Male Reproductive System - Anatomy and Functions PDF

2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1082 epg EPG-9:Desktop Folder:Totora_2568T_209: 1082 CHAPTER 28 THE REPRODUCTIVE SYSTEMS glands. The supporting structures have various functions. The...

2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1082 epg EPG-9:Desktop Folder:Totora_2568T_209: 1082 CHAPTER 28 THE REPRODUCTIVE SYSTEMS glands. The supporting structures have various functions. The MALE REPRODUCTIVE SYSTEM penis delivers sperm into the female reproductive tract and the  OBJECTIVES scrotum supports the testes. Describe the location, structure, and functions of the or- gans of the male reproductive system. Scrotum Discuss the process of spermatogenesis in the testes. The scrotum (SKRŌ-tum  bag), the supporting structure for the The organs of the male reproductive system include the testes, testes, consists of loose skin and underlying subcutaneous layer that a system of ducts (including the epididymis, ductus deferens, hangs from the root (attached portion) of the penis (Fig- ejaculatory ducts, and urethra), accessory sex glands (seminal ure 28.1a). Externally, the scrotum looks like a single pouch of skin vesicles, prostate, and bulbourethral glands), and several sup- separated into lateral portions by a median ridge called the raphe - porting structures, including the scrotum and the penis (Figure (RA -fē  seam). Internally, the scrotal septum divides the scro- 28.1). The testes (male gonads) produce sperm and secrete hor- tum into two sacs, each containing a single testis (Fig- mones. The duct system transports and stores sperm, assists in ure 28.2 on page 1084). The septum is made up of a subcutaneous their maturation, and conveys them to the exterior. Semen con- layer and muscle tissue called the dartos muscle (DAR-tōs  tains sperm plus the secretions provided by the accessory sex skinned), which is composed of bundles of smooth muscle fibers. Figure 28.1 Male organs of reproduction and surrounding structures. Reproductive organs are adapted for producing new individuals and passing on genetic material from one generation to the next. Sagittal plane Sacrum Peritoneum Seminal vesicle Urinary bladder Vesicorectal pouch Ductus (vas) deferens Coccyx Suspensory ligament Rectum of penis Ampulla of ductus Pubic symphysis (vas) deferens Ejaculatory duct Prostate Prostatic urethra Deep muscles of perineum Membranous urethra Bulbourethral Anus (Cowperʼs) gland Corpora cavernosum penis Spongy (penile) urethra Penis Bulb of penis Corpus spongiosum penis Corona Epididymis Glans penis Prepuce (foreskin) External urethral orifice Testis Scrotum (a) Sagittal section 2568T_c28_1081-1132.qxd 2/20/08 10:23 AM Page 1083 epg EPG-9:Desktop Folder:Sanjay 20/02/08:TORTORA_209: MALE REPRODUCTIVE SYSTEM 1083 The dartos muscle is also found in the subcutaneous layer of the Testes scrotum. Associated with each testis in the scrotum is the cremaster muscle (krē-MAS-ter  suspender), a series of small The testes (TES-tēz), or testicles, are paired oval glands in the bands of skeletal muscle that descend as an extension of the internal scrotum measuring about 5 cm (2 in.) long and 2.5 cm (1 in.) in oblique muscle through the spermatic cord to surround the testes. diameter (Figure 28.3 on page 1085). Each testis (singular) has a The location of the scrotum and the contraction of its muscle mass of 10–15 grams. The testes develop near the kidneys, in the fibers regulate the temperature of the testes. Normal sperm pro- posterior portion of the abdomen, and they usually begin their duction requires a temperature about 2–3C below core body descent into the scrotum through the inguinal canals (passage- temperature. This lowered temperature is maintained within the ways in the anterior abdominal wall; see Figure 28.2) during the scrotum because it is outside the pelvic cavity. In response to latter half of the seventh month of fetal development. cold temperatures, the cremaster and dartos muscles contract. A serous membrane called the tunica vaginalis (tunica  Contraction of the cremaster muscles moves the testes closer to sheath), which is derived from the peritoneum and forms during the body, where they can absorb body heat. Contraction of the the descent of the testes, partially covers the testes. A collection dartos muscle causes the scrotum to become tight (wrinkled in of serous fluid in the tunica vaginalis is called a hydrocele (HĪ- appearance), which reduces heat loss. Exposure to warmth re- drō-sēl; hydro-  water; -kele  hernia). It may be caused by in- verses these actions. jury to the testes or inflammation of the epididymis. Usually, no Functions of the Male Reproductive System 1. The testes produce sperm and the male sex hormone testosterone. 