Physiology Flashcards
what is osmolarity
concentration of osmotically active particles present in a solution
what are the units of osmolarity
osmol/l or mosmol/L (for body fluids as weaker)
how can you calculate osmolarity
the molar concentration of the solution x
the number of osmotically active particles present
e.g. 150mM NaCL = 2 x 150m = 300 mosmol/l
what is the units for osmolality
osmol/kg
what is tonicity
the effect ta solution has on cell volume
what is a isotonic solution
a solution that causes no change in cell volume, there is no net movement of water
what is a hypotonic solution
solution that causes an increase in cell volume, water moves into cell by osmosis, more water initially outside of the cell
(more water)
what is a hypertonic solution
causes a decrease in cell volume, cell loses fluid as initially less water in external environment
(less water, concentrated salt solution)
what can happen if a cell expands with water too much
lysis
what is hydrostatic pressure
pressure created by fluid- high hydrostatic will push water into lower hydrostatic pressures
what osmolarity are isotonic solutions usually
300 mosmol/l
less than 300= hypotonic
more than 300= hypertonic
what other that osmolarity affects tonicity
the permeability of the membrane (ability of solute to cross the cell membrane)
e.g. 300 mM or urea will be hypotonic as RBC have transporters for this and leave more water outside the cell
300 mM of sucrose is isotonic as RBC membrane not permeable to this
what is the osmolairty of plasma and extracellular fluid
300 mosmol/l
do male or females have more body water
males
what are the 2 main compartments of total blody water
intracellular fluid (67%) extracellular fluid (33%)
what makes up extracellular fluid
plasma (20%) (liquid component of blood)
interstitial fluid (80%)
lymph (negligible) and transcellular fluid (negligible)
what makes up transcellular fluid
CFS and pleural fluid
how can you measure body fluid
tracers can show the distribution volume (allow it to equilibrate with body water then take sample and measure its concentration)
TBW- 3H2O
ECF- inulin
plasma- labelled albumin
(dose/ sample concentration= volume of distribution)
what are the fluid inputs
fluid intake
food intake
metabolism
what are the fluid outputs
insensible loss (not controllable) (skin diffusion, lung exhalation) sensible loss (controllable) (sweat, faeces, urine)
what is water imbalance mainfested as
changes in body fluid osmolarity
what is the normal rate of urine production
1ml/min
what does a change in plasma volume affect
arterial BP
what happens to lung water loss when its cold
increases
can you completely turn off urine production
no as some waste products can only be excreted in solution
what is the ionic composition of ECF
high Na+
high Cl-
high bicarbonate (HCO3-)
what is the ionic composition of ICF
high potassium
high Mg2+
negatively charged proteins
what fluids have similar ionic composition
plasma and intersitial fluid
what is the ionic composition of plasma
high Na+
high Cl+
what separates ECF and ICF
plasma membrane
are the osmotic concentrations of ECF and ICF the same/ different
identical- 300 mosmol/l
what is fluid shift
movement of water betweem the ICF and ECF in response to an osmotic gradient
what would happen if the osmotic concentration of the ECF increases
ECF would become hypertonic meaning water would be lost from the ICF
what would happen if the osmotic concentration of the ECF decreases
ECF is now hypotonic so water would go into the ICF
what happens to the volumes of ICF and ECF when there is a loss or gain of NaCl in the ECF
(Na excluded from)
ECF NaCl gain= ECF increased, ICF decreases (water leaves)
ECF NaCl loss= ECF decreased, ICF increased (ECF hypotonic)
what are the challenges to fluid homeostasis
gain or loss of water- changes fluid osmolarity
gain or loss of NaCl- ^same
gain or loss of isotonic fluid (e.g. saline= 0.9% NaCl)
no change in osmolarity but change in ECF volume ONLY
what alters composition and volume of the ECF
kidneys
why is regulation of ECF volume important
for long term regulation of blood pressure
what is electrolyte balance
when rate of gain= rate of loss
why is electrolyte imbalance important
concentrations can affect water balance (via changes in omsolarity)
concentrations can affect cell function
what creates 90% of the ECF’s osmotic concentration
