What’s the Function of a Sperm Cell? – Definition & Structure

A spermatozoon, in plural spermatozoa, or sperm cell is the male reproductive cell that is expelled along with the seminal fluid or semen when a man ejaculates. In humans, spermatozoa determine the gender of the baby-to-be, which means that they can carry either the X or the Y chromosome.

The function of spermatozoa is to fertilize the egg cell during fertilization, creating a new organism called zygote that will develop from embryo to fetus during the 9 months of pregnancy. Human sperm cells are haploid, which means that they contain 23 chromosomes.

The various sections of this article are assembled in the following table of contents.

Definition and function

The sperms, spermatozoa or sperm cells are the male sex cells. Their function is to combine with the female sex cell and create a completely new organism. Spermatozoa are expelled with seminal fluid (semen) during ejaculation.

Spermatozoa production takes place in the testis, while oocytes or egg cells are produced in the ovaries of the woman. When an egg and a spermatozoon unite, they create a zygote, which will develop into an embryo (an unborn, developing organism), and later into a fetus.

Learn about the differences between these terms with this post: Differences between human zygote, embryo and fetus.

In humans, the sperm cell is the one responsible for determining the gender of the new organism. This means that spermatozoa can carry either a Y or an X chromosome, while egg cells always contain an X chromosome.

Human sperm cells are always haploid, that is, they contain 23 chromosomes. When a spermatozoon reaches and joins an oocyte, which also contains 23 chromosomes, they form a diploid cell of 46 cells.

Sperm cell adaptations

Spermatozoa are structurally specialized to its function through the following anatomical changes:

  • Presence of a flagellum: It propels sperm as they swim during their journey to the egg.
  • Loss of organelles: As our specie has evolved, spermatozoa have lost a number of organelles because they were no longer necessary for their functioning. Cytoplasmic organelles such as Golgi apparatus, endoplasmic reticulum, or ribosomes are present but inactive.
  • Tadpole shape: It allows them to carry genetic information in their rounded heads. Also thanks to it, they carry an enzyme that allows them to penetrate the unfertilized egg cell.
  • Power provided by mitochondria: To be able to move forward towards the ovum, the middle-piece of spermatozoa contains lots of mitochondria that produce adenosine triphosphate (ATP), the fuel of sperms.

According to experts, actually spermatozoa have a very narrow function in comparison with other cells that adapt to their function as well. For example, they lack ribosomes, since they are actually unnecessary for carrying DNA to the egg cell.

What is sperm made out of?

Before ejaculation, spermatozoa pass through the ejaculatory ducts, and mix with fluids from the seminal vesicles, bulbourethral glands, and the prostate. In fact, 65-75% of the semen expelled contains fluids from the seminal vesicles, including:

  • Amino acids
  • Enzymes
  • Proteins
  • Vitamin C
  • Citrate
  • Flavins
  • Fructose
  • Prostaglandins
  • Phosphorylcholine

Also, the sertoli cells secrete a fluid into the seminiferous tubules that helps in the transport of spermatozoa to the genital ducts. In short, semen is typically translucent with white or grey tint, sometimes yellowish.

The presence of blood in the semen is known as hematospermia and can cause a reddish or pinkish color. If this happens, it may indicate a medical problem that should be evaluated by your doctor.

Very simply put, seminal fluid is comprised of proteins, fructose, water and other components such as vitamins, minerals, etc. So, dehydration, a lack of nutrients, or vitamin deficiency can lead to male infertility if untreated.

Structure of a human sperm cell

The scientist Antonie van Leeuwenhoek was the first person who described in detail the structure of a sperm cell in 1667. Although the parts of spermatozoa are more or less common in all mammal species—a head and a long tail—there are small differences between species, especially in the morphology of the head.

Spermatozoa are the only human cells that contain flagella. They are made up of three basic parts: the head, the middle-piece, and the tail.

The head is an oval-shaped structure, which size ranges from 5 to 8 µm. It consists of two parts:

Acrosome
The size of this organelle is 40% to 70% of total sperm head area, and is located at one end of the sperm cell. It contains proteolytic enzymes that help to destroy the outer layer of the egg cell, thereby allowing the sperm to enter into it easily.
Nucleus
It contains all the 23 chromosomes of the sperm cell, that is, half the genetic information that will have the new organism. This is the only part of the sperm cell that enters into the egg cell. For this reason, it is a key part of the spermatozoon, as it is the one that unites with the egg’s nucleus to form a 46-chromosome cell called zygote.

Neck and middle-piece

The neck and the middle piece, as the name suggests, are the parts that can be found between the head and the tail. Their function is to connect both ends of the sperm cell.

As one shall she in the diagram below, the neck contains millions of spirally arranged mitochondria. Their function is to provide the sperm will all the energy required by the flagellum to allow it to swim in the female reproductive tract.

