Module 27: The Reproductive System

Lesson 1: Anatomy of the Male Reproductive System

Giải Phẫu Hệ Sinh Dục Nam

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Dưới đây là danh sách những thuật ngữ Y khoa của module The Reproductive System.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Reproductive System

(of the breast) milk-secreting cells in the mammary gland
(of the uterine tube) middle portion of the uterine tube in which fertilization often occurs
fluid-filled chamber that characterizes a mature tertiary (antral) follicle
highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling
Bartholin’s glands
(also, greater vestibular glands) glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands
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
body of uterus
middle section of the uterus
broad ligament
wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall
bulbourethral glands
(also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation
elongate inferior end of the uterus where it connects to the vagina
(also, glans clitoris) nerve-rich area of the vulva that contributes to sexual sensation during intercourse
corpus albicans
nonfunctional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum
corpus cavernosum
(plural = corpora cavernosa) either of two columns of erectile tissue in the penis that fill with blood during an erection
corpus luteum
transformed follicle after ovulation that secretes progesterone
corpus spongiosum
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
inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses
(plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation
fingerlike projections on the distal uterine tubes
ovarian structure of one oocyte and surrounding granulosa (and later theca) cells
development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins
(of the uterus) domed portion of the uterus that is superior to the uterine tubes
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
reproductive organs (testes and ovaries) that produce gametes and reproductive hormones
granulosa cells
supportive cells in the ovarian follicle that produce estrogen
membrane that covers part of the opening of the vagina
(of the uterine tube) wide, distal portion of the uterine tube terminating in fimbriae
inguinal canal
opening in abdominal wall that connects the testes to the abdominal cavity
narrow, medial portion of the uterine tube that joins the uterus
labia majora
hair-covered folds of skin located behind the mons pubis
labia minora
thin, pigmented, hairless flaps of skin located medial and deep to the labia majora
lactiferous ducts
ducts that connect the mammary glands to the nipple and allow for the transport of milk
lactiferous sinus
area of milk collection between alveoli and lactiferous duct
Leydig cells
cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell
mammary glands
glands inside the breast that secrete milk
first menstruation in a pubertal female
shedding of the inner portion of the endometrium out though the vagina; also referred to as menstruation
menses phase
phase of the menstrual cycle in which the endometrial lining is shed
menstrual cycle
approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase
mons pubis
mound of fatty tissue located at the front of the vulva
Müllerian duct
duct system present in the embryo that will eventually form the internal female reproductive structures
smooth muscle layer of uterus that allows for uterine contractions during labor and expulsion of menstrual blood
cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilization to become a haploid ovum
process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilization, the ovum
ovarian stem cells that undergo mitosis during female fetal development to form primary oocytes
ovarian cycle
approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase
female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone)
release of a secondary oocyte and associated granulosa cells from an ovary
haploid female gamete resulting from completion of meiosis II at fertilization
male organ of copulation
outer epithelial layer of uterine wall
polar body
smaller cell produced during the process of meiosis in oogenesis
(also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin
primary follicles
ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells
primordial follicles
least developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells
proliferative phase
phase of the menstrual cycle in which the endometrium proliferates
prostate gland
doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation
life stage during which a male or female adolescent becomes anatomically and physiologically capable of reproduction
(of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth
external pouch of skin and muscle that houses the testes
secondary follicles
ovarian follicles with a primary oocyte and multiple layers of granulosa cells
secondary sex characteristics
physical characteristics that are influenced by sex steroid hormones and have supporting roles in reproductive function
secretory phase
phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo
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
(also, spermatozoon) male gamete
spermatic cord
bundle of nerves and blood vessels that supplies the testes; contains ductus deferens
immature sperm cells produced by meiosis II of secondary spermatocytes
cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids
formation of new sperm, occurs in the seminiferous tubules of the testes
(singular = spermatogonium) diploid precursor cells that become sperm
transformation of spermatids to spermatozoa during spermatogenesis
suspensory ligaments
bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis
tertiary follicles
(also, antral follicles) ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum
(singular = testis) male gonads
theca cells
estrogen-producing cells in a maturing ovarian follicle
uterine tubes
(also, fallopian tubes or oviducts) ducts that facilitate transport of an ovulated oocyte to the uterus
muscular hollow organ in which a fertilized egg develops into a fetus
tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby
external female genitalia
Wolffian duct
duct system present in the embryo that will eventually form the internal male reproductive structures
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
People often use the words “female” and “male” to describe two different concepts: our sense of gender identity, and our biological sex as determined by our X/Y chromosomes, hormones, sex organs, and other physical characteristics. For some people, gender identity is different from biological sex or their sex assigned at birth. In this chapter and the next chapter, “female” and “male” refer to sex only, and the typical reproductive anatomy of XX and XY individuals is discussed.

