Renal 4 Flashcards
what is clearance
rate at which a solute disappears from the body by excretion or metabolism
clearance of x(ml/min)=
excretion rate of x (mg/min)/ (x) plasma (mg/ml)
clearance is expressed as what
the volume of plasma passing through the kidneys that has been totally cleared of solute in a given period of time (usually min)
- blood cleared of solute
1mg of solute Z in 100ml of plasma, found 0.5mg of Z appearning in urine/min
clearance of z= 0.5mg/min / 1mg/ml
= 50ml/min
- kidneys removes all solute Z in 50ml of plasma in one minute
how do we most accurately calculate GFR
look at clearance of substance that is freely filtered and neither reabsorbed or secreted
what is perfect molecule to measure clearance
inulin
- method is impractical
what is inulin
polysaccharide found in isolated nephrons to be completely filtered and not reabsorbed
what do clinicians commonly use to measure GFR and renal function
creatinine clearance
Why is creatinine not the most accurate
freely filtered but is also secreted in very small amounts
- slightly overestimates GFR
person has plasma creatinine conc. of 0.01mg/ml and an excretion rate of 1.25mg/min
1.25mg/min / 0.01 mg/ml = 125 ml/min
once we know an individuals GFR what can we look at
how their kidneys handle any filtered solute by measuring the solutes plasma conc. and excretion rate (collecting urine and blood)
filtered load of X=
[x]plasma x GFR
how can we tell how the nephron handled the substance
comparing the filtered load with its excretion rate
if less substance appears in the urine then filtered,
net reabsorption has occured
if more appears in the urine than was filtered,
net secretion has occured
what else can we compare GFR to
clearance of a solute
what is renal clearance
non-invasive method using collected urine and blood
what is purpose of renal clearance
- calculate GFR - if substance is filtered, not reabsorbed nor secreted (filtered=excreted)
- understand the net renal handling of any filtered solute
if clearance of a substance is less than GFR
Net reabsorption
if clearance of a substance is greater than GFR,
net secretion has occurred
what does comparison of clearance values only give you
net handling of a solute
- net reabsorption or net secretion
GFR=clearance
Filtered=excreted
filtered, not reabsorbed, not secreted
GFR>clearance
filtered>excreted
e.g., urea and glucose
filtered and net reabsorption
GFR<Clearance
filtered<excreted
e.g., penicillin
filtered and net secretion
what does filling of the bladder activate
stretch receptors initiating micturition reflex
what is the pathway from kidney to external environment
collecting duct - renal pelvis - ureters - urinary bladder - urethra
what do ureters undergo
rhythmic contractions (pacemaker cells)
what is bladder made up of
smooth muscle
detrusor muscle
what sphincter is at bottom of bladder
internal sphincter (smooth muscle)
passive
what is external sphincter made of
skeletal muscle, stays contracted, tonic motor output
when will you be consciously aware you must urinate
200ml
as filling exceeds 200ml what happens
walls will distend and stretch receptors will fire
sensory input by stretch receptors activate what
parasympathetic neurons fire
what do parasympathetic neurons activate
detrusor muscle contracts and internal sphincter is passively pulled open, external relaxes
what happens if not right time to urinate
descending outputs inhibit reflex and inhibit parasympathetic
once exceeding 500ml what happens
internal sphincter forced open, leading to reflexive opening of external sphincter and loss of voluntary opposition
what is left in bladder after micturition
10ml
where does sensory info of micturition reflex feed back to
sacral region of spinal cord and brainstem and cerebral cortex
incontinence
inability to control urination voluntarily
causes of incontinence
- infants- corticospinal connections not yet been established
- damage to internal or external sphincter
- spinal cord damage
- aging (loss of muscle tone, stroke, alzeihmers, prostate growth)
what are 4 parameters the homeostatic mechanisms for fluid/electrolyte balance focus on
- fluid volume
- osmolarity
- concentrations of individual ions
- pH
