Chapter 13 Flashcards
Excretion in Humans (7 cards)
Describe excretion and its importance
removal of waste products of metabolism and substances in excess of requirements
some waste products can be toxic eg. urea:
not normally harmful unless its concentration in the blood gets too high (e.g. if the kidneys fail to excrete it), in which case it starts to be converted into ammonia – a strong, toxic alkali.
State the organs in the body involved in excretion
carbon dioxide is excreted through the lungs
kidneys excrete urea and excess water + ions
Structure of excretory system
!! refer to diagram 13.1 !!
Describe deamination
the removal of the nitrogen-containing part of excess amino acids to form urea in the liver
Describe the role of the liver (assimilation of amino acids)
surplus amino acids in the bloodstream cannot be stored some are deaminated and some are assimilated by converting them into proteins.
Explain how urine is formed
the kidney receives blood containing urea, drugs, excess substances etc..from the aorta via the renal artery which (in the cortex) splits into millions of capillaries each forming a tangled glomerulus, from which the blood is filtered under pressure – the pressure forces small molecules and ions
(such as glucose, urea, water and mineral ions) out of the capillary into a renal tubule which the filtrate passes through for reabsorption – water (osmosis) and glucose and mineral ions (diffusion/active-uptake) the remaining solution (urine) passes down the collecting duct of the tubule, through the pelvis of the kidney into the ureter down into the bladder for removal through the urethra.
Explain how urine maintains water level in the body
the relative amount of water reabsorbed depends on the state of hydration of the body – if the body is dehydrated, more water is reabsorbed leading to a more concentrated urine solution – if the body has too much water less water is reabsorbed leading to a dilute urine solution
