Physiological effects of androgens and a holistic understanding of the male reproductive system
Androgens are a class of steroid hormones that play a crucial role in spermatogenesis and maturation in men, and are indispensable for maintaining male secondary sexual characteristics. The chemical structure of androgens: Natural androgens are a class of steroid hormones composed of 19 carbon atoms. Biologically active androgens in the body include testosterone, dihydrotestosterone, androstenedione, androstenedione. The biological activity of these hormones is determined by the β-OH group at C17 and the ketone group at C3 in their molecules.
Among natural androgens, testosterone has the strongest activity, while androstenedione has relatively low activity; androstenedione is an intermediate metabolite with activity between the two. Testosterone can be converted into the more active dihydrotestosterone in tissues.
Testosterone is the most abundant form of androgen, a key hormone regulating Sertoli cell function, and one of the most crucial factors in maintaining spermatogenesis. The primary tissue in the body that synthesizes testosterone is the testes; in men, 95% of testosterone originates from the interstitial cells of the testes. The adrenal cortex, ovaries, and placenta also secrete small amounts of androgens. The raw material for androgen synthesis by the interstitial cells of the testes is cholesterol. Cholesterol can come from the blood or be synthesized from acetate.
Androgens have a wide range of physiological effects. In addition to playing an important role in the male reproductive system, they also have certain effects on the human immune system, hematopoietic system, and skeletal system.
In early pregnancy, the concentration of testosterone in the blood of male fetuses is low, gradually increasing to a peak between 12 and 18 weeks of gestation, and then decreasing in late pregnancy. The sexual differentiation of the fetal reproductive tract and external genitalia is influenced by androgens produced by the testes. Androgens act on embryonic tissues, causing them to differentiate into efferent ducts, epididymal ducts, and vas deferens. Androgens act on the urogenital nodules of the embryo, causing them to develop into the male penis and scrotum, among other external genitalia. Before birth, testosterone causes the pituitary gland to develop in a male direction, completing its functional differentiation.
Testosterone is synthesized and secreted by interstitial cells. After entering Sertoli cells, it can be converted into the more potent dihydrotestosterone (DHT). Under the combined action of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), it ensures sperm production and sperm survival time in the epididymis, thus maintaining male secondary sexual characteristics and sexual function.
Androgens in the human body can promote the synthesis of immunoglobulins and accelerate the formation of antibodies, thereby enhancing the body's immunity. Androgens can also enhance the body's tolerance to exotoxins and endotoxins, providing the body with disease resistance. Furthermore, androgens stimulate erythrocyte production. In cases of impaired bone marrow hematopoiesis, androgens can stimulate bone marrow hematopoiesis; the stimulatory effect of androgens on erythrocyte production can partially explain why men have slightly higher red blood cell counts than women.
Modern medicine also believes that the reason why some men are exceptionally intelligent is due to excessive male hormones. Several years ago, Ge You, a bald celebrity, once said on television: "A busy road doesn't grow grass, and a smart head doesn't grow hair."
Actually, the main cause of baldness is excessive secretion of male hormones in the body. Since sebaceous glands are primarily controlled by male hormones, if male hormone secretion is excessive, the back, chest, and especially the face and scalp will produce too much oil. When the pores on the scalp are clogged with oil, it hinders the supply of nutrients to the hair, eventually leading to gradual hair loss and baldness. Generally, baldness caused by excessive male hormone secretion does not affect health.
**A masterpiece of nature sculpted the unique male physiology**
Some say that among all the physiological "landscapes" of humankind, none can compare to dreams. Their vibrant colors, unpredictable plots, and bizarre content often leave people both amazed and perplexed. Everyone dreams, but how many can truly explain what dreams are? Numerous philosophers and sages throughout history have attempted to interpret the essence of dreams from their own perspectives, resulting in a diverse array of explanations.
Dreams, which the ancient Greek philosopher Plato considered the "source of creation," are also a physiological phenomenon in humans and are gender-specific. Men often dream of other men, violence, sex, tools, cars, and weapons, and their dreams often take place outdoors, frequently in unfamiliar places.
Not only do men and women differ in the physiological phenomenon of dreams, but the differences in reproductive physiology are even more pronounced. Male reproductive function undergoes a gradual maturation and eventual decline throughout the life cycle of birth, growth, maturity, aging, and death. Furthermore, this process is closely related to the waxing and waning of kidney essence, kidney qi, and the balance of fertility.
