Anatomy of the Urinary System PDF

Anatomy of the Urinary Bladder BY PROF. KOMOLAFE The bladder is an organ of the urinary system. It plays two main roles: Temporary storage of urine – the bladder is a hollow organ with distensible walls. It has a folded internal lining (known as rugae), which allows it to...

Anatomy of the Urinary Bladder BY PROF. KOMOLAFE The bladder is an organ of the urinary system. It plays two main roles: Temporary storage of urine – the bladder is a hollow organ with distensible walls. It has a folded internal lining (known as rugae), which allows it to accommodate up to 400-600ml of urine in healthy adults. Assists in the expulsion of urine – the musculature of the bladder contracts during micturition, with concomitant relaxation of the sphincters.  Urinary Bladder Location and Description The urinary bladder is situated immediately behind the pubic bones within the pelvis. It stores urine and in the adult has a maximum capacity of about 400- 600ml. The bladder has a strong muscular wall.  Bladder The empty bladder is pyramidal, having an apex, a base, and a superior and two inferolateral surfaces; it also has a neck. The trigone is a triangular area at the base of the bladder where the ureters enter and the urethra exits The apex of the bladder points anteriorly and lies behind the upper margin of the symphysis pubis. It is connected to the umbilicus by the median umbilical ligament (remains of urachus).  Bladder As the bladder f il ls, it becomes ovoid, and the superior surface bulges upward into the abdominal cavity. The peritoneal covering is peeled off the lower part of the anterior abdominal wall so that the bladder comes into direct contact with the anterior abdominal wall.  Bladder The uvula vesicae is a small elevation situated immediately behind the urethral orifice, which is produced by the underlying median lobe of the prostate. The muscular coat of the bladder is composed of smooth muscle and is arranged as three layers of interlacing bundles known as the detrusor muscle. At the neck of the bladder, the circular component of the muscle coat is thickened to form the sphincter vesicae.  Bladder Blood Supply Arteries The superior and inferior vesical arteries, branches of the internal iliac arteries. Veins The veins form the vesical venous plexus that drains into the internal iliac vein. Lymph Drainage Internal and external iliac nodes.  Bladder The sympathetic nerves* inhibit contraction of the detrusor muscle of the bladder wall and stimulate closure of the sphincter vesicae. The parasympathetic nerves stimulate contraction of the detrusor muscle of the bladder wall and inhibit the action of the sphincter vesicae.  Control of Micturition Smooth or detrusor muscle at the neck is the internal sphincter, supplied by the sympathetic Parasympathetic contracts detrusor muscle and relaxes internal sphincter Sphincter urethra or external sphincter is striated muscle Supplied by perineal branch of pudendal nerve S2,3,4,  Structure of Female Urethra Urethra 3-5 cm long Enters deep pouch where it is surrounded by Sphincter urethra, also called external sphincter of bladder Urethra pierces perineal membrane No fascia between lower two thirds of urethra and vagina Opens into vestibule, between clitoris and vagina  Urethra Muscular layer continuous with bladder Spongy erectile tissue Plexus of veins Mucous membrane transitional Distal non keratinising stratified squamous Para urethral glands and ducts open into urethra, homologues of prostatic glands Smout et al 1969  Urethra Urethra is supported by the fascia of
the pelvic floor including pubo-
vesical and pubocervical ligaments If this support is insufficient, the
urethra can move downwards In times of increased abdominal
pressure resulting in stress urinary
incontinence (SUI) The physical changes that can occur during pregnancy, delivery and menopause can predispose to SUI Nuggaard and Heit in Bayliss 2010  Clinical Correlates Ureteric Calculi The ureter is narrowed anatomically where it bends down into the pelvis at the pelvic brim and where it passes through the bladder wall. It is at these sites that urinary stones may be arrested. When a calculus enters the lower pelvic part of the ureter, the pain is often referred to the testis and the tip of the penis in the male and the labium majus in the female. Palpation of the Urinary Bladder The full bladder in the adult projects up into the abdomen and may be palpated through the anterior abdominal wall above the symphysis pubis. Bladder Distention The normal adult bladder has a capacity of about 500 mL. In the presence of urinary obstruction in males, the bladder may become greatly distended without permanent damage to the bladder wall; in such cases, it is routinely possible to drain 1000 to 1200 mL of urine through a catheter. Urinary Retention In adult males, urinary retention is commonly caused by obstruction to the urethra by a benign or malignant enlargement of the prostate. An acute urethritis or prostatitis can also be responsible. Acute retention occurs much less frequently in females. The only anatomic cause of urinary retention in females is acute inf lammation around the urethra (e.g., from herpes). Suprapubic Aspiration As the bladder f ills, the superior wall rises out of the pelvis and peels the peritoneum off the posterior surface of the anterior abdominal wall. Cystoscopy The mucous membrane of the bladder, the two ureteric orifices, and the urethral meatus can easily be observed by means of a cystoscope. With the bladder distended with fluid, an illuminated tube fitted with lenses is introduced into the bladder through the urethra. Bladder Injuries The bladder may rupture intraperitoneally or extraperitoneally. Intraperitoneal rupture usually involves the superior wall of the bladder and occurs most commonly when the bladder is full and has extended up into the abdomen. 


