Male reproductive tract functions include androgen homeostasis, spermatogenesis, sperm transport and storage, and normal erectile and ejaculatory function ability. The control of these functions involves the pituitary gland, central and peripheral nervous systems, and genitalia. In addition to a review of normal male reproductive anatomy and physiology, this chapter considers two common disorders of the male reproductive tract: male infertility and benign prostatic hyperplasia.
Normal Structure & Function of the Male Reproductive Tract
The male reproductive tract is composed of the testes, genital ducts, accessory glands, and penis (Figure 23–1).
Anatomy of the male reproductive system (left) and duct system of testis (right). (Redrawn, with permission, from Barrett KE et al. Ganong’s Review of Medical Physiology, 24th ed. McGraw-Hill, 2012.)
The testes are responsible for the production of testosterone and spermatozoa. Each testis is approximately 4 cm in length and 20 mL in volume. The testis is divided into lobules consisting of seminiferous tubules (inside which sperm are produced) and connective tissue (Figure 23–2). The seminiferous tubules converge to form another network of tubules called the rete testis through which spermatozoa are transported to the epididymis.
Schematic section of testis. (Redrawn, with permission, from Barrett KE et al. Ganong’s Review of Medical Physiology, 24th ed. McGraw-Hill, 2012.)
The seminiferous tubules are surrounded by a basal membrane and a specialized epithelium containing Sertoli cells that provide protection and nourishment to germ cells. Commensurate with puberty, tight junctions develop between adjacent Sertoli cells, creating an impermeable lining called the blood-testis barrier. This barrier divides the seminiferous tubules into a basal compartment and an adluminal compartment, separating more advanced germ cells from the immune system. The separation is necessary because mature sperm are potentially antigenic since they are not present at the prepubertal interval when much of the immune tolerance is established. The Leydig cells in the intertubular connective tissue produce testosterone.
Both testosterone production and spermatogenesis are controlled by the hypothalamic-pituitary-gonadal axis. The hypothalamus produces gonadotropin-releasing hormone (GnRH) in a pulsatile fashion. GnRH courses through the hypothalamic-pituitary portal system to stimulate the anterior pituitary gonadotropes to secrete (also in a pulsatile fashion) the two gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). FSH stimulates the Sertoli cells to produce paracrine growth factors and other products supporting spermatogenesis. FSH also stimulates the production of inhibin in response to active spermatogenesis and androgen-binding globulin (ABP).
Under the influence of LH, the Leydig cells produce testosterone. Concentrations of testosterone in the seminiferous tubules are 80–100 times greater than in the general circulation. Androgens act on spermatogenesis via the Sertoli cells, and high testicular levels ...