2. The ducts transport, store, and assist in maturation of sperm. 3. The accessory sex glands secrete most of the liquid portion of semen. 4. The penis contains the urethra, a passageway for ejaculation of semen and excretion of urine. SUPERIOR Seminal vesicle Urinary bladder (opened) Ductus (vas) deferens Prostatic urethra Prostate Ejaculatory duct Pubic symphysis Membranous urethra Corpora cavernosum penis Rectum Corpus Bulb of penis spongiosum penis Bulbospongiosus Spongy (penile) muscle urethra Testis Corona Glans penis POSTERIOR ANTERIOR (b) Sagittal section ? What are the groups of reproductive organs in males, and what are the functions of each group? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1084 epg EPG-9:Desktop Folder:Totora_2568T_209: 1084 CHAPTER 28 THE REPRODUCTIVE SYSTEMS Figure 28.2 The scrotum, the supporting structure for the testes. The scrotum consists of loose skin and an underlying subcutaneous layer and supports the testes. Internal oblique muscle Aponeurosis of external oblique muscle (cut) Spermatic cord Superficial (cutaneous) Fundiform ligament of penis inguinal ring Suspensory Cremaster muscle ligament of penis Inguinal canal Transverse section of penis: Ductus (vas) deferens Corpora cavernosa penis Autonomic nerve Spongy (penile) urethra Testicular artery Corpus spongiosum penis Lymphatic vessel Scrotal septum Pampiniform plexus of testicular veins Cremaster muscle Epididymis Tunica albuginea of testis External spermatic fascia Tunica vaginalis (peritoneum) Internal spermatic fascia Dartos muscle Skin of scrotum Raphe Anterior view of scrotum and testes and transverse section of penis ? Which muscles help regulate the temperature of the testes? treatment is required. Internal to the tunica vaginalis is a white sperm at puberty. Toward the lumen of the seminiferous tubule fibrous capsule composed of dense irregular connective tissue, are layers of progressively more mature cells. In order of advanc- the tunica albuginea (al-bū-JIN-ē-a; albu-  white); it extends ing maturity, these are primary spermatocytes, secondary sperma- inward, forming septa that divide the testis into a series of inter- tocytes, spermatids, and sperm cells. After a sperm cell, or nal compartments called lobules. Each of the 200–300 lobules spermatozoon (sper-ma-tō-ZŌ-on; -zoon  life) has formed, it contains one to three tightly coiled tubules, the seminiferous is released into the lumen of the seminiferous tubule. (The plural tubules (semin-  seed; fer-  to carry), where sperm are pro- terms are sperm and spermatozoa.) duced. The process by which the seminiferous tubules of the Embedded among the spermatogenic cells in the seminiferous testes produce sperm is called spermatogenesis (sper-ma-tō- tubules are large Sertoli cells or sustentacular cells (sus-ten- JEN-e-sis; genesis  beginning process or production). TAK-ū-lar), which extend from the basement membrane to the The seminiferous tubules contain two types of cells: sperm- lumen of the tubule. Internal to the basement membrane and atogenic cells, the sperm-forming cells, and Sertoli cells, which spermatogonia, tight junctions join neighboring Sertoli cells to have several functions in supporting spermatogenesis (Fig- one another. These junctions form an obstruction known as the ure 28.4 on page 1086). Stem cells called spermatogonia (sper- blood–testis barrier because substances must first pass through ma-tō-GŌ-nē-a; -gonia  offspring; singular is spermatogonium) the Sertoli cells before they can reach the developing sperm. By develop from primordial germ cells (primordi-  primitive or isolating the developing gametes from the blood, the early form) that arise from the yolk sac and enter the testes dur- blood–testis barrier prevents an immune response against the ing the fifth week of development. In the embryonic testes, the spermatogenic cell’s surface antigens, which are recognized as primordial germ cells differentiate into spermatogonia, which re- “foreign” by the immune system. The blood–testis barrier does main dormant during childhood and actively begin producing not include spermatogonia. 