Urinary bladder

The urinary bladder is a hollow, muscular organ that serves as a temporary reservoir for urine. It has an elastic and expandable structure, allowing it to accommodate varying volumes of urine before excretion.^[2] The bladder is lined with transitional epithelium and surrounded by a smooth muscle layer known as the detrusor muscle, which aids in its storage and voiding functions.

Location

The urinary bladder is located in the pelvic cavity, posterior to the pubic symphysis. In males, it is situated anterior to the rectum and superior to the prostate gland. In females, it lies anterior to the uterus and superior to the vaginal canal.^[3]

Structure and Anatomy

The urinary bladder is a hollow, elastic organ with a variable capacity. It is roughly pyramid-shaped when empty and becomes more spherical as it fills with urine.

Layers of the Urinary Bladder Wall

Mucosa

• Lining Epithelium: The innermost layer is composed of transitional epithelium, also known as urothelium. This tissue can stretch significantly to accommodate the bladder’s changing volume.
• Lamina Propria: A layer of connective tissue beneath the epithelium, supporting blood vessels, nerves, and lymphatics.

Submucosa

• A thin layer of connective tissue that provides additional support and houses blood vessels and nerves.^[5]

Muscularis (Detrusor Muscle)

• Composition: This thick layer of smooth muscle surrounds the bladder and is organized into three layers: an inner longitudinal layer, a middle circular layer, and an outer longitudinal layer.
• Role: The detrusor muscle facilitates the contraction and relaxation of the bladder during the storage and voiding of urine.

Adventitia/Serosa

• Adventitia: A connective tissue layer that covers most of the bladder and anchors it to surrounding structures.
• Serosa: A layer of peritoneum partially covering the superior surface of the bladder in regions exposed to the abdominal cavity.

Regions of the Urinary Bladder

Apex

The pointed anterior region of the bladder, directed toward the pubic symphysis. The median umbilical ligament (a remnant of the embryonic urachus) extends from this point to the umbilicus.

Base (Fundus)

The posterior part of the bladder, opposite the apex. In males, it is in close proximity to the rectum, and in females, it is near the anterior vaginal wall and uterus.^[7]

Neck

The lowest and most narrow part of the bladder, located near the urethra. It is surrounded by the internal urethral sphincter, which helps control the flow of urine.

Trigone

A triangular, smooth region at the base of the bladder, defined by three points: the two ureteral orifices (where urine enters from the ureters) and the internal urethral orifice (where urine exits into the urethra). The trigone remains smooth even as the bladder expands, distinguishing it from the rest of the bladder’s mucosal lining.

Blood Supply and Innervation

Blood Supply

• Arterial Supply: Primarily from the superior and inferior vesical arteries, branches of the internal iliac artery. In females, the vaginal artery also contributes.
• Venous Drainage: Venous blood is drained by the vesical venous plexus, which empties into the internal iliac veins.^[8]

Innervation

• Sympathetic Nerves: Originate from the hypogastric plexus and regulate bladder relaxation during urine storage.
• Parasympathetic Nerves: Arise from the pelvic splanchnic nerves and stimulate detrusor muscle contraction during urination.
• Somatic Nerves: The pudendal nerve controls the external urethral sphincter.

Position and Support Structures

Ligaments

• Pubovesical Ligaments (females) and Puboprostatic Ligaments (males): Anchor the bladder to the pubic bone.^[1]
• Median Umbilical Ligament: Provides support at the bladder’s apex.

Surrounding Structures

• In males, the bladder is bordered by the prostate gland inferiorly and the rectum posteriorly.
• In females, it is bordered by the uterus and vaginal canal posteriorly and is closely associated with the pelvic floor muscles.^[4]

Function

The urinary bladder’s primary function is to serve as a temporary reservoir for urine and facilitate its controlled excretion from the body. Its ability to store and release urine efficiently is critical for maintaining fluid and electrolyte balance.

Urine Storage

• The bladder stores urine produced by the kidneys until a sufficient volume is accumulated for excretion.
• Its elastic walls and transitional epithelium allow the bladder to expand significantly as it fills, accommodating volumes of up to 400–600 mL in adults without a significant rise in internal pressure.

Controlled Urine Excretion

• The bladder works in coordination with the urethral sphincters and pelvic floor muscles to regulate the voluntary release of urine.
• When the bladder fills, stretch receptors in its walls send signals to the brain, triggering the sensation of needing to urinate (micturition reflex).
• During urination, the detrusor muscle contracts, the internal urethral sphincter relaxes, and urine is expelled through the urethra.

Protection Against Infection

• The bladder’s mucosa provides a barrier to prevent bacterial adhesion and infection.
• Regular flushing of urine through the bladder and urethra helps maintain urinary tract cleanliness.

Clinical Significance

The urinary bladder plays a vital role in the urinary system, and its dysfunction or disorders can significantly impact overall health. Understanding its clinical relevance helps diagnose and manage various urological conditions.

Common Clinical Conditions

• Urinary Incontinence
  • The inability to control bladder function, leading to involuntary urine leakage. It can result from weakened pelvic muscles, neurological disorders, or overactive bladder syndrome.^[6]
• Urinary Tract Infections (UTIs)
  • The bladder (cystitis) is a common site for bacterial infections, causing symptoms like frequent urination, burning sensation, and pelvic discomfort.
• Bladder Stones
  • Mineral deposits can form in the bladder, leading to irritation, pain, and obstruction of urine flow.
• Bladder Cancer
  • Often arising from the urothelium, bladder cancer presents with symptoms like blood in the urine (hematuria) and changes in urinary habits.
• Neurogenic Bladder
  • A condition caused by nerve damage, leading to improper bladder function, such as retention or incontinence.
• Bladder Outlet Obstruction
  • Obstruction at the bladder neck or urethra can result from conditions like benign prostatic hyperplasia (in males) or pelvic organ prolapse (in females).

Diagnostic and Therapeutic Importance

• Diagnostic Procedures: Cystoscopy, urine analysis, and imaging studies (e.g., ultrasound, CT scan) are commonly used to evaluate bladder health.
• Treatment Approaches: Depending on the condition, treatment can range from lifestyle modifications and medications to surgical interventions, such as bladder augmentation or removal (cystectomy).