Physiology of Micturition Flashcards
Label this diagram [PM1]
A - Median umbilical ligament B - Ureter C - Peritoneum D - Detrusor muscle E - Ureteral openings F - Trigone G - Neck of urinary bladder H - Internal urethral sphincter I - External urethral sphincter (in urogenital diaphragm) J - Muscosa Ji - Transitional epithelium Jii - Lamina propria Jiii - Adventitia K - Detrusor muscle L - Adventitia
1 - Body
2 - Trigone
3 - Neck
What is the purpose of the body of the bladder?
Temporary store of urine
What are at the angles of the trigone area?
Ureteric orifaces and internal urethral orifice
What does the neck of the bladder do?
Connects the bladder to the urethra
What is the detrusor urinae muscle made from?
A meshwork of muscle fibres in roughly 3 layers
What are the layers of the detrusor urinae muscle?
Inner longitudinal
Middle circular
Outer longitudinal
What does the arrangement of muscle fibres of the detrusor muscle give?
The bladder strength, irrespective of the direction it’s being stretched in
What is the detrusor urinae muscle supplied by?
The autonomic nervous system
Is the detrusor urinae muscle under voluntary control?
No
Is the spinal nerve supply of the detrusor urinae muscle unilateral or bilateral?
Bilateral
Label this diagram [PM2]
A and B (lol oops) - Transitional Epithelium
C - Mucosa
D - Submucosa
1 - Inner layer of longitudinal muscle
2 - Middle layer of circular muscle
3 - Outer layer of longitudinal muscle
What is the internal urethral sphincter a continuation of?
The detrusor muscle
What is the internal urethral sphincter made of?
Smooth muscle
What kind of sphincter is the internal urethral sphincter?
Physiological
What is meant by the internal urethral sphincter being a physiological sphincter?
There is no muscle thickening, the action is due to structure
Where is the internal urethral sphincter found?
At the bladder neck
What is the importance of the internal urethral sphincter?
It is the primary muscle of continence
What kind of sphincter is the external urethral sphincter?
Anatomical sphincter
What facilitates the action of the external urethral sphincter?
Localised circular muscle thickening
What is the external urethral sphincter derived from?
The pelvic floor muscles
What kind of muscle is the external urethral sphincter?
Skeletal muscle
What control is the external urethral sphincter under?
Somatic, voluntary control
How does the external urethral sphincter work?
Contracts to constrict urethra and ‘hold in urine’
What are the kinds of innervation of the detrusor muscle?
Parasympathetic
Sympathetic
What is the parasympathetic innervation of the detrusor muscle?
Pelvic nerve (S2-S4)
What is the result of pelvic nerve stimulation to the detrusor muscle?
ACh simulates M3 receptors
What is the result of stimulation of M3 receptors at the detrusor muscle?
Contraction
What is the sympathetic innervation to the detrusor muscle?
Hypogastric nerve (T10-L2)
What is the result of hypogastric nerve stimulation of the detrusor muscle?
NA stimulates ß3-receptors
What is the result of stimulation of ß3 receptors at the detrusor muscle?
Relaxation
What is the type of innervation of the internal urethral sphincter?
Sympathetic, via hypogastric nerve (T10-L2)
What is the result of hypogastric nerve stimulation to the internal urethral sphincter?
NA stimulates alpha-1 receptors
What is the result of alpha-1 receptor stimulation of the internal urethral sphincter?
Contraction
What kind of innervation does the external urethral sphincter receive?
Somatic
What is the somatic innervation of the external urethral sphincter?
Pudendal nerve (S2-S4)
Where does the spinal motor outflow come from with the pudendal nerve supply of the external urethral sphincter?
Onof’s nucleus of the ventral horn of the cord
What is the result of pudendal nerve stimulation to the external urethral sphincter?
ACh stimulates the nicotinic receptor
What is the result of the stimulation of the nicotinic receptor ion the external urethral sphincter?
Contraction
Label this diagram illustrating the innervation of the bladder [PM3]
A - ACh B - Bladder C - M3 receptor (+) D - ß3 receptor (-) E - Detrusor muscle F - Urethra G - alpha-1 receptor (+) H - External urethral sphincter J - Nicotinic receptor (+) K - ACh L - NA M - NA
1 - Pelvic nerve (parasympathetic)
2 - Hypogastric nerve (sympathetic)
3 - Pudendal nerve (somatic)
What is the threshold for feelings suggestive of a full bladder?
~400ml
What happens when the bladder is full?
An urge to urinate arises
What is the nervous stimulation for the urge to urinate?
Brain micturition centres → Spinal micturition centres → Parasympathetic neurones
How to parasympathetic neurones cause the urge to urinate?
The increase in parasympathetic stimulation to the bladder via the pelvic nerve causes the detrusor muscle to contract and increase intravesicular pressure
What is the conscious aspect of micturition?
The external urethral sphincter
What controls the external urethral sphincter?
The cerebral cortex
How does the cerebral cortex control the external urethral sphincter?
The cerebral cortex makes a conscious, executive decision to urinate, reducing somatic stimulation to the external urethral sphincter
What does the contraction of the detrusor coupled with the relaxation of the external urethral sphincter result in?
Emptying through the urethra
What works together to pass urine into the urinary bladder?
The ureters, urinary bladder, and internal and external urethral sphincter
How long can urine be stored in the urinary bladder?
Many hours
When may urine need to be stored for many hours?
At night
What feature do the walls of the bladder have?
Many folds
What happens to the walls of the bladder when filling with urine?
The folds allow distension
What is the result of the distention of the bladder wall on filling with urine?
As the bladder fills, intravesicular pressure hardly changes
What happens at around 400ml of filling?
Afferent nerves from the bladder wall start to signal the need to void the bladder
What kind of receptors are those of the afferent nerves from the bladder wall?
Possible stretch receptors