Micturition + assessing renal function Flashcards
What happens to plasma conc. of a drug if GFR falls
increases which can –> toxicity
Plasma clearance tests determine what
ability of the kidney to clear the plasma of various substances (note: relates to clearance of a volume of plasma, NOT clearance of a specific substance in plasma) i.e. renal function
Gold standard measurement of GFR (i.e. excretory renal function) is (although this actually isn’t used much despite being gold standard)
Inulin clearance
Inulin is not reabsorbed or secreted in the nephron once filtered into it so would a substance that IS reabsorbed have a higher or lower clearance than insulin
lower as urine concentration of this substance would be less since plasma concentration of it rises as it’s being reabsorbed
Despite being gold standard, inulin clearance as a measurement of GFR/renal function is too complex so clearance of what is more routinely measured to ESTIMATE GFR
creatinine (breakdown product of muscle) clearance
Why is creatinine clearance only an estimate go GFR
because creatine clearance actually exceeds GFR as peritubular capillaries secrete small amounts of creatinine
Factors affecting serum creatinine levels (3)
Muscle mass
Dietary intake
Medication
With a higher muscle mass, serum creatinine will be lower or higher
higher
A common mistake made when assessing renal function by just looking at serum creatinine to is the failure to account for
muscle mass
-as the same serum creatinine level may indicate renal dysfunction in an old lady but actually be normal for a young muscular person
Normal GFR per min
> 90
Is clearance of urea more or less than inulin + why
less because some urea is reabsorbed, inulin is not
PAH (para-amino hippuric) acid clearance, an anion (-vely charged), is a measurement of what
renal plasma flow, i.e. the amount of plasma flowing through the kidneys at any given time
Urine flows from kidneys to ureters via what action of the ureters
peristalsis
Name the smooth muscle of the bladder
detrusor
Internal urethral sphincter is not a
true sphincter - just refers to smooth muscle at the start of the urethra which acts as a sphincter when it relaxes
External urethral sphincter composed of what muscle type + under what control
skeletal muscle
somatic voluntary
Bladder line day what epithelium
transitional
What is the trigone of the bladder
triangular area of the floor of the bladder formed by the 3 openings - two ureteric orifices coming from kidney and the internal urethral orifice
Describe the shape of the volume-pressure curve of the bladder
Intravesical pressure rises slightly when there’s a first urge to void
Then there’s a long flat line of the curve as urine volume increases
When 350ml urine reached, sudden sharp rise of the curve as detrusor contraction stimulated causing big increase in intravesical pressure –> initiating micturition
Bladder volume for initiation of micturition reflex in adults is about
350mls
What nerve innervates the external urethral sphincter and allows voluntary control to keep it closed
Motor fibres of the pudenal nerve (S2-S4 origin)
List the 3 motor innervations of the bladder that control micturition
Parasympathetic - pelvic nerve (S2-S4) - contracts detrusor muscle to stimulate micturition
Sympathetic - hypogastric nerve (T12-L1) - relaxes detrusor muscle, closes internal sphincter - to retain urine
Somatic motor - pudenal nerve (S2-S4) - innervates the external sphincter to allow voluntary control
Micturition is a … reflex
spinal reflex
Micturition is stimulated in response to
stretch of bladder