chap8: excretion in humans Flashcards
what is excretion
excretion is the removal of metabolic waste products, toxic substances and substances in excess in the body
what are some metabolic waste products
carbon dioxide, urea, mineral sals, water
why is excretion important
to prevent metabolic waste products from accumulating to harmful levels
describe ultrafiltration
ultrafiltration occurs in the bowman’s capsule. high blood pressure in the glomerulus causes high hydrostatic pressure that forces water and small molecules like mineral salt ions, amino acids and urea through the partially permeable glomerulus capillary walls and into the glomerulus. large molecules like plasma protein and blood cells cannot pass through glomerulus and remains in the blood in the glomerular capillaries. ultrafiltration does not require energy.
describe selective reabsorption
selective reabsorption occurs at the proximal convoluted tubule. useful substances like glucose, amino acids, mineral salt ions and water are reabsorbed form the filtrate into the blood. water is absorbed via osmosis. all glucose, all amino acids and some mineral salt ions are reabsorbed via diffusion and active transport (requires energy). the remaining fluid passes out of the collecting duct as urine. urine is made out of of excess water and mineral salt ions an metabolic waste products like urea.
what is urea
urea is a metabolic waste product that is formed through the process of deamination. proteins in the food we eat contain anion acids. amino acids are used by the body to grow and repair tissues. excess amino acids are transported to the liver to undergo deamination to produce urea. urea is a metabolic waste product that is formed in the liver and removed by the kidneys.
what is osmoregulation
osmoregulation is the control of water potential and solute concentration in the blood to maintain a constant water potential in the body
what happens when the water potential of blood plasma decreases
when water potential of blood plasma decreases, it stimulate the hypothalamus in the brain to produce more ADH. the pituitary glands releases more ADH into the bloodstream. this results in the cells in the alls of the collecting duct to become more permeable to water. more water is reabsorbed from the collecting duct into the blood capillaries. hence a smaller volume of more concentrated urine is produced. water potential of blood returns to normal.
what happens when the water potential in blood plasma increases.
when the water potential in blood plasma increases, the hypothalamus in the brain is stimulated to produce less ADH. the pituitary gland releases less ADH which results in the cells in the capillary walls to become less permeable to water. this results in less water being reabsorbed from the collecting duct into the blood capillaries. a larger volume of more diluted urine is produced. water potential in blood plasma returns back to normal.
what causes kidneys to fail
high blood pressure
diabetes
alcohol abuse
features of a dialysis machine
dialysis contains same concentration of essential substances as healthy blood
this ensures that essential substances like glucose, water, mineral salt ions and amino acids do not diffuse out to the blood and into the dialysis fluid. furthermore if the patients’ blood lacks any of these substances, the substances will diffuse from the dialysis fluid into the blood.
dialysis fluid do not contain metabolic waste product
this maintains a concentration gradient that allows waste products like urea and excess water and mineral salts to diffuse out of the blood and into the dialysis fluid to be removed. this maintains the correct solute composition and water potential of the blood.
tubing of the machine is long, narrowed and coiled
this increases surface area to volume ratio which helps to speed up rate of exchange of substances between patients’ blood and dialysis fluid.
the dialysis fluid and patients’ blood flows in opposite direction
this maintains the concentration gradient for the removal of waste products
how is urea removed
by the kidneys (urine)
by skin (sweat)