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1085 epg EPG-9:Desktop Folder:Totora_2568T_209: MALE REPRODUCTIVE SYSTEM 1085 Figure 28.3 Internal and external anatomy of a testis. The testes are the male gonads, which produce haploid sperm. Sagittal Spermatic cord plane Blood vessels and nerves Ductus (vas) deferens Head of epididymis Efferent duct Seminiferous tubule Body of epididymis Straight tubule Rete testis Tunica vaginalis Tunica albuginea Ductus epididymis Lobule Septum Tail of epididymis (a) Sagittal section of a testis showing seminiferous tubules SUPERIOR Testicular blood vessels, lymphatic vessels, and nerves Rete testis Seminiferous Head of tubules Body of epididymis epididymis Tunica vaginalis Testis Testis Tunica Tunica Tail of albuginea vaginalis epididymis POSTERIOR ANTERIOR (b) Lateral view of testis and associated structures (c) Sagittal section ? What tissue layers cover and protect the testes? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1086 epg EPG-9:Desktop Folder:Totora_2568T_209: 1086 CHAPTER 28 THE REPRODUCTIVE SYSTEMS Figure 28.4 Microscopic anatomy of the seminiferous tubules and stages of sperm production (spermatogenesis). Arrows in (b) indicate the progression of spermatogenic cells from least mature to most mature. The (n) and (2n) refer to haploid and diploid numbers of chromosomes, respectively. Spermatogenesis occurs in the seminiferous tubules of the testes. Basement membrane Sertoli cell Spermatid (n) Transverse plane Secondary spermatocyte (n) Primary spermatocyte (2n) Spermatogonium (2n) (stem cell) LM 160x (a) Transverse section of several seminiferous tubules Leydig cell Blood capillary SPERMATOGENIC CELLS: Basement membrane Spermatogonium (2n) (stem cell) Sertoli cell nucleus Primary spermatocyte (2n) Blood–testis barrier (tight junction) Secondary spermatocyte (n) Early spermatid (n) Cytoplasmic bridge Late spermatid (n) Sperm cell or spermatozoon (n) Lumen of seminiferous tubule (b) Transverse section of a portion of a seminiferous tubule ? Which cells secrete testosterone? Sertoli cells support and protect developing spermatogenic and the release of sperm into the lumen of the seminiferous cells in several ways. They nourish spermatocytes, spermatids, tubule. They also produce fluid for sperm transport, secrete the and sperm; phagocytize excess spermatid cytoplasm as develop- hormone inhibin, and regulate the effects of testosterone and ment proceeds; and control movements of spermatogenic cells FSH (follicle-stimulating hormone). 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1087 epg EPG-9:Desktop Folder:Totora_2568T_209: MALE REPRODUCTIVE SYSTEM 1087 In the spaces between adjacent seminiferous tubules are clus- A unique process occurs during spermatogenesis. As sper- ters of cells called Leydig (interstitial) cells (Figure 28.4). matogenic cells proliferate, they fail to complete cytoplasmic These cells secrete testosterone, the most prevalent androgen. An separation (cytokinesis). The cells remain in contact via cyto- androgen is a hormone that promotes the development of mas- plasmic bridges through their entire development (see Fig- culine characteristics. Testosterone also promotes a man’s libido ures 28.4b and 28.5). This pattern of development most likely (sexual drive). accounts for the synchronized production of sperm in any given area of seminiferous tubule. It may also have survival value in CLINICAL CONNECTION Cryptorchidism that half of the sperm contain an X chromosome and half con- tain a Y chromosome. The larger X chromosome may carry The condition in which the testes do not descend into the scrotum is genes needed for spermatogenesis that are lacking on the smaller called cryptorchidism (krip-TOR-ki-dizm; crypt-  hidden; orchid  Y chromosome. testis); it occurs in about 3% of full-term infants and about 30% of pre- The final stage of spermatogenesis, spermiogenesis (sper- mature infants. Untreated bilateral cryptorchidism results in sterility mē-ō-JEN-e-sis), is the development of haploid spermatids into because the cells involved in the initial stages of spermatogenesis are sperm. No cell division occurs in spermiogenesis; each sper- destroyed by the higher temperature of the pelvic cavity. The chance of testicular cancer is 30–50 times greater in cryptorchid testes. The matid becomes a single sperm cell. During this process, spheri- testes of about 80% of boys with cryptorchidism will descend sponta- cal spermatids transform into elongated, slender sperm. An acro- neously during the first year of life. When the testes remain unde- some (described shortly) forms atop the nucleus, which scended, the condition can be corrected surgically, ideally before 18 condenses and elongates, a flagellum develops, and mitochon- months of age. dria