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Anatomy and physiology of the testicles
The testicles, or testes, are a part of a man’s reproductive system. A man has 2 testicles. Each testicle is egg-shaped and about 5 cm long. The testicles are covered by a sac of skin called the scrotum. The scrotum hangs below the penis, between the legs. The testicles make sperm. They also make testosterone, which is a male sex hormone.
Each testicle is covered by tough, fibrous layers of tissue called the tunica. The outer layer is called the tunica vaginalis and the inner layer is called the tunica albuginea.
The testicle is divided into parts called lobules. Each lobule contains tiny U-shaped tubes called seminiferous tubules. There are about 800 seminiferous tubules tightly coiled within the testicle.
The seminiferous tubules open into a series of uncoiled, interconnected channels called the rete testis. Ducts, or tubes, connect the rete testis to a tightly coiled tube called the epididymis. The epididymis joins to a long, large duct called the vas deferens.
Each testicle is held in the scrotum by a spermatic cord. Each spermatic cord is made of tough connective tissue and muscle. It contains the vas deferens, blood vessels, lymph vessels and nerves.
Lymph fluidLymph fluidA clear, yellowish fluid that contains nutrients, lymphocytes (a type of white blood cell that fights germs, foreign substances or cancer cells) and antibodies. Lymph fluid circulates throughout the body in lymph vessels and bathes body tissues. travels through vessels in the spermatic cord and drains from the testicles into several groups of lymph nodes at the back of the abdomen. These lymph nodes are called the retroperitoneal lymph nodes.
The testicles make sperm and male hormones. The 2 main types of cells in the testicles that perform these functions are germ cells and stromal cells.
The process of making sperm starts in germ cells, which line the seminiferous tubules. As they mature into sperm cells, germ cells move from the lining, through the maze of seminiferous tubules and to the epididymis. The epididymis stores sperm cells so they can completely mature.
Mature sperm cells travel through the vas deferens. Along the way, fluids made by the seminal vesicles and the prostate gland mix with the sperm cells to create semen. The semen is pushed out of body through the urethra during ejaculation. Sperm in the semen can fertilize a female egg to start a pregnancy.
Stromal cells are supportive cells within the testicle. Different types of stromal cells have different jobs.
Sertoli, or nurse cells, are a type of stromal cell found in the seminiferous tubules. They support the germ cells by helping make and transport sperm.
The soft connective tissue in the space between the seminiferous tubules contains specialized stromal cells called Leydig cells. They make male sex hormones, mostly testosterone. Testosterone helps germ cells make sperm. Testosterone also helps the reproductive organs develop and function. It gives men:
- sex drive, or libido
- fully developed genitals
- a deep voice
- body and facial hair
- bigger muscles and body size