The sperm is the male sex cell or “gamete.” These cells carry half the amount of genetic material (chromosomes) than a normal body cell. 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 fertilize the egg in order to create new genetic material. This fertilized sperm and egg cell combination is known as a zygote, and the singular cell will start to divide rapidly in the days following successful fertilization. The fertilized egg goes on to become the embryo, and fetus, which will eventually become a baby. So the sperm is at the center of the male half of reproduction.
What does a sperm cell look like?
The mature sperm cell is shaped like a tadpole and is 0.05 milliliters long. It consists of a head, body and tail. The head is smooth, oval-shaped, and is about 5-6 micrometers long and 2.5-3.5 micrometers wide (less than the size of a needle point). It is covered by a well-defined cap that covers 40 % to 70% of the head. The head contains a nucleus of dense genetic material from the 23 chromosomes. It is attached from the neck to the body containing mitochondria (for energy) that supply the energy for the sperm’s activity. The tail is made of protein fibers that contract on alternative sides, giving a characteristic wavelike movement that drives the sperm through the seminal fluid, which also supplies additional energy. Sperm cells that have two heads or tails are abnormal and a high concentration of their numbers can be associated with infertility.
How is mature sperm produced?
Unlike the female who is born with all her female sex cells or eggs which depletes and finishes by the time she reaches menopause, the male sperm cell production starts during puberty in the male and continues throughout life although like the female, the quality and motility of the sperm cells reduce with age. A normal male who has reached puberty will produce millions of sperm cells every day. Sperm is produced within a system of tiny tubes called the seminiferous tubules in the male testicles which hang in the scrotum. At birth, these tubules contain simple round cells. During puberty, testosterone and other hormones cause these cells to transform into sperm cells. The cells divide and change until they have a head and short tail, like tadpoles. The immature sperm move into the epididymis (a tortuously coiled structure topping the testis). The epididymis receives immature sperm from the testis and stores it for several days before they complete their development.
It takes about 72 days for one sperm to grow and be fully mature. Sperm production requires a temperature which is three to five degrees below body temperature (95° – 97° F or 35° to 36° C). The scrotum has a built-in thermostat, which keeps the sperm at the correct temperature while they being stored in the epididymis. If it becomes too cool on the outside, the scrotum will bring the testicles closer to the body for warmth. That is why the testes hang away from the body, so sperm can develop at the temperature they need. The male will produce more than 12 trillion sperm over the course of his life.
In males that are celibate for various reasons and do not have sex or masturbate, the unused sperm cells produced and stored are simply reabsorbed by the body or released via nocturnal emissions (wet dreams).
What happens to the mature sperm during ejaculation?
When a male is sexually excited, the seminal vesicles (structures located very close to the prostate which joins the spermatic cord to form the ejaculatory duct that passes through the prostate gland and empties into the urethra); together with the prostate gland, make a whitish fluid called seminal fluid. When ejaculation occurs during male orgasm, sperm is forcefully expelled from the epididymis into the deferent duct. Sperm then travels through the deferent duct, up the spermatic cord into the pelvic cavity to the ejaculatory duct in the prostate gland. The sperm cells mixes with the seminal fluid to form semen (cum). This is the semen that is released when a male ejaculate. Each time a male ejaculate, it can contain up to 500 million sperm.
What happens to the sperm and how long does it live after ejaculation?
After ejaculation, into the female vagina, the sperm must be capable of propelling themselves through the environment of the female vagina and up the cervix. This environment in the female, must be favorable to admit the sperm without destroying them. The sperm must also possess the capability of converting to a form that can penetrate the cell membrane of the egg (capacitation).
Following ejaculation, the semen forms a gel which provides protection for the sperm from the acidic environment of the vagina. The gel is liquefied within 20-30 minutes by enzymes in the semen. This liquefaction is important to free the sperm so transportation may occur. The seminal plasma or fluid is left in the vagina. The protected sperm with the greatest motility travel through the layers of cervical mucus that guard the entrance to the uterus. During ovulation, this barrier becomes thinner and changes its acidity creating a friendlier environment for the sperm. The cervical mucus acts as a reservoir for extended sperm survival. Once the sperm have entered the uterus, contractions propel the sperm upward into the fallopian tubes. The first sperm enter the tubes minutes after ejaculation. The first sperm, however, are likely not the fertilizing sperm. Motile sperm can survive in the female reproductive tract for up to 5 days. The cervical mucus of the female prevents it from drying out.
If, however, the sperm have a chance to dry out, they basically die. Ejaculated sperm that land on cold, dry objects may die after a few minutes. They may last up to 30 minutes in rare cases. They may die even faster in a hot bath or a hot tub due to the heat or chemicals in the water.
Which sperm will fertilize the egg?
It is important to note that out of the 200 to 500 million sperm cells contained in the ejaculate of a normal male, only about 2 million sperm enter the woman’s cervix, and around 1 million actually make it to the uterus. For the 1 million sperm that reach the uterus, about 10,000 make it to the top of the uterus. For the 10,000 sperm that make it to this point, around half of them actually go in the right direction heading to the ovulated egg cell, while the rest head to the wrong fallopian tube. Then out of the nearly 5,000 sperm that make it into the junction of the uterus and the fallopian tube, around 1,000 of these reach the inside of the Fallopian tube. Then for the 1,000 sperm entering the tube, only around 200 actually reach the egg. In the end, only 1 lucky sperm out of this group of 200 actually penetrates and fertilizes the egg!