Micturition

LO 1

What is the primary brainstem center that coordinates micturition?

The Pons (Micturition control center).

What is the goal and primary nervous system for the Filling & Storage phase of micturition?

Goal: Store urine. System: Sympathetic Mnemonic: The Sympathetic system is for Storage.

During Storage, what are the 3 actions of the nervous system? (Hint: Sympathetic nerve, receptors, and Somatic nerve)

Sympathetic (Hypogastric N.): Activates beta3-receptors -> Relaxes detrusor muscle. Sympathetic (Hypogastric N.): Activates alpha1-receptors -> Contracts internal sphincter. Somatic (Pudendal N.): Activates Nicotinic receptors -> Contracts external sphincter.

What is the goal and primary nervous system for the Voiding & Micturition phase?

Goal: Empty the bladder. System: Parasympathetic Mnemonic: The Parasympathetic system helps you Pee.

During Voiding, what is the main action of the Parasympathetic (Pelvic) nerve?

It strongly activates M3-receptors on the detrusor muscle, causing it to contract and empty the bladder.

To initiate Voiding, what two systems/nerves must be inhibited?

The Sympathetic system (storage reflex is turned off). The Pudendal nerve (to relax the voluntary external sphincter).

Clinical Case: A patient has post-operative urinary retention due to an atonic bladder. Drug & Mechanism?

Drug: Bethanechol Mechanism: Muscarinic (M3) Agonist. It mimics the parasympathetic system to contract the detrusor muscle.

Clinical Case: A patient has urgency incontinence from an overactive bladder (detrusor spasms). Drug & Mechanism?

Drug: Oxybutynin Mechanism: Muscarinic (M3) Antagonist. It blocks M₃ receptors to relax the detrusor muscle and stop spasms.

What are the classic anticholinergic side effects associated with Oxybutynin?

"Dry as a bone" (dry mouth) "Blind as a bat" (blurry vision) "Mad as a hatter" (confusion) "Hot as a hare" (hyperthermia)

Clinical Case: A patient with urgency incontinence needs an alternative to Oxybutynin due to side effects. Drug & Mechanism?

Drug: Mirabegron Mechanism: Beta3-Agonist. It mimics the sympathetic storage reflex, activating Beta3 receptors to relax the detrusor and increase capacity.

Clinical Case: An elderly man has overflow incontinence (dribbling) due to BPH. Drug & Mechanism?

Drug: Tamsulosin Mechanism: Alpha1-Antagonist. It blocks Alpha1 receptors at the bladder neck and prostate, relaxing the smooth muscle to open the "gate."

What are two high-yield side effects of Tamsulosin?

Orthostatic hypotension (dizziness upon standing) Retrograde ejaculation

What is the difference between a UMN and LMN lesion in neurogenic bladder (location, bladder type)?

UMN Lesion: Location: Above the sacral cord (S2-S4) (e.g., MS, spinal cord injury >T12). Bladder: Spastic Bladder (Overactive). LMN Lesion: Location: At the sacral cord (S2-S4) or pelvic nerve (e.g., Diabetic neuropathy, Cauda Equina). Bladder: Flaccid Bladder (Atonic/Underactive).

What is the mechanism, symptoms, and treatment for a Spastic Bladder (UMN Lesion)?

Mechanism: Loss of pontine inhibition. The sacral reflex arc is intact but uncontrolled. Symptoms: Urgency incontinence, detrusor hyper-reflexia, small/frequent voids. Treatment: Oxybutynin or Mirabegron (to relax the spastic detrusor).

What is the mechanism, symptoms, and treatment for a Flaccid Bladder (LMN Lesion)?

Mechanism: The sacral reflex arc is destroyed. The bladder is atonic and cannot contract. Symptoms: Overflow incontinence & Retention. High post-void residual volume. Treatment: Bethanechol (to stimulate the detrusor) + Intermittent Catheterization.

What is Detrusor-Sphincter Dyssynergia (DSD)?

A complication of UMN lesions (e.g., MS, spinal cord transection) where the detrusor muscle contracts at the same time as the external sphincter contracts (instead of relaxing). Result: The patient tries to pee "against a closed door," leading to high bladder pressures and urinary retention.

A patient leaks urine when coughing or sneezing. Type, Cause, & Treatment?

Type: Stress Incontinence Cause: Weak pelvic floor muscles. Treatment: Kegel exercises.

A patient has constant dribbling and a high post-void residual. Type & Two Main Causes/Treatments?

Type: Overflow Incontinence Cause 1 (Obstruction): BPH => Tx: Tamsulosin (relax Alpha1). Cause 2 (Atonic Bladder): LMN Lesion (e.g., diabetes) => Tx: Bethanechol (stimulate M3)