kidneys

hyperosmotic environment of renal medulla

creates a gradient that drives water reabsorption in collecting ducts; high concentration of solutes; concentrates urine & conserves water

rhabdomyolysis

condition where damaged muscle tissue releases its contents, including the protein myoglobin, into the bloodstream

if the solute concentration is high (water concentration is low) the thirst center is

stimulated & ADH is released from the pituitary gland

antidiuretic hormone (ADH) stimulates the insertion of

water channel proteins (aquaporins) into the cells of the collecting duct which increases the reabsorption of water and conserves water during dehydration

final concentrations of Na+ & K+ in the urine vary according to the needs of the body

fine tuning occurs in the late distal tubule and the cortical region of the collecting ducts, controlled by the actions of aldosterone

effects of aldosterone in the distal tubule and collecting duct

increased sodium retention, increased potassium secretion

as the filtrate enters the proximal tubule, the total solute concentration of the filtrate is essentially the same as

that of the plasma; filtrate is iso-osmotic relative to the plasma

proximal tubule: osmosis cannot occur unless the plasma concentration of the

peritubular capillaries is altered; active transport is required

approximately 65% of the salt and water in the original filtrate is

reabsorbed from the proximal tubule

proximal tubule: reabsorption in the early regions of the nephron

is independent of the individuals hydration state, is not subject to hormonal influences, and requires a very large expenditure of energy (ATP)

an additional 15% of ultrafiltrate is returned to the

vascular system by reabsorption from the loop of henle

the loop of Henle creates a hyperosmotic environment in the

interstitial space surrounding the collecting ducts

the loop of Henle forms a hairpin-like segment between the

proximal and distal tubules

loop of Henle: the events in the descending loop are dependent on

the actions of the ascending loop

loop of Henle: ascending loop

sodium is actively reabsorbed from the ascending loop; the ascending loop is relatively impermeable to water

loop of Henle: descending loop

sodium is not reabsorbed from the descending loop, descending loop is highly permeable to water; there is a net diffusion of water out of the descending loop into the interstitial space

collecting ducts

must transport fluid through the hyperosmotic environment of the medulla, can be a source of water to compensate for dehydration

glomerular filtration rate (GFR)

volume of filtrate produced per minute by both kidneys

average GFR

120-125 ml/min

urea

waste product, catabolism of proteins

renal absorption of water

99.0%

renal absorption of sodium

99.5%

renal absorption of glucose

100%

vasa recta: in order for the kidney to be effective

most of the salt that is extruded from ascending limbs must remain in the tissue fluid of the medulla, most of the water that leaves the descending limbs must be removed by the vasa recta

vasa recta: solutes diffuse into the descending capillary, but then diffuse back out of the ascending capillary

solutes are recirculated and trapped within the medulla, water is removed because of plasma proteins (primarily albumin), that exert osmostic pressure

diuretics are

medications that increase the volume of urine

diuretics lead to a decrease in blood volume which is useful for

hypertension because less blood volume leads to lower blood pressure

loop diuretics

inhibit sodium transport in the loop of Henle

when blood flow and pressure in the renal artery are reduced, cells of the juxtaglomerular apparatus

release the enzyme renin

renin converts angiotensinogen to angiotensin I then

angiotensin converting enzyme (ACE) convert angiotensin I to angiotensin II

angiotensin II produces a number of effects

potent vasoconstrictor, stimulates thirst, stimulates aldosterone secretion

angiotensin II: potent vasoconstrictor

increases blood pressure

angiotensin II: stimulates thirst

increases blood volume

angiotensin II: stimulates aldosterone secretion

increases salt and water retention

micturition is

another name for urination

micturition involves reflexive contraction of the detrusor muscle and reflexive relaxation of the

internal urethral sphincter; it also requires voluntary relaxation of the external urethral sphincter