Unique for its role in reproduction, a gamete is a specialized sex cell, which in humans carries 23 chromosomes—one half the number in body cells. In almost all sexually reproducing species, these two haploid cells differ in size; the smaller gamete is called the male gamete and the larger one is called the female gamete. At fertilization, the chromosomes in one male gamete, called a sperm (or spermatozoon), combine with the chromosomes in one female gamete, called an ovum. The function of the male, or testicular, reproductive system (Figure 1) is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In male humans, the most important androgen is testosterone. For people with a penis, several accessory organs and ducts aid the process of sperm maturation and transport the sperm and other seminal components to the penis, which may deliver sperm to the female reproductive tract. In this section, we examine each of these different structures, and discuss the process of sperm production and transport.
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 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 2). It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments, each housing one testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles, which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather (or water), moving the testes closer to the body and decreasing the surface area of the scrotum to retain heat. Alternatively, as the environmental temperature increases, the scrotum relaxes, moving the testes farther from the body core and increasing scrotal surface area, which promotes heat loss. Externally, the scrotum has a raised medial thickening on the surface called the raphae.
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.

Paired ovals, adult testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure 2). They are surrounded by two distinct layers of protective connective tissue (Figure 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. Not only does the tunica albuginea cover the outside of the testis, it also invaginates to form septa that divide the testis into 300 to 400 structures called lobules. Within the lobules, sperm develop in structures called seminiferous tubules. During the seventh month of the developmental period of a male fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity. This is called the “descent of the testis.” Cryptorchidism is the clinical term used when one or both of the testes fail to descend into the scrotum prior to birth.

The tightly coiled seminiferous tubules form the bulk of each testis. They are composed of developing sperm cells surrounding a lumen, the hollow center of the tubule, where formed sperm are released into the duct system of the testis. Specifically, from the lumens of the seminiferous tubules, sperm move into the straight tubules (or tubuli recti), and from there into a fine meshwork of tubules called the rete testes. Sperm leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross the tunica albuginea.

Inside the seminiferous tubules are six different cell types. These include supporting cells called sustentacular cells, as well as five types of developing sperm cells called germ cells. Germ cell development progresses from the basement membrane—at the perimeter of the tubule—toward the lumen. Let’s look more closely at these cell types.

A. Sertoli Cells

Surrounding all stages of the developing sperm cells are elongate, branching Sertoli cells. Sertoli cells are a type of supporting cell called a sustentacular cell, or sustentocyte, that are typically found in epithelial tissue. Sertoli cells secrete signaling molecules that promote sperm production and can control whether germ cells live or die. They extend physically around the germ cells from the peripheral basement membrane of the seminiferous tubules to the lumen. Tight junctions between these sustentacular cells create the blood–testis barrier, which keeps bloodborne substances from reaching the germ cells and, at the same time, keeps surface antigens on developing germ cells from escaping into the bloodstream and prompting an autoimmune response.

B. Germ Cells

The least mature cells, the spermatogonia (singular = spermatogonium), line the basement membrane inside the tubule. Spermatogonia are the stem cells of the testis, which means that they are still able to differentiate into a variety of different cell types throughout adulthood. Spermatogonia divide to produce primary and secondary spermatocytes, then spermatids, which finally produce formed sperm. The process that begins with spermatogonia and concludes with the production of sperm is called spermatogenesis.

C. Spermatogenesis

As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis (see Figure 3). The process begins at puberty, after which time sperm are produced constantly throughout a male’s life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm counts—the total number of sperm a person produces—slowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age.

The process of spermatogenesis begins with mitosis of the diploid spermatogonia (Figure 4). Because these cells are diploid (2n), they each have a complete copy of the person’s genetic material, or 46 chromosomes. However, mature gametes are haploid (1n), containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.

Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte, the next stage in the process of spermatogenesis. As in mitosis, DNA is replicated in a primary spermatocyte, before it undergoes a cell division called meiosis I. During meiosis I each of the 23 pairs of chromosomes separates. This results in two cells, called secondary spermatocytes, each with only half the number of chromosomes. Now a second round of cell division (meiosis II) occurs in both of the secondary spermatocytes. During meiosis II each of the 23 replicated chromosomes divides, similar to what happens during mitosis. Thus, meiosis results in separating the chromosome pairs. This second meiotic division results in a total of four cells with only half of the number of chromosomes. Each of these new cells is a spermatid. Although haploid, early spermatids look very similar to cells in the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm. A process called spermiogenesis transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which occurs in the portion of the tubule nearest the lumen. Eventually, the sperm are released into the lumen and are moved along a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation.
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 6). 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 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.

Both sexual arousal and REM sleep (during which dreaming occurs) can induce an erection. Penile erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the penis than is leaving in the veins. During sexual arousal, nitric oxide (NO) is released from nerve endings near blood vessels within the corpora cavernosa and spongiosum. 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 also secrete NO and perpetuate 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. The result of this increased blood flow to the penis and reduced blood return from the penis is erection. Depending on the flaccid dimensions of a penis, it can increase in size slightly or greatly during erection, with the average length of an erect penis measuring approximately 15 cm.
To fertilize an egg without medical intervention, 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.

