Physiology Flashcards
what is osmolarity
concentration of osmotically active particles in solution
calculation of osmolarity?
multiply molar concn by number of osmotically active particles present
are osmolarity and osmolality the same
if in weak salt solutions and body fluid compartments yes
what is the osmolarity of typical body fluid
~300mosmol/l
what is tonicity
is the effect a solution has on cell volume
what is an isotonic solution
no change in cell volume
what is a hypertonic solution
decrease in cell volume
what is a hypotonic solution
increase in cell volume
total body water in L for 70kg male
42L
intracellular fluid makes up __% of TBW
66%
ECF makes up __% of TBW
33%
what part of the body make up ECF
plasma
interstitial fluid
transcellular fluid
lymph
tracer for TBW
triated water
tracer for ECF
inulin
tracer for plasma
radiolabelled albumin
how do tracers measure volume of distribution
add known quantity of tracer to the body
measure equilibrium volume in the body
what are insensible water losses and what are they
losses of water in the body with no control
skin diffusion
lung
what are sensible water losses and what are they
sweat
faeces
urine
losses with physiological control
concentration of Na in ICF/ECF
10mM ICF
140mM ECF
concentration of K in ICF/ECF
140mM ICF
4.5mM ECF
concentration of bicarb in ICF/ECF
10mM ICF
28mM ECF
concentration of Cl in ICF/ECF
7mM ICF
115mM ECF
what electrolytes make up the majority in ECF
Na
Bicarb
Cl
what electrolytes make up the majority in skeletal muscle ICF
K
Mg
describe the fluid shift if there is an increase osmolarity of ECF
ECF becomes hypertonic and so there is fluid shift to ECF to increase ECF volume
cell volume decreases
describe the fluid shift id there is a decrease osmolarity of ECF
ECF becomes hypotonic and so there is fluid shift to ICF to increase cell volume and maintenance of ECF balance
True/false - gain or loss of isotonic fluid causes fluid shift
false - but kidneys do alter the composition and volume of ECF
what electrolytes are the main components of osmolarity of ECF/ICF
Na/K
Na is mostly intra/extracellular
extracellular
K is mostly intra/extracellular
intracellular - small ECF changes have devastating effects on skeletal muscle and cardiac contractility
functions of the kidney
water/salt balance maintains plasma volume and osmolarity acid-base balance excrete waste excrete exogenous compounds secrete renin secrete erythropoietin converts Vit D to active
3 functional mechanisms of the kidney
filtration
secretion
reabsorption
Components of the glomerulus
glomerulus bowmans capsule proximal convoluted tubule loop of henle distal convoluted tubule collecting duct juxtaglomerular apparatus
types of nephron and the key differences
juxtamedullar/cortical
JM have a longer loop of henle and have a vasa recta instead of peritubular capillary
produce more concentrated urine
what makes up the glomerular capillary
endothelial cells
basal lamina
podocytes
describe blood flow to the glomerus
enters by afferent arteriole and exits by efferent arteriole
where is the juxtaglomerular apparatus located anf what two sections does it encompass
distal tubule comes in between afferent/efferent arteriole
granular cells
macula densa
function of granular cells
secrete renin
sit between afferent/efferent arterioles and distal tubule
function of macula densa
detect salt between tubular fluid as it passes through the distal tubule
can signal through chemical messengers to influence afferent arteriole
what % of blood is filtered by the glomerulus
20%
calculation of rate of filtration
[X]plasma x GFR
calculastion of rate of excretion
[X]urine x Vu (volume urine produced)
calculating rate of reabsorption
rate of filtration-rate of excretion
calculating rate of secretion
rate of excretion-rate of filtration
if rate filtratrion>rate of excretion then reabsorption/secretion has taken place
reabsorption
if rate excretion>rate of filtration then reabsorption/secretion has taken place
secretion
true/false - the diameter of the efferent arteriole is greater than that of the afferent arteriole
false - the afferent arteriole is bigger to accomodate for GFR
what does the glomerular capillary endothelium function to do?