multiply. Sertoli cells dispose of the excess cytoplasm that sloughs off. Finally, sperm are released from their connections to Spermatogenesis Figure 28.5 Events in spermatogenesis. Diploid cells (2n) Before you read this section, please review the topic of repro- have 46 chromosomes; haploid cells (n) have 23 chromosomes. ductive cell division in Chapter 3 on pages 97–99. Pay particular Spermiogenesis involves the maturation of attention to Figures 3.33 and 3.34, which appear on pages 98 spermatids into sperm. and 99, respectively. In humans, spermatogenesis takes 65–75 days. It begins with Basement membrane of seminiferous tubule the spermatogonia, which contain the diploid (2n) number of Some spermatogonia remain chromosomes (Figure 28.5). Spermatogonia are types of stem Superficial as precursor stem cells Spermatogonium cells; when they undergo mitosis, some spermatogonia remain 2n near the basement membrane of the seminiferous tubule in an 2n Mitosis undifferentiated state to serve as a reservoir of cells for future Some spermatogonia cell division and subsequent sperm production. The rest of the pushed away from 2n spermatogonia lose contact with the basement membrane, basement membrane squeeze through the tight junctions of the blood–testis barrier, Differentiation undergo developmental changes, and differentiate into primary Primary spermatocyte spermatocytes (SPER-ma-tō-sı̄tz). Primary spermatocytes, 2n DNA replication, like spermatogonia, are diploid (2n); that is, they have 46 tetrad formation, chromosomes. and crossing-over Meiosis I Shortly after it forms, each primary spermatocyte replicates MEIOSIS Secondary spermatocytes its DNA and then meiosis begins (Figure 28.5). In meiosis I, ho- Each mologous pairs of chromosomes line up at the metaphase plate, n n chromosome has two and crossing-over occurs. Then, the meiotic spindle pulls one Meiosis II chromatids (duplicated) chromosome of each pair to an opposite pole of the Spermatids Cytoplasmic dividing cell. The two cells formed by meiosis I are called secon- bridge dary spermatocytes. Each secondary spermatocyte has 23 chro- n n n n mosomes, the haploid number (n). Each chromosome within a secondary spermatocyte, however, is made up of two chromatids SPERMIOGENESIS Spermatozoa (two copies of the DNA) still attached by a centromere. No Deep n n n n replication of DNA occurs in the secondary spermatocytes. In meiosis II, the chromosomes line up in single file along the metaphase plate, and the two chromatids of each chromosome separate. The four haploid cells resulting from meiosis II are called spermatids. A single primary spermatocyte therefore pro- Lumen of seminiferous tubule duces four spermatids via two rounds of cell division (meiosis I and meiosis II). ? What is “reduced” during meiosis I? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1088 epg EPG-9:Desktop Folder:Totora_2568T_209: 1088 CHAPTER 28 THE REPRODUCTIVE SYSTEMS Sertoli cells, an event known as spermiation. Sperm then enter Hormonal Control of the Testes the lumen of the seminiferous tubule. Fluid secreted by Sertoli Although the initiating factors are unknown, at puberty certain cells pushes sperm along their way, toward the ducts of the hypothalamic neurosecretory cells increase their secretion of testes. At this point, sperm are not yet able to swim. gonadotropin-releasing hormone (GnRH). This hormone in Sperm turn stimulates gonadotrophs in the anterior pituitary to increase their secretion of the two gonadotropins, luteinizing hormone Each day about 300 million sperm complete the process of sper- (LH) and follicle-stimulating hormone (FSH). Figure 28.7 matogenesis. A sperm is about 60 m long and contains several shows the hormones and negative feedback loops that control se- structures that are highly adapted for reaching and penetrating a cretion of testosterone and spermatogenesis. secondary oocyte (Figure 28.6). The major parts of a sperm LH stimulates Leydig cells, which are located between sem- are the head and the tail. The flattened, pointed head of the iniferous tubules, to secrete the hormone testosterone (tes-TOS- sperm is about 4–5 m long. It contains a nucleus with 23 highly te-rōn). This steroid hormone is synthesized from cholesterol in condensed chromosomes. Covering the anterior two-thirds of the the testes and is the principal androgen. It is lipid-soluble and nucleus is the acrosome (acro-  atop; -some  body), a cap- readily diffuses out of Leydig cells into the interstitial fluid and like vesicle filled with enzymes that help a sperm to