chapter 8 - excretion Flashcards
excretion
removal of metabolic waste products from the body, which is important as metabolic waste accumulated in excess is toxic
waste products of excretion
carbon dioxide, water, urea, mineral salts
how are metabolic waste products excreted?
sweat : urea, excess water and mineral salts
expired air : carbon dioxide and excess water vapour
faeces : bile pigment
urine : urea, excess water and mineral salts
parts and functions of human urinary system
kidneys : produce urine
ureters : connects kidneys to bladder
bladder: stores urine temporarily
urethra : passage where urine is discharged from the bladder
sphincter muscle : controls exit of urine from the bladder. when the muscle relaxes, it allows urine to flow into the urethra
blood circulation at the kidney tubules
blood enters the kidney via the renal artery. the renal artery branches into many arterioles and the arterioles branch into a mass of blood capillaries known as teh glomerulus. blood leaves the glomerulus and enters the blood capillaries surrounding the kidney tubules. blood capillaries unite to form venules, and venules join to form the renal vein, where blood exits
ultrafiltration
ultrafiltration : there is a high hydrostatic blood pressure at the glomerulus due to the afferent arteriole being wider than the efferent arteriole. blood is forced out of and filtered through the partially permeable basement membrane of the glomerulus into the Bowman’s capsule via ultrafiltration. smaller molecules like water, glucose and urea can be filtered through while larger molecules like plasma proteins and blood cells cannot
selective reabsorption
useful substances are reabsorbed back into the blood. water is reabsorbed via osmosis, glucose/amino acids are reabsorbed via active transport, and mineral salts are reabsorbed via diffusion and active transport.
water reabsorption
at the loop of henle, some water is reabsorbed from teh filtrate back into the blood vessels via osmosis
at the distal convulated tubule, some salts are reabsorbed back into the blood vessel via active transport. blood pH is also regulated by selectively reabsorbing H+ ions
at the collecting duct, some water is reabsorbed back into the blood vessel via osmosis
the remaining fluid in the tubule passes out of the collecting duct into the renal pelvis to form urine
osmoregulation
regulation of the water potential of blood plasma. the water potential depends on the amount of eater and solutes (glucose and amino acids) in the plasma. the water potential of blood plasma is controlled by ADH, which is produced by the hypothalamus and released by the pituitary gland. ADH increases reabsorption of water by kidney tubules
lose too much water
the loss of water causes the water potential of blood plasma to decrease. this stimulates the hypothalamus in the brain and the pituitary gland releases more ADH into the bloodstream. cells in the walls of the collecting ducts becomes more permeable to water and more water is reabsorbed from the collecting duct into the blood capillaries. there is a smaller volume of water produced, and the urine is more concentrated. the water potential of blood then increases back to the norm.
too much water intake
the large intake of water causes the water potential of the blood plasma to increase beyond the norm. this stimulates the hypothalamus in teh brain and the pituitary gland releases less ADH into the bloodstream. cells in the walls of the collecting duct becomes less permeable to water and less water is reabsorbed form the collecting duct into the blood capillaries. there is a larger volume of urine produced, but the urine is more diluted. the water potential of plasma decreases back to the norm.
how does dialysis machine work?
blood is drawn from a vein in the patient’s arm and pumped into the dialysis machine. the dialysis fluid in the machine has a similar concentration of glucose and amino acids as blood but lacks nitrogenous waste. it also has a partially permeable membrane for diffusion. blood flows in the opposite direction of dialysis fluid to maintain a constant concentration gradient of nitrogenous waste. smaller molecules such as urea and other nitrogenous waste diffuse out of the tubing from a region of high concentration in the patient’s blood to a region of low concentration in the dialysis fluid . larger molecules like glucose and amino acids remain in the tubing and the filtered blood is returned to the patient’s body through a vein.
differences between a dialysis machine and kidneys
- dialysis machine only involves diffusion, but the kidneys involves both diffusion and active transport
- dialysis machine does not involve ultrafiltration / selective reabsorption but the kidneys involves ultrafiltration / selective reabsorption
- dialysis machine involves diffusion of molecules down a concentration gradient, but kidney involves use of hydrostatic blood pressure during ultrafiltration to force the filtrate at the glomerulus
