Physiology Flashcards
osmolarity is… and how do you calculate it?
no of osmotically active particles in solution
no of particles x molar concentration
osmolarity of body is
300mmol/l
tonicity is…
effect solution has on cell- hypo (inc cell size), hyper (dec cell size), isotonic (normal)
what are the 2 components that make up total body water
ECF- interstitial fluid (80%), plasma, lymph
ICF
what are some tracers used to measure vol distribution and how to measure?
TBW- 3H2O, ECF- inulin, plasma- labelled albumin
unknown V= dose/ sample [ ]
T/F: ICF has more Na+
F: ECF- more Na+, Cl- and HCO3-. ICF- more K+
what is electrolyte balance important?
- total electrolyte [ ] can directly affect water balance
- [ ] of individual electrolytes can affect cell function
(e.g. small changes in K+ may result in cardiac arrest, small changes in Na+ may results in inc BP)
name some functions of the kidneys
water balance, salt balance, plasma vol & osmolarity maintenance, acid-base balance, metabolic waste excretion, renin & erythropoietin secretion, vitD to calcitriol conversion
name the functional unit of the kidney, what it does, and its blood supply
the nephron- filters, reabsorbs and secretes (from capillaries > tubules and vice versa).
BS: artery > afferent artery > glomerulus > efferent arteriole > peritubular capillaries > vein
T/F: not all of the nephron is found in the medulla
T: only loop of henle and collecting duct found in medulla
what is the difference between juxtamedullary and cortical nephrons
juxtamedullary has much longer loop of hele
what is the juxtamedullary apparatus
region where efferent and afferent arterioles bifurcate. contains the granular cells (secrete renin) and the macula densa which detects salt levels in tubule fluid- main regulators of downstream blood flow through capillaries
what are the methods of filtering blood
glomerular filtration (occurs in glomeruli in bowman’s capsule), tubular reabsorption and tubular secretion
know how to calculate rate of filtration and rate of excretion, as well as rate of reabsorption and rate of secretion.
what is an important golden rule when it comes to net reabsorption and net sceretion
if rate of filtration > rate of excretion= net reabsorption has taken place
if rate of excretion> rate of filtration= net secretion has occurred
how much plasma is filtered in glomerulus
20%
what are the 3 barriers proposed by glomerular membrane that block filtration
glomerular capillary endothelium, basement membrane, slit processes of podocytes
there are 4 forces that allow for net filtration pressure (driving force of plasma across glomerular membrane)- 2 oppose and 2 drive, these are?
favouring: glomerular capillary BP, bowman’s capsule oncotic pressure
oppsoing: bowman’s capsule hydrostatic pressure, capillary oncotic pressure
how to calculate net filtration pressure
net filtration= add up forces favouring filtration - forces opposing filtration
GFR is… and how to calculate
rate at which protein-free plasma is filtered from glomeruli into BC per unit time
GFR = Kf x net filtration pressure
normal GFR= 125ml/min
2 regulators of blood flow and GFR
extrinsic: sympathetic control via baroreceptor reflex- constriction of afferent arteriole
intrinsic:
- myogenic mechanism: if vascular SM is stretched it contracts thus constricting arteriole
- tubuloglomerular feedback system: ^ GFR= macula densa detects inc NaCl so releases vasoactive chemicals, SM contraction of afferent arteriole
what may have affects on GFR
anything affecting glomerular capillary BP, bowman’s capsule oncotinc pressure, bowman’s hydrostatic pressure, glomerular capillary oncotic pressure
e.g. diarrhoea inc oncotic pressure of glomerular capillary so dec GFR
what is key to markers
should be filtered but not secreted or reabsorbed
how to measure clearance of substance
clearance of X=( [X] in urine x Vurine ) / [X] plasma
ANS= ml/min
what are 2 main clearance markers (GFR markers)
inulin (exogenous so hard to administrate), creatinine (slightly secreted so close approx for GFR)
T/F: glucose is completely reabsorbed
T: clearance value of 0
urea filtration, secretion and reabsorption?
filtered, partly reabsorbed and not secreted. therefore clearance
what do we mean by secretion and reabsorption
secretion- from peritubular caplirries to renal tubule lumen
reabsorption- from renal tubule lumen to peritubular capillaries
what marker is used for renal plasma flow and its normal value
paro-amino hippuric acid (exogenous anion)
650ml/min
what is the equation for filtration fraction
FF= GFR/renal plasma flow (how much plasma entering glomeruli is being filtered- normal value 20%)
what does the glomerular filtrate not contain that the blood does
doesn’t have RBCs, large plasma proteins
the first fluid to reach proximal tubule is…
iso-isosmotic
2 pathways for Proximal tubule absorption
transcellular (through tubular lumen > epithelial cells)
paracellular (pass through tight/leaky junctions)
what are 3 carrier-mediated membrane transports
1y active transport
2y active transport (ion coupled)
facilitated diffusion
Na movement in PT?
