Physiology of Micturition and Renal Assessment Flashcards
When is ability to measure GFR particularly useful?
In patients with renal disease
When monitoring drug dosages
How are plasma clearance tests used to assess renal function?
They measure the ability of the kidney to clear the plasma of various substances
What substance is used to measure GFR through plasma clearance tests?
Inulin but now more commonly 51Cr-EDTA
Why is inulin a good choice for plasma clearance tests?
It is not metabolised by the kidney and it does not interfere with normal renal function
Why is GFR not usually measured now and what is done instead?
Too complex and expensive
Estimating a GFR through creatinine clearance
What factors can affect serum creatinine?
Muscle mass
Dietary intake
Drugs
What is the normal range of GFR?
90-120mls/min/1.73m^2
What is used to measure real plasma flow?
Para-amino-hippuric acid (PAH)
What is the bladder made out of?
Spiral, longitudinal and circular bundles of smooth muscle known as detrusor muscle
Which urethral sphincter is a true sphincter and which is not?
The external urethral sphincter is a true sphincter but the internal is not, but is where the smooth muscle at the start of the urethra acts as a sphincter when the smooth muscle is relaxed
What causes the sudden, sharp rise seen on the pressure-volume curve of the bladder?
The triggering of the micturition reflex
Describe the motor innervation of micturition
Rich parasympathetic supply from pelvic nerves
Sparse sympathetic supply from hypogastric nerves
Somatic motoneurones (pudendal nerves) innervate external urethral sphincter
Describe the sensory innervation of micturition
Stretch receptor afferents from the bladder wall causes sensation of fullness
Describe the pathway of the local spinal reflex involved in micturition
As the bladder fills, it becomes distended and stretch receptors are increasingly stimulated until their output becomes great enough to cause bladder contraction via stimulation of parasympathetic and relaxes the external sphincter by inhibiting somatic motoneurones
What are the three types of abnormalities of nicturition due to neural lesions?
Interruption of afferent nerves
Interruption of both afferent and efferent nerves
Interruption of facilitatory and inhibitory descending pathways from the brain
