Semen composition, sperm quality and fertility
Male reproductive fluids (semen)
Semen is the male reproductive fluid, and its components can be divided into two parts. One is reproductive cells, namely sperm, which are produced by the testes. The other is seminal plasma, which is composed of fluids secreted by glands such as the prostate gland, seminal vesicles, and bulbourethral glands.
Normal semen is milky white, gelatinous, and highly viscous, with a distinctive odor when freshly ejaculated. Normal semen is weakly alkaline, with a pH of around 7.5. Semen coagulates quickly after ejaculation, then gradually liquefies within minutes. Sperm motility is very weak in coagulated semen, but highly active in liquefied semen.
Normal sperm count and quality are crucial for male fertility. A normal male ejaculates approximately 2-6 ml of semen per ejaculation, containing about 100 million sperm per milliliter, meaning each ejaculation typically releases at least 400 million sperm. If the sperm count is less than 20 million per liter of semen, the chances of fertilization decrease significantly, and less than 4 million makes fertilization difficult. Ejaculation volume is closely related to the frequency of intercourse; excessive intercourse reduces both the volume and sperm count. This explains why men who indulge in excessive sexual activity often have difficulty conceiving. One case involved a man desperate for a child who, for two years, insisted on having intercourse at least once every night except during his wife's menstrual period, exhausting himself without success. A doctor's examination revealed that his semen was thin and contained very few sperm. Under the doctor's guidance, he reduced intercourse to once a week, and his wife became pregnant six months later.
Sperm quality undoubtedly plays a crucial role in fertility. Normal sperm resembles a tadpole, about 60 micrometers long, and can only be seen under a microscope. Sperm consists of two parts: a flattened, racket-shaped head and a long, slender tail. Sperm movement is mainly achieved through the undulation of the tail. With regular tail undulation, a sperm can move 50-60 micrometers per second. Interestingly, in addition to movement, sperm can also climb; highly fertile sperm can climb to a height of about 5 centimeters. Sperm ejaculated can generally survive for 8 hours. In normal semen, about 85% of sperm are motile, and no more than 15% are immotile or dead. Otherwise, fertilization will be difficult.
The head of a sperm cell contains a nucleus, which contains chromosomes containing genes and storing various genetic information and codes, playing a role in heredity. In addition, sperm contains essential substances necessary for sperm survival, providing the energy required for sperm motility. It also contains various enzymes that help sperm penetrate the egg's outer membrane and enter the egg. It is worth noting that not all sperm produced by the testes are viable; a certain proportion are infertile sperm, i.e., abnormal sperm, such as those with small heads, large heads, double heads, short layers, no layers, double layers, and headless sperm. However, the proportion of abnormal sperm is very small; normal semen should not contain more than 10% abnormal sperm. Too many abnormal sperm reduce the chances of fertilization.
Sperm are delicate and easily damaged and killed by various factors. Medical experts have found that smoking and excessive alcohol consumption are major enemies of sperm. Nicotine in cigarettes reduces the secretion of sex hormones and can directly kill sperm. Adult men who smoke 30 cigarettes a day may have 50% of their sperm killed, and the rate of sperm abnormalities will increase significantly. Men who drink alcohol regularly may have 70% of their sperm that are underdeveloped or lack vitality. Radiation can damage sperm chromosomes, causing them to break and become abnormal. Therefore, men exposed to X-rays have lower fertility rates, and their offspring are more likely to have birth defects. Pregnant women should avoid X-ray exposure to prevent fetal malformations. Certain medications, such as anti-tumor drugs, sedatives, and hormone-like drugs, can also damage sperm, causing abnormalities and affecting fertility. Furthermore, temperature has a significant impact on testicular reproductive capacity. Under normal circumstances, the temperature of the testes in the scrotum is 1-2°C lower than body temperature. Higher temperatures can affect the spermatogenic capacity of the testes. Cryptorchidism occurs because the testicles are located inside the body, where the temperature is higher than in the scrotum. This can lead to impaired sperm production and a higher risk of developing cryptorchidism. Therefore, maintaining proper ventilation and heat dissipation in the scrotum is crucial for protecting fertility. Wearing tight underwear not only hinders scrotal heat dissipation but also impairs venous blood return, which is detrimental to sperm production.
Besides sperm, the main component of semen is seminal plasma. Seminal plasma is a secretion from the male accessory glands and is in a liquid state, thus giving semen its fluidity. The main component of seminal plasma is water, accounting for about 90%, with the remainder containing a large amount of nutrients, vitamins, minerals, and various enzymes to ensure sperm survival and stimulate sperm motility. Although seminal plasma contains such rich substances, it has no reproductive capacity itself; its main function is to maintain and protect sperm function. Therefore, seminal plasma is crucial for male fertility.