filters red blood cells to prevent entry to bowmans capsule
what does the basal lamina of the glomerular capillary do
acts as a barrier to plasma proteins
what do the slit processes of podocytes function to do within the glomerular capillary
barrier to plasma proteins
value of glomerular capillary blood pressure
55mmHg
value of bowmans capsule hydrostatic pressure
15mmHg
value of capillary oncotic pressure
30mmHg
value of bowmans capsule oncotic pressure
0mmHg
calculation of net filtration pressure
forces favouring filtration-forces opposing filtration
rough net filtration pressure of the glomerular capillary
10mmHg
calculation of GFR
Kf (filtration coefficient) x net filtration pressure
what is the rough normal GFR
125ml/min
true/false - the filtration coefficient is the main determinant of GFR
false - glomerular capillary blood pressure is - which increases net filtration rate
true/false - increase in blood pressure increases GFR
true - but up to a point as the kidneys are autoregulated
describe the control of GFR in decreased blood pressure
detected by aortic/carotid baroreceptors causing increased sympathetic output and SVR
this constricts afferent arterioles to reduce GFR and urine volume
what is the myogenic mechanism of GFR control
vascular smooth muscle stretch causes constriction of the afferent arteriole
what is the tubuloglmerular feedback mechanism and how does it act to control GFR
involves juxtaglomerular apparatus
increasing GFR increases Na flow to macula densa, causing release of vasoactive substances to vasoconstrict the affernt arteriole
describe the effects of a kidney stone on GFR
leads to back pressure onto bowmans capsule and opposes filtration, leading to reduced GFR
describe the effects of diarrhoea on GFR
loss of plasma fluid leads to plasma protein concentration, and increase in capillary oncotic pressure. this leads to reduced GFR
describe the effect of significant burns on GFR
loss of plasma proteins in the blood, reducing capillary oncotic pressure and subsequently increasing GFR
describe the effect of a change in Kf on GFR
increase in Kf increases GFR and decrease decreases it
this is a measure of the membranes permeability
what is plasma clearance
how effectively the kidneys clean the blood
calcuation for plasma clearance
[X]urine x [V]urine/[X]plasma
describe how inulin can be used to determine plasma clearance and its unique characteristic
it is a non toxic exogenous chemical and is fully filtered at glomerulus with no secretion/reabsorption
this means it can be used to determine GFR using clearance calulation
describe the clearance of creatinine and its uses over inulin
it is endogenous and so doesnt need constant infusion, less expensive to measure
it is not as effective as inulin as it doesn undergo minor secretion in the tubules, but can be used to measure GFR
what is the clearance value of glucose and explain why
clearance =0
it is filtered by the glomerulus but undergoes full reabsorption
what is the clearance of urea relative to GFR and explain why
clearance
what is the clearance of H+ ions relative to GFR and explain why
clearance>GFR
it undergoes full filtration and secretion into the tubules by the peritubular capillaries
if clearance >GFR then substance is _____
secreted
if clearance is
reabsorbed
what is the function of pan-amino-hippuric acid
used to measure renal plasma flow, it is not fully filtered by glomerulus but the rest is secreted, therefore determines renal plasma flow
healthy level of renal plasma flow?
650ml/min
what is filtration fraction, how is it calculated and what is it roughly equal to
fraction of plasma flowing through glomerulus that is filtered into the tubules
GFR/RPF
20%
calculation of renal blood flow and rough estimate
RPF x 1/1-HCT
1200ml/min
fluid reabsorbed in the proximal tubule is hypo/iso/hyper osmotic?