Tail

The tail, also known as flagellum, is a long structure which main function is to allow sperm motility by means of a slithering, snake-like movement.

The length of the tail is about 50 µm, allowing a swimming velocity of 3 millimeters per minute approximately.

Sperm tail defects or alterations can lead to male fertility problems, being asthenozoospermia the most frequent one.

What is the lifespan of human sperm?

After ejaculation, most sperm die within minutes outside the woman’s genital tract. If spermatozoa enter the female reproductive system (the cervix and uterus), they can survive 1-2 days, some up to 5 days.

Even though some sperms are able to survive for up to 5 days, almost all pregnancies can be attributed to intercourse that occurred 1-2 days prior to ovulation, as the percentage of sperms that are able to survive less than five days is higher.

On the other hand, when sperm are processed and stored under strict laboratory conditions in a nutrient-rich medium, they can remain alive for up to 7 days. If collected at home into a sterile container, their fertilizing capability will drop dramatically within 60 minutes.

So, in conclusion, the lifespan of human spermatozoa is 24-48 hours, but it depends on the environment, which is to say, the conditions under which they are held. If exposed to air or deposited on clothing, they dry out rapidly and die within minutes after ejaculation.

Sperm cell diseases and defects

Sperm cell diseases or defects are more common than one may think. They occur in the structure of the sperm cell and can lead to male infertility, thereby preventing fertilization from taking place.

Teratozoospermia is a common abnormality that affects sperm morphology, that is, the shape of the sperm cells is altered (for example, sperm cells with 2 heads). Defects can be found either in the head, neck, tail, or in several parts simultaneously.

The sperm cell uses flagella to move towards the Fallopian tube; if they are damaged or not working, it will never meet the egg and subsequently fertilization will not occur. When male fertility issues are caused by alterations related to sperm motility, the patient is diagnosed with asthenozoospermia through a sperm analysis (SA).

Vitamin supplements are often recommended as a home remedy when a man has issues related with the motility of his sperm.

Sperm diseases related to the anatomy of spermatozoa can translate into a man being infertile in the most severe cases. They can be caused by defects during spermatogenesis (sperm production), or by alterations acquired during the sperm maturation process and pathway until the sperms come out with ejaculation.

FAQs from users

What’s the difference between sperm and spermatozoa?

A spermatozoon (in plural spermatozoa) is a motile sperm cell, that is, the reproductive cell of human males, carried in semen, that fertilizes the ovum to create a new human being, while the term sperm is commonly used to refer to the semen.

How many chromosomes does a human sperm cell contain?

Sperm cells cannot divide because they are haploid, that is, they contain 23 chromosomes. However, after the fusion with the egg cell, which contains 23 chromosomes as well, they create a diploid cell of 46 chromosomes (totipotent zygote).

How far does a human sperm cell travel to fertilize an egg?

Approximately, the distance that spermatozoa travel through the female reproductive tract is about 15 to 18 cm. Experts have discovered that sperms have to travel distances that are around 1,000 times their own length while they swim in the right direction towards the egg.

Why does the human sperm cell have lots of mitochondria?

Mitochondria supply energy to the sperm cells and are responsible for carrying out the process of respiration, necessary to provide the tail (flagellum) with the energy supply that it needed to allow the sperm cell to swim towards the egg.

Is a human sperm cell haploid or diploid?

As explained above, spermatozoa are haploid: they contain 23 chromosomes. Both sperm cells and egg cells contain half the chromosomes contained in normal diploid cells (a.k.a. somatic cells). Haploid cells are produced during meiosis.

What is the difference between a sperm cell and an egg cell?

Egg cells are the complete opposite of sperm cells, actually. The main and most obvious difference is that egg cells are produced in the female reproductive system, while sperm cells develop in the testes, which are part of the male reproductive system.

On the other hands, while spermatozoa are one of the smallest cells in the male body, ova are one of the largest cells present in the body of human females.

Is sperm made out of blood?

Not literally, but in a way yes. Actually, blood brings oxygen and nutrition to the testicles. In fact, everything in our body (both in males and females) gets oxygen and nutrients from blood. So, while blood should not present in the semen, it is responsible for the sperm production process.

What is the probability that a human sperm cell carries an X chromosome?

While there exist many old-wives tales and myths about this, the truth is that there is a 50% chance that a sperm cell will carry an X chromosome and a 50% chance that it will carry a Y chromosome. So, in short, the assignment of gender occurs 100% randomly.

Suggested for you

We have laearned about the anatomy of sperm cells, but do you know how they are formed and where? This process, called spermatogenesis, is explained in detail here: How are sperm produced?

Now that we have learned about the parts and functions of a sperm cell, you may want to find out what is the pathway of sperm in their journey to the egg. Check this out to get more information: Sperm’s journey to the egg.

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