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A Professional Guide to Sperm Cells and Their Function
Laboratory Manager
2021-07-26

A Professional Guide to Sperm Cells and Their Function

When considering the causes behind problems related to fertility, you’ll often have to think of the quality of the male partner’s sperm cells, or the sperm cells offered by any potential donor. But what are sperm cells, exactly? What do sperm cells do in the fertilisation process? How do sperm and egg cells eventually become foetuses? 

Here, we have provided a guide to answer these questions, as well as others, and left some information on our own assessments and tests that we conduct to determine male infertility. Read on to learn more, or contact us to book a consultation.

What are Sperm Cells?

Sperm cells, which might also be called spermatozoon when singular or spermatozoa when plural, are gametes (sex cells) produced by most animals. This includes human beings. They will normally carry a total of 23 chromosomes, which are the result of a process known as meiosis. 

How and Where are Sperm Cells Produced?

Sperm production in most mammals, including humans, takes place in the testicular organ of biologically male members of the species. Inside the testicles, there is a series of extremely small tubes called the seminiferous tubules. These house the sex cells that hormones (including testosterone, the male sex hormone) will eventually turn into sperm. 

Once the cells are formed, they will be pushed into a tube located behind the person’s testes, called the epididymis. The immature sperm cells will then spend about five weeks travelling through the epididymis in order to complete their development, before moving to the vas deferens. This is a long, muscular tube that travels from the epididymis into the pelvic cavity, just behind the bladder. 

The vas deferens will eventually transport the mature sperm cells to the urethra (the tube that carries sperm or urine away from the body), in preparation for ejaculation. When the person is then stimulated for sexual activity, the sperm will be mixed with a seminal fluid (a whitish fluid produced by the seminal vesicles and the prostate gland) in order to produce semen.

Once stimulated enough during sexual activity, up to 500 million sperm will be pushed out of the penis through the urethra, which is the process known as ejaculation.

When a biologically male human being reaches puberty, they will produce millions of sperm cells every day. A full sperm regeneration cycle (the creation and maturation of new sperm cells, which is also called spermatogenesis) will take about 64 days. This ensures that the body is constantly supplied with new sperm cells with the ability to perform their created function.

Having fewer than 15 million sperm per millilitre of semen is considered a low sperm count, though you may also find that some home tests state that lower than 20 million is a low sperm count. If you are unsure in your own case, you may wish to consult with a specialist in order to confirm.

What Does a Sperm Cell Do?

The purpose of a sperm cell is to be released during sexual intercourse and to eventually meet with an ovum (egg cell), which is produced by a biologically female body. Once united, the sperm will penetrate and fertilise the egg in order to create new genetic material. This fertilised sperm and egg cell combination is known as a zygote, and the singular cell will start to divide rapidly in the days following successful fertilisation. 

After about the fifth day, it will reach a stage known as a blastocyst and will then implant in the uterus and develop into a foetus. If left, and the resulting pregnancy is viable, this will eventually lead to the birth of a child, or multiple children in some cases.

As a specialist fertility clinic, we also understand that not every patient’s sperm cells will be able to perform their given function without assistance. This is why we offer a series of laboratory methods that may help our expert embryologists to improve the chances of success in IVF treatments. These include:

  • Intracytoplasmic sperm injection (ICSI), in which a single sperm and egg cell will be brought together through an injection in order to potentially create a zygote

  • Physiological intracytoplasmic sperm injection (PICSI), in which a sperm cell is selected by the embryologist for the ICSI procedure with the help of special dishes/chemicals that should highlight the better sperm

We must also specify that while PICSI has shown some promising results and has been around for a number of years, the Human Embryology and Fertilisation Authority (HFEA) does class it as red, owing to the fact that it has not been proven to increase the chances of pregnancy or birth rates.

The Morphology of Sperm Cells

The general morphology (shape) of sperm cells consists of three parts; a head, a midpiece (or body), and a tail. While most will have the same basic appearance, they won’t always all look exactly alike. Instead, various abnormalities will mean that they differ in shape and size, and there may be distinctive differences on each part of each individual cell.

The Head of the Sperm

On a normal mature sperm cell, the head will be smooth and oval-shaped, resembling an egg or an almond. It should measure between 2.5 and 3.5µm (micrometres) in diameter and 4.0 to 5.5µm in length. The cell should also have a well-developed cap-like structure, called the acrosome, which helps to penetrate the egg.