sodium salts (as this is mainly present in the ECF is a major determinant of ECF volume)
what follows sodium
water
what affects sodium reabsorbtion in the kidneys
aldosterone
what is a key role of potassium
establishing membrane potential
is potassium intracellular or extracellular
intracellular
what can fluctuations in the concentration of plasma potassium cause
muscle weakness, paralysis, cardiac arrhythmias, cardiac arrest
where do you lose salt
sweat and faeces 0.5 g
urine 10 g
what is salt imbalance manifested as
changes in extracellular fluid volume
what are the functions of the kidneys
water and salt balance maintain plasma volume and osmolarity acid base balance excretion of metabolic waste and exogenous compounds secretion of renin and erythopoietin conversion of vit D into clcitriol
what is the active form of vit D and its role
calcitriol- calcium absorption in the GI tract
what controls the conversion of vit d to calcitriol
parathryoid hormone
when is erythropoietin release
when hypoxic- stimulates RBC production
what muscles line the ureters
smooth muscles- peristaltic action to push urine down to baldder- colicky pain
does the urine get modified when it enters the ureter
no- same as when leaves bladder
what is the ‘appearance’ of the inside of the kidney
cortex is granular
medulla is striated
what is the functional unit of the kidney
the nephron
what are the functions of the nephron
filtration reabsorption (move things back into the blood) secretion (move from blood into tubular fluid)
what makes up the wall of the nephrons
single layer of epithelial cells
describe the blood supply of a cortical nephron (80% of the nephrons)
renal artery- afferent artery- glomerulus- efferent arteriole- pertibular capillary (meshwork closely related to the tubular component of nephron)- venules- renal vein
what supplies the tubular nephron and secretes/ recieves reabsorbed particles
peritublar capillaries
where does the collect duct start and end
starts in cortex, goes through medulla connecting with proximal tubules, ends in renal pelvis
what is the fluid in the nephron called
tubular fluid (still being modified- when it enters collecting duct=urine)
what are the parts of the nephron
bowmans capsule- proximal tubule- descending then ascending limb of loop of henle- distal tubule- collecting duct
describe the blood supply of a juxtamedullary nephron
single capillary (vasa recta) which follows the route taken by the loop of henle
which type of nephron has a bigger loop of henle
juxtamedullary
what creates the striated appearance of the medulla
the loops of henle ad the collecting ducts (as arranged in a radial fashion)
does the afferent or efferent artery have a bigger diameter
afferent bigger- maintains pressure
what muscles line the afferent arterioles
smooth- contraction reduces the amount of blood that flows into the glomerulus
what makes up the glomerular membrane
capillary endothelium
basal lamina
podocytes
what are the roles of the juxtaglomerular aparatus
macula densa cells are salt sensitive- monitor salt in tubular fluid
granular cells produce and secrete renin
what is urine
modified filtrate of blood
what are the renal processes
glomerular filtration
tubular reabsorption and secretion
how much of plasma that enters the glomerulus is filtered
20%
what does rate of excretion=
rate of filtration + rate of secretion - rate of reabsorption
what does rate of filtration =
concentration of X in plasma x GFR
what is a healthy GFR
125 ml/min
what does rate of excretion =
concentration of x in urine x volume of urine produced
what does rate of reabsorption =
rate of of filtration of X - rate of excretion of X
what does rate of secretion =
rate of excretion of X - rate of filtration of X
what must have happened if rate of filtration > rate of excretion
net reabsorbtion
what are the filtration barriers
Glomerular Capillary Endothelium (barrier to RBC) Basement Membrane (basal lamina) (plasma protein barrier) Slit processes of podocytes (plasma protein barrier) (Glomerular epithelium)
what makes up the basement membrane
collagen and glycoprotein
why cant plasma proteins cross the basement membrane
as plasma proteins are negatively and so too is the basement membrane
should RBC get through into the lumen on bowens capsule
no- if RBCs in urine then something is wrong
what forces make up the net filtration pressure
