What are the testis and scrotum?
The testes or male gonads are important parts of male reproductive system. They are paired oval organs located between upper thighs suspended by the spermatic cord in a skin pouch called scrotum. The scrotal skin is corrugated because of underling muscle called dartos. In the fluid filled membranous layers lies the testis. Both testes develop in the abdomen during the development in the womb and then descend to their permanent position later. The testicular temperature is about 3-40 C below the core body temperature. Adjacent to testis is a coiled tube called epididymis that serves to store, mature and transport sperm between the testis and vas deferens ( a thick muscular tube to carry sperm). Each testis produces male hormone testosterone (a steroid hormone) and sperm (spermatozoa).
Figure 2: Seminiferous Tubule showing various stages of sperm development
Spermatogenesis
Each testis is subdivided into hundreds of coiled tubules known as seminiferous tubules (ST) which are production houses of spermatozoa (also called sperm). Spermatogenesis is essentially an elaborate cell differentiation process starting with spermatogonia (germ cell) which line the ST and ending as a highly specialized motile cell spermatozoa containing half the number of chromosomes. Each tubule is lined with germ cells which progress to become sperm (Figure 2). STs also contain special cells called Sertoli cells (Figure 3) which support the lining of ST and help in maturation of sperm. Sertoli cells are crucial for sperm development.
Figure 3: Sertoli Cell nursing developing sperm
Sperm leave the testis through epididymis into vas which join with the seminal vesicles near prostate opening ultimately into prostate. The secretions from seminal vesicles and prostate (see below) mix with the sperm to make up the volume of semen during ejaculation.
Seminal vesicles: They are 2 glands at the base of the bladder and connected to the prostate. Like prostate they provide nutrients for the sperms
Prostate: It is walnut sized gland situated below the bladder in front of the rectum and behind the pubic bone. It is closely linked with the urinary system. It secretes much of the liquid portion of the seminal fluid
Urethra: It is the tube (duct) that carries urine from the bladder and sperm from the prostate out through the penis.
Urinary bladder: Although urinary bladder is not related to the reproductive system its continuity with urethra makes an important adjacent organ. It is a hollow, muscular and distensible organ above the prostate on the pelvic floor. The urinary bladder is responsible for storage and evacuation of urine. The ureters are two hollowmuscular tubes that connect kidney and bladder.
Figure 4 : Male genito-urinary system
What is the role of testosterone?
Testosterone and its more potent product Dihydrotestosterone are called androgens. Testosterone is responsible for the regulation of pituitary hormones (LH and FSH) initiation and maintenance of sperm production. Androgens help with sexual differentiation in embryo. Later in life they help to mature sexual organs and give sexual characteristic features. They increase bone density and muscle mass. They also have a role in bodily, spiritual, self-confidence and mood aspects of the mind. The influence of androgens on red blood cell production is well known. There is a progressive decline in androgen production with aging. This phenomenon is termed as andropause, male climacteric or progressive or partial androgen deficiency of the aging male.
Other hormones of Testis: Sertoli cells produce a hormone called inhibin which regulates Follicle Stimulating Hormone (FSH) in men.
