The kidneys have four functions:
• Regulation of blood water levels
• Reabsorption of useful substances into the blood
• Adjustment of the levels of salts and ions in the blood
• Excretion of urea and other metabolic wastes
A nephron is a the smallest unit that filters the blood
Blood at high pressure entering the aorta passes through the walls of the bowman’s
capsule except the blood cells and protein (O2,
CO2 glucose, Urine salts and amino acids only
enter). Most substances including O2 glucose
most of the water and some salts are absorbed
at the tubules to join the renal artery. The rest
of the substances then go down the loop of
Henle. Then the rest of the unwanted
substances are passed to the urter and then
out of the body. Most of the nephrone is in the
cortex only the loop of Henle is in the medulla
and the collecting duct heads to the pelvis and
collected as the ureter (there are about 1
million nephrons in each kidney.)
Osmoregulation
Is keeping the water and salt levels constant in the blood. They are regulated by the
hypothalamus. If the concentration of water is too low e.g. during heavy exercise as a
lot of water is removed by sweating the blood becomes too concentrated so the
hypothalamus senses too little water in the blood. A message is sent to the pituitary
gland to release anti-diuretic hormone. This makes the membranes of the collecting
ducts become more permeable to water so more water passes. Usually when someone
goes to the toiled during exercise the urine is concentrated and is a t low quantity. If the
concentration of water in the blood is too high then water moves into the cells by
osmosis and could cause them to burst so the water in the blood stops the
hypothalamus signalling the pituitary. The membranes of the collecting ducts become
lass permeable to water and large amounts of dilute urine produced. The concentration
of urine depends on many factors e.g. diet, exercise and temperature.
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