THE KIDNEYS Flashcards
Where does blood enter the kidney through and where does it go
through the renal artery the passes through the capillaries in the cortex of the kidney
ultrafiltration (10 steps)
- blood from the renal artery enter smaller arterioles in the cortex
- each arteriole splits into glomerulus (a bundle of capillaries looped inside a hollow ball called a bowman capsule.
- afferent arteriole takes blood into the glomerulus
- efferent arteriole takes blood away from the glomerulus
- afferent is wider than efferent- so blood in the glomerulus is under high pressure
- high pressure forces liquid and small molecules (water, amino acids, sodium chloride) in the blood out of the capillary into the bowman’s capsule
- the liquid and small molecules (filtrate) pass through three layers to get into the bowman capsule and enter nephron tubules, the capillary endothelium and the basement membrane and the epithelium of the bowman’s capsule
- larger molecules like proteins and blood cells can’t pass through so stay in the blood.
- the filtrate passes along the rest of the nephron and and useful substances are reabsorbed along the way
- filtrate flows through the collecting duct and passes out of the kidney along the ureter
where does ultrafiltration take place
in the glomerulus and the bowman capsule.
selective reabsorption
- useful substances (e.g glucose, vitamins, aa, some salts) leave the tubule of the nephrons and enter the capillary network around them.
- the epithelium of the PCT wall has microvilli to provide a large surface area for reabsorption of useful subs from the filtrate in the tubules, (some urea is also re-ab)
- reabsorbed by active transport and facilitated diffusion
- water enters the blood by osmosis - water potential is lower in the blood than the filtrate
- water reabsorbed from the LOH, DCT and collecting fact
- filtrate that remains is urine- passes along the ureter to the bladder.
what is urine made up of
water, dissolved salts, urea and other substances such as hormones and excess vitamins.
why doesn’t urine contain proteins or blood cells
too big to be filtered out of the blood
what happened if water content of the blood is too low (body=dehydrated)
more water is reabsorbed by osmosis in to the blood from the tubules in the nephrons. urine is therefore more concentrated, so less water is lost during excretion
what happens if the water content of the blood is too high (too hydrated)
less water is reabsorbed by osmosis into the blood from the tubules of nephrons. urine is therefore more dilute so more water is lost during excretion
where does water regulation take place in the kidner
in the LOH of the nephron, the DCT and collecting duct
what control volume of water reabsorbed
ADH
the LOH
descending and ascending limbs set up a mechanism called the countercurrent multiple mechanism - helps reabsorb water back into the blood
whats the role of Na+ and Cl- in the LOH
establish the water potential that drives the reabsorption of water from the filtrate back into the blood.
describe the countercurrent mechanism
- top of ascending limb- Na+ and Cl- ions are actively pumped out into the medulla
- ascending limb is impermeable to water so the water stays inside the tubule- creating a low water potential in the medulla (high conc of ions)
- lower water potential in the medulla than in the descending limb- water moves out of descending limb into medulla by osmosis
- this makes the filtrate more concentrated (ions can’t diffuse out of the descending limb as it’s impermeable to them)
- water is reabsorbed into the blood through the capillary network
- bottom of the ascending limb Na+ and Cl- ions diffuse out into the medulla further lowering the water potential in the medulla. (ascending limb is imperable to water so water stays in the tubule).
- ALL OF THESE INCREASE THE CONC OF IONS IN THE MEDULLA, LOWERS WATER POTENTIAL
- causing water to move out of the collecting duct by osmosis .
- same again the water is reabsorbed into the blood through the capillary network.
how is the volume of water reabsorbed from the collecting duct into the capillary controlled
by the changing permeability of the collecting duct
what does a longer LOH in some animals mean
that more water can reabsorb from the filtrate.
when there;s a longer ascending limber ions are actively pumped out into the medulla which creates a really low water potential in the medulla- so more water moves out of the nephron and collecting duct into the capillaries- giving very concentrated urine.
ANIMALS THAT LIVE IN DRY PLACEs/LACK OF WATER
in order to conserve water
frogs and toads don’t have much a LOH- so they can’t produce concentrated urine- live in water- water available don’ need to conserve
