L 40, 41, 42

The process of sperm development in the testes. Begins with spermatogonia, progresses through stages like primary spermatocytes, secondary spermatocytes, and spermatids, culminating in mature sperm.

The fluid ejaculated by a male, composed primarily of sperm and seminal fluid. It contains fructose, fatty acids, and proteins to nourish sperm.

Specialized cells within the testes that undergo spermatogenesis to become mature sperm.

The front portion of a sperm cell containing enzymes that break down the outer layer of an egg, enabling fertilization.

The middle section of a sperm cell filled with mitochondria that provide energy for the tail's movement.

The tail of a sperm cell that propels it forward, using energy from the mitochondria in the midpiece.

A microscopic structure found in the sperm's head, carrying the genetic material (chromosomes) needed for fertilization.

The process of releasing semen from the male reproductive system, involving a series of muscle contractions.

Sperm cells gain their ability to move and fertilize an egg after spending 18-24 hours in the epididymis. Before that, inhibitory proteins in the epididymal fluid keep them inactive.

The epididymis stores sperm and keeps them fertile for at least a month.

The epididymis secretes fluids containing essential nutrients, enzymes, and hormones like testosterone and estrogen, which help mature sperm.

Mature sperm have a higher chance of fertilization in a neutral to slightly alkaline environment, while acidic conditions hinder their activity.

The seminal vesicles contribute a mucoid fluid rich in fructose, citric acid, nutrients, prostaglandins, and fibrinogen to the semen.

The prostate gland releases a thin, milky fluid containing calcium, citrate, phosphate, a clotting enzyme, and profibrinolysin, which helps create an alkaline environment essential for sperm survival.

A sperm count below 20 million sperm per milliliter is associated with infertility.

Abnormal sperm shape or reduced motility can lead to infertility, even if the sperm count is normal.

FSH, a hormone from the anterior pituitary, stimulates the Sertoli cells in the testes, which are crucial for the transformation of spermatids into mature sperm cells - a key part of spermatogenesis.

Estrogen, formed from testosterone by Sertoli cells under the influence of FSH, plays a vital role in the process of sperm development.

Growth hormone, essential for metabolism throughout the body, has a crucial role in the early stages of sperm cell division. Without sufficient GH, spermatogenesis is severely compromised, leading to infertility.

This is the process of the penis becoming erect, triggered by parasympathetic impulses that travel from the spinal cord to the penis, causing blood flow to increase and the penis to stiffen.

Parasympathetic stimulation causes the urethral and bulbourethral glands to produce mucous, which acts as a lubricant during sexual activity.

This process involves the expulsion of sperm from the testes and the mixing of fluids from various glands to form semen. It is controlled by the sympathetic nervous system.

The interstitial cells of Leydig in the testes are responsible for producing testosterone, the primary male sex hormone. Other androgens, like dihydrotestosterone and androstenedione, are also produced.

Testosterone is converted into dihydrotestosterone within the target cells. Dihydrotestosterone, the more active form, influences the development of male characteristics.

The lining of the uterus breaks down and is shed, resulting in menstrual bleeding. This occurs approximately every 28 days.

The thickening of the uterine lining in preparation for a potential pregnancy. It occurs after menstruation and before ovulation.

The release of a mature egg from the ovary, usually around day 14 of the menstrual cycle. This is the point at which fertilization can occur.

The four key hormones that regulate the menstrual cycle are: follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone.

The menstrual cycle is a recurring series of events that prepare the female body for potential pregnancy. It repeats every 28 days and is controlled by hormones.

Normal sexual function in men encompasses a series of processes including libido (desire), the ability to achieve and maintain an erection, ejaculation, and detumescence (returning to a flaccid state).

The sexual response cycle is a four-stage process that describes the physiological changes during sexual arousal and activity. It includes the excitement phase (initial arousal and erection), plateau phase (intensified arousal and physiological changes), orgasmic phase (ejaculation and peak arousal), and resolution phase (return to pre-arousal state).

Erections are primarily controlled by a combination of central (psychogenic) and peripheral (reflexogenic) neural innervation. The central nervous system stimulates or inhibits spinal pathways that regulate erection and ejaculation, while peripheral innervation involves sensory nerves from the penis and reflexes triggered by tactile stimulation.

