Urethra

What is the urethra?

• The membranous canal (tube) that leads from the bladder and transports and discharges urine outside the body

In males, what does the urethra carry?

seminal fluid

Describe the male urethra.

• Fibromuscular tube 18– 20 cm long. In the flaccid state of penis, the long axis of urethra shows two curvatures, and therefore it is S-shaped. In the erect state of penis, the distal curve is obliterated and it becomes J-shaped.

Describe the course & termination of the male urethra.

• It extends from the internal urethral orifice at the neck of the bladder

• Runs through the prostate, deep perineal space and penis

• Terminates at the external urethral orifice at the tip of penis (glans penis)

What are the 3 parts of the male urethra?

• Prostatic part passes through the prostate.

• Membranous part is surrounded by sphincter urethrae.

• Spongy or penile part passes through the bulb and corpus spongiosum of penis.

Describe the prostatic part of the male urethra including where it is situated, where it begins & terminates.

• Situated in the prostate, 3 cm long

• Begins at the internal urethral orifice

• Terminates by continuing as membranous urethra

• Most dilated part

• On transverse section it is semilunar in shape, with its convexity directed forwards.

What does the posterior wall (floor) of the prostatic urethra present?

Describe each one.

1. Urethral crest (verumontanum), a median longitudinal ridge of mucous membrane.

2. Colliculus seminalis is an elevation in the middle part of the crest, on which the slit-like orifice of prostatic utricle is situated. On each side of this orifice there are openings of the ejaculatory ducts.

3. Prostatic sinuses are two vertical grooves situated one on each side of the crest. Each sinus presents about 20- 30 openings of the prostatic glands.

What is the prostatic utricle?

a blind sac, about 6 mm long, which lies within the prostate. It is directed upwards and backwards between the median and posterior lobes of the prostate.

What is the prostatic utricle homologous to in females?

uterus

Describe the membranous part of the male urethra including where it is situated, where it begins & terminates.

• Shortest (1.5 - 2 cm), narrowest and least dilatable part of male urethra.

• Situated in the deep perineal space

• Begins as a continuation of prostatic urethra. It runs downwards and slightly forwards through the sphincter urethrae, and pierces the perineal membrane about 2.5 cm below and behind the pubic symphysis.

• Terminates by continuing as spongy urethra.

• On transverse section, it is star-shaped (stellate).

Describe 3 features of the membranous urethra in males.

1. Membranous urethra is surrounded by sphincter urethrae (external urethral sphincter).

2. Bulbourethral glands (of Cowper) are placed one on either side of membranous urethra, although their ducts open into spongy part of urethra after piercing the perineal membrane.

3. Numerous urethral glands also open into it.

Describe the penile/spongy part of the male urethra, including where it begins & terminates.

• Longest part (15 cm), situated in the penis

• Begins as a continuation of membranous urethra

• The fixed part of penile urethra runs forwards and upwards in the bulb

of penis. It bends downwards in front of the lower part of pubic

symphysis to continue as the free part of penile urethra in the corpus

spongiosum penis.

• It terminates at the external urethral orifice situate at the tip of the

glans penis.

• It is narrow with a uniform diameter of about 6 mm in the body of

penis. It is dilated: (a) at its commencement, to form the intrabulbar

fossa on the floor and sides; and (b) within the glans penis, to form the

navicular fossa on the roof and sides.

• External urethral orifice is the narrowest part of male urethra. It forms a

sagittal slit about 6 mm long, and is bound on each side by a small

labium.

• On transverse section, the lumen is a transverse opening, except for

the external urethral orifice which is vertical.

Describe 3 features of the penile (spongy) part of the male urethra.

1. Ducts of bulbourethral glands open in the fixed part of penile

urethra about 2.5 cm below the perineal membrane.

2. Except in the most anterior part, there are numerous orifices of the

urethral glands (of Littre) facing forwards.

3. In addition, there are several small pit-like recesses or lacunae (of

Morgagni) which open obliquely forwards . One lacunae in the roof

of navicular fossa is largest (Lacunae magna). Lacunae receives

openings of the urethral glands.

Describe the internal urethral sphincter (sphincter vesciae) including where it is situated, type of muscle & nerves) in males.

• Situated at the neck of the bladder around the internal urethral orifice

• Its a part of detrusor muscle (of urinary bladder)

• made of smooth muscle, therefore it is involuntary– supplied by autonomic nerves

• Primary muscle for prohibiting the release of urine

Describe the external urethral sphincter (sphincter vesciae) including where it is situated, type of muscle & nerves) in males.

• Situated at the deep perineal space around the membranous

part of urethra

• made of skeletal muscle, therefore it is under voluntary control – supplied by pudendal nerve

• is a secondary sphincter to control the flow

Describe the 3 types of epithelium found in the lining of the male urethra.

• Transitional epithelium – upper part of prostatic part

• Pseudostratified epithelium – lower part of prostatic part, membranous part, most of spongy part

• Stratified squamous non-keratinised – terminal part of spongy part

What is the blood supply of the male urethra?

