Factors influencing sperm production and the mysteries of semen composition
3. Excessive obesity: Excessive obesity can affect pituitary function, affect the secretion of sex hormones, and reduce sperm production.
4. Smoking and drinking: Smoking can interfere with the function of the hypothalamus-pituitary-gonadal axis, reducing semen quality. Nicotine in tobacco affects sperm motility and morphology. Alcohol reduces sperm count, increases the number of abnormal sperm, and decreases sperm motility.
5. Drug abuse: Drugs such as marijuana and cocaine can reduce sperm count in semen. Nitrofurantoin can interfere with spermatogenesis, and cimetidine and sulfonamides can also impair sperm production.
6. The impact of age on sperm production: In childhood, the seminiferous epithelium does not develop. Starting in puberty, under the influence of gonadotropins secreted by the pituitary gland, the number of interstitial cells in the testes increases, the Sertoli cells enlarge, and spermatogonia begin to divide and proliferate, developing into spermatogenic cells at various stages and mature sperm. Generally, a man's spermatogenic function begins to decline after the age of 50. There is also a view that men should complete their reproductive process before the age of 35.
**Like fish in water, sperm migration follows a regular pattern.**
During the Han Dynasty, the main script was clerical script, but at the end of the Han Dynasty, another script emerged: it was written with a pointed tip and was characterized by a thick head and a thin tail. This script was called "tadpole script" because it resembled a tadpole.
Located in Danzhu Township, Xianju County, Zhejiang Province, lies the majestic Weiqiang Mountain, with its towering peaks and deep ravines. The area is characterized by its crisscrossing valleys, ancient trees, secluded bamboo groves, and babbling streams, offering picturesque scenery in all four seasons. Among its many attractions is a mysterious cultural landscape: on a sheer cliff called Tadpole Cliff, strange patterns and symbols, resembling sun, moon, insects, and fish, are carved into its surface. These are the famous Tadpole Script, traditionally attributed to Yu the Great.
Why did the ancients carve characters on sheer cliffs? What are the meanings of these pictographic symbols? For thousands of years, countless scholars and enthusiasts have ventured there to explore this mystery.
There are two things in the world that closely resemble tadpoles: one is the famous "tadpole script," and the other is a man's sperm. Sperm are mature male reproductive cells. If we prepare a smear from a man's semen and observe it under a light microscope, we will see many tadpole-shaped, constantly swimming cells; these are sperm. The peak velocity distribution of sperm motility is 36 micrometers per second, and its average velocity is 35 micrometers per second.
Just like fish swimming in water and tadpoles swirling around in the water, the movement and circulation of sperm also follows a pattern.
While sperm produced in the testes are morphologically mature, they lack motility and the ability to recognize and fertilize an egg. Only after entering the epididymis and undergoing a series of structural, biochemical, metabolic, and physiological changes during their transport and storage can they ultimately acquire motility, sperm-egg recognition, and the ability to fertilize an egg. This process is known as sperm maturation in the epididymis. The epididymis is not only a sperm storage organ but also plays a crucial role in sperm maturation.
Sperm maturation in the epididymis involves a series of complex changes, such as changes in shape and size, changes in membrane permeability, changes in cold and heat resistance, changes in motility and movement, changes in metabolism, changes in sperm structure, and changes in sperm membrane antigenicity. Most importantly, it acquires the ability to be fertilized.
During the maturation process, epididymal sperm undergoes minimal morphological changes. The most significant maturational change is the modification of the sperm membrane. This modification includes the renewal of membrane lipids, proteins, and glycosyl components, as well as alterations in membrane transport capacity, fluidity, surface charge, and the properties of surface receptors, along with the attachment of substances such as epididymal secreted glycoproteins. These changes further alter the structure and properties of the sperm membrane, enabling mature sperm within the epididymis to achieve fertilization capacity.
During spermatogenesis, the nuclear protein composition of spermatogenic cells undergoes significant changes, with lysine-rich histones eventually being replaced by protamines rich in arginine and desaminoglycans. After sperm enter the epididymis, the composition of its nuclear proteins generally remains unchanged, and the sperm nucleus becomes more concentrated and stable, which protects the structure and genes of the sperm nucleus. The degree of chromatin condensation in the sperm nucleus is related to the sperm's fertilization capacity (fertilization rate).
Semen is primarily composed of seminal plasma and sperm. Seminal plasma accounts for over 95% of the composition. Normal semen is a mixture of testicular fluid, epididymal fluid, and secretions from the bulbourethral glands, prostate gland, and seminal vesicles. Seminal vesicle secretions are the most abundant, accounting for about 60%. Prostate gland components make up the second largest portion, about 30%, while components from the epididymis, ampulla of vas deferens, bulbourethral glands, and urethral glands account for only 5%–10%. Seminal plasma determines the biochemical and physiological characteristics of semen. Water accounts for approximately 90% of seminal plasma, and many of its components are similar to those in blood plasma, although the content of some components varies considerably. Simultaneously, seminal plasma contains unique components such as prostaglandins, capacitation factors, and protease inhibitors, which directly affect sperm motility and fertilization capacity. Semen is also rich in fructose and certain amounts of acid phosphatase, citric acid, carnitine, and various inorganic elements such as potassium, sodium, calcium, and magnesium, as well as sterols and sex hormones, all of which significantly influence sperm production, maturation, motility, and fertilization.
Semen is a semi-liquid with a certain viscosity. Both excessively high and low viscosity indicate poor semen quality. Freshly ejaculated semen is generally considered grayish-white or grayish-yellow, and after liquefaction, it becomes translucent milky white or grayish-yellow. Semen from men who have not ejaculated for a long time may have a slightly pale yellow tint. Semen from older men is dark yellow. If the semen is brownish-red or contains blood, it is called hemospermia, and may indicate conditions such as seminal vesiculitis or prostatitis. Clear, white or yellow semen suggests azoospermia; some medications can also cause semen to have a color.
Normal semen has a pungent odor, which is caused by secretions from the prostate gland. Freshly ejaculated semen is thick and gel-like. Due to the presence of proteases secreted by the prostate gland, the semen liquefies from a coagulated state within 5 minutes, a process that takes approximately 30 minutes. This process is called semen liquefaction. The coagulation and gradual liquefaction of semen are normal physiological phenomena. If semen does not coagulate during analysis, it may be due to congenital defects in the seminal vesicles or ejaculatory ducts. If semen fails to liquefy after 1 hour at room temperature (25°C), it should be considered abnormal, possibly indicating a deficiency in the function of liquefaction factors secreted by the prostate gland, leading to a lack of proteases.