REB 32. Urinary Bladder and Micturition Reflex Flashcards
What are the walls of the ureters made up of? What cells are present?
- 2 smooth muscle layers in walls (circular + longitudinal)
- transitional epithelium lining
Why is the transitional epithelium lining in the ureters important?
- it allows for stretch
- if the bladder is really full, the urine may enter the ureters (backflow)
Where does the ureter enter into the bladder?
- bladder enters through the detrusor muscle in bladder trigone
What is the purpose of the middle circular layer of smooth muscle?
the circular muscle helps with contraction
- this moves the urine down the ureter
HOW does the ureter enter the bladder?
- enters with OBLIQUE pathway through the detrusor muscle
- it crosses a large portion of the bladder
What does the tone of the detrusor muscle do? What is its function?
- the ureter enters the bladder with oblique pathway through the detrusor muscle
- tone of the detrusor muscle keeps the ureter compressed
- as the bladder contracts, the ureter is compressed – it ensures that urine doesn’t flow back up through the ureters
What is the ureterorenal reflex?
- the ureters are heavily innervated with pain fibres
- blockage of the ureter causes build up of urine above the block and pain
- this causes reflex activation of sympathetic nerves to the afferent arteriole
- reduces blood supply to the kidney (to decrease urine coming out)
- this decreases urine output
What is the vesico-ureteric reflux?
- this may occur if the ureters do not enter the bladder in the right fashion
OR - loss of muscle tone in bladder
- there may be a short passage of the ureter through the bladder wall
- bladder contration in microturition may NOT always occlude the ureters
- there is urine left in bladder
- reflux of urine is when urine goes back up the ureters
- this may lead to renal damage
- – swelling of the kidney due to buildup of urine (hydronephrosis)
What is the function of the bladder?
- storage and periodic elimination of urine
What type of control is the bladder under?
- regulated by neural control systems
- normally under voluntary control (learned behaviour!)
What type of muscle and cell types is the bladder made up of?
[1] Inner Transitional Epithelium
[2] Detrusor Muscle
- has 3 layers of smooth muscle
Where is the external urethral sphincter located?
located in the urogenital diaphragm
What type of innervation is the internal sphincter supplied by?
- sympathetic + parasympathetic control
- involuntary control
What type of innervation is the external sphincter supplied by?
- voluntary control
- in the urogenital diaphragm
What is the normal urine formation rate in the kidneys?
1mL/min
What volume remains in the bladder after microturition?
hopefully NONE
- if there is some urine left in the bladder, this means that there is some damage or deficiency
Explain how laplace’s law relates to the filling of the bladder.
- as the volume increases in the bladder, the bladder gets stretched and the tension increases
- – V = T
- as the tension/volume increases, the pressure does NOT change though
- the pressure does not change because the radius increases as well
Laplace Law: P = T/R
e.g. 1/1 = P
2/2 = P
- the ratio stays the same
What are the 2 phases in bladder filling?
[1] Filling phase
[2] Voiding phase
Explain the pressure change (or not) in the filling phase of the bladder
the pressure remains steady
Explain the pressure change (or not) in the voiding phase of the bladder
the pressure quickly drops as the bladder CONTRACTS and the RADIUS DECREASES
How full should the bladder be to feel:
[1] Awareness
[2] Urge to Void
[3] Pain
[1] Awareness
- 150 mL
[2] Urge to Void
- 300 mL
[3] Pain
- 600 mL
What is the innervation of the external urethral sphincter?
- pudendal nerve
- somatic nerve
What is the innervation of the internal urethral sphincter?
- vesical plexus
- pelvic splanchnic nerve
- – they both relax the sphincter
(and the hypogastric and vesical plexuses)
- it contracts the sphincter
What is the innervation of the detrusor muscle?
- hypogastric and vesical plexuses
* also innervates internal urethral sphincter
What are the 4 components of the innervation of the bladder?
[1] Primary Afferent Neurons
[2] Spinal Efferent Neurons
[3] Spinal Interneurons
[4] Neurons in the brain that activate/modulate spinal reflex pathways
– note: the spinal reflex to urinate can be controlled through higher brain centres
Explain the sympathetic nervous innervation of the bladder
innervation from the SYMPATHETIC CHAIN through the HYPOGASTRIC NERVES
Explain the parasympathetic nervous innervation of the bladder
innervation through the PELVIC PLEXUS and directly to the BLADDER WALL
Explain the somatic nervous innervation of the bladder
directly to EXTERNAL SPHINCTER from MOTOR NUCLEUS in the SPINAL CORD
Explain the afferent nervous innervation of the bladder
fibres travel to SPINAL CORD via PELVIC HYPOGASTRIC and PUDENDAL NERVES
What is the origin, nerves, neurotransmitter and receptor of the SYMPATHETIC efferents?
Origin:
- T10 to L4
Nerves:
- Hypogastric
Neurotransmitter:
- Noradrenaline (NA)
Receptor:
(a) Beta-3
- relaxes the detrusor muscle
(b) Alpha-1
- constricts/contracts the internal sphincter
What is the origin, nerves, neurotransmitter and receptor of the PARASYMPATHETIC efferents?
Origin:
- S2 to S4
Nerves:
- Pelvic
Neurotransmitter:
- Acetacholine (ACh)
- Nitric Oxide (NO)
Receptor:
Muscarinic M3 ACh
- contracts the detrusor muscle
- relaxes the internal sphincter
What is the origin, nerves, neurotransmitter and receptor of the PARASYMPATHETIC efferents?
Origin:
- S2 to S4
Nerves:
- Pudendal nerve
Neurotransmitter:
- Acetylcholine (ACh)
Receptor:
- Nicotinic ACh
- contracts the external sphincter
Which branch of the autonomic nervous system richly supplies the bladder?
parasympathetic nerves
Which branch of the autonomic nervous system only has sparse innervation of the bladder?
sympathetic nerves
Explain the storage reflexes in the bladder that occurs during the filling/storage phase.
- low level afferent firing from stretch receptors
- organized by circuits in the spinal cord
- inhibits parasympathetic activity which relaxes detrusor and contracts internal sphincter
- signal sent to midbrain (pontine storage centre) increase external urethral sphincter activity and decrease parasympathetic activity
What are some actions that occur during the void phase?
- relaxation of urethral sphincters
- contraction of detrusor muscle
- increased bladder pressure
- flow of urine
- Valsalva Manoeuvre (forced expiration against a closed glottis)
- – increases pressure in the whole abdomen and makes sure all urine comes out
What is the Valsalva Manoeuvre?
forced expiration against a closed glottis
— increases pressure in the whole abdomen and makes sure all urine comes out
Explain the steps/mechanical and biochemical process that is involved in the control of micturition
- increased firing of afferents from bladder
- signals to Rostral Brain Stem
- processed in Periaqueductal Gray (PAG) and Pontine Micurition Centre
- sensation of bladder fullness
- if it is appropriate, conscious decisio to micturate is made
- inhibition of the somatic (voluntary) pathway to the external sphincter
- — External Sphincter Relaxation
- activation of descending pathways to bladder and urethra
- — Bladder Contraction and Internal Sphincter Relaxation
- higher centre control is absent or deficient with cord injury, infants, dementia, intellectual disability
When is the higher centre control absent or deficient?
those with cord injury, infants, dementia, intellectual disability
What are the 2 types of spinal cord injury which leads to a loss of voluntary control?
[1] Areflexic
- urinary retention
- bladder doesn’t know it’s full - there are no signals sent to the brain
[2] Hyperreflexic
- neurogenic detrusor overactivity
- due to emergence of spinal mictourition reflex pathway
