The structures in the male reproductive system are the testes, the vas deferens (ductus deferens) and the seminal vesicles, the penis, and certain accessory glands, such as the prostate gland and Cowper’s gland (bulbourethral gland)
In Male Reproductive system, the testes, which produce sperm and sex hormones, hang well outside the pelvis, in the scrotum. The rest of the male reproductive system consists of a pair of tubes called the vasa deferentia (singular, vas deferens), the accessory sex glands (the seminal vesicles and the prostate), and the urethra.
The reproductive organs of an adult male manufacture and supply sperm (spermatozoa), together with the secretions of various glands that make up the semen, or ejaculate. In addition the testes, which are the site of sperm production and storage, produce the male sex hormone testosterone.
SPERM PRODUCTION:
The production of sperm cells (spermatozoa) in the testes is known as spermatogenesis. Each testis contains about 500 tightly packed tubes called seminiferous tubules, containing the immature male germ cells (spermatogonia). The germ cells initially multiply by normal cell division, or mitosis (see p.21), to produce spermatocytes. These undergo a special reproductive division called meiosis, in which the number of chromosomes in each cell is halved from 46 to 23.
These cells, carrying half the genetic material needed to create a new human, are called haploid cells (all other body cells are diploid). Further divisions form sperm precursors (spermatids), which develop into mature spermatozoa, completing the process. Sperm are produced at a rate of several hundred million per day, from puberty into old age.
TESTES AND SCROTUM:
The seminiferous tubules make up about 95 percent of testicular volume. They contain male germ cells, from which sperm develop, and Sertoli cells, which provide the developing sperm with nourishment. Fibrous tissue between the tubules contains Leydig cells, which produce testosterone.
Each testis has a tough coat called the tunica albuginea and sits within a pouch of skin and muscle called the scrotum. Scrotal muscles are vital for thermoregulation of sperm, which must stay 3.5–5.5° F (2–3° C) below core body temperature to survive. The scrotum moves the testes to and away from the body in response to fluctuations of air temperature, to promote fertility.
Temperature regulation:
When it is cold, scrotal muscles contract to wrinkle the skin and elevate the testes, conserving temperature. When warm, they relax, smoothing scrotal skin and lowering the testes to cool them.
Path of Sperms:
Sperm make up less than 5 percent of semen volume. As they pass from the seminiferous tubules into a long duct called the epididymis, they undergo further maturation to become motile and fertile before entering the vas deferens,
a muscular tube that joins the duct of the seminal vesicle (behind the bladder) to form an ejaculatory duct.
The seminal vesicle adds a fructoserich solution that provides energy and nutrients for the sperm, and
contributes around two-thirds of the total semen volume. It is highly alkaline (to counteract vaginal acidity) and contains prostaglandins, which dampen vaginal immune responses to semen. As semen enters the urethra, the prostate gland contributes a slightly alkaline fluid that makes up around a quarter of the seminal fluid. Finally, Cowper’s gland secretes a fluid (comprising less than 1 percent of the total volume) to lubricate the urethra and flush out any urine before ejaculation.
ERECTILE FUNCTIONS:
The penis has a dual role in the urinary and reproductive systems, by conveying both urine and semen through the urethra. The urethra is contained within a tube called the corpus spongiosum, which runs the length of the penis.
On either side are two larger tubes called the corpora cavernosa, each of which has a large central artery surrounded by an expansile, spongy tissue that fills with blood during erections, prompted by nerve impulses that cause the blood vessels to dilate. This usually occurs due to sexual arousal, but can be unprompted. Prior to ejaculation, contractions within the duct system drive the semen into the urethra. Rhythmic contractions of perineal muscles during male orgasm then eject the semen from the body.
