Lesson 2: The Male Reproductive System
By the end of this lesson, students will be able to:
- Describe the overall functions of the male reproductive system
- Describe the external genitalia and the significance of external placement of the male gonad
- Illustrate the role of each male reproductive structure in producing, storing, and transporting semen.
- Examine the process of spermatogenesis and the composition and functions of semen, and the physiological changes that occur during erection and ejaculation.
- Examine the hormonal control of male reproductive function.
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Male Reproductive Anatomy and Physiology
The male reproductive system is specialized for the production, maturation, nourishment, and delivery of sperm to a close physical proximity to the female gamete. Successful reproduction requires coordinated structural organization and precise hormonal regulation. This chapter examines the anatomy of the testes, the process of spermatogenesis, the duct system responsible for sperm transport, the accessory glands that contribute to semen formation, and the mechanisms underlying erection and ejaculation.
Structure of the Male Reproductive System
The external male reproductive system (Fig. 1) consists of the penis (the copulatory organ containing erectile tissue) and the scrotum (which contains the bilaterally-paired testes, the sites of spermatogenesis).
Optimal spematogenesis (as will be further discussed below) requires a temperature several degrees below body temperature, which necessitates the position of the scrotum outside the body cavity. Furthermore, testicular temperature can be controlled by the contraction of muscle in the wall of the scrotum and testes (Fig. 2), that tighten the scrotum and pull in closer to the body when the temperature is too low or loosen and allow descent of the scrotum away from the body when the temperature is too high.
The testes are the male gonads and serve two primary functions: sperm production and secretion of testosterone. Structurally, each testis is divided into lobules containing tightly coiled seminiferous tubules. These tubules are the site of sperm production. Within the seminiferous tubules (Figs. 3 and 4), developing sperm cells are arranged in layers that reflect progressive stages of maturation. Supporting cells and interstitial cells coordinate nourishment and hormonal regulation necessary for spermatogenesis.
Spermatogenesis
Spermatogenesis is the process by which sperm are produced from diploid precursor cells. This process occurs within the seminiferous tubules and involves mitotic division, meiotic division, and cellular differentiation (Figure 4). The first step in this process, the mitotic division of a stem cell, produces a daughter primary spermatocyte (an exact copy of the parent cell) that then undergoes meiosis (Fig. 3). During meiosis, which consists of one duplication of chromosomal DNA but two subsequent divisions, gametes are created that contain half of the genetic material of the parent cell (or one copy of each gene instead of two). These haploid spermatids then differentiate into mature spermatozoa. The process produces large numbers of sperm continuously after puberty.
Once produced, mature sperm are a remarkable example of simplicity of structure and function (Figure 5): the head contains a single copy of the male’s genetic material and enzymes that facilitate entry into the ovum, the midpiece contains mitochondria for production of ATP and the rotary motor producing movement, and the tail (flagellum) moves in a whip-like fashion to enable propulsion.
Hormonal Regulation of Spermatogenesis
Spermatogenesis is regulated by hormones originating in the hypothalamus and anterior pituitary. Gonadotropin-releasing hormone (GnRH) stimulates secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH; Figure 6). LH stimulates interstitial (Leydig) cells to produce testosterone. FSH acts on supporting cells within the seminiferous tubules to facilitate sperm development. Testosterone also supports spermatogenesis and exerts negative feedback on the hypothalamus and pituitary to regulate hormone levels. This endocrine coordination ensures continuous sperm production following puberty.
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- Figure 6A. Hormonal Control of the Testes. GnRH release from the hypothalamus, stimulation of LH and FSH from the anterior pituitary, testosterone production by interstitial cells, and feedback regulation. `Hypothalamic Pituitary Gonadal axis in males’ By Lu Kong, Ting Zhang, Meng Tang and Dayong Wang, CC BY 4.0, via Wikimedia Commons.
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- Figure 6B. Hormonal Control of the Testes. FSH binding to Sertoli cells in the seminiferous tubules enables the onset of spermatogenesis, while LH binding to Leydig cells triggers testosterone release. Figure 27.8 by Openstax A&P, 2e
The Duct System and Sperm Transport
After formation in the seminiferous tubules, sperm are transported through a series of ducts. They first move into a storage and maturation structure (the epidymis), then into a duct that ascends into the pelvic cavity (the vas deferens). During transport, sperm gain motility and fertilizing capability. This is due, in large part, to the products of several accessory glands (described below). The duct system ultimately delivers sperm into the urethra, where they are expelled from the body during ejaculation. Efficient transport is essential for reproductive success, as sperm must remain viable and motile to reach the female reproductive tract.
Accessory Glands and Semen Formation
Several accessory glands contribute secretions that combine with sperm to form semen (Fig. 8). These secretions provide nutrients, buffering capacity, and fluid volume to support sperm survival and motility. The seminal vesicles contribute a nutrient-rich fluid. The prostate gland adds alkaline secretions that help neutralize acidity. Additional glands provide lubricating secretions that facilitate sperm delivery. Together, these glandular contributions create an environment that enhances sperm function within the male and female reproductive tracts.
The Penis and Mechanisms of Erection
The penis serves as the copulatory organ and contains specialized erectile tissue. Sexual stimulation triggers neural pathways that cause dilation of blood vessels within this tissue. Increased blood flow produces engorgement and rigidity, resulting in erection. This vascular process is essential for successful deposition of semen into the female reproductive tract in relatively close proximity to the female gamete. It is this close proximity that improves the chances of successful fertilization and consequently, reproduction.
Ejaculation
Ejaculation is the coordinated expulsion of semen from the urethra. It involves rhythmic muscular contractions within the reproductive ducts and accessory structures. This process is under neural control and typically occurs during sexual climax. Ejaculation ensures delivery of sperm into the female reproductive system, where fertilization may occur.
Chapter Summary
The male reproductive system is structured to produce, mature, and deliver sperm efficiently. The testes contain seminiferous tubules where spermatogenesis occurs under hormonal regulation. The hypothalamic–pituitary–gonadal axis ensures sustained testosterone production and continuous sperm formation.
A specialized duct system transports sperm, while accessory glands provide supportive secretions that form semen. The penis, through vascular mechanisms, enables sperm deposition, and ejaculation ensures coordinated delivery.
Together, these anatomical and physiological components enable successful male reproductive function
Multilingual Approach Lesson Slides with translations
Module Slide Decks in Eight Languages
Lesson Video
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Practice Questions
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