Tactile stimulation of the penis, primarily via sensory nerves in the glans and skin, triggers a reflex through the pudendal nerve. Psychogenic stimuli originate in the limbic system and are transmitted through the autonomic nervous system.

Tactile stimulation triggers a reflex that activates the parasympathetic nervous system (PSNS) through the pelvic splanchnic nerves (originating from S2-4). This activates the release of nitric oxide (NO) from endothelial cells, leading to smooth muscle relaxation and increased blood flow into the corpora cavernosa. Prostaglandins also contribute to smooth muscle relaxation, and the sympathetic nervous system (SNS) is inhibited.

An erection is primarily a vascular event. It involves the corpora cavernosa and corpus spongiosum, which are cylindrical vascular structures within the penis. Normally, these structures have limited blood flow. During an erection, the inflow arteries dilate, causing increased blood flow and rigidity. The outflow veins are compressed, trapping blood within the corpora and creating the rigid state.

Ejaculation is a two-stage process: Emission and expulsion. Emission, controlled by the sympathetic nervous system (SNS), involves contraction of the epididymis, ductus deferens, seminal vesicles, and prostate, resulting in the movement of semen towards the posterior urethra. The internal vesical sphincter closes tightly to prevent urine expulsion during ejaculation. Expulsion, driven by somatic motor impulses through the pudendal nerve, involves contraction of the bulbospongiosus and ischiocavernosus muscles, increasing pressure within the penis and leading to the expulsion of semen.

Detumescence is the process of returning to a flaccid state after an erection. This occurs through a combination of factors: (1) the sympathetic nervous system (SNS) releases norepinephrine (NA), (2) vascular endothelium releases endothelin, and (3) smooth muscle contraction induced by postsynaptic adrenergic receptors. These actions lead to increased venous outflow and the restoration of the flaccid state.

Sperm cells, after their initial formation in the seminiferous tubules, need several days to mature in the epididymis. During this journey, they become motile. Before this, they are not fully capable of fertilization.

Both central and peripheral nervous systems are involved in sexual arousal and response. Central innervation (psychogenic) originates from the brain and involves the limbic system, while peripheral innervation (reflexogenic) originates from sensory nerves in the penis and is activated by tactile stimulation. These pathways intersect at the spinal level, coordinating the complex process of erection and ejaculation.

Testosterone, a hormone produced by the testes, plays a crucial role in the development of male characteristics during fetal life. It triggers the formation of the penis, scrotum, prostate gland, seminal vesicles, and male genital ducts, while simultaneously suppressing the development of female reproductive organs.

During the final months of pregnancy, the testes start producing significant amounts of testosterone. This surge in testosterone is responsible for the descent of the testes from the abdomen into the scrotum, where they are better positioned for sperm production later on.

After puberty, increased testosterone levels trigger a range of changes typically associated with male adulthood. These include the enlargement of the penis, scrotum, and testes, as well as the emergence of secondary sexual characteristics.

Testosterone directly influences hair growth patterns in males. It stimulates hair growth in specific areas like the pubic region, abdomen, face, and chest, while often leading to hair loss on the top of the head, contributing to male-pattern baldness.

Testosterone's impact on the voice is distinctive: it causes the larynx to enlarge, leading to a deeper, more masculine voice. This change is due to the thickening of the laryngeal mucosa.

Testosterone contributes to the development of acne by increasing skin thickness and the production of sebum, an oily substance secreted by the sebaceous glands. This excess sebum can clog pores and lead to acne breakouts.

Testosterone has a significant anabolic effect, promoting protein synthesis and muscle growth. This results in a substantial increase in muscle mass, typically around 50% more than in females, after puberty.

Testosterone's anabolic effects extend to bone development by increasing bone density and promoting calcium retention. This leads to thicker bones and a higher total bone matrix. Additionally, testosterone influences the shape of the pelvis, making it narrower and more funnel-shaped compared to the broader, ovoid shape of the female pelvis. It also accelerates bone growth, resulting in earlier closure of the epiphyses.