Gametes are the reproductive cells that combine to form offspring. Organs called gonads produce the gametes, along with the hormones that regulate human reproduction. The male gametes are called sperm. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that make up most of the testis. The scrotum is the muscular sac that holds the testes outside of the body cavity.
Spermatogenesis begins with mitotic division of spermatogonia (stem cells) to produce primary spermatocytes that undergo the two divisions of meiosis to become secondary spermatocytes, then the haploid spermatids. During spermiogenesis, spermatids are transformed into spermatozoa (formed sperm). Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature. During ejaculation, sperm exit the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum. The ampulla of the ductus deferens meets the seminal vesicle, a gland that contributes fructose and proteins, at the ejaculatory duct. The fluid continues through the prostatic urethra, where secretions from the prostate are added to form semen. These secretions help the sperm to travel through the urethra and into the female reproductive tract. Secretions from the bulbourethral glands protect sperm and cleanse and lubricate the penile (spongy) urethra.
The penis is the male organ of copulation. Columns of erectile tissue called the corpora cavernosa and corpus spongiosum fill with blood when sexual arousal activates vasodilatation in the blood vessels of the penis. Testosterone regulates and maintains the sex organs and sex drive, and induces the physical changes of puberty. Interplay between the testes and the endocrine system precisely control the production of testosterone with a negative feedback loop.
blood–testis barrier
tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm
bulbourethral glands
(also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation
corpus cavernosum
either of two columns of erectile tissue in the penis that fill with blood during an erection
corpus spongiosum
(plural = corpora cavernosa) column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis
ductus deferens
(also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens
ejaculatory duct
duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra
epididymis
(plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation
gamete
haploid reproductive cell that contributes genetic material to form an offspring
glans penis
bulbous end of the penis that contains a large number of nerve endings
gonadotropin-releasing hormone (GnRH)
hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland
gonads
reproductive organs (testes in men and ovaries in women) that produce gametes and reproductive hormones
inguinal canal
opening in abdominal wall that connects the testes to the abdominal cavity
Leydig cells
cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell
penis
male organ of copulation
prepuce
(also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin
prostate gland
doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation
scrotum
external pouch of skin and muscle that houses the testes
semen
ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands
seminal vesicle
gland that produces seminal fluid, which contributes to semen
seminiferous tubules
tube structures within the testes where spermatogenesis occurs
Sertoli cells
cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell
sperm
(also, spermatozoon) male gamete
spermatic cord
bundle of nerves and blood vessels that supplies the testes; contains ductus deferens
spermatid
immature sperm cells produced by meiosis II of secondary spermatocytes
spermatocyte
cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids
spermatogenesis
formation of new sperm, occurs in the seminiferous tubules of the testes
spermatogonia
(singular = spermatogonium) diploid precursor cells that become sperm
spermiogenesis
transformation of spermatids to spermatozoa during spermatogenesis
testes
(singular = testis) male gonads
Watch this video to learn about vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain?
Sperm remain in the epididymis until they degenerate.
Watch this video to explore the structures of the male reproductive system and the path of sperm that starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?
Sperm enter the prostate.
1. What are male gametes called?
A) ova
B) sperm
C) testes
D) testosterone
B
2. Leydig cells ________.
A) secrete testosterone
B) activate the sperm flagellum
C) support spermatogenesis
D) secrete seminal fluid
A
3. Which hypothalamic hormone contributes to the regulation of the male reproductive system?
A) luteinizing hormone
B) gonadotropin-releasing hormone
C) follicle-stimulating hormone
D) androgens
B
4. What is the function of the epididymis?
A) sperm maturation and storage
B) produces the bulk of seminal fluid
C) provides nitric oxide needed for erections
D) spermatogenesis
A
5. Spermatogenesis takes place in the ________.
A) prostate gland
B) glans penis
C) seminiferous tubules
D) ejaculatory duct
C
1. Briefly explain why mature gametes carry only one set of chromosomes.
A single gamete must combine with a gamete from an individual of the opposite sex to produce a fertilized egg, which has a complete set of chromosomes and is the first cell of a new individual.
2. What special features are evident in sperm cells but not in somatic cells, and how do these specializations function?
Unlike somatic cells, sperm are haploid. They also have very little cytoplasm. They have a head with a compact nucleus covered by an acrosome filled with enzymes, and a mid-piece filled with mitochondria that power their movement. They are motile because of their tail, a structure containing a flagellum, which is specialized for movement.
3. What do each of the three male accessory glands contribute to the semen?
The three accessory glands make the following contributions to semen: the seminal vesicle contributes about 60 percent of the semen volume, with fluid that contains large amounts of fructose to power the movement of sperm; the prostate gland contributes substances critical to sperm maturation; and the bulbourethral glands contribute a thick fluid that lubricates the ends of the urethra and the vagina and helps to clean urine residues from the urethra.
4. Describe how penile erection occurs.
During sexual arousal, nitric oxide (NO) is released from nerve endings near blood vessels within the corpora cavernosa and corpus spongiosum. The release of NO activates a signaling pathway that results in relaxation of the smooth muscles that surround the penile arteries, causing them to dilate. This dilation increases the amount of blood that can enter the penis, and induces the endothelial cells in the penile arterial walls to secrete NO, perpetuating the vasodilation. The rapid increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-walled penile venules, preventing venous drainage of the penis. An erection is the result of this increased blood flow to the penis and reduced blood return from the penis.
5. While anabolic steroids (synthetic testosterone) bulk up muscles, they can also affect testosterone production in the testis. Using what you know about negative feedback, describe what would happen to testosterone production in the testis if a male takes large amounts of synthetic testosterone.
Testosterone production by the body would be reduced if a male were taking anabolic steroids. This is because the hypothalamus responds to rising testosterone levels by reducing its secretion of GnRH, which would in turn reduce the anterior pituitary’s release of LH, finally reducing the manufacture of testosterone in the testes.