Composition of semen Semen consists of seminal plasma and the spermatozoa that swim within it. Spermatozoa are produced in the testes, and seminal plasma is a mixture of secretions produced by the epididymis, prostate gland, seminal vesicle gland, urethral bulb gland, and paraurethral gland. Human spermatozoa are tadpole-shaped in form, 60µm in length, and divided into three parts: head, middle neck, and tail. They are the only “elves” in the human body that can move on their own, and have a great team spirit and sacrifice! The head of the sperm consists of a highly concentrated nucleus and an acrosome at the front of the nucleus, which contains the genetic material of the paternal line and carries the genetic information of the paternal line. The acrosome contains a variety of enzymes and is the key chemical for the sperm to cross the egg’s radioactive crown, zona pellucida and egg cell membrane. The spermatozoa have a flagellated tail equipped with delicate axonemes and mitochondrial sheaths. The mitochondria provide a constant source of energy for sperm activity, while the oscillation of the axoneme propels the sperm forward. The head of the spermatozoon is flat and oval, about 4-5 um long, 2.5-3.5µm wide and 1.0µm thick. The head of the spermatozoon is oval when viewed from the front and pear-shaped when viewed from the side. The special head shape of sperm increases the floating ability of sperm and greatly reduces the resistance to forward motion, and is suitable for the coordinated forward movement of sperm populations. The acrosome of spermatozoa is a flat vesicle-like structure that covers the first 2/3 of the sperm cell nucleus. The acrosome consists of three parts: the acrosomal outer membrane, the acrosomal inner membrane, and the acrosomal lumen. It is a special lysosome containing hydrolytic enzymes associated with fertilization, such as acrosome protease, hyaluronidase, β-N-acetylaminoglucosidase, acid phosphatase, aryl sulfatase A, collagenase-like peptidase, phospholipase, and radial crown penetrating enzyme. Among them, acrosomal protease and hyaluronidase are crucial. The middle neck of the spermatozoon is located between the head and tail of the spermatozoon. The neck, also known as the connecting segment, consists of a small head, a nodal column, and a centrally located centriole. The microtubules at the tail extend from this centriole and drive the elongation of the spermatozoa. The middle part of the sperm is about 5-7µm long and is mainly composed of axoneme, peripheral dense fibers, mitochondrial sheath, and cell membrane. The caudal part of the sperm is the longest part of the sperm, about 45µm, consisting of axoneme, peripheral dense fibers, and this section no longer has a mitochondrial sheath. Sperm production Spermatozoa are produced by spermatogonia in the testicular varicose ducts. From the beginning of the spermatogonial stem cells to the formation of spermatozoa, an extremely complex process of cell differentiation is required. It consists of three main stages: proliferation and differentiation of spermatogonia, meiosis of spermatocytes, and sperm formation. The process of spermatogenesis takes approximately 64 to 72 days. Spermatogenesis is continuous and the release of spermatozoa is also continuous. The efficiency of human spermatogenesis is such that approximately 3 × 106 to 7 × 106 spermatozoa can be produced per gram of testicular tissue per day. Maturation of spermatozoa The spermatozoa just produced in the testis are only “half-baked”. Although they are basically mature in terms of morphology and chromatin, they are not yet motile or have very little motility, nor do they have the ability to recognize sperm and eggs or the ability to unite them. When these little elves enter the epididymis with the testicular output ducts, the spermatozoa undergo a series of morphological and structural, biochemical and metabolic, physiological and functional changes in the process of running from the head of the epididymis to the body of the epididymis and the tail of the epididymis, and then grow and mature. This process takes about 10-14 days. This process takes about 10 to 14 days. There are numerous and varied biochemicals in the human environment, including those already present in nature and those produced by humans. A significant number of these substances have toxic effects on human fertility and constitute the main factors of environmental pollution. The main categories include the following: drugs, food, food additives, cosmetics, veterinary drugs, agricultural products and drugs (pesticides, herbicides), household items, industrial chemicals, etc. In addition to environmental pollution, they also include: lifestyle changes and excessive stress in life, sedentary, drug abuse, obesity, spread of sexually transmitted diseases, alcoholism, excessive smoking, and drug abuse. These factors can not only cause changes in sperm activity and quantity, directly affecting the fertilization ability of sperm, but can also affect the integrity of the paternal genetic material carried by sperm. Changes in sperm quality can cause infertility, spontaneous abortion, fetal abortion, chromosomal ploidy and congenital malformations. World Health Organization (WHO) recommended reference values for routine semen analysis: Semen volume: ≥2.0ml pH: 7.2-8.0 Sperm density: ≥20×106/ml Total sperm count: ≥40×106/per ejaculation Sperm motility: ≥50% forward linear motion sperm (a+b) or ≥25% fast forward linear motion sperm (a) (within 1h after ejaculation) Sperm Survival rate: 75% or more (live staining) Semen appearance: homogeneous, off-white, milky white, yellowish Semen liquefaction time: within 60 minutes Semen viscosity: stretched length not more than 2cm