homeostasis Flashcards
(33 cards)
why does blood enter glomerulus under high pressure
the afferent (arriving) arteriole is wider than the efferent (exiting) arteriole
what substances leave the glomerulus
smaller molecules - ions, glucose, water, urea
what substances stay in the capillaries
proteins and blood cells
what 3 layers do molecules pass through as they leave the glomerulus
capillary pore
basement membrane
filtration site of podocyte
where does selective reabsorption happen
proximal convoluted tubule
how are glucose and sodium ions reabsorbed
(co-transport) sodium ions actively transported out of cell to maintain concentration gradient between filtrate and PCT cells → glucose + sodium ions enter PCT cells via co-transport → glucose enters blood via facilitated diffusion
how is the proximal convoluted tubule adapted for reabsorption
microvilli increase surface area
co-transport proteins in membrane
mitochondria provide energy
what happens in the descending limb of the loop of henle
- permeable to water; impermeable to sodium ions
- water moves out of filtrate via osmosis into medulla
- filtrate becomes more concentrated as it descends
what happens in the ascending limb of the loop of henle
- impermeable to water; permeable to sodium ions
lower part→ sodium ions diffuse into medulla via facilitated diffusion upper part → sodium ions actively transported into medulla - lowers the filtrate water potential → increases ion concentration in medulla → maintains water potential gradient across medulla
why is it called the counter current multiplier mechanism
fluid flows in opposite directions in the two limbs of the loop → the deeper the medulla, the more concentrated the Na+ become in interstitial fluid, the lower the water potential
what happens in the distal convoluted tubule and collecting duct
- water moves out of the filtrate in the DCT and collecting duct via osmosis
- remaining filtrate → renal pelvis → ureter → bladder → excreted
what is ADH and what does it do
anti-diuretic hormone produced by the pituitary gland in the hypothalamus → regulates water concentration in blood and urine
what happens when blood water potential too low ie when dehydrated
osmo-receptors in hypothalamus detect drop (osmosis out causes them to shrink)
stimulates posterior pituitary gland to release more ADH
ADH makes walls of distal convoluted tubule and collecting duct more permeable → inserts aquaporins (water channels)
more water reabsorbed into the blood by osmosis, increasing water potential
urine more concentrated (small volume, higher concentration)
what happens when blood water potential too high ie after drinking a lot
osmoreceptors in hypothalamus detect increase (osmosis causes them to swell)
reduces the release of ADH from the posterior pituitary gland
walls of the distal convoluted tubule and collecting duct less permeable → aquaporins removed
less water reabsorbed into blood by osmosis → more lost in urine
urine more dilute (larger volume, lower concentration)
what is homeostasis
maintenance of a constant internal environment
what is negative feedback
reverse change in the body
change is detected by receptors → reversal brought about to effectors
enable conditions to fluctuate within reasonable limits
what hormone reduces blood sugar levels
insulin
how does insulin reduce blood sugar levels once bound to receptors on liver and muscle cells
increases membrane permeability to glucose
stimulates glycogenesis
increases rate of respiration
what is glycogenesis
conversion of glucose to glycogen
what hormone increases blood sugar levels
glucagon
how does glucagon increase blood sugar levels once bound to receptors on liver cells
stimulates glycogenolysis
decreases rate of respiration
stimulates gluconeogenesis
what is glycogenolysis
conversion of glycogen to glucose
what is gluconeogenesis
conversion of fatty acids and amino acids to glucose
what is adrenaline
hormone secreted from adrenal glands in response to stress / low blood glucose levels
