The male reproductive system consists of external genitals (the penis, testes, and scrotum) as well as internal organs such as the prostate gland, vas deferens, and urethra. The fertility and sexual characteristics of a man are dependent on the regular functioning of the male reproductive system as well as hormones secreted by the brain.

The male reproductive organs perform the following functions:

• Spermatozoa generation, maturation, and storage.
• Spermatozoa delivery in semen into the female reproductive canal.

The urethra also serves as a route for urine excretion.

Male reproductive system is further divided in to 2 categories-

• External male Reproductive organ
• Penis
• Testes
• Scrotum
• Internal male Reproductive Organ

It includes

1. Vas deferens
2. Prostate
3. Urethra

Penis

• The penis consists of a root and a shaft. The root secures the penis in the perineum, whereas the shaft (body) is the organ’s externally visible, cell component. Three cylindrical masses of erectile tissue and smooth muscle make up the structure. The erectile tissue is supported by fibrous tissue and skin, and it has a plentiful blood supply.
• The two lateral columns are known as the corpora cavernosa, and the column between them, which houses the urethra, is known as the corpus spongiosum.
• The glans penis is a triangle structure formed by the penile tip. The skin folds on itself just above the glans, forming a moveable double layer known as the foreskin or prepuce.
• The deep, dorsal, and bulbar arteries of the penis, which branch from the internal pudendal arteries, supply arterial blood.
• A network of veins transports blood to the internal pudendal and iliac veins. Autonomic and somatic nerves supply the penis.
• The strong sensory innervation of the penis aids in erection.
• The autonomic nervous system regulates the filling of its erectile tissue by regulating the diameter of blood vessels supplying and draining it.
• Parasympathetic stimulation causes blood to fill the spongy erectile tissue due to arteriolar dilatation and venoconstriction, which increases blood flow into the penis while obstructing outflow. As a result, the penis gets engorged and erect, which is required for sexual intercourse.

Scrotum

The scrotum is a pigmented pouch of skin, connective tissue, and smooth muscle. It’s split into two portions, each with one testis, one epididymis, and the testicular end of a spermatic cord. It’s beneath the pubic symphysis, in front of the upper thighs, and behind the penis.

Testes

The testes are the male reproductive glands that function similarly to the ovaries in females. The spermatic cords suspend them in the scrotum and they are roughly 4.5 cm long, 2.5 cm wide, and 3 cm thick. Three layers of tissue surround them.

Three layers of tissues are-

Tunica vaginalis

This is a double membrane that forms the testicular outer covering and is a downgrowth of the abdominal and pelvic peritoneum. The testes form in the lumbar region of the abdominal cavity, immediately behind the kidneys, during early foetal development. They subsequently descend into the scrotum, carrying peritoneum, blood and lymph vessels, nerves, and the deferent duct with them. The peritoneum finally separates from the abdominal peritoneum and surrounds the testes in the scrotum. The testes should have descended into the scrotum by the eighth month of foetal life.

Tunica albuginea

This is the fibrous layer that lies beneath the tunica vaginalis. Septa are formed by ingrowths that divide the glandular tissue of the testes into lobules.

Tunica vasculosa.

This consists of a network of capillaries supported by delicate connective tissue.

Structure

There are 200-300 lobules in each testis, and within each lobule are 1-4 convoluted loops of germinal epithelial cells called seminiferous tubules. After puberty, clusters of rut interstitial cells (of Leydig) produce the hormone testosterone between the tubules. The tubules merge to create a single tubule at the upper pole of the testis. This tubule, which is about Sin in length, is repeatedly folded and firmly packed into a mass known as the epididymis. It enters the spermatic cord as the deferent duct (vas deferens) from the scrotum. In the spermatic cords, blood and lymph vessels travel to the testes.

Functions

• Spermatozoa (sperm) grow in the testes by the process of spermatogenesis and mature as they move through the long and convoluted epididymis, where they are stored.
• FSH produced by the anterior pituitary gland increases sperm production.
• A mature sperm has a head, a body, and a long whip-like tail that allows it to move. The nucleus, which contains the DNA, almost fully fills the skull.
• It also contains the enzymes needed to pierce the ovum’s outer layers and merge with its nucleus. The mitochondria in the sperm’s body fuel the pushing activity of the tail, which propels the sperm along the female reproductive system.
• Spermatogenesis occurs at a temperature around 3°C lower than normal body temperature. The testes are kept cool by their position outside the abdominal cavity, and the scrotum’s thin outer coat has relatively little insulating fat.
• However, this exposed posture exposes the testis to injury and extreme cold, thus a pouch of smooth muscle, the cremaster muscle, wraps around the tunica vaginalis, extends upwards over the spermatic cord, and attaches to structures in the groyne.
• When it contracts, it draws the scrotum closer to the body, most likely for protection. 18.10
• In contrast to females, who do not create new gametes after birth, male sperm production begins around adolescence and continues throughout life, frequently into old age, under the influence of testosterone.

