the kidney Flashcards
outline the sources of water and salt?
How water and salt are lost and gained in a human?
sources of water: diet, metabolism (respiration)
loss of water: urine, expired air, evaporation, skin, faeces, sweat
source of salt: diet
loss of salt: urine, faeces, sweat
what is the high hydrostatic pressure in the kidneys caused by
high hydrostatic pressure is caused by efferent arteriole having a narrower lumen then afferent arteriole
describe ultrafiltration and production of glomerular filtrate
- afferent arteriole is larger than efferent arteriole causing high hydrostatic pressure in the glomerulus
- water, glucose, urea, mineral ions (glomerular filtrate) forced out of the capillary into the renal capsule
- blood cells and proteins are too large to pass through
- movement of filtrate out of the glomerulus is resisted by capillary endothelial cells, epithelial cell of renal capsule, hydrostatic pressure of fluid in renal capsule, low water potential in blood
explain how the structure of a nephron enhances ultrafiltration
podocytes in renal capsule: spaces between them allow filtrate to pass around them
endothelium of glomerular capillaries has spaces between the cells allowing fluid to pass round not through the cells
explain how glucose is absorbed into the proximal convoluted tubule
- Na+ are actively transported out of epithelial cells lining PCT into capillary
- higher concentration of sodium ions in lumen of PCT than cells lining PCT
- Na+ diffuse down their concentration gradient by facilitated diffusion through carrier proteins from the lumen of the PCT into the epithelial cells lining the PCT
- glucose and Na+ are co transported from lumen into epithelial cells
- specific type of carrier protein co transports glucose with Na+
- glucose moved by facilitated diffusion into blood down concentration gradient
what is the role of the kidneys in homeostasis
osmoregulation
regulate water potential of blood
explain the role of the loop of Henle in the absorption of water from the filtrate (6 marks)
- in the ascending limb Na+ ions actively removed
- ascending limb impermeable to water
- in descending limb Na+ ions diffuse in
- descending limb water moves out
- low water potential/high concentration of ions in medulla/tissue fluid
- the longer the loop/the deeper into medulla/ the lower the water potential in the medulla/tissue fluid
- water leaves collecting duct/distal convoluted tubule
- by osmosis/down a water potential gradient
explain how the loop of Henle acts as a counter current multiplier
the water potential of the filtrate in the loop of Henle reduces as it moves down, meeting interstitial fluid with an even lower water potential
this ensures a small but constant water potential gradient along the whole length of the loop of Henle. This also applies to the collecting duct
explain the role of the DCT and collecting duct in reabsorbing water
-DCT has microvilli on its epithelial cells and many mitochondria, increasing reabsorption from the filtrate by active transport.
-DCT makes final adjustments to water and salts that are reabsorbed and controls blood pH by selecting which ions to reabsorb
-Water moved by osmosis from the collecting duct into the interstitial fluid and then into the blood
Define osmoregulation
Maintenance of water potential of the blood plasma and therefore tissue fluid
Explain how the water potential of the blood is regulated
Water potential of the blood depends on the solutes and well as volume of water.
Water potential of the blood is detected, the hormone ADH is either secreted or stopped, the permeability of the collecting ducts to water is altered and more or less water is absorbed
Describe the roles of hypothalamus, posterior pituitary and antidiuretic hormone in osmoregulation
-Osmoreceptors in the hypothalamus detect a fall in the water potential of the blood (water is lost by osmosis from these cells and they shrink)
-This causes the hypothalamus to produce antidiuretic hormone (ADH)
-ADH passes to the posterior pituitary gland and is secreted into the capillaries
-ADH travels in the blood to the kidneys and increases the permeability of the DCT and collecting duct to water
-Specific protein receptors in the membranes of the cells making up the walls of the DCT and collecting duct bind to ADH and cause activation of phosphorylase enzymes in the cell
-Phosphorylase causes vesicles in the cell containing aquaporins to move to and fuse with the cell membrane
-ADH also increases permeability to urea which passes out further lowering water around the collecting duct
-More water leaves the collecting duct and is reabsorbed into the blood
-When the above and drinking restore water potential of blood the osmoreceptors detect this and the process is reversed
