Male Reproductive Anatomy

Male vs female pelvises

Male sexual anatomy

• Primary sex organ: testes → sperm + testosterone

• Secondary sex organs: ducts, glands + penis → transport/support sperm

Functions: (SECSH)

• Spermatogenesis

• Hormone secretion

• Semen production

• Ejaculation

• Copulation

External genitalia

Penis

• Root: 2 crura → attach to inferior pubic rami

• Bulb: expansion of shaft at base

• Body: shaft

• Glans: distal end

Erectile tissue – “2 for erection, 1 for protection”

• 2 corpora cavernosa → dorsal → erection

• 1 corpus spongiosum → ventral → contains urethra

  • Protects + keeps urethra open during ejaculation

  • Forms glans (“acorn”)

Scrotum

• Skin-covered sac → divided by median septum

• Thermoregulation: 2–3°C below body temp

• Dartos muscle: wrinkles skin

• Cremaster muscle: elevates testes

Homologous structures

• Homologous = same embryonic origin, but may develop differently and have different functions.

**know the table

Cross section anatomy of the penis

Erectile Tissues

• 2 corpora cavernosa

• 1 corpus spongiosum → contains urethra

• Tunica albuginea → fibrous covering around erectile tissue

Blood supply

• Deep + dorsal penile arteries ← internal pudendal artery

Innervation

• Pudendal nerve → somatic/sensory

• Pelvic splanchnic nerves → autonomic

Perineum

• Diamond-shaped region between thighs, ↓ pelvic diaphragm

• Boundaries: anterior = pubic symphysis; posterior = coccyx; lateral = ischial tuberosities

• Roof: pelvic diaphragm

• Floor: skin + superficial fascia

• Divided into 2 triangles:

  • Urogenital

  • Anal

Anterior Urogenital Triangle

Contents

• Root of penis

• Scrotum

• Penile/spongy urethra

• Bulbourethral glands + membranous urethra → deep perineal pouch

Muscles

• Bulbospongiosus

• Ischiocavernosus

• Superficial transverse perineal

Penis pics

Scrotum

• Sac of loose skin, fascia + smooth muscle, divided into 2 pouches by a septum

• Function: temperature regulation of testes

Contents:

• Testes

• Epididymis

• Spermatic cord → vas deferens, blood vessels + nerves

Layers — “Some Damn Englishman Called It The Testes”

1. Skin

2. Dartos muscle/fascia

3. External spermatic fascia

4. Cremaster muscle/fascia

5. Internal spermatic fascia

6. Tunica vaginalis → serous membrane surrounding testes

7. Tunica albuginea → dense, white capsule

Scrotum pics

Temperature regulation of the testes

Temperature Regulation of Testes

• Dartos muscle: smooth muscle lining of scrotum

  • Cold/arousal → elevates testes

  • Wrinkles skin → ↓ surface area → ↓ heat loss

• Cremaster muscle: in spermatic cord; slip of internal abdominal muscle

  • Cold → elevates testes

• Pampiniform plexus: counter-current heat exchange

  • Testicular artery + vein

  • Cool venous blood cools arterial blood travelling to testes

Easy mnemonic: Cool Down Please!

• Cremaster → elevates testes

• Dartos → wrinkles skin

• Pampiniform → cools arterial blood

Testes

Testes

• Paired, oval glands

  • Left usually lower than right

• Covered by:

  • Tunica vaginalis

  • Tunica albuginea

• Develop in abdomen → descend through inguinal canal just before birth

Internal structure:

• Septa → divide testes into 200–300 lobules

• Each lobule → 2–3 seminiferous tubules

• Seminiferous tubules → spermatogenesis

• Rete testis → efferent ductules (12-20)→ epididymis

• Blood supply: testicular artery

• Venous drainage: pampiniform plexus

Seminiferous Tubules

Seminiferous Tubules

Contain:

• Sperm-forming cells

• Sertoli cells

  • Form blood-testis barrier

  • Support/nourish developing sperm

  • Secrete inhibin → ↓ spermatogenesis

  • Produce fluid + control sperm release into lumen

• Leydig cells (interstitium)

  • Secrete testosterone

  • “S = Support, L = Libido”

Epididymis

Epididymis

• Single, coiled duct posterolateral to testis

• Head → receives efferent ductules

• Body

• Tail

• Site of sperm maturation + storage

• Smooth muscle → aids sperm movement

Vas deferens (Ductus Deferens)

• Long, muscular duct → carries sperm from epididymis → urethra

• Ampulla → dilated portion

• Passes through spermatic cord

• Joins seminal vesicle duct → forms ejaculatory duct in pelvic cavity

• One per testicle

Accessory Glands

Seminal Vesicles (2)