Na moves via Na/K pump, Cl- follows transcellular as electrical gradient formed, and water follows down osmotic gradient
what is a transport maximum
maximum rate at which a pericellular substance can be reabsorbed. once reached excretion of substance inc
what is the main function of loop of henle
creates cortico-medullary concentration gradient allowing formation of hypertonic urine
the descending limb is permeable to ___ but not to ___
H2O, not to NaCl
the ascending limb is prone to ___ reabsorption but impermeable to ___
NaCl, H2O
how does Na reabsorption occur in ascending loop
triple co-transoporter
describe what happens in LH
fluid enters iso-isometricly into descending limb > H2O lost, no Na picked up > inc osmolarity (concentrated filtrate) > NaCl reabsorption in spending limb but no H2O lost so osmolarity dec again to 100mmol
if tubular osmolarity dec, what happens to interstitial fluid osmolarity
inc
what is the other substance that adds solute to IF
urea (2-solute hypothesis)
why is it important for urine to be dilute when it enters the collecting duct
allows kidneys to produce urine of different volumes and [ ] according to how much ADH present in blood, creates hypertonic solution (less H2O- allows for more H2O to be reabsorbed into body)
what is the counter current exchanger
vasa recta/ capillary blood equilibrates with IF. does this my inc osmolarity as dips into medulla (NaCl retention and H2O loss), and dec osmolarity as climbs back up into cortex (NaCl loss, H2O gain)
what happens in collecting duct
progressively inc osmolarity as it descends through medulla
what controls fluid and salt retention in distal tubule and collecting ducts
hormones- specifically ADH (water), aldosterone (Na), PTH (dec phosphate, inc Ca reabsorption)
what happens in distal tubule
early segment: inc NaCl reabsorption via Na-K-2Cl transport
late segment: Ca2+ reabsorption, H+ secretion
T/F: distal tubule has high permeability to H2O and urea
F: has low permeability to H2O and urea
what happens in collecting ducts
low ion permeability, H2O and urea permeability influenced by ADH
high ADH…
high ADH > high water permeability (inc reabsorption) > hypertonic urine (concentrated)
what is a measure of concentrated urine in the collecting ducts
1400mosmol/L
low ADH…
Low ADH > not permeable to H2O (less H2O reabsorption) > diluted urine (50mosmol/L)
ADH Hormone
secreted by posterior pituitary
signal of dehydration is trigger to release (osmorecpetors in brain), stretch receptors in left atrium
binds to T2 receptors on basolateral membrane of cells in DT and CD > cascade initiated recruiting AQP2s to apical membrane
aldosterone hormone
secreted by Cortex of adrenals
stimulus is inc K+ or dec Na+ or RAAS activation
effect is to inc Na+ reabsorption, inc K+ secretion
when is RAAS activtaed
if there is a dec in NaCl, ECF vol or Arterial BP
3 mechanisms by which 3 renin is stimulated
- reduced pressure in afferent arterioles
- macula densa detects less NaCl
- inc sympathetic activity as result of reduced BP (and granular cells directly innervated by sympathetic system)
Aldosterone inc Na reabsorption by…
inc no of Na/K pumps on basolateral membrane, and inc Na co-transport at apical membrane
3rd hormone involved in fluid and salt retention is…
atrial natriuretic peptide (ANP)- stimulated by stretch receptors in atrial muscles cell due to inc plasma vol. act to excrete Na+ and acts on CV to lower BP
micturition physiology…
- micturition reflex: bladder can accommodate 250-300ml. once this is reached stretch receptors stimulated in detrusor muscle- simultaneous contraction of muscle and relaxation of sphincter= micturition
- voluntary control: can actively tighten external sphincter
abnormal pH levels
<7.35-acidic
>7.45- alklaotic
what must = what for a chemical reaction to take place
pK (dissociation constant)=pH
how is H+ continually added to body
- carbonic acid formION
- inorganic acid produced during breakdown of nutrients
- organic acids resulting from metabolism
what is a buffer system
made up of 1 substance that adds H+ and one that removes H+
how do you rearrange pk=pH to solve for pH
pH= pK + log [A-]/ [HA]
carbonic acid is a…
buffer
kidneys control bicarbonate, they do this by…
variable reabsorption of HCO3-
kidneys add new HCO3-
both dependent on H+ secretion into tubule
how is HCO3- reabsorbed
cannot pass into cell so must bind to H+ > H2CO3 > dissociates to CO2 + H2O > crosses membrane via carbonic anhydrase > HCO3- reformed intracellular > leaves at BL membrane via Na co-transpoter
in what 2 forms is HCO3- replenished
titratable acid- H2PO4- and ammonium- NH4+
what 3 things must occur for a person to have norma acid-base balance
- plasma pH close to 7.4
- HCO3- close to 25mmol/l
- arterial pCO2 close to 40mmHg
compensation is…
restoring pH to 7.4 asap, correction is restoration of HCO3- and pCO2
respiratory acidosis…
retention of CO2 emphysema, restricted lungs ^H+, pH <7.35, pCO2 >45 compensation: renal- H+ secretion, HCO3- reabsorbed and inc production correction: resp rate back to normal (
respiratory alkalosis
loss of CO2 hyperventilation, altitude hypoxia dec H+, pH >7.45, pCO2 <35 compensation: renal- dec H+ secretion, HCO3- excreted and not produced correction: normal ventilation
metabolic acidosis
excess H+ for reasons other than pCO2, most common
acid ingestion, DKA, excessive base (HCO3-) loss
pH: <7.35, HCO3- low
compensation: resp- inc resp- inc CO2 blown off
correction: kidneys- H+ secretion, HCO3- reabsorption and production
metabolic alkalosis
loss of H+
HCl loss, alkali ingestion
pH >7.45, HCO3- inc
compensation: dec vent (inc PCO2 retention in lungs)
correction: renal- inc HCO3- excretion ( a lot so overflows into excretion), no new HCO3- production