iso-osmotic
what is reabsorbed in the prox tubule
sugars amino acids Na PO4 Sulphate lactate
what is secreted into the prox tubule
neurotransmitters bile pigments H drugs toxins
how much salt and water is roughly absorbed in the pro tubule
2/3
how is Na reabsorbed in the prox tubule
Na/K ATPase at basolateral membrane
Na/glucose, Na/amino acid co-transport and Na/H countertransport
reabsorbed transcellular
this allows for passive H2O and Cl to follow
this passes into vasa recta by oncotic drag
what is oncotic drag in respect to the vasa recta
there isnt much fluid in the vasa recta, so it soaks it up from interstitial fluid
how is glucose reabsorbed
Na/K ATPase at basolateral membrane
Na/Glucose co-transporter, enters cell transcellular and exits basolateral membrane by facilitated diffusion into vasa recta
what is Tm
transport maximum
there is a threshold to secretion/reabsorption due to channel saturation
excess remains wither in blood or remains in urine as it cannot pass quick enough
describe what is reabsorbed/secreted in the ascending limb of the loop of henle
impermeable to water
urea secreted
NaCl exits by the triple co-transporter
describe what is reabsorbed/secreted in the descending limb of the loop of henle
cannot reabsorb salt but water exits
describe the action of the loop of henle in countercurrent multiplication and concentrating urine
solute is removed from ascending limb and water cannot follow
tubular fluid becomes diluted to raise interstitial osmolarity
water leaves descending limb by osmosis, concentrating fluid in descending limb and creating a cycle
besides the action of NaCl in countercurrent multiplication, what else contributes?
urea, reabsorbed from collecting duct and secreted back into ascending loop of henle
describe the action of the triple co-transporter
Na/K/Cl are pumped into cell from tubular fluid
potassium channels are present to pump potassium back out to the ascending limb
Na/K ATPase on basolateral membrane
water isnt reabsorbed
what drug blocks the triple co-transporter
loop diuretics
describe the action of the vasa recta as a countercurrent exchanger
capillary blood equilibrates with interstitial fluid on descent into the renal medulla
blood osmolarity raises and falls with the loop of henle respectively
this is to prevent blood flow washing away NaCl and water
as a result, there is no net gain of water/solute in the vasa recta
fluid in the distal tubule is hyper/hypo-osmotic
hypo
what is reabsorbed in the early distal tubule?
Na/Cl by triple co-transport
what is reabsorbed in the late distal tubule
calcium
potassium
sodium
what is secreted in the late distal tubule
potassium, when aldosterone present
H ions
what is central DI
failure to produce ADH
what is nephrogenic DI
failure to respond to ADH
describe the secretion of ADH from the posterior pituitary
made by nerve cells in supraoptic and paraventricular cells
transport down nerves to terminals where it is stored in granules
released into blood when AP down nerves leads to Ca release
describe the effect of ADH on urine concentration and the late distal tubule
binds to ATII receptor on basolateral membrane to increase cAMP and cause aquaporins to fuse with apical membrane
due to high interstitial osmolarity difference water flows along osmotic gradient into the interstitium
what inhibits ADH?
alcohol and upper GI stretch receptors
what stimulates ADH
nicotine
besides the effect of ADH on the distal tubule and collecting duct, what else does it do
stimulates thirst
describe the action of aldosterone on the nephron
stimulates Na reabsorption and K secretion
increase in plasma K promotes aldosterone OR indirectly through juxtaglomerular apparatus
increases action of Na/K ATPase at basolateral membrane and leads to futher Na reabsorption in Na channels
passive Cl diffusion
describe the RAA system
decrease in NaCl, ECF, BP activate renin to cleave angiotensinogen to AT I
converted to AT II by ACE inb lungs
stimulates aldosterone release to increase Na reabsorption, Cl and hence H2O
AT II releases ADH, increase thirst and promote afferent vasodilation
describe how congestive heart failure leads to fluid and salt retention
reduced CO leads to reduced BP and activates RAAS, but increases preload so worsens heart failure, this is a cycle
describe the release of renin
macula densa cells sense reduced NaCl so promote aldosterone release
ie reduced GFR stimulates renin
increased sympathetic activity can cause renin release due to low BP
describe the secretion of ANP and its action
promotes Na excretion and diuresis to reduce plasma volume
inhibits Na reabsorption and RAAS
less stimulation of SNS so less CO and BP
less tonic stimulation of afferent arteriole so increased GFR to increase Na and H2O filtration
what type of contractions push urine through the ureter
peristaltic
what overrides involuntary bladder emptying by external/internal urethral sphincters
tightening of external sphincter and pelvis diaphragm by voluntary control
