renal Flashcards
intracellular fluid
all fluid in cells, 2/3 total body fluid, has water, ions, proteins and enzymes
extracellular fluid
interstitial fluid (holds cells in place), plasma and trans-cellular fluids
difference between interstitial fluid and plasma
plasma has more proteins than interstitial fluid
forces that move water
hydrostatic pressure and colloid osmotic pressure
hydrostatic pressure
force from a fluid against a wall, causes movement of fluid between different compartments
colloid osmotic pressure
relies on selectively permeable membranes, small ions moving
osmolality
conc of substance in 1L solvent (water) measured in mosmoles / Kg
renal cortex
outermost ring of the kidney, start of the urine making
renal medulla
inner region of kidney, loops of nephrons drop down into it
how many nephrons in a kidney on average
1.5million
the juxtoglomerular apparatus
afferent arteriole brings blood to glomerulus, HP forces fluid through bowmans capsule
what do macula densa cells dp
sense DCT flow and release factors that affect afferent arteriole diameter
main components of Juxtaglomerular apparatus
- macula densa cells
- granular cells
- mesangial cells
granular cells
respond to macula densa cells and then signal to vasoconstrict/dilate
what is the glomerular filtration rate dependent on
- capillary permeability
- HP in capillaries
- HP in tubules
- osmotic pressure of plasma and tubular filtrate
BP in a capillary compared to bowmans capsule
bowmans capsule is lower
GFR equation
GFR = Kf (Pcap - Pbc - Pi cap)
what happens to GFR if there is afferent vasoconstriction
GFR decreases
what happens in the PCT
reabsorption of glucose, bicarbonate and Na+, Na+ sets up gradient so water is reabsorbed. Secretion of H+ ions so there can be bicarbonate reabsorption
what happens in loop of henle
water reabsorption by osmosis in descending limb, ascending limb impermeable to water, reabsorption of salts
what happens in DCT
Na+ actively reabsorbed
what is the countercurrent multiplier
by reabsorbing NaCl in ascending limbs the filtrate becomes more concentrated which therefore drives the water to be reabsorbed.
where is most of the Na+ reabsorbed
PCT (60-70%)
hormonal control of the kidney - Renin-angiotensin-aldoserone system (RAAS)
regulates fluid balance, stage 1: release renin (enzyme) from granular cells, stage 2: release of ACE, stage 3: angiotensin 2 exerts actions on body
what is renin released in response to
decrease in perfusion pressure, increase in SNS drive, decrease in Na+ conc at DCT
what does angiotensin converting enzyme (ACE) do
converts angiotensin 1 to 2 by cleaving
what does renin do
convert angiontensinogen into angiotensin 1
what does angiotensin 2 effect
adrenal gland, kidneys and vasculature
what do renal baroreceptors do?
decrease renal perfusion, increasing renin release
what do catecholamines do
beta-adrenoreceptor stimulation leads to renin release
what is aldosterone
steroid hormone from zona glomerulosa
what are the consequences of aldosterone
Na+ retention, K+ loss, H+ loss
hormonal control of the kidney - ADH
synthesised in hypothalamus, 2 main receptors are osmoreceptors and baroreceptors
what does ADH do
makes urine more concentrated, pulls water back into the body. It causes vasoconstriction which increases arterial pressure
where does ADH act and how
late part of DCT and in collecting duct, increases aquaporins
hormonal control of the kidney - ANP
opposite of RAAS, inhibits renin, causes Na+ and water loss and increases GFR. Acts to reduce plasma volume
what diuretics work mainly work in PCT
osmotic diuretics and carbonic anhydrase inhibitors
what do diuretics do
trap ions etc to increase urine volume (diuresis)
osmotic diuretics
alter osmolarity of plasma, suck water into tubule. issue is it doesn’t block sodium reabsorption so water can be reabsorbed in DCT
Mannitol
osmotic diuretic for when there is a build up of volume in brain or eye
carbonic anhydrase inhibitors
in PCT, carbonic anhydrase is inhibited. stops the absorption of bicarbonate back into the body by blocking the conversion of carbonic acid into water and CO2. water and Na+ trapped in tubular fluid
why are carbonic anhydrase inhibitors not great
the Na+ they trap in the PCT causes an increased delivery to the macula densa cells so there is a reduced GFR
what are carbonic anhydrase inhibitors used for
glaucoma - ocular swelling, heart failure and altitude sickness
Acetazolamide
carbonic anhydrase inhibitor, inhibits reabsorption of bicarbonate, is a weak diuretic and is associated with metabolic acidosis
what are loop diuretics
act on ascending limb to block Na+/ K+ and 2Cl- symporter. 1/4 of the Na+ is trapped in tubules and therefore water follows.
what do loop diuretics treat
pulmonary oedema
Furosemide
loop diuretic used to treat chronic heart failure and renal failure
What are thiazides
DCT diuretics, rely on good GFR, block Na+ and Cl- reabsorption at DCT
Bendroflumethiazide
moderately powerful diuretic, traps Na+ in tubular fluid, effective as a hypotension treatment and for heart failure
Potassium sparing diuretics
dont act on Na+ pump, block Na+ channels and less H+ and K+ are exchanged and therefore less K+ and H+ lost compared to other diuretics
spironolactone
potassium sparing diuretics, blocks effects of aldosterone