Spermatic cords

• The spermatic cords hold the testes in place in the scrotum. Each cord has a testicular artery, testicular veins, lymphatics, a deferent duct, and testicular nerves that connect from their numerous origins in the abdomen to form the cord.
• The cord runs into the inguinal canal and is linked to the testis on the posterior wall by a sheath of smooth muscle (the cremaster muscle) and connective and fibrous tissues.

Blood supply, lymph drainage and nerve supply

Arterial supply

The testicular artery branches from the abdominal aorta, just below the renal arteries.

Venous drainage: The testicular vein passes into the abdominal cavity. The left vein opens into the left renal vein and the right into the inferior vena cava.

Lymph drainage: This is through lymph nodes around the aorta.

Nerve supply: This is provided by branches from the 10th and 11th thoracic nerves.

Deferent duct

• This is 45 cm long and is also known as the vas deferens.
• It ascends medially from the testis through the inguinal canal to the posterior wall of the bladder, where it joins the duct from the seminal vesicle to form the ejaculatory duct.
• Sperm can remain viable in the deferent duct for several weeks.

Seminal vesicles

• The seminal vesicles are two small 5 cm long fibromuscular pouches lined with columnar epithelium and located immediately posterior to the bladder.
• Each seminal vesicle opens into a small duct at its lower end, which unites with the matching deferent duct to produce an ejaculatory duct.

Functions of Seminal vesicles

During ejaculation, the seminal vesicles constrict and discharge their accumulated contents, seminal fluid. Seminal fluid, which accounts for 60% of the volume of sperm, is viscous and alkaline in order to shield the sperm from the acidic environment of the vagina, and it contains fructose to fuel the sperm on their travel through the female reproductive tract.

Ejaculatory ducts

• The ejaculatory ducts are two 2 cm long tubes created by the union of a seminal vesicle duct and a deferent duct.
• They pass via the prostate gland and connect to the prostatic urethra, where they transport seminal fluid and spermatozoa.
• The walls of the ejaculatory ducts are made up of the same tissue layers as the seminal vesicles.

Prostate gland

• The prostate gland lies in the pelvic cavity in front of the rectum and behind the symphysis pubis, completely surrounding the urethra as it emerges from the bladder.
• It has an outer fibrous covering, enclosing glandular tissue wrapped in smooth muscle.
• The gland weighs about 8 g in youth but progressively enlarges (hypertrophies) with age, and is likely to weigh about 40 g by the age of 50.

Functions of Prostate Gland

The prostate gland secretes a thin, milky fluid that accounts for approximately 30% of the volume of sperm and contributes to its milky appearance.

It contains a clotting enzyme that thickens the vaginal semen, increasing the possibility of semen retention close to the cervix.

Urethra

• The male urethra serves as a conduit for the movement of urine and sperm. It’s around 19-20 cm long and made up of three pieces.
• The prostatic urethra begins at the bladder’s urethral orifice and travels through the prostate gland.
• After passing through the perineal membrane, the membranous urethra continues from the prostate gland to the bulb of the penis.
• The spongiosa or penile urethra runs from the corpus spongiosum of the penis to the external urethral orifice in the glans penis.
• There are two urethral sphincters.
• The internal sphincter is a ring of smooth muscle at the neck of the bladder above the prostate gland.
• The external sphincter is a ring of skeletal muscle surrounding the membranous part.

Ejaculation

• During male orgasm, spermatozoa are released from the epididymis and travel through the deferent duct, the ejaculatory duct, and the urethra.
• The semen is driven by intense rhythmical contractions of smooth muscle in the deferent duct’s walls; the muscular contractions are sympathetically mediated.
• Muscle in the seminal vesicles and prostate gland contracts as well, contributing their contents to the fluid flowing via the genital ducts.
• The force produced by these combined actions causes the sperm to exit via the external urethral sphincter.
• Sperm make up only 10% of the final ejaculate, with the rest consisting primarily of seminal (60%) and prostatic (30%) fluids, which are added to the sperm during male orgasm, as well as mucus formed in the urethra.
• To counteract the acidity of the vagina, sperm is somewhat alkaline.
• A normal ejaculate produces between 2 and 5 mL of semen and contains between 40 and 100 million spermatozoa per ml.
• If sperm is not ejaculated, it loses its fertility over time and is reabsorbed by the epididymis.

Puberty in the male

Between the ages of 10 and 14, this occurs. LH from the pituitary glands anterior lobe activates the interstitial cells of the testes, increasing testosterone synthesis.

Sexual maturation and the development of male secondary sexual characteristics occur under the influence of testosterone, including:

• Muscular and bone development, as well as significant height and weight gain.
• Laryngeal enlargement and depth of the voice, which ‘breaks’.
• Hair growth on the face, axillae, chest, abdomen, and pubis.
• Maturation of the seminiferous tubules and the production of spermatozoa; and Enlargement of the penis, scrotum, and prostate gland.
• Skin thickening, resulting in oilier skin.