The sperm cell’s head is the most important part, as it contains the nucleus.

The Midpiece of the Sperm

A normal body on a sperm cell will be the same length as the head, and will make up about 10% of the cell’s total length. It contains tightly packed mitochondria that give the cell enough energy to swim and locate an egg cell. 

The Tail of the Sperm

The tail of a sperm cell is thin, long, and at about 45µ long should make up roughly 80% of the cell’s overall structure. While it will appear to be a long, continuous part, it is often divided up into several different parts. These include:

  • The connecting piece, which connects the tail to the head of the sperm
  • The principal piece, which helps to generate the waveform that allows the sperm cell to move
  • The end piece

Some professionals may also describe the midpiece of the sperm cell as a part of the tail, as it provides the energy required for movement.

How Sperm Cells Have Adapted for Their Function

Sperm cells have a number of adaptations that allow them to perform their function:

  • Acrosomes, which help to identify the target female reproductive cell and contain enzymes that break down the outer membrane of the egg, allowing the sperm to achieve fertilisation
  • Basic amines, such as cadaverine and spermine, account for the alkaline (basic) nature of semen. This protects the sperm and the DNA it contains from denaturation, as the vaginal canal is acidic
  • Spiral nanostructures, which are located inside the microtubules at the tip of the flagellum. It is suggested that these serve as “corks” within the microtubules, to stop them from growing and shrinking
  • Streamlined bodies, which allow sperm cells to move rapidly in order to reach the target egg cell
  • Tightly packed mitochondria, which provides the energy required to reach the egg cell. The midpiece will carry about 70 mitochondria for this purpose and are discarded once the sperm head penetrates the egg

The Motility of Sperm Cells

Alongside morphology, motility is the other noted characteristic of a normal sperm cell. Two types of physiological motility have been noted

  • Activated motility, which is observed in the early stages of motility. In this type, the sperm cell’s tail will beat gently from side to side as the cell moves along a straight path
  • Hyperactivated motility, which is the second type of physiological motility, and mostly occurs once the sperm is inside the female reproductive tract. Hyperactivated motility is more erratic and resembles a symmetrical waveform in the cell’s movements. It also uses more energy, helps to prevent the sperm from becoming trapped, propels it through the reproductive system, and enhances sperm penetration into the egg

Motility is only possible if the sperm cell is well-developed and fully functional, with a source of energy to support its movement.

How Sperm is Analysed

In laboratories, sperm cells may be analysed in order to look at characteristics such as morphology and motility. These methods of analysis will also usually be able to determine sperm count, and the results determined from this may be able to pinpoint the reason (or one of the reasons) for a person’s infertility. 

Some common methods of analysis include:

  • Microscopy, in which the specialist will look at the morphology, sperm count, and the movement of the cells under a microscope
  • Staining, which makes it possible to clearly recognise all the different parts of a sperm cell and any potential defects. However, it also kills the sperm cells used in the process

Our Assessments and Investigations

GENNET City Fertility is able to provide a number of different options for male fertility tests in the UK, whether you are looking to go ahead with a treatment that could put you on the path to parenthood, or even if you are simply looking to assess your own fertility. 

When carrying out these tests, we will look at a sample of your sperm to determine if the cells are contributing to infertility in some way, and may allow for the treatment of conditions that may be preventing you and your partner from conceiving naturally. It may also lead to the diagnosis of previously undiagnosed diseases or genetic disorders which, while causing infertility and potentially leading to birth defects, may have also had a negative impact on a patient’s health

To give an example of our offered assessments, during our Male Fertility Assessment we will perform a semen assessment that determines a patient’s sperm count, motility, and morphology. Once you’ve had this assessment carried out, you will then be informed of the results via email or over the phone. 

All results given will be explained in full by one of our fertility specialists, and they will be able to provide any professional advice you may need about changes to your lifestyle which may have an impact on your fertility.

Contact Us to Book an Assessment

We are always on hand to offer understanding advice and comfort at a time which may be difficult, and we can guarantee discreet procedures carried out by experts. We can soon book you in for a free 30 minute consultation with one of our specialists at our private clinic in London, who will then be able to offer you advice and take you through the steps and assessments necessary to help form the family you’ve always wanted.

Carleen Heath
Laboratory Manager