Chapter027

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 27Disorders of the Bladder and

Lower Urinary Tract

Chapter 27Disorders of the Bladder and

Lower Urinary Tract


Micturition ReflexMicturition Reflex

• Begins when bladder contains 150–250 mL of urine

ureters

urine produced in

kidneys

bladder fills with urine


Stretch Receptors in the BladderStretch Receptors in the Bladder

stretch receptors

stretch receptors


micturition center in

pons stimulated

spinal reflex stimulated


UrinationUrination

• Detrusor muscle of bladder contracts to push urine out

• Abdominal muscles may also be used

• Internal sphincter relaxes

• External sphincter relaxes


Question Question

Tell whether the following statement is true or false:

Abdominal muscles are used during forced urination.


Answer Answer

True

Passive urination occurs when the bladder’s detrusor muscle contracts, and both internal and external sphincter muscles are relaxed. Abdominal muscles contract in order to force the excretion of urine.


Parasympathetic NervesParasympathetic Nerves

M3 receptors

stretch receptors

M3 receptors


detrusor muscle

contracts

internal sphincter relaxes and is pulled

open

parasympathetic neurons

spinal reflex stimulated


Micturition Center Allows Conscious ControlMicturition Center Allows Conscious Control

stretch receptors


detrusor muscle

contracts

internal sphincter relaxes and is pulled

open

micturition center in

pons stimulated

external sphincter

relaxes


Question Question

All but which of the following stimulates urination?

a. Parasympathetic nervous system neurons

b. Micturition center

c. Sympathetic nervous center

d. Spinal reflex


Answer Answer

c. Sympathetic nervous system

The micturition center in the pons and the spinal reflex respond to stretch receptors in the bladder to stimulate urination. The parasympathetic nervous system neurons are stimulated by the spinal reflex to cause urination.

SNS (fight-or-flight) decreases activity in both the excretory and digestive systems.


ScenarioScenario

A 63-year-old woman complains of stress incontinence, and her 60-year-old husband complains of difficulty voiding.

Question:

• Why do people of the same age and lifestyle have opposite problems with urination?


Male vs. Female UrethraMale vs. Female Urethra

• Female is urethra 2.5–3.5 cm long

• Allows urine to pass more freely

• Male urethra 16.5–18.5 cm long

• Passes through prostate


Question Question

Tell whether the following statement is true or false:

Benign prostatic hypertrophy (BPH) has no effect on the elimination of urine.


Answer Answer

False

Because the male urethra passes through the prostate gland, if the gland increases in size the urethra may become compressed or obstructed. This decreases the diameter of the urethra’s lumen, and the ability to urinate is diminished.


ScenarioScenario

Six months later, the husband develops urgency and incontinence…

• The doctor explains that it is due to his muscle strength.

Question:

• Which muscles is the doctor talking about?

• How did they cause incontinence?


Bladder Wall HypertrophyBladder Wall Hypertrophy

• The bladder may also pouch outward in diverticuli

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