L2: Adobe Flashcards

What is micturition?

-urination

-process of expelling urine from the bladder through the excretory system to eliminate metabolic products and toxic wastes filtered by the kidneys

What are the components of the urinary system involved in micturition?

-comprises the upper tract (kidneys and ureters) and the lower tract (bladder and urethra)

-lower tract is involved in the micturition reflex

What are the roles of the sympathetic, parasympathetic, and somatic nervous systems in micturition?

• Sympathetic: Allows bladder filling by closing the internal urethral sphincter. ​

• Parasympathetic: Contracts the bladder and opens the internal sphincter when the bladder is full. ​

• Somatic: Controls the external sphincter, allowing voluntary holding or releasing of urine.

What is the micturition reflex?

• At low bladder volumes, stretch receptor firing is low, leading to bladder relaxation. ​

• At high bladder volumes, stretch receptor firing increases, creating a conscious sensation of urinary urge. ​

• If the reflex is strong enough, it relaxes the external sphincter, leading to urination

What neurotransmitters and receptors are involved in micturition?

• Parasympathetic: Acetylcholine (ACh) stimulates M3 muscarinic receptors, causing detrusor muscle contraction. ​

• Sympathetic: Adrenaline and noradrenaline act on α1, β2, and β3 adrenergic receptors. ​

  • α1 receptors contract the internal sphincter. ​

  • β3 receptors relax the detrusor muscle. ​

What are the steps in the mechanism of micturition?

1. Bladder fills, detrusor muscle contracts, stimulating stretch receptors. ​

2. Parasympathetic fibers excite, releasing ACh to stimulate M3 receptors, increasing bladder pressure. ​

3. Internal sphincter opens, urine flows into the urethra. ​

4. Pudendal nerve inhibition relaxes the external sphincter, allowing urine expulsion.

What are the problems associated with micturition?

1. Atonic bladder: Loss of sensory nerve fibers, no micturition reflex, overflow incontinence. ​

2. Automatic bladder: Spinal injuries cranial to sacrum, suppressed reflex initially, excitability returns over time. ​

3. Uninhibited neurogenic bladder: Interruption of inhibitory brain signals, leading to frequent urination even with small urine volume

What factors influence normal micturition?

-normal muscle tone

-absence of physical obstructions

-psychological inhibition are essential for proper micturition

What happens during bladder filling?

• Sympathetic activity keeps the internal sphincter closed. ​

• Stretch receptors remain inactive, and the brain maintains tonic reflex drive on external sphincter motor neurons, preventing urination

How does voluntary control of urination occur?

Signals from the brain cease tonic reflex drive on external sphincter motor neurons → relaxing the sphincter and allowing voluntary urination