biology - topic 6 - kidneys + control of blood water

functions of the kidney

filter blood and remove nitrogenous waste

osmoregulation

osmoregulation

maintaining balance of water and dissolved solutes in blood

functions of nephron

ultrafiltration selective reabsorption secretion

ultrafriltration

small soluble molecules filtered from blood in glomerulus,

filtrate similar to blood plasma (no cells or proteins) filtrate enters bowermans capsule

adaptations for filtrate formation

afferent arteriole has wider lumen than efferent increasing hydrostatic pressure

endothelium has pores allowing filtrate to pass through

connective tissue acts as a molecular sieve - proteins and cells

foot like processes of podocyte cells allow filtrate to pass through

selective reabsorption

ensures useful products e.g. glucose, amino acids and chloride ions are reabsorbed into blood as filtrate passes through tubule - 85% absorbed in PCT - all glucose and some water and salt

selective reabsorption process

sodium potassium pump actively transports 3 na+ ions out of the PCT cell into the lumen and 2 k+ ions into the PCT cell, lowering the conc of na+ in PCT cells. na+ diffuses into cells from lumen through cotransporter proteins with glucose. glucose passes into lumen of capillary via facilitated diffusion. amino acids and chloride ions transported the same way

selective reabsorption counter current mechanism

water drawn out of descending limb via osmosis , lowering the water potential and making the fluid more and more concentrated. at the bottom of the descending limb the fluid is highly concentrated. ascending limb is impermeable to water . as fluid moves up ascending limb, na+ diffuses out via fd and is then actively transported out - very dilute

secretion

fluid empties into collecting duct which passes through very conc medullary region. fluid travels through pelvis to ureter where it is stored in the bladder and leaves body via urethra

blood too conc/WP too low…

osmoreceptors in hypothalamus detect change. posterior pituitary gland secretes more ADH into the blood. increases permeability of DCT and CD as more aquaporins inserted into the CSM of epithelial cells. more water reabsorbed urine more conc and blood less conc. smaller volume of more conc urine produced