Urinary Bladder

1. Overview

The urinary bladder is a hollow, muscular organ that serves as the temporary storage reservoir for urine before it is excreted via the urethra. It is capable of significant distension and contraction, adjusting its volume and wall tension as it fills and empties. The bladder is under voluntary and involuntary neural control, allowing for the coordinated processes of urine storage and micturition.

2. Location

The urinary bladder is located in the pelvis, posterior to the pubic symphysis. Its position varies slightly based on sex and whether it is empty or distended:

• In males: Located anterior to the rectum and superior to the prostate gland.

• In females: Situated anterior to the vagina and inferior to the uterus.

When full, the bladder rises into the abdominal cavity and can be palpated above the pubic bone.

3. Structure

The bladder has four anatomical surfaces and key structural features:

• Apex: Directed anteriorly toward the pubic symphysis.

• Base (fundus): Posteroinferior surface containing the trigone.

• Neck: Lowest part, continuous with the urethra at the internal urethral orifice.

The wall of the bladder comprises several layers:

• Mucosa: Lined with transitional epithelium (urothelium) that allows stretch.

• Submucosa: Loose connective tissue containing blood vessels and nerves.

• Muscularis (detrusor muscle): Three layers of smooth muscle—inner and outer longitudinal, and middle circular—responsible for bladder contraction.

• Adventitia (or serosa): Outer connective tissue layer; the superior surface has peritoneal covering.

Trigone Region

The trigone is a smooth, triangular area on the internal posterior wall defined by:

• The two ureteric orifices (superior angles)

• The internal urethral orifice (inferior angle)

It remains smooth during bladder filling and plays a key role in directing urine flow and preventing reflux.

4. Function

The urinary bladder has two principal functions:

• Urine storage: Temporarily holds urine, typically up to 400–600 mL in adults, under low pressure.

• Urine expulsion: Contracts to empty stored urine during micturition via the urethra.

These functions are regulated by complex neural pathways that coordinate bladder muscle contraction and sphincter relaxation.

5. Physiological Role(s)

The bladder contributes to urinary system physiology through:

• Compliance and elasticity: Accommodates increasing urine volumes without significant pressure rise.

• Neural control: Sensory afferents detect stretch and fullness, while motor efferents control detrusor muscle contraction and sphincter relaxation.

• Micturition reflex: A spinal reflex involving parasympathetic activation of the detrusor and inhibition of somatic control of the external sphincter.

• Barrier function: Urothelium forms a tight barrier preventing reabsorption of waste and pathogens.

6. Clinical Significance

Urinary Tract Infections (UTIs)

Common, especially in women due to a shorter urethra. Infection leads to:

• Dysuria (painful urination)

• Urgency and frequency

• Suprapubic discomfort

Diagnosed via urinalysis and culture; treated with antibiotics.

Bladder Outlet Obstruction

Occurs when urine flow is blocked, often due to:

• Benign prostatic hyperplasia (BPH) in men

• Urethral stricture or pelvic masses

Leads to incomplete emptying, urinary retention, and increased risk of infection.

Neurogenic Bladder

Dysfunction in bladder control due to:

• Spinal cord injury

• Multiple sclerosis

• Diabetes

Results in overactive or underactive bladder, managed by catheterization, medications, or surgical interventions.

Bladder Stones

Result from urinary stasis or infection. Symptoms include:

• Hematuria

• Frequency and urgency

• Interrupted urine stream

Diagnosed with ultrasound or CT; treated with cystolitholapaxy or surgery.

Bladder Cancer

Most common type: transitional cell carcinoma. Risk factors include smoking and exposure to industrial chemicals. Presents with:

• Painless hematuria

• Urinary irritation

Diagnosed via cystoscopy and biopsy; treated with TURBT, intravesical therapy, or cystectomy based on stage.

Incontinence

Loss of voluntary control over urination due to sphincter weakness, overactive bladder, or nerve damage. Types include:

• Stress incontinence

• Urge incontinence

• Overflow incontinence

Management involves pelvic floor therapy, medications, or surgical options like slings and sphincter implants.

Catheterization

Bladder catheterization is a common clinical procedure for:

• Urinary retention

• Incontinence management

• Surgical drainage

Careful technique is essential to prevent trauma and infection.