• Supplied by blood vessels of prostate and penis

What is the lymphatic drainage of the male urethra?

• From prostatic and membranous part of urethra passes to internal and external iliac nodes.

• From spongy part to the deep inguinal, superficial inguinal and external iliac nodes.

Describe the autonomic innervation of the male urethra.

Autonomic Innervation (Involuntary) → Smooth Muscle Control

This controls the internal urethral sphincter and smooth muscle within the urethra.

Sympathetic (T11–L2, Hypogastric Nerve)

• Origin: Inferior mesenteric ganglion → travels via the hypogastric nerve.

• Function:

• Contracts the internal urethral sphincter → prevents urine leakage.

• Prevents retrograde ejaculation by closing the bladder neck during ejaculation.

Parasympathetic (S2–S4, Pelvic Nerve)

• Origin: Sacral spinal cord (S2–S4) → travels via the pelvic nerve.

• Function:

• Relaxes the internal urethral sphincter → allows urination.

• Stimulates detrusor muscle contraction to empty the bladder

Describe the somatic innervation of the male urethra.

Somatic Innervation (Voluntary) → Skeletal Muscle Control

This controls the external urethral sphincter (rhabdosphincter), allowing voluntary control of urination.

Pudendal Nerve (S2–S4)

• Origin: Sacral spinal cord (S2–S4).

• Function:

• Contracts the external urethral sphincter (rhabdosphincter) → maintains continence.

• Relaxes during urination to allow urine flow.

What did the anterior wall of the prostatic urethra above the opening of the prostatic utricle derived from?

Vesicourethral canal.

What is the posterior wall of the male urethra derived from?

absorbed portions of the mesonephric ducts

What did the lower part of the prostatic and membranous urethra developed from?

definitive urogenital sinus

What was the penile part of the urethra derived from?

urethral plate

What are dimensions of the female urethra in terms of length and diameter?

Only 4 cm long and 6 mm in diameter.

Developmentally, what does the female urethra correspond to in the male urethra?

Developmentally, it corresponds to the upper part of prostatic urethra of

males that lies above the opening of prostatic utricle.

What is the course of the female urethra?

• Begins at the internal urethral orifice at the neck of the bladder, roughly 5 cm behind the middle of the pubic symphysis.

• It runs downwards and forwards embedded in the anterior wall of vagina, traverses urogenital diaphragm, and ends at the external urethral orifice in the vestibule of vagina.

What epithelium is found in the upper and major lower part of the female urethra?

• Upper part is lined by transitional epithelium and major lower part is lined by stratified squamous epithelium.

What is the paraurethral glands (of Skene) in the female urethra and what are the homologous to?

• The collections of mucous glands one on each side of the upper part of

the urethra are called the paraurethral glands (of Skene) which are

homologous with the male prostate.

Where is the internal urethral sphincter (IUS) located in females?

At the bladder neck, where the urethra begins.

What type of muscle is the internal urethral sphincter (IUS) in females?

smooth- involuntary

What is the function of the internal urethral sphincter (IUS) in females?

Prevents urinary leakage and retrograde semen flow (though less relevant in

females).

Describe the innervation of the internal urethral sphincter (IUS) in females.

Autonomic nervous system (ANS)

• Sympathetic (T11–L2, hypogastric nerve) → Contracts the sphincter to retain urine.

• Parasympathetic (S2–S4, pelvic nerve) → Relaxes the sphincter to allow urination.

Where is the external urethral sphincter (EUS) located in females?

Mid-urethra, surrounding the urethra.

What type of muscle is the external urethral sphincter (EUS) in females?

skeletal muscle- voluntary

What is the function of the external urethral sphincter (EUS) in females?

Provides conscious control over urination (e.g., delaying urination when necessary).

Describe the innervation of the external urethral sphincter (EUS) in females.

Somatic nervous system

• Pudendal nerve (S2–S4) → Allows voluntary contraction and relaxation.

What are the support muscles in the female urethra?

The EUS is part of a broader complex called the rhabdosphincter

(synonymous with external urethral sphincter in both males and females), which includes:

• Compressor urethrae → Wraps around and compresses the urethra.

• Urethrovaginal sphincter → Constricts the urethra and vagina together.

The compressor urethrae and urethrovaginal sphincter are muscles that contribute to continence and pelvic floor support, working with the levator ani (especially the puborectalis) to prevent involuntary leakage

What is the narrowest part of the male urethra and why is this important to know?

• External urethral meatus is the narrowest part of male urethra.

• Catheterization of bladder: in cases of retention of urine the bladder is catheterised with rubber or metallic catheter one should remember the normal curvatures of the urethra.

What is urethritis?

Acute urethritis can have STI and non STI causes. A common STI cause is gonococcal infection. This gives rise to a purulent discharge from urethra and frequent painful micturition.

What is Hypospadias?

Hypospadias is a common anomaly in which the urethra opens on the

under surface of penis or in perineum. Epispadias is rare and is

associated with ectopia vesicae.