Bladder Flashcards
Urine formulation is a continuous process. Whats the journey of the urine?
Urine is produced in the nephrons of the kidneys and from the collecting duct it enters the papillary duct in the renal pyramid. It then enters the minor calyx, then the major calyx, then the renal pelvis where it enters the ureter. Peristaltic contractions of the ureter facilitate the movement of urine into the bladder.
Explain the structure of the urinary bladder.
The urinary bladder is a muscular sac, it is collapsed and relaxed when empty.
The main muscle of the bladder wall is the detrusor - this is composed of three layers of smooth muscle fibres all arranged differently (spiral, longitudinal and circular). Urine is stored in the bladder then excreted via the urethra.
Name the two muscular rings that control the urethral opening.
Internal sphincter (involuntary) - this is smooth muscle that's usually closed (passive contraction). External sphincter (voluntary) - this is skeletal muscle that's normally closed (tonic contraction).
Whats the bladders stretch receptor?
The trigone muscle.
Explain the structure of the bladder wall.
The bladder has a thick layer of detrusor mucle of musclaris surrounded by adventitia. In the lumen side of the bladder, the muscle has a layer of submucosa, then lamina propria then transitional epithelium.
Neural regulation of bladder control involves the PNS and CNS. Explain the influence of these two nervous systems.
An involuntary spinal micturition reflex arc is present from birth in continent individuals. This includes:
- Stretch receptors in the wall of the bladder.
- Afferent sensory nerve fibres convey impulses to the spinal cord
- Efferent PS nerve fibres convey impulses to detrusor and internal spincter.
Voluntary nervous control excercised by the CNS develops in early childhood. It is controlled by the cortex, cerebellum and the micturition centre located in the pons.
Explain the involuntary reflex of micturition.
1 - Urine fills the bladder and stretches its wall.
2 - Stretch receptors in the bladder wall send a signal via sensory afferent nerve fibres to the sacral portion of the spinal cord.
3 - Parasympathetic efferent fibres stimulate the detrusor muscle to contract and the internal urethral sphincter to relax.
As bladder volume increases detrusor pressure remains constant to a point - here the involuntary reflex kicks in. In adults the voluntary control will overcome urination until appropriate.
Explain how the voluntary control of micturition occurs, following the involuntary reflex.
Interneurons in the spinal cord communicate the ‘full bladder’ signal to the micturition centre in the pons.
If micturition is appropriate, the cerebral cortex facilitates this process by allowing the external urethral sphincter to relax and urination occurs.
