Testis and appendages

Figure 1: Testis and its appendages

What are the testis and scrotum?

The testis or male gonad is an important part of the male reproductive system. Testes are paired oval organs located between upper thighs suspended by the spermatic cord in a skin pouch called the scrotum. The scrotal skin is corrugated because of an underlying muscle called the dartos. In the fluid filled membranous layers lie the testes.

Each testis develops in the abdomen during development in the womb and then descend to their permanent position later. The testicular temperature is about 3-40 C below the core body temperature. Adjacent to the testis is a coiled tube called the epididymis that serves to store, mature and transport sperm between each testis and the vas deferens (a thick muscular tube that carries sperm). Each testis produces the male hormone testosterone (a steroid hormone) and sperm (spermatozoa).

Seminiferous Tubule showing various stages of sperm development

Figure 2: Seminiferous Tubule showing various stages of sperm development

 

What is Spermatogenesis?

Each testis subdivides into hundreds of coiled tubules known as seminiferous tubules (ST). These are production houses of spermatozoa (sperm). Spermatogenesis is essentially an elaborate cell differentiation process starting with spermatogonia (germ cells). These line the ST and end as a highly specialised motile cell spermatozoa containing half the number of chromosomes. Each tubule is lined with germ cells, which progress to become sperm (Figure 2). STs also contain special cells called Sertoli cells (Figure 3). They support the lining of the ST and also help in the maturation of sperm. Sertoli cells are crucial for sperm development.

Sertoli Cell nursing developing sperm

Figure 3: Sertoli Cell nursing developing sperm

Sperm leave the testes through the epididymis, which joins with the seminal vesicles near the prostate, opening ultimately into the prostate. The secretions from seminal vesicles and the prostate (see below) mix with the sperm to make up the volume of semen during ejaculation.

Seminal Vesicles

The seminal vesicles are two glands at the base of the bladder and connected to the prostate. Like the prostate, they also provide nutrients for the sperm.

Prostate

The prostate is a gland the size of a walnut that is below the bladder, in front of the rectum and behind the pubic bone. It is closely linked with the urinary system. The prostate secretes much of the liquid portion of the seminal fluid.

Urethra

The urethra is the tube (duct) that carries urine from the bladder and sperm from the prostate out through the penis.

Urinary Bladder

Although the urinary bladder is not related to the reproductive system, its continuity with urethra makes an important adjacent organ. It is a hollow, muscular and distensible organ above the prostate on the pelvic floor. The urinary bladder is responsible for the storage and evacuation of urine. The ureters are two hollow muscular tubes that connect the kidney and bladder.

What is the main function of the testes?

The testes’ main function as part of the male body are to produce and hold sperm until it is mature enough for ejaculation. Its secondary function, but equally as important, is to produce hormones and androgens. These hormones are responsible for sex drive, development of muscle mass and development of bone mass.

Male genito-urinary system

Figure 4 : Male genito-urinary system

What is the role of testosterone?

Testosterone and its more potent product Dihydrotestosterone are called androgens. Testosterone is responsible for the regulation of pituitary hormones (LH and FSH) and the initiation and maintenance of sperm production. Androgens help with sexual differentiation in the embryo. Later in life, they help to mature sexual organs and give sexual characteristics. They also increase bone density and muscle mass and have a role in mental development and mood. Androgens have an influence on red blood cell production. There is a progressive decline in androgen production with ageing. This phenomenon is termed as andropause (male climacteric, progressive or partial androgen deficiency of the ageing male).

Other hormones of the Testis: Sertoli cells produce a hormone called inhibinwhich regulates Follicle Stimulating Hormone (FSH) in men.

What is the purpose of the scrotum?

The main purpose of the scrotum is to keep the testicles at a regulated temperature to avoid them from overheating. The ideal temperature for the testicles is around 2 degrees below body temperature, which provides an optimal environment for the male to be able to produce and store sperm.

What is the function of the scrotal sac?

The scrotal sac is the loose bit of skin that hangs both below and behind the penis. Its main function is to produce, maintain and transport sperm from the scrotal area to the penis for the purpose of ejaculation.

The scrotal sac also has a protective functionality; it acts as a climate control system for the testes.  For sperm to development in a safe environment, the scrotal sac must be approximately 2 degrees cooler than regular body temperature. There are special muscles located within the scrotal sac that expand and retract to help maintain this temperature.

Why are the testes in the scrotum?

Unlike female reproductive organs, which are inside the body, male reproductive organs are situated on the outside. They are located inside the scrotum, which provides the perfect environment to regulate temperature and produce sperm.

When a male is first developing in the womb, the testes grow in the abdomen area of the body. After or around the 7th month of development, they then drop down into the scrotum. This provides a protective environment and enough room for them to expand and retract as needed to regulate the temperature inside the sac.

Which structure connects the testes to the urethra?

The testes connect to the urethra in two different ways. The first is via the epididymis. The function of the epididymis is to transport sperm out of the testicles; it then transfers to the Vas Deferens. The Vas Deferens, most commonly known as the ejaculatory duct, moves sperm from the epididymis to the urethra.

Vinod Nargund

Mr Vinod Nargund is a Consultant Urological Surgeon specialising in Urological cancer, male sexual and fertility problems. He was trained in Urology at the City Hospital Belfast, the Royal Infirmary Bradford and the Churchill and John Radcliffe Hospitals in Oxford. You can view all of his qualifications on his biography page.

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