Anatomy of male reproductive organs

What are the three major functions of the male reproductive system?

1. Secretion of sex hormones

2. Production of sperm

3. Deposition of sperm into the female reproductive tract

Testes

Organs responsible for secreting sex hormones and producing sperm. Located in the scrotum, outside the abdominal cavity.

Q: What structure performs the function of depositing sperm into the female reproductive tract?

The ejaculatory ducts and penis.

Scrotum

A pouch of skin containing the testes; divided into two compartments by a median septum to reduce the spread of infection or trauma.

• rich in sensory nerves especially near inner thigh, can lead to sexual arousal when stimulated.

What is the dartos (tunica dartos), and what does it do?

It's a layer of fascia and smooth muscle under the scrotal skin, innervated by the sympathetic nervous system. It contracts in response to temperature, helping regulate testicular temperature (e.g., shrinkage in cold water).

What glands are found in the scrotal skin and what is their function?

Sebaceous (oil) glands; they help produce sweat to aid in temperature regulation.

Cremaster muscle

A skeletal muscle derived from the internal oblique muscle; supports the testes and regulates temperature by contracting or relaxing in response to cold or warmth.

• It is a skeletal (striated) muscle, meaning it can be voluntarily controlled, but also contracts involuntarily through reflexes.

How does the cremaster muscle respond to temperature?

Cold triggers contraction (pulling testes closer to the body), while warmth causes relaxation (allowing them to descend), helping regulate sperm production temperature.

Gubernaculum

A connective tissue structure that anchors the testes and epididymis to the scrotum.

Each testis is enclosed by two tissue layers:

1. The outer tunica vaginalis: a thin serous membrane derived from peritoneum 

2. The inner tunica albuginea: a tough fibrous capsule that lies directly on the testis surface. Projections from the tunica albuginea extend inward and divide the testis into multiple lobules. Each lobule contains several seminiferous tubules, which are tightly packed and densely coiled structures responsible for sperm production. When combined th total length of seminiferous tubules in both testes is approx 700 feet. 

Seminiferous tubules

Highly coiled tubules within each testicular lobule responsible for producing sperm; total combined length in both testes is approximately 700 feet.

• where spermatogensis occurs, they are surrounded by connective tissue that cointains scattered Laydig cells

Rete testis

A network of fine ducts that collect sperm from the seminiferous tubules and channel them toward the efferent ductules.

Efferent ductules

Ducts that connect the rete testis to the epididymis, acting as a bridge for sperm transport.

What are the three regions of the epididymis and their functions?

• Head (caput): Receives sperm from the testis

• Body (corpus): Site of sperm maturation

• Tail (cauda): Stores sperm until ejaculation

What is the pathway of sperm from the seminiferous tubules to the vas deferens?

Seminiferous tubules → Rete testis → Efferent ductules → Epididymis (head → body → tail) → Vas deferens.

What is the vas deferens, and what is its function?

The vas deferens is a muscular duct that carries mature sperm from the tail of the epididymis to the pelvic urethra during ejaculation.

Male accessory glands

Glands that add seminal fluid to sperm along the vas deferens route, including the

1. ampullae

2. seminal vesicles

3. prostate gland

4. and bulbo-urethral (Cowper’s) glands.

The penis contains three erectile bodies

two corpora cavernosa on the dorsal (upper) side and one corpus spongiosum on the ventral (underside), which encloses the penile urethra.

Tunica albuginea

A fibrous, non-stretchable capsule that surrounds each erectile body in the penis. It supports the structure and limits excessive expansion during erection.

How does an erection occur in terms of tissue structure?

The erectile tissues are sponge-like and vascular, filling with blood during sexual arousal, which causes the penis to become erect.

What is the glans penis and how is it formed?

The glans penis is the sensitive tip of the penis, formed by the expansion of the corpus spongiosum at the distal end.

External urinary meatus

The external opening of the urethra located at the tip of the glans penis, through which urine and semen exit the body.

What is the function of the prepuce (foreskin)?

The prepuce is the skin covering the glans and shaft of the penis. It protects the underlying tissues from friction and abrasion.

What muscle surrounds each corpus cavernosum and what is its function?

Each corpus cavernosum is surrounded by the ischiocavernosus muscle. Its spasmodic contractions increase blood pressure within the erectile tissues, helping to maintain an erection.

What muscle surrounds the corpus spongiosum and what is its function?

The bulbospongiosus muscle surrounds the corpus spongiosum. It contracts to help eject semen during ejaculation and also assists in urine expulsion.

What triggers an erection and how does it work at the molecular level?

Nitric oxide (NO), released by parasympathetic nerves and endothelial cells, triggers erection by stimulating cGMP production. cGMP closes calcium channels, reducing calcium in smooth muscle, causing relaxation of penile arteries and vasodilation, which allows blood to fill erectile tissues.