penetrate a then into blood. Via negative feedback, testosterone suppresses secondary oocyte to bring about fertilization. Among the en- secretion of LH by anterior pituitary gonadotrophs and sup- zymes are hyaluronidase and proteases. The tail of a sperm is presses secretion of GnRH by hypothalamic neurosecretory subdivided into four parts: neck, middle piece, principal piece, cells. In some target cells, such as those in the external genitals and end piece. The neck is the constricted region just behind the and prostate, the enzyme 5 alpha-reductase converts testosterone head that contains centrioles. The centrioles form the micro- to another androgen called dihydrotestosterone (DHT). tubules that comprise the remainder of the tail. The middle FSH acts indirectly to stimulate spermatogenesis (Fig- piece contains mitochondria arranged in a spiral, which provide ure 28.7). FSH and testosterone act synergistically on the Sertoli the energy (ATP) for locomotion of sperm to the site of fertiliza- cells to stimulate secretion of androgen-binding protein (ABP) tion and for sperm metabolism. The principal piece is the into the lumen of the seminiferous tubules and into the intersti- longest portion of the tail, and the end piece is the terminal, ta- tial fluid around the spermatogenic cells. ABP binds to testos- pering portion of the tail. Once ejaculated, most sperm do not terone, keeping its concentration high. Testosterone stimulates survive more than 48 hours within the female reproductive tract. the final steps of spermatogenesis in the seminiferous tubules. Once the degree of spermatogenesis required for male reproduc- Figure 28.6 Parts of a sperm cell. tive functions has been achieved, Sertoli cells release inhibin, a protein hormone named for its role in inhibiting FSH secretion About 300 million sperm mature each day. by the anterior pituitary (Figure 28.7). If spermatogenesis is pro- ceeding too slowly, less inhibin is released, which permits more FSH secretion and an increased rate of spermatogenesis. Acrosome HEAD Testosterone and dihydrotestosterone both bind to the same androgen receptors, which are found within the nuclei of target Nucleus cells. The hormone–receptor complex regulates gene expression, Neck turning some genes on and others off. Because of these changes, the androgens produce several effects: Mitochondria Prenatal development. Before birth, testosterone stimulates Middle piece the male pattern of development of reproductive system ducts and the descent of the testes. Dihydrotestosterone stimulates development of the external genitals (described on page 1121). Testosterone also is converted in the brain to estrogens (feminizing hormones), which may play a role in TAIL Principal the development of certain regions of the brain in males. piece Development of male sexual characteristics. At puberty, testosterone and dihydrotestosterone bring about develop- ment and enlargement of the male sex organs and the devel- opment of masculine secondary sexual characteristics. Secondary sex characteristics are traits that distinguish males and females but do not have a direct role in reproduc- End piece tion. These include muscular and skeletal growth that results in wide shoulders and narrow hips; facial and chest hair (within hereditary limits) and more hair on other parts of the ? What are the functions of each part of a sperm cell? body; thickening of the skin; increased sebaceous (oil) gland 2568T_c28_1081-1132.qxd 2/14/08 5:04 AM Page 1089 epg EPG-9:Desktop Folder:Totora_2568T_209: MALE REPRODUCTIVE SYSTEM 1089 secretion; and enlargement of the larynx and consequent mones; that is, they stimulate protein synthesis. This effect deepening of the voice. is obvious in the heavier muscle and bone mass of most men Development of sexual function. Androgens contribute to as compared to women. male sexual behavior and spermatogenesis and to sex drive A negative feedback system regulates testosterone production (libido) in both males and females. Recall that the adrenal (Figure 28.8). When testosterone concentration in the blood in- cortex is the main source of androgens in females. creases to a certain level, it inhibits the release of GnRH by cells Stimulation of anabolism. Androgens are anabolic hor- in the hypothalamus. As a result, there is less GnRH in the portal Figure 28.7 Hormonal control of spermatoge- Figure 28.8 Negative feedback control of blood level of nesis and actions of testosterone and dihydrote- testosterone. stosterone (DHT). In response to stimulation by Gonadotrophs