman’s capsule and extends to the loop of henle
• What are the distal convoluted tubules

  Comes from the loop of Henle and connects to the collecting duct
• Where is the loop of henle


  Medulla
• What is the afferent arteriole

  Carries blood into the glomerulus
• What is the efferent arteriole

  Carried blood out of glomerulus
• Function of bowman’s capsule

  Ultrafiltration
• Function of proximal tubules

  Selective reabsorption
• What are podocytes 


  Cells that line the bowman’s capsule. They have finger like processes with gaps between them
• What are the gaps between podocytes called

  Filtration slits
• What is the basement membrane

  A layer of mesh fibres that separates the capillary from the podocytes - acts as a filter
• What can’t pass through the basement membrane

  Red blood cells , platelets and plasma proteins
• Why is the afferent arteriole wider than the efferent

  Creates high hydrostatic pressure and forces out water and small molecules
• how are the cells lining the proximal convoluted tubules adapted

  Microvilli and many mitochondria
• How is glucose reabsorbed 


  Co transport
• What is the function of the loop of henle

  To create a concentration gradient of sodium ions and therefore a water potential gradient
• What happens to conc of filtrate as it flows down the descending limb

  Conc increases as there is a loss of water
• What happens to conc of tissue fluid deeper into medulla

  More concentrated
• What happens to the concentration of filtrate as it moves up ascending limb 


  Decreases as Na+ leaves by active transport
• What happens first in the loop of henle

  Na+ ions are actively transported out of the ascending limb
• When Na is transported out of ascending limb what happens

  The water potential of the medulla tissue is lowered so water moves out of descending limb via osmosis
• Where does the water that leaves the loop of Henle go

  Capillaries
• Why is the loop of henle a counter current system

  Fluid flows in the opposite direction in the two limbs
• Why might desert animals have a thicker medulla

  They will have a longer loop of henle. Which means more Na is pumped out so more water is absorbed
• Where is ADH released

  Pituitary Gland
• Where is ADH synthesised

  Hypothalamus
• What does adding ADH to blood do?

  Makes cells of collecting duct more permeable to water so more water leaves and is reabsorbed.
• What affect does high ADH have on urine

  Low volume of highly concentrated wee
• What affect does less ADH have on urine

  Collecting duct is less permeable to water so less is reabsorbed. Produces lots of urine
• How does ADH increase permeability of the collecting duct

  Increases transcription of genes coding for aquaporins
• What are aquaporins 


  protein water channels