physiology Flashcards
which should be higher when comparing urine osmolality to serum osmolality?
urine should be higher
-> helpful if very similar or very different
define osmolarity
concentration of osmotically active particles present in a solution
mosmol/l
how can osmolarity be calculated?
molar concentration of a solution
number of osmotically active particles present
osmolarity if 150mM NaCl = 150 x 2 (Na+Cl) = 300mosmol/l (osmotically active particles)
osmolarity vs osmolality
osmolarity = conc of osmotically active particles present in a SOLUTION
osmolality = osmol per kg (osmolarity = per L)
tonicity
effect solution has on cell
hypotonic = swell, increases volume, cell lysis
hypertonic = shrinks cell, decreases volume (conc salt, less water)
effect on RBC when added to urea
swells + lysis - hypotonic
should be isotonic but RBC permeble to urea, due to osmosis water follows
total body water compartments
intracellular fluid compartment (67%)
extracellular fluid compartment (33%)
- plasma (20%)
- interstitial fluid (80%)
- lymph
how can total body water be measured?
tracers - obstain distrubution volume of a tracer
give example of tracers and what they measure
3H20 = TBW
insulin = ECF
labelled albumin = plasma
how can total body water be calculated using tracers?
TBW = ECF + ICF
–> ICF = TBW (3H20) - ECF (insulin)
how do you calculate GFR?
(urine concentration x urine volume) / plasma conc
osmolarity of tubular fluid when it leaves proximal tubule
iso-osmotic - around 300
where is most sodium reabsorbed? what is this driven by?
proximal tubules due to action of Na/K ATPase
–> cause fluid to flow from proximal tubules to peritubular capillaries
effect of dehydration on RAAS and ADH
increases activation of RAAS - zona glomerulosa releases aldosterone
ADH increases to increase reabsorption in collecting duct
factors that stimulate renin secretion
hypotension causing reduced renal perfusion hyponatraemia sympathetic nerve control catecholamines erect posture
drugs that reduce renin secretion
beta blockers
NSAIDs
effect of angiotensin II on filtration fraction
vasoconstriction of vascular smooth muscle –> raised bp, vasoconstriction of EFFerent arteriole of glomerulus
–> increase filtration fraction to preserve GFR
what is filtration fraction? how is it calculated?
fraction of plasma flowing through the glomeruli that is filtered into tubules
FF = GFR / renal plasma flow
–> = 125 / 650 = 0.19 = 20% –> 20% filtered, 80% goes to peritubular capillaries
angiotensin II actions
stimulates thirst - via hypothalamus
stimulates aldosterone + ADH release
increase proximal tubule Na/H activity
vasoconstriction -> rasied bp ->increased filtration fraction
In normal functioning kidneys, what detects changes in salt concentrations (such as sodium chloride) and adapts the glomerular filtration rate accordingly?
macula densa
- make contact with afferent arteriole
- act as chemoreceptors, detect NaCl conc
- in convoluted tubules + ascending loop of henle
