Skip to main content
Medicine LibreTexts

22: The Reproductive System (Male)

  • Page ID
    12542
        • Anatomy and Physiology of the Male Reproductive System

          • Describe the structure of the organs of the male reproductive system

          • Describe the structure of the sperm cell

      image

      Figure 22.1 Male Reproductive System The structures of the male reproductive system include the testes, the epididymis, the penis, and the ducts and glands that produce and carry semen. Sperm exit the scrotum through the ductus deferens, which is bundled in the spermatic cord. The seminal vesicles and prostate gland add fluids to the sperm to create semen.

      Scrotum

      The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis (see Figure 22.1). This location is important in sperm production, which occurs within the testes, and proceeds more efficiently when the testes are kept 2 to 4°C below core body temperature. The dartos muscle makes up the subcutaneous muscle layer of the scrotum (Figure 22.2).

      image

      Figure 22.2 The Scrotum and Testes This anterior view shows the structures of the scrotum and testes.

      Testes

      The testes (singular = testis) are the male gonads—that is, the male reproductive organs. They produce both sperm and androgens, such as testosterone, and are active throughout the reproductive lifespan of the male.

      Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure 22.2). They are surrounded by two distinct layers of protective connective tissue (Figure 22.3). The outer tunica vaginalis is a serous membrane that has both a parietal and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer covering the testis itself. The tightly coiled seminiferous tubules form the bulk of each testis.

      image

      Figure 22.3 Anatomy of the Testis This sagittal view shows the seminiferous tubules, the site of sperm production. Formed sperm are transferred to the epididymis, where they mature. They leave the epididymis during an ejaculation via the ductus deferens.

      Structure of Formed Sperm

      image

      Sperm are smaller than most cells in the body; in fact, the volume of a sperm cell is 85,000 times less than that of the female gamete. Approximately 100 to 300 million sperm are produced each day, whereas women typically ovulate only one oocyte per month. As is true for most cells in the body, the structure of sperm cells speaks to their function. Sperm have a distinctive head, mid-piece, and tail region (Figure 22.4). The head of the sperm contains the extremely compact haploid nucleus with very little cytoplasm. These qualities contribute to the overall small size of the sperm (the head is only 5 μm long). A structure called the acrosome covers most of the head of the sperm cell as a “cap” that is filled with lysosomal enzymes important for preparing sperm to participate in fertilization. Tightly packed mitochondria fill the mid- piece of the sperm. ATP produced by these mitochondria will power the flagellum, which extends from the neck and the mid-piece through the tail of the sperm, enabling it to move the entire sperm cell. The central strand of the flagellum, the axial filament, is formed from one centriole inside the maturing sperm cell during the final stages of spermatogenesis.

      Figure 22.4 Structure of Sperm Sperm cells are divided into a head, containing DNA; a mid-piece, containing mitochondria; and a tail, providing motility. The acrosome is oval and somewhat flattened.

      Sperm Transport

      To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.

      Role of the Epididymis

      From the lumen of the seminiferous tubules, the immotile sperm are surrounded by testicular fluid and moved to the epididymis (plural = epididymides), a coiled tube attached to the testis where newly formed sperm continue to mature (see Figure 22.3).

      Duct System

      During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens (also called the vas deferens). The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord (see Figure 22.1 and Figure 22.2).

      Seminal Vesicles

      As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated

      seminal vesicle (see Figure 22.1). Prostate Gland

      As shown in Figure 22.1, the centrally located prostate gland sits anterior to the rectum at the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, the prostate is formed of both muscular and glandular tissues.

      Bulbourethral Glands

      The final addition to semen is made by two bulbourethral glands (or Cowper’s glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to clean urine residues from the penile urethra. The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly before the release of the semen. It is therefore sometimes called pre-ejaculate.

      The Penis

      The penis is the male organ of copulation (sexual intercourse). It is flaccid for non-sexual actions, such as urination, and turgid and rod-like with sexual arousal. When erect, the stiffness of the organ allows it to penetrate into the vagina and deposit semen into the female reproductive tract.