of the anterior pituitary produce FSH and testosterone, Sertoli cells secrete luteinizing hormone (LH). androgen-binding protein (ABP). Dashed red lines indicate negative feedback inhibition. Release of FSH is stimulated by GnRH and inhibited by inhibin; release of LH is stimulated by GnRH and Some stimulus disrupts homeostasis by inhibited by testosterone. Hypothalamus GnRH Increasing Blood level of testosterone Testosterone decreases release of GnRH and LH Anterior pituitary Receptors Inhibin decreases Gonadotroph Cells in hypo- release of FSH thalamus that secrete GnRH Together with testosterone, LH stimulates FSH stimulates FSH LH testosterone spermatogenesis Input Decreased GnRH secretion in portal blood Control center Return to Inhibin homeostasis when response brings Anterior blood level of Testosterone pituitary testosterone back to ABP normal gonadotrophs Spermatogenic cells Output Decreased LH Sertoli cells Leydig cells secrete in systemic blood secrete androgen- Dihydro- testosterone binding protein testosterone Effectors (ABP) (DHT) Leydig cells in the testes secrete less testosterone Male pattern of development (before birth) Enlargement of male sex organs and expression of male secondary sex characteristics (starting at puberty) Anabolism (protein synthesis) Decrease in blood level of testosterone Key: LH FSH Testosterone ? Which hormones inhibit secretion of FSH and LH by LH receptor FSH receptor Androgen the anterior pituitary? receptor ? Which cells secrete inhibin? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1090 epg EPG-9:Desktop Folder:Totora_2568T_209: 1090 CHAPTER 28 THE REPRODUCTIVE SYSTEMS blood that flows from the hypothalamus to the anterior pituitary. attaches the loops of the ductus epididymis and carries blood Gonadotrophs in the anterior pituitary then release less LH, so vessels and nerves. the concentration of LH in systemic blood falls. With less stim- Functionally, the epididymis is the site of sperm maturation, ulation by LH, the Leydig cells in the testes secrete less testos- the process by which sperm acquire motility and the ability to terone, and there is a return to homeostasis. If the testosterone fertilize an ovum. This occurs over a period of about 14 days. concentration in the blood falls too low, however, GnRH is again The epididymis also helps propel sperm into the ductus (vas) released by the hypothalamus and stimulates secretion of LH by deferens during sexual arousal by peristaltic contraction of its the anterior pituitary. LH in turn stimulates testosterone produc- smooth muscle. In addition, the epididymis stores sperm, which tion by the testes. remain viable here for up to several months. Any stored sperm  that are not ejaculated by that time are eventually reabsorbed. CHECKPOINT 1. Describe the function of the scrotum in protecting the Ductus Deferens testes from temperature fluctuations. 2. Describe the internal structure of a testis. Where are Within the tail of the epididymis, the ductus epididymis be- sperm cells produced? What are the functions of Sertoli comes less convoluted, and its diameter increases. Beyond this cells and Leydig cells? point, the duct is known as the ductus deferens or vas deferens 3. Describe the principal events of spermatogenesis. (see Figure 28.3a). The ductus deferens, which is about 45 cm 4. Identify the parts of a sperm cell, and list the functions of (18 in.) long, ascends along the posterior border of the epi- each. didymis through the spermatic cord and then enters the pelvic 5. What are the roles of FSH, LH, testosterone, and inhibin cavity. There it loops over the ureter and passes over the side and in the male reproductive system? How is secretion of down the posterior surface of the urinary bladder (see Figure these hormones controlled? 28.1a). The dilated terminal portion of the ductus deferens is the ampulla (am-PUL-la  little jar; Figure 28.9). The mucosa of the ductus deferens consists of pseudostratified columnar epithe- Reproductive System Ducts lium and lamina propria (areolar connective tissue). The muscu- in Males laris is composed of three layers of smooth muscle; the inner and outer layers are longitudinal, and the middle layer is circular. Ducts of the Testis Functionally, the ductus deferens conveys sperm during sex- Pressure generated by the fluid secreted by Sertoli cells pushes ual arousal from the epididymis toward the urethra by peri- sperm and fluid along the lumen of seminiferous tubules and staltic contractions of its muscular coat. Like the epididymis, then into a series of