HISTOLOGY OF URINARY SYSTEM Urinary Bladder: The histological details of urinary bladder is same as that of the ureter except that: The lamina muscularis is present as small isolated bundles of smooth muscles. The tunica muscularis is thick and the muscles are collectively called as Detrusor muscle. Rest of the features are same. ANATOMY OF THE URETHRA The urethra is the vessel responsible for transporting urine from the bladder to an external opening in the perineum. It is lined by stratif ied columnar epithelium, which is protected from the corrosive urine by mucus secreting glands. MALE URETHRA The male urethra is approximately 15-20cm long. In addition to urine, the male urethra transports semen – a f luid containing spermatozoa and sex gland secretions. According to the latest classif ic ation, the male urethra can be divided anatomically into three parts (proximal to distal): Prostatic urethra: Begins as a continuation of the bladder neck and passes through the prostate gland. Receives the ejaculatory ducts (containing spermatozoa from the testes and seminal f luid from the seminal vesicle glands) and the prostatic ducts (containing alkaline fluid). It is the widest and most dilatable portion of the urethra. Membranous urethra: Passes through the pelvic floor and the deep perineal pouch. Surrounded by the external urethral sphincter – which provides voluntary control of micturition. It is the narrowest and least dilatable portion of the urethra. Penile (bulbous) urethra: Passes through the bulb and corpus spongiosum of the penis, ending at the external urethral orifice (the meatus). Receives the bulbourethral glands proximally. In the glans (head) of the penis, the urethra dilates to form the navicular fossa. URETHRA Neurovascular Supply
The arterial supply to the male urethra is via several arteries: Prostatic urethra – supplied by the inferior vesical artery (branch of the internal iliac artery which also supplies the lower part of the bladder). Membranous urethra – supplied by the bulbourethral artery (branch of the internal pudendal artery) Penile urethra – supplied directly by branches of the internal pudendal artery. The nerve supply to the male urethra is derived from the prostatic plexus, which contains a mixture of sympathetic, parasympathetic and visceral afferent fibres. Lymphatic Drainage
Lymphatic drainage also varies according to the region of the urethra. The prostatic and membranous portions drain to the obturator and internal iliac nodes, while the penile urethra drains to the deep and superficial inguinal nodes. CLINICAL CORRELATES Male Catheterisation Urinary catheterisation is the process of inserting a tube through the urethra and into the bladder. This is typically performed in situations where urine output needs to be monitored (such as sepsis), or when the patient is unable to pass urine (urinary retention). Catheterisation is more complex in males, as there are two angles to consider – the infrapubic and prepubic angles. The prepubic angle can be diminished by holding the penis upwards during urinary catheterisation. It is also important to note the three constrictions in the male urethra – the internal urethral sphincter, external urethral sphincter, and external urethral orifice. Anatomy of the Female Urethra
In females, the urethra is relatively short (approximately 4cm). It begins at the neck of the bladder, and passes inferiorly through the perineal membrane and muscular pelvic floor. The urethra opens directly onto the perineum, in an area between the labia minora, known as the vestibule. Within the vestibule, the urethral orif ice is located anteriorly to the vaginal opening, and 2-3cm posteriorly to the clitoris. The distal end of the urethra is marked by the presence of two mucous glands that lie either side of the urethra – Skene’s glands. They are homologous to the male prostate. Neurovascular Supply
The arterial supply to the female urethra is via the internal pudendal arteries, vaginal arteries and inferior vesical branches of the vaginal arteries. Venous drainage is given by veins of the same names. The nerve supply to the female urethra arises from the vesical plexus and the pudendal nerve. Visceral afferents from the urethra run in the pelvic splanchnic nerves. Lymphatic Drainage
Lymphatic drainage of the proximal female urethra is to the internal iliac nodes, while the distal urethra drains to the superficial inguinal lymph nodes. Clinical Relevance
Urinary Tract Infections Due to the short length of the urethra, women are more susceptible to infections of the urinary tract. This usually manifests as cystitis, an infection of the bladder. Common symptoms of cystitis are dysuria (pain upon urination), frequency, urgency, and haematuria (blood in the urine). A mid- stream urine sample can be tested for the presence of nitrites and leukocytes (both of which indicate infection). Simple urinary tract infections are typically treated with a three- day course of antibiotics.