physiology

Question 1

which should be higher when comparing urine osmolality to serum osmolality?

Answer 1

urine should be higher

-> helpful if very similar or very different

Question 2

define osmolarity

Answer 2

concentration of osmotically active particles present in a solution
mosmol/l

Question 3

how can osmolarity be calculated?

Answer 3

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)

Question 4

osmolarity vs osmolality

Answer 4

osmolarity = conc of osmotically active particles present in a SOLUTION

osmolality = osmol per kg (osmolarity = per L)

Question 5

tonicity

Answer 5

effect solution has on cell

hypotonic = swell, increases volume, cell lysis

hypertonic = shrinks cell, decreases volume (conc salt, less water)

Question 6

effect on RBC when added to urea

Answer 6

swells + lysis - hypotonic

should be isotonic but RBC permeble to urea, due to osmosis water follows

Question 7

total body water compartments

Answer 7

intracellular fluid compartment (67%)

extracellular fluid compartment (33%)

• plasma (20%)
• interstitial fluid (80%)
• lymph

Question 8

how can total body water be measured?

Answer 8

tracers - obstain distrubution volume of a tracer

Question 9

give example of tracers and what they measure

Answer 9

3H20 = TBW

insulin = ECF

labelled albumin = plasma

Question 10

how can total body water be calculated using tracers?

Answer 10

TBW = ECF + ICF

–> ICF = TBW (3H20) - ECF (insulin)

Question 11

how do you calculate GFR?

Answer 11

(urine concentration x urine volume) / plasma conc

Question 12

osmolarity of tubular fluid when it leaves proximal tubule

Answer 12

iso-osmotic - around 300

Question 13

where is most sodium reabsorbed? what is this driven by?

Answer 13

proximal tubules due to action of Na/K ATPase

–> cause fluid to flow from proximal tubules to peritubular capillaries

Question 14

effect of dehydration on RAAS and ADH

Answer 14

increases activation of RAAS - zona glomerulosa releases aldosterone

ADH increases to increase reabsorption in collecting duct

Question 15

factors that stimulate renin secretion

Answer 15

hypotension causing reduced renal perfusion
hyponatraemia
sympathetic nerve control
catecholamines
erect posture

Question 16

drugs that reduce renin secretion

Answer 16

beta blockers

NSAIDs

Question 17

effect of angiotensin II on filtration fraction

Answer 17

vasoconstriction of vascular smooth muscle –> raised bp, vasoconstriction of EFFerent arteriole of glomerulus

–> increase filtration fraction to preserve GFR

Question 18

what is filtration fraction? how is it calculated?

Answer 18

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

Question 19

angiotensin II actions

Answer 19

stimulates thirst - via hypothalamus
stimulates aldosterone + ADH release
increase proximal tubule Na/H activity
vasoconstriction -> rasied bp ->increased filtration fraction

Question 20

In normal functioning kidneys, what detects changes in salt concentrations (such as sodium chloride) and adapts the glomerular filtration rate accordingly?

Answer 20

macula densa

• make contact with afferent arteriole
• act as chemoreceptors, detect NaCl conc
• in convoluted tubules + ascending loop of henle