Anatomy of the Urinary Bladder

Anatomy of the Urinary Bladder

• The bladder is a hollow organ in the urinary system, with distensible walls.
• It stores urine, accommodating 400-600 mL in healthy adults.
• The bladder's internal lining, rugae, allows expansion.
• The bladder contracts during micturition (urination), aided by sphincter relaxation.

Urinary Bladder - Location and Description

• Located immediately behind the public bones, within the pelvis.
• Holds approximately 400-600 mL of urine in adults.
• Possesses a strong muscular wall.

Bladder - Additional Features

• The empty bladder is pyramidal, having an apex, base, and two inferolateral surfaces, plus a neck.
• The trigone is a triangular area at the bladder base where ureters enter and the urethra exits.
• The bladder's apex lies behind the pubic symphysis and connects to the umbilicus (via the median umbilical ligament).
• As the bladder fills, its superior surface bulges upward into the abdominal cavity, and the peritoneal covering peels back, enabling direct contact with the anterior abdominal wall.

Bladder - Internal Structure

• The bladder's muscular coat consists of smooth muscle; three interlacing layers collectively known as detrusor muscle.
• At the neck of the bladder, the circular component of the detrusor muscle forms the sphincter vesicae.
• The uvula vesicae is a small elevation behind the urethral orifice, formed by the median lobe of the prostate.

Bladder - Blood Supply

• The bladder is supplied by the superior and inferior vesical arteries (branches of the internal iliac arteries).
• Veins form the vesical venous plexus, draining into the internal iliac vein.
• Lymph drainage occurs through internal and external iliac nodes.

Bladder - Nerve Supply

• Sympathetic nerves inhibit detrusor muscle contraction and stimulate sphincter vesicae closure.
• Parasympathetic nerves stimulate detrusor muscle contraction and inhibit sphincter vesicae action.

Control of Micturition

• The internal sphincter is smooth muscle at the bladder neck.
• It is supplied by sympathetic nerves and contracts the detrusor muscle.
• Internal sphincter relaxes when parasympathetic nerves activate.
• The external sphincter is striated muscle, supplied by the perineal branch of the pudendal nerve (S2,3,4).

Structure of Female Urethra

• Approximately 3-5 cm in length.
• Enters a deep pouch, surrounded by the external urethral sphincter.
• Pierces the perineal membrane.
• Does not have fascia between the lower two-thirds of the urethra and vagina.
• Opens into the vestibule between clitoris and vagina.

Urethra - Structure

• The urethral muscular layer is continuous with the bladder.
• Contains spongy erectile tissue and a plexus of veins.
• The lining is transitional epithelium initially, becoming non-keratinized stratified squamous distally.
• Contains paraurethral glands analogous to prostatic glands.

Urethra - Support and Function

• Supported by pelvic floor fascia, pubovesical, and pubocervical ligaments.
• Insufficient support can lead to downward displacement during increased abdominal pressure (stress urinary incontinence).
• Pregnancy, delivery and menopause can increase susceptibility to stress urinary incontinence.

Urethra - Clinical Correlates

• Ureteric calculi (kidney stones) may become lodged where the ureter narrows in the pelvis and passes through the bladder wall.
• A full bladder in the adult can be palpated above the pubic symphysis through the anterior abdominal wall.

Bladder distention

• Normal adult bladder capacity is 500 mL.
• Significant bladder distension can occur with urinary obstruction; up to 1000-1200 mL can be drained via catheter in such cases.
• Adult male urinary retention commonly arises from prostate enlargement, acute urethritis or prostatitis.
• In females, acute urinary retention is less common, except for conditions like urethral inflammation (e.g., herpes).
• As the bladder fills, the superior wall rises out of the pelvis, lifting the peritoneum off the anterior abdominal wall.

Cystoscopy

• An illuminated tube fitted with lenses is inserted through the urethra into the bladder. This enables examination of the bladder's mucous membrane and urethral/ureteric orifices.
• Distension of the bladder with fluid facilitates observation.

Bladder Injuries

• Ruptures can be intraperitoneal or extraperitoneal, predominantly impacting the superior bladder wall when full and extended into the abdomen.

Histology of Urinary Bladder

• Histological details of the urinary bladder are comparable to the ureter, excluding the lamina muscularis.
• Small, isolated bundles of smooth muscles constitute the lamina muscularis.
• The tunica muscularis is thick, grouped muscles collectively named detrusor muscle.

Anatomy of the Male Urethra

• Approximately 15-20 cm long.
• Transports urine and semen (spermatozoa plus secretions from the sex glands).
• Comprises prostatic, membranous, and penile (bulbous) portions.
• Prostatic urethra begins at the bladder neck, traversing the prostate gland.
• Receives ejaculatory and prostatic ducts.
• Bulbous urethra passes through the bulb and corpus spongiosum of the penis, terminating at the urethral meatus.
• Membranous urethra is located within the pelvic floor and deep perineal pouch, contains external urethral sphincter, narrowest and least dilatable.
• The ejaculatory ducts add semen and prostatic secretions.
• The urethra's penile segment dilates within the penile glans to form the navicular fossa.

Male Urethra - Neurovascular Supply

• Arterial supply from inferior vesical (prostatic urethra), branches of internal pudendal (membranous and penile urethra).
• Nerve supply arises from the prostatic plexus (sympathetic, parasympathetic and visceral afferent fibres).

Male Urethra - Lymphatic Drainage

• Prostatic and membranous portions drain to obturator and internal iliac nodes.
• Penile portion drains to deep and superficial inguinal nodes.

Male Catheterization

• Process of inserting a catheter through the urethra into the bladder.
• Important clinically when monitoring urinary output or when patients can't void (urinary retention).
• More complex in males due to infrapubic and prepubic angles, requiring special considerations in positioning.

Anatomy of Female Urethra

• Relatively short (approximately 4 cm).
• Begins at the bladder neck and descends through perineal membrane and pelvic floor muscles, exiting into the vestibule.
• Urethral opening anterior to vaginal opening and slightly posterior to clitoris.
• Two mucus-producing Skene's glands located on each side of the urethra, homologous to the male prostate.

Female Urethra - Neurovascular Supply

• Arterial supply via internal pudendal, vaginal arteries, and inferior vesical branches of vaginal arteries.
• Venous drainage by similar-named veins.
• Nerve supply from vesical plexus and pudendal nerve.
• Visceral afferents travel through pelvic splanchnic nerves.

Female Urethra - Lymphatic Drainage

• Proximal urethra drains to internal iliac nodes.
• Distal urethra drains to superficial inguinal lymph nodes.

Clinical Relevance - Urinary Tract Infections

• Women more susceptible due to shorter urethra.
• Infections typically involve bladder (cystitis).
• Common symptoms include dysuria, frequency, urgency, and haematuria.
• Urine samples can be tested for nitrites and leukocytes to confirm infections.
• Simple infections are often treated with a 3-day course of antibiotics.

Explore the structure and function of the urinary bladder in this quiz. Learn about its location, capacity, and unique features such as the trigone and rugae. Perfect for anatomy students seeking to understand this vital organ.