Physiology of the Renal System VI: Bladder Physiology Flashcards
Where does urine flow into from the bladder?
Funnel shaped dilation of the upper ureter called the renal pelvis
How does urine propagate down the ureter?
Peristaltic waves initiated in the renal pelvis from atypical smooth muscle cells
What commonly causes obstruction to flow of urine in the ureter?
Kidney stones
What are kidney stones?
Crystals forming due to precipitation of barely soluble substances
How can kidney stones be treated?
Percutaneous nephrostomy
Extracorporeal shock wave lithotripsy
How much can the bladder vary in size?
From empty (<100ml) to maximum volumes between 500-1000ml
What do the walls of the urinary tract consist of?
Urothelium
Lamina propria
Detrusor smooth muscle
Serosa
What are the specialised cells of the urothelium?
Umbrella cells,
involved in signalling from the urothelium to the underlying lamina propria and detrusor cells.
What are the purpose of tight junctions in the urothelium?
High resistance tight junction between cells to prevent urine from entering the interstitial space of the bladder.
What are the components of the lamina propria?
Contains blood vessels
lymphatics
nerves
interstitial cells in a connective tissue mesh
What are the purpose of the sensory nerves in the lamina propria?
Detects chemical and mechanical stimuli including the filling state of the bladder.
What is the detrusor of the bladder?
Smooth muscle cells running in bundles arranged in an irregular basket weave pattern.
How are the muscle bundles of the detrusor muscles innervated?
By autonomic nerves
Parasympathetic nerves represent dominant innervation and main Nt is ACh acting of M3 muscarinic receptors
Sympathetic nerves release NAd onto beta3 adrenoreceptors to cause relaxation
What is continence?
Low pressure reservoir for storage of waste produces
Continually active sphincter to prevent linkage
What is voiding?
Relaxation of sphincters
Increase pressure of the reservoir
For continence and voiding to occur what is required?
Sensory mechanisms to inform about filling
Higher control centres for voluntary voiding
Reflex pathways to generate voiding
The right muscles to do it
What is the pelvic floor?
series of muscle layers that support of the organs and in maintaining continence.
How is continence controlled?
Somatic system active:
Keeps striated sphincter contracted
Sympathetic system active:
Constricts smooth muscle
Parasympathetic system inactive:
Keeps storage element relaxed
How is voiding controlled?
Somatic system and sympathetic system switched off
Parasympathetic system activated:
storage element walls contract
What are the components of the storage (continence) reflex?
Mild stretch on sensory nerve fibres of the pelvic nerve.
Signalled to the sacral spinal cord to activate skeletal muscle to keep external urethral sphincter closed
Also signalled to lumber section of spinal cord so the sympathetic nerves (hypogastric nerve) stimulate relaxation of the bladder.
Pontine Micturition centre (in the brain) sends tonic signals down to the external urethral sphincter to keep it closed.
What are the components of the voiding reflex?
Sensory nerves signal to the pontine micturition centre to cause micturition.
Sends signals down the spinal cord to the sacral cord to relax the sphincter but stimulate the parasympathetic nerves so cause the bladder to contract.
What happens to pressures to cause the urine to flow?
Urethral pressure falls and the intravesical pressure rises which leads to and increase in urine flow
What is the most common problem with the urinary tract?
Urinary tract infection
What is a UTI?
Chemical stimuli increase bladder activity and hence urge to void.
What other issues are there with the urinary tract?
Spinal cord injury MS Strokes Pelvic floor injury Detrusor overactivity Atonic bladder (no stimulation of bladder contraction)
How can overactive bladders be treated?
Antimuscarinic drugs
beta3 agonist
What is prostatomegaly?
enlargement of the prostate