• Elongated outgrowths of vas deferens

• Posterior to bladder, between bladder + rectum

• Secrete clear, fructose-rich alkaline fluid + prostaglandins, ATP & coagulating enzymes

• Nutrition for sperm → supports optimal function

Prostate (1, unpaired)

• Walnut-sized, inferior to bladder

• Posterior to pubic symphysis, anterior to rectum

• Continuous with bladder neck

• Surrounds urethra

• Ejaculatory ducts pass through posterior aspect → open into prostatic urethra

• Secretes milky prostatic fluid (enzymes + citrate) → kills bacteria

Bulbourethral (Cowper’s) Glands (2)

• Small, pea-sized mucous glands, inferior to prostate

• Lateral to membranous urethra

• Open into spongy urethra at root of penis

• Secrete alkaline pre-ejaculate (mucus-like)

  • Lubrication

  • Urethral neutralisation

Accessory glands pic

Semen

• Sperm + seminal fluid from accessory glands

• Composition:

  • 60% seminal vesicles

  • 30% prostate

  • 5% bulbourethral glands

• Slightly alkaline, milky appearance

• Typical ejaculate: 2.5–5 mL

• Normal sperm count: 50–150 million/mL

• <20 million/mL → sterile (per lecture)

Duct System

Vas deferens (2)

• Thick, muscular wall → propels sperm during ejaculation

• Joins seminal vesicle duct → ejaculatory duct

Ejaculatory ducts (2)

• Pass through prostate → prostatic urethra

Urethra

Prostatic → Membranous → Spongy/Penile

• Prostatic urethra

  • Receives ejaculatory ducts

• Membranous urethra

  • Shortest + least protected

  • Common injury site in pelvic trauma

  • Runs through urogenital diaphragm

• Penile/Spongy urethra

  • Within corpus spongiosum

  • Opens at external urethral meatus

Urethra pic

Inguinal canal

• Short, oblique passage in lower anterior abdominal wall (~4 cm)

• Spermatic cord passes through

• Extends deep inguinal ring → superficial inguinal ring

• Potential site of inguinal hernia

• Herniation: abnormal exit of tissue/organ through the wall of the cavity where it normally lies

Spermatic Cord

Spermatic Cord

• Passes through inguinal canal

• Contains:

  • Vas deferens

  • Testicular artery

  • Pampiniform plexus → heat exchange

  • Cremaster muscle

  • Lymphatics + nerves

• Clinical: inguinal hernia + torsion of the cord

Spermatogenesis

• Production of sperm in the seminiferous tubules

• Spermatogonia → mature spermatozoa through:

  • Mitosis

  • Meiosis

  • Spermiogenesis

How semen exits

Semen Exit: Erection → Emission → Ejaculation

1. Erection

• Sexual stimulation → parasympathetic reflex

• Arterioles dilate → ↑ blood flow → veins compressed → blood trapped

• Penile blood sinuses engorge → erection

• Bladder sphincter closes

2. Emission

• Sympathetic reflex

• Fluids propelled through vas deferens → seminal vesicles → ejaculatory ducts → bulb of penis

• Prostatic fluid enters urethra

3. Ejaculation

• Skeletal muscle contractions → squeeze semen through urethra

• Smooth muscle at bladder neck prevents reflux into bladder

Pathway of sperm

SEVEN-UP — Sperm Pathway

S → Seminiferous tubules
E → Epididymis
V → Vas deferens
E → Ejaculatory duct
N → Nothing
U → Urethra
P → Penis

Blood Supply & Innervation

Arterial supply

• Testes: testicular artery ← abdominal aorta

• Penis: internal pudendal artery → dorsal + deep penile arteries

Venous drainage

• Testes → pampiniform plexus → testicular vein

  • Right → IVC

  • Left → left renal vein

Innervation

• Pudendal nerve → sensory/motor to most perineal muscles

• Autonomic: pelvic splanchnics + hypogastric plexus

• Genitofemoral nerve → cremaster reflex

Clinical considerations and Male timeline

Clinical Considerations

• Vasectomy: cut vas deferens → sterilisation; potentially reversible

• Prostate enlargement (e.g. carcinoma, prostatitis) → difficulty urinating

• Varicocele: dilated pampiniform veins

  • → infertility risk

  • → testicular atrophy + ↓ sperm production

Male Timeline

• Infancy: Erections begin

• 11–14 yrs: Secondary sex characteristics appear

• 13–16 yrs: Sperm produced in adult amounts (puberty onwards)

• Late teens: Peak sexual urges

• Throughout life: If healthy → sex drive + ability to fertilise an ovum