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22.4: Male Reproductive System

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    Male Reproductive System

    The testes produce spermatozoa (sperm), the male reproductive cells. Spermatozoa are produced in the seminiferous tubules and collected by the rete testis (rete = net). Spermatozoa travels from the rete testis to the head of the epididymis where they mature and are stored until ejaculation. The vas deferens transports spermatozoa from the tail of the epididymis to the prostate gland. Seminal glands, the prostate gland, and the bulbourethral glands add fluid secretions to spermatozoa to form semen. These additional fluids support the spermatozoa and their survival as well as facilitate their transfer to the female reproductive tract.

    Diagram of male reproductive anatomy. urinary bladder ejaculatory duct prostatic urethra membranous urethra corpus cavernosum corpus spongosum spongy urethra glans penis external urethral orifice scrotum vas deferens epididymis testis .ectum anus Seminal Vesicle Prostate gland Bulbourethral gland (Cowper's gland)

    Above: Male reproductive system, lateral view of the left side with structures shown with sagittal sections.

    The epididymis, vas deferens, ejaculatory duct and urethra form a system of tubules for the transport of spermatozoa from testes to the pelvic cavity. There they will be combined with the secretions of the accessory glands to form semen.

    Diagram of male reproductive anatomy. Ureters Urinary bladder Seminal vesicle Ejaculatory duct Prostate gland Vas deferens Epididymis (Head) (Body) (Tail) Glans penis External urethral orifice Prostatic urethra Membranous urethra Spongy urethra Rete testis Seminiferous tubules Corpus cavernosum Corpus spongiosum

    Above: Structures of the male genitalia.

    In order for proper and efficiently development of spermatozoa, the testes must be cooler than core body temperature (95°F is optimal for spermatogenesis and 98.6°F is core body temperature). The testes cool some just from being suspended away from the body, but the core temperature arterial blood from the gonadal artery must also be cooled before reaching the testis capillary beds. As blood is cooled in the peripheral capillary beds of the scrotal walls, it collects into a network of gonadal veins called the pampiniform plexus (pampiniform = shaped like a vine or tendril). As it ascends to the abdomen, this venous plexus wraps around the gonadal artery, cooling the arterial blood to sufficient temperature.

    Diagram and cadaver image showing structure within a testis and epididymis. spermatic cord efferent ductu le epididymis (body) epididymis (tail) epididymis (head) rete testes straight tubule lobule Epididymis (head) Rete testis Epididymis (body) Seminiferous tubules (tiny) Tunica albuginea sem iniferous tunica Vas deferens (cut) albuginea tunica Epididymis (tail) vaginalis

    Above: Internal structure of the testis and epididymis.

    Sperm cells are produced in the seminiferous tubules in the testes. A cross section through the process of spermatogenesis (a type of meiosis). Close examination of a cross section of a seminiferous tubule shows that sperm cells develop beginning close to the inner lining of the seminiferous tubule, beginning with specialized stem cells called spermatogonia, and develop as they move closer to the lumen of the seminiferous tubules. Primary spermatocytes (cells that undergo the first meiotic division) and secondary spermatocytes (cells that undergo the second meiotic division) are intermediate cells produced as spermatozoa develop. Spermatogenesis produces immature spermatids that ultimately mature into spermatozoa.

    Microscopic image of testis and epididymis cross section. tunica albuginea testis tunica vaginalis epididymis vas deferens seminiferous tubules

    Above: The testis is both an exocrine (producing spermatozoa) and an endocrine (producing androgens) gland. This immature testis, cut in cross section, provides an overview of the testis proper, its enclosing tunics, and its location in the scrotum. Also seen are the epididymis and the ductus deferens lying posterior to the testis. Tissue is magnified by 10x.

    Cross section of seminiferous tubule with developing spermatids. lumen spermatids secondary spermatocytes primary spermatocytes lumen of seminiferous tubule 00 000 sperma togonia of seminiferous tubule spermatic's seco nda ry sperma tocytes primary sperma tocytes spermatogonia

    Above: The exocrine function of the testis is performed by the epithelium lining the convoluted portions of seminiferous tubules. Each convoluted tubule is lined by a stratified epithelium composed of two cell types. Germ cells divide and cytodifferentiate to form haploid spermatozoa. Sertoli cells nourish and protect germ cells during their formation before releasing them into the lumen of the tubule. Tissue is magnified by 1000x.

