water and electrolytes Flashcards
(16 cards)
how is water gained and lost?
gains water ingested formed in metabolism losses excretion evaporation eg sweat
which water balance factor is under homeostatic control?
urinary excretion
what is the function of a glomerulus?
filtration of plasma
GFR:120ml/min
renal blood flow
what is the function of a proximal convoluted tubule?
reabsorption of 60-70% of glomerular filtrate
ions + small molecules reabsorbed
what is the function of a loop of henle?
concentrates urine
conc. depends on active transport pumps in ascending limb
length of loop correlates with ability to concentrate urine
some reabsorption (10%)
what is the function of a distal convoluted tubule?
reabsorption of water, Na+, Cl-,Ca2+, secretion of H+, K+ activity controlled by hormones: aldosterone atrial natriuretic hormone ADH PTH
what is the function of collecting ducts?
water reabsorption under the influence of ADH-membrane channels
water moves along osmotic gradients created by counter current exchange mechanism
how are water and electrolytes regulated?
ADH
renin-angiotensin-aldosterone
atrial natriuretic hormone
describe water regulation by ADH
produced in hypothalamus, released from posterior pituitary
acts on distal convoluted tubules and collecting ducts to increase water permeability by insertion of aquaporin channels
water moves passively
how is ADH secretion increased?
low ECF vol.
high ECF osmolarity
how are electrolytes controlled?
ions present in ICF + ECF
homeostatic control
Na+, K+, H+, Ca2+
kidneys determine how much is secreted
how is sodium controlled?
renin-angiotensin-aldosterone system
promotes Na+ reabsorption in DCT, K+, H+ exchange
potent vasoconstrictor
atrial natriuretic hormone
increases excretion of Na+
opposite effect
how is potassium controlled?
cell membrane potentials depend on ECF
small changes in K+ can have big effects on nerve/muscle function
K+ regulated by aldosterone
Na+ swapped for K+ or H+
what is hypo-secretion?
ADH undersecretion
diabetes insipidus
large vol. urine
what is hypersecretion?
ADH oversecretion
excess ADH-> water retention
what are the effects of K+ on nerve function?
increasing ECF->depolarisation
depolarisation causes axons to fire AP
MP does not return to resting levels
axon remains in extended refractory period
K salts used in toothpastes to desensitise hypersensitive dentine
