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Summary AQA A Level Biology- Kidneys Notes
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Summary of everything you need to know about kidneys for the AQA A Level Biology new specification.
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The Kidneys:Key Terminology:
★ Afferent arteriole: takes blood into glomerulus.
★ Efferent arteriole: take filtered blood away from glomerulus.
★ Glomerulus: bundle of capillaries looped inside a hollow ball called Bowman’s
capsule.
★ Bowman’s capsule: cup-like sac that performs the first step in ultrafiltration;
glomerulus enclosed in here.
★ Proximal convoluted tubule (PCT): convoluted portion of the nephron between
Bowman’s capsule and the loop of Henle; mainly involved in reabsorption.
★ Distal convoluted tubule (DCT): convoluted portion of the nephron between the
loop of Henle and the collecting duct; involved in secretion.
, ★ Loop of Henle: a long, hairpin loop that extends from the cortex into the medulla of
the kidney and back again; surrounded by blood capillaries; the longer the loop of
henle, the more glucose will be absorbed.
★ Ureter: tube that carries urine from the kidney to the urinary bladder.
★ Osmoregulation: control of water and salt.
Ultrafiltration:
➔ Blood enters the smaller arterioles in the cortex of the kidney from the renal artery.
➔ Blood is filtered in the glomerulus.
➔ Blood into glomerulus= afferent arteriole; blood away from glomerulus= efferent
arteriole
➔ Efferent arteriole has a smaller diameter than the afferent arteriole, therefore it
creates some resistance to blood flow and blood in the glomerulus is under high
pressure.
➔ Due to the high pressure, liquid and small molecules (e.g. glucose, some salt and
water) in the blood (a.k.a glomerular filtrate) are forced out of the capillary and into
the Bowman’s capsule. Large molecules like proteins and RBCs cannot be filtered
because they are too big to pass through the filter.
Bowman’s capsule:
➢ 1st layer: endothelium- has holes to let plasma pass
➢ Basement membrane: mesh-like structure that acts as a filter during
ultrafiltration.
➢ 2nd layer: wall of Bowman’s capsule- epithelial cells in this wall are called
podocytes. They have a foot-like structure and do not fit tightly together,
therefore the filtrate can pass because they have gaps between each other.
➔ Reabsorption is done by blood capillaries, which are closely wrapped around tubules.
Blood capillaries:
➢ Glomerular capillaries are within the Bowman’s capsule; plasma is filtered
here.
➢ The capillary bed reforms into an arteriole.
➢ Glomerular capillaries have afferent and efferent arteriolar ends.
➢ Glomerular capillaries are able to autoregulate blood flow so that here is a
constant flow over a wide range of blood pressure.
➔ The waste, consisting of water, some salt and urea is urine.
➔ The urine is collected by the collecting duct, taken to the ureters and then to the
blood.
Q: Describe the process of ultrafiltration. (5)
A: Blood enters the glomerulus under high pressure via the afferent arteriole and enters the
Bowman’s capsule. Small molecules like water, glucose and ions are able to leave the
capillaries as they are filtered via the podocytes in the basement membrane. Large
molecules like proteins and red blood cells stay behind because they are too large to pass
through the endothelium.
If proteins are in the urine, it means that the basement membrane would be damaged.
Selective Reabsorption:
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