    Layers of tissue surrounding the testis. spermatic cord testis arteries vans lymphatic vessels tunica vaginalis internal spermatic fascia cremaster muscle external spermatic fascia dartos muscle scrotum (skin)

    Above: Structures of the spermatic cord and structures enveloping the testis.

    Structure

    Location

    Function

    bulbourethral glands (Cowper's glands)

    pair (right and left) of glands posterior to the bulb of the penis and membranous urethra

    produce ~1% of the total volume of semen; produce a thick mucus that cleans and neutralizes the urethra of residual urine and increases the mobility of sperm in the vagina

    corpus cavernosum

    two of the three bodies of erectile tissue bodies in the penis

    become engorged with blood, causing an erection

    corpus spongiosum

    one of the three bodies of erectile tissue in the penis; the spongy urethra passes through the corpus spongiosum

    become engorged with blood, causing an erection

    cremasteric muscle

    very thin muscle that surrounds the spermatic cord and testes

    elevate the testes to warm them when the testes become too cold for optimal sperm production and development

    dartos muscle

    a very thin muscle in the walls of the scrotum

    elevate the scrotum to warm it when the testes are too cold for optimal sperm production and development

    ejaculatory ducts

    channels in the prostate gland formed when vas deferens joins with duct from the seminal vesicle

    spermatozoa and semen fluids flow through toward the prostatic urethra

    epididymis

    paired organ (right and left) located on the posterior aspect of the testes; consists of head, body and tail regions

    location where spermatids mature and become spermatozoa; store spermatozoa until ejaculation; spermatozoa account for about 3% of semen volume; an average of 200 – 500 million sperm released from an ejaculation

    external urethral orifice

    urethral opening on the penis

    location where urine and semen leave the body

    glans penis

    the highly sensitive bulbous structure at the end of the corpus spongiosum and tip of the penis

    contains the external urethral orifice and is covered by the prepuce in uncircumcised males

    membranous urethra

    short segment of the urethra that passes through the floor of the pelvis

    transports urine and semen

    penis

    external genitalia composed of shaft and glans penis

    male copulatory organ

    prepuce (foreskin)

    loose skin of the penis which covers the glans and is often removed by a process called circumcision

    protects glans penis

    prostate gland

    gland inferior to the urinary bladder; prostatic urethra and ejaculatory ducts pass through

    contributes ~26% to the volume of semen; secretes fluid that stabilizes sperm and protects them from the acidic environment of the vagina

    prostatic urethra

    region of the urethra that passes through the prostate; occurs from the bladder to the membranous urethra

    transports urine and semen

    scrotum

    skin surrounding the testis

    protection of the testis and associated tissues

    seminal vesicles

    pair (right and left) of tubular glands; posterior to the urinary bladder

    produce fluid that mixes with spermatozoa in the vas deferens just before the prostate gland; fluid from the seminal vesicles contributes the majority (~70%) of the volume of semen (semen = the mixture of sperm and supporting fluids); fluid from the seminal vesicles contains a lot of fructose, a sugar that is used by spermatozoa as their main energy source

    seminiferous tubules

    tubules within the testes

    site of spermatogenesis (production of spermatozoa); produce millions of spermatozoa per day

    spermatic cord

    bundle of vessels (blood and lymphatic vessels) and nerves traveling from the trunk to the testes

    a connective tissue sheath consisting of blood vessels, nerves and the cremaster muscle

    spongy urethra

    region of the urethra between the membranous urethra and the external urethral orifice; passes through the corpus spongiosum

    transports urine and semen

    testis (pl. testes)

    pair of organs within the scrotum; located outside of the abdominopelvic cavity; covered with tunica albuginea ("white tunic")

    produces spermatozoa and testosterone (a hormone)

    tunica albuginea

    a dense connective tissue capsule or "white tunic" that covers the testes; inward extensions of the tunica albuginea divides the seminiferous tubules into lobes

    vas deferens (ductus deferens)

    Passes from the epididymis, through the spermatic cord, through the inguinal canal, into the pelvic cavity and superiorly over the bladder

    upon ejaculation, sperm is received here from the epididymis by peristalsis

    External male genitalia and cross section diagram of the penis

    Above: (Left) External male genitalia. (Right) Cross section of the penis.

    This page titled 22.4: Male Reproductive System is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline.

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