Sperm Cell

A sperm cell, also called a spermatozoon, is a male reproductive cell that develops from the male reproductive organ. This female unites with the egg cell to form a diploid zygote.

Sperm cells are formed by the process of spermatogenesis in the seminiferous tubules of the testicles. Once matured, the sperm cells are released into the epididymis, where they acquire motility and become ready for fertilization.

Like egg cells, sperm cells are haploid with only half the number of chromosomes and the fusion of these cells forms a diploid organism.

Anatomy and structure of the sperm cell
A sperm cell is a microscopic and flagellated motile cell with a unique structure consisting of a head, a midpiece, and a tail. The whole body of the sperm is covered by a layer of plasma membrane.

Anatomy and structure of the sperm cell

Sperm has three main parts:

Head:

The head region is usually a flattened pear-shaped structure with a pointed tip and a broad base that contains the genetic material of the sperm cell within the nucleus of the cell. It is covered by a cap-like structure called the acrosome, which contains the hydrolytic enzymes necessary to penetrate the layers of the egg during fertilization. This process is called acrosome reaction. The human sperm cell nucleus is haploid meaning it contains only 23 chromosomes. When this haploid cell is fertilized with an ovule, it produces a diploid zygote containing 46 chromosomes.

Body:

The body, also known as the midpiece, is the middle part of the sperm cell that contains the mitochondria. This region is essential for providing the energy needed for cell movement.

Tail:

The tail or flagellum of the sperm makes up about 80% of its entire length. The tail moves the sperm cell. It contains the axoneme, which is a bundle of microtubules surrounded by mitochondria. In Aconium, there are two central singlet microtubules surrounded by nine microtubule doublets. Movement of the flagellum is driven by the dynein motor protein that uses energy from ATP hydrolysis produced by mitochondria in the midpiece.

What is Spermatogenesis?
Spermatogenesis is the process of formation of sperm cells in the testes. The testes are the male reproductive organs that produce sperm and testosterone. They contain tightly connected structures called seminiferous tubules within which sperm cells develop. Scattered throughout these tubules are specialized cells called Sertoli cells, which provide nutrients to the developing sperm cells.

Spermatogenesis begins with spermatogonia, which are immature cells derived from stem cells called primordial germ cells in the outer wall of the seminiferous tubules. These stem cells migrate to the testis during early embryogenesis and proliferate continuously through mitosis. Half of the resulting cells remain as stem cells, while the others stop proliferating and go on to become future sperm cells.
Cells that mature into sperm cells differentiate into primary spermatocytes. These primary sperm cells migrate to the Sertoli cells where they develop further. Then, primary spermatocytes undergo meiotic division I to become secondary spermatocytes. While the nucleus of primary sperm cells contains 46 chromosomes, secondary sperm cells contain only 23 chromosomes like the egg. Secondary spermatocytes proceed through meiotic division II to produce haploid spermatids.
Haploid spermatids mature and differentiate into mature sperm cells called spermatozoa through spermatogenesis. This maturation process involves specific changes in the structure of the sperm cell. The nucleus takes on an oval shape that forms the head of the sperm. At the opposite end of the head is the tail, which arises from the cytoplasm of the secondary sperm cell. Once fully matured, sperm are stored in the epididymis of the testicles.

Functions of sperm cells
The main function of sperm cells is to fertilize the female egg cell to form a new individual. The fusion of a sperm cell with an egg forms a zygote that undergoes cell division to form an embryo.
A sperm cell provides a haploid set of chromosomes to its offspring. This genetic material determines the genetic traits and characteristics of the offspring.
Sperm cells are highly specialized for motility and have a flagellum that allows them to swim through the female reproductive tract. This movement is necessary for the egg to reach inside the fallopian tube for fertilization.
Sperm cells contain specialized structures and enzymes within the acrosome that cover the sperm head. Acrosomes contain enzymes that help penetrate the egg’s protective layers. Once the sperm reaches the egg, these enzymes are released in a process called the acrosome reaction.

Sperm cell diseases and disorders
Azoospermia is one of the main causes of male infertility. It is a disorder caused by the absence of sperm in the ejaculate. Causes of azoospermia may include obstructions in the reproductive tract, hormonal imbalances or certain genetic conditions. Diagnostic tools for azoospermia include hormonal tests, seminal biomarkers, ultrasonography, testicular biopsy, and vasography. Treatment options for azoospermia include surgery, hormonal therapy, and sperm retrieval using assisted reproductive technologies such as in vitro fertilization (IVF).
Intracytoplasmic Sperm Injection (ISCI) in humans

Oligozoospermia is a condition caused by low sperm count, where the sperm count is below the normal range. Oligozoospermia can affect fertility. Various factors can contribute to oligospermia, including genetic disorders such as Klinefelter syndrome, infections, hormonal abnormalities, obstructions in the reproductive tract, exposure to toxins, and certain medications. Diagnostic tests may include semen analysis, sperm function tests, imaging tests, measurement of hormone levels, and genetic testing.
Asthenozoospermia is a condition caused by decreased sperm motility. Sperm motility is important to reach and penetrate the egg during fertilization. Sperm with low motility have difficulty reaching and fertilizing the egg. This can reduce the chances of successful fertilization.
Teratozoospermia is characterized by abnormal sperm morphology. Abnormal sperm morphology can lead to difficulty penetrating egg barriers for fertilization. This condition also reduces the chances of successful fertilization.
Testicular cancer is an abnormal growth of cells in the testicles. These cancerous cells grow rapidly, spreading to other parts of the body. Most testicular cancer begins in germ cells in the testicles. The causes of testicular cancer are not clearly understood. It usually starts when certain factors change the DNA of the cells in the testicles, causing them to grow and grow abnormally. The diagnosis of testicular cancer involves several tests and procedures, including physical examination, ultrasound, serum tumor marker tests, and other imaging tests. Treatment options usually include surgical intervention, radiation therapy, and chemotherapy.
Varicocele is a condition caused by swelling of the veins within the scrotum that drain blood from the testicles. Varicocele causes low sperm count, low sperm motility, and abnormal sperm morphology. These problems can significantly affect fertility. They can also affect the growth and function of the testicles. Varicocele surgery improves sperm motility and morphology.
Reproductive system infections such as epididymitis and some sexually transmitted infections can also affect sperm production. These infections can block the passage of sperm.