A. Structure of Formed Sperm

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 females 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 5). 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.

B. 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 3). Though the epididymis does not take up much room in its tightly coiled state, it would be approximately 6 m (20 feet) long if straightened. It takes an average of 12 days for sperm to move through the coils of the epididymis, with the shortest recorded transit time in humans being one day. Sperm enter the head of the epididymis and are moved along predominantly by the contraction of smooth muscles lining the epididymal tubes. As they are moved along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use this ability to move independently toward the unfertilized egg. The more mature sperm are then stored in the tail of the epididymis (the final section) until ejaculation occurs.

C. 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 1 and Figure 2). Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt sperm delivery can be performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is called a vasectomy, and it is an effective form of birth control. Although it may be possible to reverse a vasectomy, clinicians consider the procedure permanent, and advise people to undergo it only if they are certain they no longer wish to have children.

From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the abdominal wall. From here, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder where it dilates in a region called the ampulla (meaning “flask”).

Sperm make up only 5 percent of the final volume of semen, the thick, milky fluid that is ejaculated. The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands.

D. 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 1). The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume. Seminal vesicle fluid contains large amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female reproductive tract.

The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct, a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.

E. Prostate Gland

As shown in Figure 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. It excretes an alkaline, milky fluid to the passing seminal fluid—now called semen—that is critical to first coagulate and then decoagulate the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing time for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm can then pass farther into the female reproductive tract.

The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again. This enlargement does not usually cause problems; however, abnormal growth of the prostate, or benign prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a sensation that the bladder has not emptied completely. By age 60, approximately 40 percent of males have some degree of BPH. By age 80, the number of affected individuals has jumped to as many as 80 percent. Treatments for BPH attempt to relieve the pressure on the urethra so that urine can flow more normally. Mild to moderate symptoms are treated with medication, whereas severe enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.

Another common disorder involving the prostate is prostate cancer. According to the Centers for Disease Control and Prevention (CDC), prostate cancer is the second most common cancer in males. However, some forms of prostate cancer grow very slowly and thus may not ever require treatment. Aggressive forms of prostate cancer, in contrast, involve metastasis to vulnerable organs like the lungs and brain. There is no link between BPH and prostate cancer, but the symptoms are similar. Prostate cancer is detected by a medical history, a blood test, and a rectal exam that allows physicians to palpate the prostate and check for unusual masses. If a mass is detected, the cancer diagnosis is confirmed by biopsy of the cells.

F. 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. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at

The structures of the testicular reproductive system include the testes, the epididymides, 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.

This anterior view shows the structures of the scrotum and testes.

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.

(a) Mitosis of a spermatogonial stem cell involves a single cell division that results in two identical, diploid daughter cells (spermatogonia to primary spermatocyte). Meiosis has two rounds of cell division: primary spermatocyte to secondary spermatocyte, and then secondary spermatocyte to spermatid. This produces four haploid daughter cells (spermatids). (b) In this electron micrograph of a cross-section of a seminiferous tubule from a rat, the lumen is the light-shaded area in the center of the image. The location of the primary spermatocytes is near the basement membrane, and the early spermatids are approaching the lumen (tissue source: rat). EM × 900. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

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.

Three columns of erectile tissue make up most of the volume of the penis.

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  1. Gametes are the reproductive cells that combine to form offspring.
  2. Organs called gonads produce the gametes, along with the hormones that regulate human reproduction.
  3. The male gametes are called sperm.
  4. Spermatogenesis, the production of sperm, occurs within the seminiferous tubules that make up most of the testis.
  5. The scrotum is the muscular sac that holds the testes outside of the body cavity.
  6. Spermatogenesis begins with mitotic division of spermatogonia to produce primary spermatocytes that undergo the two divisions of meiosis to become secondary spermatocytes, then the haploid spermatids.
  7. During spermiogenesis, spermatids are transformed into spermatozoa, which is the formed sperm.
  8. Upon release from the seminiferous tubules, sperm are moved to the epididymis where they continue to mature.
  9. During ejaculation, sperm exit the epididymis through the ductus deferens, a duct in the spermatic cord that leaves the scrotum.
  10. The ampulla of the ductus deferens meets the seminal vesicle, a gland that contributes fructose and proteins, at the ejaculatory duct.
  11. The fluid continues through the prostatic urethra, where secretions from the prostate are added to form semen.
  12. These secretions help the sperm to travel through the urethra and into the female reproductive tract.
  13. Secretions from the bulbourethral glands protect sperm and cleanse and lubricate the penile or spongy urethra.
  14. The penis is the male organ of copulation.
  15. 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.
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