What is Semen Made of? How is Sperm Produced & Stored?

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sperm production seminiferous tubules

Semen and sperm are often used interchangeably, like they are one and the same, but they aren’t. Sperm is one of the vital components of semen while semen itself is an organic fluid containing spermatozoa.

Semen is fluid secreted by the male sexual glands and contains sperm that can fertilize the female ovum. The process of discharging the semen is known as ejaculation.

A typical male can ejaculate around 3 to 6mL of semen. To put it in perspective, the standard size of a teaspoon is 5mL, so the amount of semen produced is little more than the amount of vanilla extract needed for baking cookies.

Production of sperm happens in the testes, and it is stored in the epididymis. Epididymis acts as a reservoir from which the sperm starts its travel upstream to the ejaculatory duct from where it will be set for launch.

For its journey through the vas deferens, the sperm needs the help of other components of like seminal vesicles, prostate, as well as bulbourethral glands.

Let’s take a closer look at sperm.

What is Sperm?

The spermatozoon is an extraordinarily complex metabolic locomotive, as well as genetic machine. The length of a spermatozoon is nearly 60 microns.

sperm form function

It is divided into three sections – head, neck, and tail. The sperm head (oval) comprises of a nucleus that consists of highly compacted DNA, as well as acrosome containing enzymes necessary for penetrating the eggshell to initiate fertilization.?

The neck connects the head and tail. It comprises a connecting component as well as a proximal centriole. The sperm tail has a principle section, midpiece, and endpiece. The midpiece contains the engine of the sperm (axoneme) and is the source of energy for movement (the mitochondrial sheath).

Physiologically speaking, the sperm axoneme requires nearly 200 to 300 proteins for proper functioning. The best-understood component is sperm microtubules arranged in the 9+2 pattern – 9 outer doublets circling an inner central pair. Any defect in the sperm axoneme can result in ciliary dyskinesia associated with male infertility.

The male genitalia consists of the scrotum (housing testicles, epididymis, as well as vas deferens), and the penis. Tunica albuginea, a white fibrous layer, covers the testes. This layer extends inwards, dividing the testis into nearly 300 lobules.

Sperm production happens in seminiferous tubules (the tightly coiled and long tubules) located in these lobules. The sperm get the essential nutrients from Sertoli cells, which line these seminiferous tubules. When spermatogenesis does not take place, one can only view Sertoli cells on a testicular biopsy.

How is Sperm Produced

Production of sperm is hormonally driven and governed by the hormones present in the brain. Within the brain, the anterior pituitary gland and the hypothalamus control the production of sperm.

The brain produces GnRH (gonadotropin-releasing hormone), which acts on the anterior pituitary gland, forcing it to release LH (luteinizing hormone) and FSH (follicle-stimulating hormone)

Both FSH and LH are released into the bloodstream and act on the testes. It encourages spermatogenesis in the seminiferous tubules (see fig below) and aids production of testosterone by Leydig cells present beside the seminiferous tubules.

sperm production seminiferous tubules

Leydig cells helps produce testosterone, the necessary male hormone. Testosterone is required for the development of typical male secondary sex characteristics, libido, as well as normal erections.

Testosterone plays a major role in sperm production, hormonal levels of this are nearly 50x more in the testis than in the blood. Having a normal hormonal balance is necessary for the production of healthy sperm.

Sperm is produced within the seminiferous tubules, the 700 feet tubing present in the adult testicle. Sperm is prepared from precursor cells (germ cells) that produce nearly 120 million sperm in a day through spermatogenesis or approximately 1200 sperm per heartbeat.

This process takes around 60 days. The germ cells are arranged in a highly organized pattern (outside to inside) within the seminiferous tubule.

Lining the seminiferous tubules are adult testis stem cells that initiate the process of sperm production. An average human testis has 13 recognizable types of germ cells:

  • dark type A spermatogonia (Ad)
  • pale type A spermatogonia (Ap)
  • type B spermatogonia (B)
  • preleptotene (R), leptotene (L), pachytene primary spermatocytes (p), and zygotene (z)
  • secondary spermatocytes (II)
  • Sa, Sb, Sc, Sd1, and Sd2 spermatids.
Despite the production of such a high volume, nature has equipped the human body with various quality check posts to ensure that the integrity (biological and genetic) of ejaculated sperm is maintained.

Where is Sperm Stored

Common belief is that the human body takes approximately three months to produce and ejaculate sperm. However, studies have shown that this time frame is much shorter, and it takes only 50 to 60 days to develop the sperm.

This sperm is then transported to the coiled ducts present in the epididymis, where they wait for another 10 to 14 days to mature. Sperm that is going to be ejaculated remains in the epididymis, which is located near the scrotal base.

During ejaculation, sperm gets pushed through the vas deferens present within the spermatic cord into the abdominal cavity. It then joins the seminal vesicles, which pumps in alkaline fluid necessary for supporting the sperm.

The ejaculate comprises fluids from three different sources – the vas deferens, seminal vesicles, as well as prostate. The bulk of the total semen volume (80%) comprises of seminal vesicle fluid. The vas deferens adds 10%, and the prostate gland adds the remaining 10%. It is this mix that is ejected out of the penis.

Dr Harshi Dhingra is a Medical Doctor and specialized Pathologist with clinical, teaching and research experience of over a decade, currently employed as Assistant Professor, Pathology in a medical school and research center.

Her specialties include Histopathology, Haematology, Cytology and Clinical Pathology. Her research papers on sperm characteristics, testicular malignancies and endometrium lesions were well received.