Andrology

Male Anatomy

There are three main anatomical structures necessary for male reproduction: the testis, the epididymis, and the vas deferens (Figure 1) The testis are where sperm initially develop. The epididymis is a series of tubes that sit behind the testis and serves as the place where sperm are stored and can mature until they are made available at ejaculation. The vas deferens is a long tube that connects the epididymis to the ejaculatory ducts, so that mature sperm can come through the penis during ejaculation.

Of critical importance for the patient is the concept that any sperm surgically extracted from the testis will require in vitro fertilization (IVF) with intracytoplasmic sperm injection (ICSI)—inserting the sperm into the woman’s egg underneath a microscope—as these sperm will be immotile and will not gain the ability to move effectively until they enter the epididymis and vas deferens. Sperm are produced at a very high rate of nearly 1000 per second in the average fertile male. This anatomy is demonstrated in Figure 2.

Figure 1: Male anatomy

figure 1

Figure 2: Role of the testicle in sperm development

figure 2

Physiology of the Male Endocrine Axis

The male endocrine system has multiple levels of regulation. The hypothalamus, pituitary, and testes all produce substances that help to regulate the androgenic or male endocrine system (Figure 3). The hypothalamus and the pituitary gland, both in the brain, regulate hormonal control for many processes in the body. The hypothalamus produces GnRH or gonadotrophin releasing hormone that drives the pituitary to produce FSH or follicular stimulating hormone and LH or luteinizing hormone.

FSH and LH act on receptors in specialized cells in the testicles. FSH acts on the Sertoli cells. Sertoli cells help to produce sperm and FSH activates them to do so. Typically, the higher the FSH, the more the endocrine system has been activated to produce sperm. This relationship is complex and higher FSH levels do not necessarily result in greater sperm production. LH acts on the Leydig cells to increase their production of testosterone. Testosterone helps to optimize spermatogenesis (sperm production) in the male, in particular, the bioavailable testosterone or high-octane form of testosterone is vital to spermatogenesis. Although sperm production can occur with low levels of testosterone, production will significantly increase if these levels are brought up to normal levels through the use of medication. In the fatty tissues of the body, aromatase (an enzyme or “biological machine”) changes testosterone to estrogen. While all men have some estradiol, elevated levels can significantly impair sperm production. High levels of estradiol can also be treated through oral medication.

Sperm production is a highly regulated, complex process that is dependent on the local architecture of the testis tissue as well as exquisite hormonal control. It takes approximately 72 days from the time a sperm cell begins development as a stem cell until it completes its development into a mature and motile sperm. Any significant insult to spermatogenesis, such as a heat shock from time spent in a hot tub or sauna (hot showers, bike riding, and any type of underwear are fine), it takes 72 days for completely new sperm to be generated that remain unaffected by this insult.

Figure 3: Male endocrine axis

male endocrine axis

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