Human reproductive function is a physiological function possessed through the coordinated and integrated function of the internal organs, meridians, and qi and blood, with the kidneys as the primary organ. In the generation and maintenance of reproductive function, the physiological role of the kidneys is paramount. Essence (jing) is the most fundamental substance constituting the human body, maintaining its life activities, and promoting its growth and development.
During a man's youth, when his kidney essence and kidney qi reach a certain level, a subtle substance called Tian Gui is produced. This substance promotes the development and maturation of the reproductive organs, manifesting as ejaculation and the maturation of the sexual organs, thus enabling reproduction. As kidney essence and kidney qi continuously replenish and produce Tian Gui, male reproductive function is maintained. With age and aging, male reproductive function gradually declines, and Tian Gui production decreases accordingly until it ceases. Without the sustaining effect of Tian Gui, male reproductive function gradually declines, reproductive organs atrophy, and eventually, physiological function is lost, leading to old age. Kidney essence and kidney qi are crucial to male reproductive physiology and are the foundation of human reproduction. Insufficient kidney essence and kidney qi can lead to underdeveloped reproductive organs and delayed sexual function in young men, while middle-aged men may experience pathological changes such as decreased or lost reproductive function, resulting in low sperm count, infertility, and other reproductive problems.
Under normal circumstances, human reproductive function can last for 30 to 40 years. In old age, as the body undergoes physiological changes, the reproductive essence gradually decreases or even disappears, and the function of the sexual organs and reproductive function also gradually declines until they are completely lost.
Male genitalia include external genitalia and internal genitalia.
1. External genitalia
The penis is composed of two corpora cavernosa and one corpus spongiosum surrounding the urethra, covered by the penile fascia and skin. In its flaccid state, the penis is 45–85 mm long and can be divided into three parts: the root, the body, and the glans penis. The penis is richly supplied with blood, lymph, and nerves. The corpora cavernosa contain many cavities; when these cavities fill with blood, the penis naturally becomes erect. The penis is the organ for male sexual intercourse and also serves as the passage for urination and ejaculation.
The initial section of the urethra primarily functions as a urination site, while the remaining sections serve both urination and ejaculation functions.
The scrotum is a skin-like sac that surrounds the testes and epididymis, and is also a continuation of the anterior abdominal wall. The main functions of the scrotum are: to regulate temperature and protect the testes, epididymis, and spermatic cord from damage.
2. Internal reproductive organs
The testes are the main male reproductive glands, located within the scrotum. They are responsible for producing sperm and secreting male hormones (androgens). The testes are a pair of oval organs, 3.5–4.5 cm long and 2–3 cm wide, each weighing 10–15 grams. The surface of the testes is covered by a tunica vaginalis, which is actually surrounded by a dense connective tissue fascia (tunica albuginea). During fetal development, the testes reside in the abdominal cavity, descending into the scrotum shortly after birth. If the testes fail to descend into the scrotum and remain in the abdominal cavity, it is called cryptorchidism, which can lead to infertility.
The epididymis is attached to the posterolateral aspect of the testis, and is a slender, flattened, round body of varying thickness at both ends, which feels uneven to the touch. The larger end, called the "head of the epididymis," is attached to the posterior border and upper part of the testis; the middle end, attached to the upper part of the testis, is called the "body of the epididymis"; the thinner, rounder end, called the "tail of the epididymis," connects to the vas deferens. The epididymis is covered by an outer membrane composed of connective tissue and blood vessels, and contains epididymal lobules. The efferent ductules of the testis spirally coil within the epididymal lobules, forming the epididymal duct. Sperm are mainly stored in the tail of the epididymis and mature within it. The epididymal wall has a layer of secretory cells that secrete fluid containing glycoproteins and potassium, which has a nutritional function and is conducive to sperm maturation; in addition, it secretes glycerophosphate choline, which is beneficial to sperm survival.
The vas deferens is approximately 40 centimeters long and is divided into five segments: the epididymal segment, the spermatic cord segment, the inguinal segment, the pelvic segment, and the ampulla segment. The vas deferens has peristaltic function and the ability to transport semen; the ampulla segment can also store semen.
The spermatic cord is a soft, cord-like structure composed of the cremaster muscle, vas deferens, and its blood vessels. Varicocele occurs when the internal spermatic vein becomes obstructed in its return flow for some reason, resulting in a piedrous, tortuous dilation. Since the left internal spermatic vein drains directly into the left renal vein, and the right vein drains into the inferior vena cava (and in rare cases, the right renal vein), the left side is more prone to obstruction, thus varicocele is more common on the left side. This can affect sperm maturation and quality, leading to infertility.