Scrotum and its contents: Testicles

Scrotum and Testicles:

The scrotum or scrotal sac is visible on every male as it lies underneath the penis, hanging from the midline of the pelvic region just between both thighs. It is a part of the male external genitalia.

Please read an introduction to the male reproductive system here.

Inside the scrotal sac are two oval shaped testicles or testes (singular -> testis) which are responsible for the formation and storage of sperm. The process of sperm formation is referred to as spermatogenesis.

• Sperm is the male gamete in humans and other animals while the egg or ova is the female gamete. You can think of a gamete as the sex cell. The union of both sex cells (sperm + ova) is termed fertilization. A zygote is formed immediately after fertilization. It is this zygote that develops into the embryo, then a foetus (or fetus) and eventually a neonate or newly born child.

The scrotum is located outside the body and that's ideal. This is so because the testis requires a temperature slightly lower than that of the normal body temperature (36.5^oC) to properly form the sperm cells. In fact, this is the ideal reason why the testes descends from the abdominal cavity (inside the body) to the scrotum (outside the body). This external position of scrotum therefore presents a temperature reduction by -1^oC to -7^oC.

The scrotum is divided in its midline by the perineal raphe. The perineal raphe is present in males and females. It is visible as a midline seen on some parts of the human body.

The image below shows the scrotum, its internal contents and the perineal raphe:

You can read on seminal vesicles and bulbourethral glands here.

What are the Testicles?

The testicle is the male reproductive gland in humans (males) and all other male animals. Its primary function is to produce sperm and the male sex hormone 'testosterone'.

Generally, males have two testicles of similar sizes with both located within either half of the scrotum. Interestingly, the scrotal sacs are not always equal in length; and as a result, one of the testicle (or testis) typically extends farther downwards into the scrotum in relation to the other.

Inside the developing male embryo (in the mother's womb), the testicles begin their formation in the abdominal region. After 8 weeks of gestation, the testicles gradually descend from the abdomen into the scrotum via through a tube-like structure in the inguinal canal. For this reason, the testicles are located outside the body (scrotum) and this is crucial for sperm formation or spermatogenesis.

As a male, one may have observed that on cold days, the scrotum hang towards the body. Conversely, it tends to move downwards (away from the body) on warmer days. This is so because at cooler temperatures, the cremaster muscle contracts, moving both testes towards the body with a resultant rise in the scrotal temperature. Conversely, the cremaster muscle relaxes when the environmental temperature rises, ultimately pushing the testes away from the body.

Sperm is produced by the testes present within the scrotum; and the surrounding temperature is extremely important for it's formation. To this end, the cremaster muscles of the scrotum have got a great ability to contract and relax, thus aiding the testes to either move closer to the body or away from it; depending on the surrounding temperature.

Please read on homeostasis here.

Structurally, both testes are covered by a membranous sheet called the tunica albuginea. The testes comprises of very minute and highly coiled tubes called seminiferous tubules. The cells lining the seminiferous produces the male gamete or spermatozoa or sperm cells.

From the seminiferous tubules, the sperm is conveyed into a another tubular structure termed rete testis. The rete testis is located in the mediastinum testis.

The sperm cells are conveyed from the rete testis into the ductuli efferentes testis (efferent ducts), and then to the epididymis. The maturation of sperm cells occur in the epididymis.

From the epididymis, the sperm travels into the vas deferens and eventually the spermatic cord. The vas deferens therefore functions to transport sperm from the epididymis to the spermatic cord as they are eventually moved through the urethra and out of the external urethral orifice through a series of muscular contractions.

Meanwhile, understand that sperm and semen aren't the same thing. Sperm is the male sex cell (and it happens to be the smallest cell in the human body). It is exactly what meets and fertilizes the female sex cell (ova or egg). Ironically, the ova is the biggest cell in the human body.

Semen refers to the thick whitish (or slightly yellowish) and viscous fluid released from the penis. The process of releasing semen in males is termed ejaculation.

You can read on amazing facts in biology here.

During ejaculation, millions of sperm cells are introduced into the female’s vagina; and they swim upwards (towards the oviduct or fallopian tube in the female) with the aid of their tail-like structure called flagella.

Ejaculation is always accompanied with a characteristic feeling of pleasure. In fact, this pleasurable feeling is the climax of sexual excitement and it's referred to as orgasm.

Note: The sperm cells are present within the semen. This is shown in the image below:

In summary, the semen contains the following:

• Sperm cells

• Amino acids

• Enzymes

• Vitamin C

• Zinc prostate specific antigen

• Mucus

• Prostagladins

• Phosphatases

• Silic Acid

• Flavins

Understand that apart from the sperm cells, many of these components making up the semen are secretions from the male accessory reproductive glands.

Please read on the male accessory sex organs here.

Apart from the testicles, also found in the scrotum are:

• Epididymis

• Vas deferens

• Spermatic cord

• Cremaster muscle

Please read on the epididymis, vas deferens, spermatic cord and cremaster muscle here.