      The shaft of the penis surrounds the urethra (Figure 22.5). The shaft is composed of three column-like chambers of erectile tissue that span the length of the shaft. Each of the two larger lateral chambers is called a corpus cavernosum (plural = corpora cavernosa). Together, these make up the bulk of the penis. The corpus spongiosum, which can be felt as a raised ridge on the erect penis, is a smaller chamber that surrounds the spongy, or penile, urethra. The end of the penis, called the glans penis, has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation (see Figure 22.1). The skin from the shaft extends down over the glans and forms a collar called the prepuce (or foreskin). The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive skin of the glans penis. A surgical procedure called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth.

      image

      Figure 22.5 Cross-Sectional Anatomy of the Penis Three columns of erectile tissue make up most of the volume of the penis.

      B

      LAB 22 EXERCISES 22-1

      image

      image

      4

      1

      A

      Label the following: Deep artery * Dorsal vein * Urethra * Corpora cavernosa * Copora spongiosa * Median septum of the penis * Skin.

      Label the following: Spermatic cord * Epididymis * Seminiferous tubule * Tunica albuginea * Tunica vaginalis * Rete testis * Vas deferens

      3

      1

      2

      2

      5

      image

      7

      6

      4

      7

      6

      3

      5

      LAB 22 EXERCISES 22-2

      Label the following: Fascia of spermatic cord * Glans * Cremaster muscle * Pampiniform plexus * Tunica vaginalis * Ureter.

      1

      2

      3

      5

      4

      6

      LAB 22 EXERCISES 22-3

      Label the following: Testis * Epididymis * R. vas deferens * L. vas deferens *

      Ampulla (of vas deferens) * Seminal vesicle * Prostate * Urinary bladder.

      4

      1

      5

      2

      6

      7

      3

      8

      image

      image

      9

      10

      LAB 22 EXERCISES 22-4

      Label the following: Rectum * Prostate * Ejaculatory duct * Prostatic urethra * Membranous urethra * Spongy urethra * Shaft of penis * Root of penis * Urinary bladder * Urogenital diaphragm.

      1

      2

      6

      4

      3

      7

      5

      8

      image

      image

      LAB 22 EXERCISES 22-5

      HISTOLOGY

      A

      B

      Label the following: Head * Acrosome *

      Midpiece * Tail

      1. Name this organ sample *

        2

      2. Label the following: Spermatogonia * Spermatozoa * Interstitial cells * Nurse cells * Lumen

        1

        1

        2

        4

        4

        3

        3

        5

        Organ:

        6

        image

        LAB 22 EXERCISES 22-6

        HISTOLOGY

        A

        B

        1. Name this organ *

          2

        2. Label the following: Lumen * Mucosa * Submucosa * Muscularis externa.

    1. Name this gland

    2. label the following: Concretion * glandular epithelium.

      1

      1

      4

      3

      2

      Organ: Organ (gland):

      5

      3

      MODELS: Male Hemi-Pelvis and Torso

      image

       Scrotum

      • Dartos muscle

      • Raphe

         Testes:

      • Tunica albuginea

      • Tunica vaginalis

      • Seminiferous tubules

      • Rete testis

      • Epididymis

         Inguinal Canal

      • Spermatic cord

      • Testicular arteries

      • Pampiniform plexus (blood vessels)

      • Vas deferens (ductus deferens)

      • Cremasteric muscle

         Ejaculatory duct

         Urethra:

      • Prostatic * membranous * spongy

      • External urethral orifice

         Penis

      • Shaft

      • Root

      • Crus (Crura)

      • Corpora cavernosa (x2)

      • Corpora spongiosa

      • Glans penis

      • Dorsal artery/vein Deep artery

         Accessory glands:

      • Seminal Vesicles

      • Prostate

      • Bulbourethral (Cowpers) Glands

     Rectum

     Bladder

     Urogenital diaphragm

     Pubis Symphisis

    Histology:

    • Penis:

       corpora cavernosa

       corpora spongiosa

       Erectile tissue

       Urethra

       Central artery

       Deep dorsal vein

    • Testis

       tunica albuginea

       tunica vaginalis

       seminiferous tubules

       lumen *

       interstitial cells

       spermatids

       spermatogonia

    • Sperm

       Acrosome

       head

       midpiece

       tail/flagellum

    • Vas deferens & urethra

       Mucosa

       Submucosa

       Muscularis externa

    • Prostate gland

     Glandular epithelium

     concretion