excretion Flashcards
(15 cards)
define excretion
the removal of metabolic waste products, toxic materials and substances in excess of the body’s requirement
function of kidneys
contain numerous kidney tubules which remove urea, excess water and salts from blood to form urine
responsible for osmoregulation which is keeping the water potential of body fluids constant
ureter
a tube that connects the kidney to the urinary bladder. Urine flows from the kidneys ot the bladder through the ureters
bladder
a muscular extensible bag which stores urine
urethra
a muscular tube through which urine flows from the bladder to the exterior
process of ultrafiltration
non-selective filtering process which occurs at the glomerulus. renal artery splits into numerous afferent arterioles each leading to a nephron. arteriole splits into the glomerulus.
lumen of the afferent arteriole that brings blood into the glomerulus in wider than the efferent arteriole which bring bloods away hence blood enters the glomerulus more readily and leave through narrower efferent arteriole. as a result blood dams up in the glomerulus creating high blood pressure which forces blood plasma out of the glomerular capillaries into the Bowman’s capsule along the entire length of the glomerulus.
blood plasma that is forced out contains water and small molecules like glucose, amino acids, minerals forming filtrate in Bowman’s capsule.
large molecules like blood proteins and fats, blood cells, platelets remain in the blood and leave the glomerulus via the efferent arteriole
what is selective reabsorption
the transport of useful substances from the filtrate back to the bloodstream by active transport and facilitated diffusion.
water is reabsorbed by osmosis.
selective reabsorption of most of the useful substances in completed at the proximal convoluted tubule where all glucose, amino acids and vitamins are reabsorbed through walls of the nephron into surrounding capillaries. 85% of sodium ions, chloride ions and water are reabsorbed. active uptake of sodium and other ions into the blood increases the water potential in nephron causing water to leave nephron into surrounding capillaries by osmosis.
some water and ions are reabsorbed at loop of henle
water and smaller concentration of sodium ions and chloride ions are reabsorbed at the distal convoluted tubule
remaining water reabsorbed at collecting duct
what is the composition of urine
water 96.0g
salts 1.8g
urea 2.0g
other nitrogenous substances 0.2g
total 100g
what does the composition of urine depend on
a protein rich diet will result in more urea in urine as urea is formed when excess amino acids are deaminated in the liver
taking in more liquid or water rich food increases water potential of blood hence larger volume of urine is excreted. this also happens in cold weather when sweat production is reduced
taking in lots of salty food will result in excess salts being excreted in the urine
diabetic patient excretes large amount of glucose in urine. they are unable to store excess glucose as glycogen in the body hence there is a high concentration of glucose in the blood. Glucose is filtered off at the glomerulus and since nephrons are unable to reabsorb all the glucose back into the blood fast enough, lots of glucose passes out in the urine.
what is osmoregulation
is the maintenance of a correct balance between water and dissolved solutes in the blood to maintain constant water potential in the body
what happens when there is an increase in water potential in blood
osmorecptors in hypothalamus detect the increase in water potential. Hypothalumus in the brain send signals to the pituitary gland. pituitary gland releases less ADH into the bloodstream. ADH is transported to kidneys via the blood.
walls of the collecting duct become less permeable to water. Less water is reabsorbed back into the blood.
Urine is more diluted, higher volume of urine.
water potential decreases back to normal. negative feedback is sent to hypothalamus via osmoreceptors to prevent further correct actions
what happens when there is a decrease in water potential
osmoreceptors in the hypothalamus detects decrease in water potential. hypothalamus in the brain sends signals to the pituitary glad. pituitary gland releases more ADH into the blood. ADH is transported to the kidney via the blood.
walls of the collecting duct become more permeable. more water is reabsorbed back into the blood. urine is more concentrated and lesser volume of urine.
water potential increases
process of hemodialysis
blood is drawn from a fistula in the patient’s arm and pumped through a dialysis machine
in the dialysis machine, blood is passed through a dialyser containing many tubes. the walls of the tubing are partially permeable . dialysis fluid will be introduced into the dialyser. dialysis fluid will be in contact with the tubing carrying the patient’s blood and diffusion of waste materials from the blood into the surrounding dialysis fluid occurs.
small molecules such as urea and other metabloic waste products diffuse out of the tubing into the dialysis fluid. Blood cells, platelets and other large molecules remain in the tubing. blood is then returned into a vein in the patients arm
features of dialyser
the tubing is long and narrow to increase surface area to volume ratio to increase rate of diffusion between blood and dialysis fluid
the direction of blood flow is opposite to the flow of dialysis fluid to maintain concentration for removal of waste products
contents of dialysis fluid
dialysis fluid has the same concentration of essential substances as a healthy persons blood to prevent essential substances in the blood from diffusing out of tubing into the dialysis fluid.
if a person is lacking in essential substances, the essential substance can diffuse from the dialysis fluid into the blood
