Physiology of the Renal System VI: Bladder Physiology

Question 1

Where does urine flow into from the bladder?

Answer 1

Funnel shaped dilation of the upper ureter called the renal pelvis

Question 2

How does urine propagate down the ureter?

Answer 2

Peristaltic waves initiated in the renal pelvis from atypical smooth muscle cells

Question 3

What commonly causes obstruction to flow of urine in the ureter?

Answer 3

Kidney stones

Question 4

What are kidney stones?

Answer 4

Crystals forming due to precipitation of barely soluble substances

Question 5

How can kidney stones be treated?

Answer 5

Percutaneous nephrostomy

Extracorporeal shock wave lithotripsy

Question 6

How much can the bladder vary in size?

Answer 6

From empty (<100ml) to maximum volumes between 500-1000ml

Question 7

What do the walls of the urinary tract consist of?

Answer 7

Urothelium
Lamina propria
Detrusor smooth muscle
Serosa

Question 8

What are the specialised cells of the urothelium?

Answer 8

Umbrella cells,

involved in signalling from the urothelium to the underlying lamina propria and detrusor cells.

Question 9

What are the purpose of tight junctions in the urothelium?

Answer 9

High resistance tight junction between cells to prevent urine from entering the interstitial space of the bladder.

Question 10

What are the components of the lamina propria?

Answer 10

Contains blood vessels
lymphatics
nerves
interstitial cells in a connective tissue mesh

Question 11

What are the purpose of the sensory nerves in the lamina propria?

Answer 11

Detects chemical and mechanical stimuli including the filling state of the bladder.

Question 12

What is the detrusor of the bladder?

Answer 12

Smooth muscle cells running in bundles arranged in an irregular basket weave pattern.

Question 13

How are the muscle bundles of the detrusor muscles innervated?

Answer 13

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

Question 14

What is continence?

Answer 14

Low pressure reservoir for storage of waste produces

Continually active sphincter to prevent linkage

Question 15

What is voiding?

Answer 15

Relaxation of sphincters

Increase pressure of the reservoir

Question 16

For continence and voiding to occur what is required?

Answer 16

Sensory mechanisms to inform about filling
Higher control centres for voluntary voiding
Reflex pathways to generate voiding
The right muscles to do it

Question 17

What is the pelvic floor?

Answer 17

series of muscle layers that support of the organs and in maintaining continence.

Question 18

How is continence controlled?

Answer 18

Somatic system active:
Keeps striated sphincter contracted

Sympathetic system active:
Constricts smooth muscle

Parasympathetic system inactive:
Keeps storage element relaxed

Question 19

How is voiding controlled?

Answer 19

Somatic system and sympathetic system switched off

Parasympathetic system activated:
storage element walls contract

Question 20

What are the components of the storage (continence) reflex?

Answer 20

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.

Question 21

What are the components of the voiding reflex?

Answer 21

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.

Question 22

What happens to pressures to cause the urine to flow?

Answer 22

Urethral pressure falls and the intravesical pressure rises which leads to and increase in urine flow

Question 23

What is the most common problem with the urinary tract?

Answer 23

Urinary tract infection

Question 24

What is a UTI?

Answer 24

Chemical stimuli increase bladder activity and hence urge to void.

Question 25

What other issues are there with the urinary tract?

Answer 25

Spinal cord injury
MS
Strokes
Pelvic floor injury
Detrusor overactivity
Atonic bladder (no stimulation of bladder contraction)

Question 26

How can overactive bladders be treated?

Answer 26

Antimuscarinic drugs

beta3 agonist

Question 27

What is prostatomegaly?

Answer 27

enlargement of the prostate