glomerular capillary blood pressure (largest: 55mmHg)
bowmans capsule oncotic pressure (0 as no plasma proteins in bowens)
bowmans capsule hydrostatic pressure (fluid within capsule- opposes net filtration)
capillary oncotic pressure (plasma proteins within lumen pull water back into capillaries opposing net filtration)
is filtration active or passive
passive- driven by net filtration pressure
how can glomerulae capillary pressure remain constant across the capillary
as efferent diameter smaller than afferent
what is the usual net filtration pressure
10mm Hg
what are starling forces
the balance of hydrostatic pressure and osmotic (oncotic) pressures
what is GFR
rate a which protein free plasma is filtered from the glomeruli into bowmans per unit time
= Kf (filtration coefficient- how permeable the glomerular membrane is) x net filtration pressure
what is the major determinant of GFR
glomerular capillary fluid pressure
what is the extrinsic control of GFR
sympathetic control via baroreceptor reflex
what is the intrinsic control of GFR
autoregulation:
myogenic
tubuloglomerular feedback mechanism
how does arterial blood flow affect GFR
if increases causes increased net filtration pressure, increasing GFR (opposite applies)
vasoconstriction of smooth muscles of afferent arterioles decreases blood supply to glomerulus, decreasing GFR
vasodilation of afferent ateriole increases blood flow, increasing GFR
how is GFR controlled by changes in arterial blood pressure
e.g fall in blood volume decreased ABP detected by aortic and carotid sinus baroreceptors increased sympathetic activity arteriolar vasoconstriction decreased glomerular blood flow decreased GFR decreased urine volume helps compensate for lack of blood
what allows the GFR to remain fairly constant despite MABG
autoregulation- intrinsic control
myogenic and tubuloglomerular feedback
what is myogenic intrinsic control
if vascular smooth muscle is stretched (increased ABP) then it contracts constricting the arteriole
aims to maintain constant blood flow to the kidneys
what is tubuloglomerular feedback
involves the juxtaglomerular apparatus (macula densa cells- release vasoactive substances)
if GFR rises more NaCl flows through the tubule leading to the constriction of afferent arterioles
this decreases blood flow and decreases GFR
what senses the NaCl content of the tubular fluid
macula densa cells in the juxtaglomerular apparatus
what cause cause increased bowmans capsule fluid pressure
e.g. kidney stone, blockage in drainage
what cause cause increased capillary oncotic pressure
diarrhoea (losing water but not plasma proteins)
what cause cause decreased capillary oncotic pressure
severe burns (losing plasma proteins but not water)
what can decrease the filtration coefficient
a decrease in the surface area available for filtration
what is plasma clearance
a measure of how efficiently the kidneys can clean the blood of a substance
= the volume of plasma completely cleared of a substance per minute (each substance has specific plasma clearance value)
how do you calculate clearance of a subance
rate of excretion of X / plasma concentration of X
= [X]urine x Vurine / [X] plasma
what substance does plasma clearance = GFR
inulin (rate of excretion matches rate of filtration)
is inulin secreted or reabsorbed
no
what can be used instead of inulin
creatinine
what is the down side to creatinine
undergoes small amount of tubular secretion
name a substance that is completely reabsorbed and not secreted
glucose
clearance= 0
name a substance where clearance less than GFR
urea- as is partly reabsorbed and not secreted
name a substance where clearance is more than GFR
H+ as is secreted but not reabsorbed
what has happened when clearance
substance is reabsorbed
what has happened when clearance = GFR
substance is neither reabsorbed or secreted
what has happened when clearance > GFR
substance is secreted into tubule
what can be used to calculate renal plasma flow
para-amino hippuric acid (is freely filtered at glomerulus and secreted into tubule- is not reabsorbed (completely cleared from plasma)
what is a normal renal plasma flow
650 ml/min
what should a GFR marker be
freely filtered
not secreted or reabsorbed
what should a RPF marker be
filtered and completely secreted
what is filtration fraction
the fraction of plasma flowing through the glomeruli that is filtered into the tubules
GFR/ renal plasma flow