very short ducts called straight tubules (see the ductus deferens also can store sperm for several months. Figure 28.3a). The straight tubules lead to a network of ducts in Any stored sperm that are not ejaculated by that time are even- the testis called the rete testis (RĒ-tē  network). From the rete tually reabsorbed. testis, sperm move into a series of coiled efferent ducts in the epididymis that empty into a single tube called the ductus Spermatic Cord epididymis. The spermatic cord is a supporting structure of the male repro- ductive system that ascends out of the scrotum (see Figure 28.2). Epididymis It consists of the ductus (vas) deferens as it ascends through the The epididymis (ep-i-DID-i-mis; epi-  above or over; -didymis scrotum, the testicular artery, veins that drain the testes and carry  testis) is a comma-shaped organ about 4 cm (1.5 in.) long that testosterone into circulation (the pampiniform plexus), auto- lies along the posterior border of each testis (see Figure 28.3a). nomic nerves, lymphatic vessels, and the cremaster muscle. The The plural is epididymides (ep-i-did-ĪM-i-dēs). Each epi- term varicocele (VAR-i-kō-sēl; varico-  varicose; -kele  her- didymis consists mostly of the tightly coiled ductus epididymis. nia) refers to a swelling in the scrotum due to a dilation of the The efferent ducts from the testis join the ductus epididymis at veins that drain the testes. It is usually more apparent when the larger, superior portion of the epididymis called the head. the person is standing and typically does not require treatment. The body is the narrow midportion of the epididymis, and the The spermatic cord and ilioinguinal nerve pass through the tail is the smaller, inferior portion. At its distal end, the tail of inguinal canal (IN-gwin-al  groin), an oblique passageway in the epididymis continues as the ductus (vas) deferens (discussed the anterior abdominal wall just superior and parallel to the medial shortly). half of the inguinal ligament. The canal, which is about 4–5 cm The ductus epididymis would measure about 6 m (20 ft) in (about 2 in.) long, originates at the deep (abdominal) inguinal length if it were uncoiled. It is lined with pseudostratified ring, a slitlike opening in the aponeurosis of the transversus ab- columnar epithelium and encircled by layers of smooth muscle. dominis muscle; the canal ends at the superficial (subcuta- The free surfaces of the columnar cells contain stereocilia, neous) inguinal ring (see Figure 28.2), a somewhat triangular which despite their name are long, branching microvilli (not opening in the aponeurosis of the external oblique muscle. In fe- cilia) that increase the surface area for the reabsorption of de- males, the round ligament of the uterus and ilioinguinal nerve generated sperm. Connective tissue around the muscle layer pass through the inguinal canal. 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1091 epg EPG-9:Desktop Folder:Totora_2568T_209: MALE REPRODUCTIVE SYSTEM 1091 CLINICAL CONNECTION Vasectomy tion continues in the testes, sperm can no longer reach the exterior. The sperm degenerate and are destroyed by phagocytosis. Because the The principal method for sterilization of males is a vasectomy (vas-EK- blood vessels are not cut, testosterone levels in the blood remain nor- tō-mē; -ectomy  cut out), in which a portion of each ductus deferens mal, so vasectomy has no effect on sexual desire, performance, and is removed. An incision is made on either side of the scrotum, the ducts ejaculation. If done correctly, it is close to 100% effective. The proce- are located and cut, each is tied (ligated) in two places with stitches, dure can be reversed, but the chance of regaining fertility is only and the portion between the ties is removed. Although sperm produc- 30–40%. Figure 28.9 Locations of several accessory reproductive organs in males. The prostate, urethra, and penis have been sectioned to show internal details. The male urethra has three subdivisions: the prostatic, membranous, and spongy (penile) urethra. Functions of Accessory Sex Gland Secretions 1. The seminal vesicles secrete alkaline, viscous fluid that helps neutralize acid in the female reproductive tract, provides fructose for ATP production by sperm, contributes to sperm motility and viability, and helps semen coagulate after ejaculation. 2. The prostate secretes a milky, slightly acidic fluid that helps semen coagulate after ejaculation and subsequently breaks down the clot. 3. The bulbourethral (Cowper’s) glands secrete alkaline fluid that neutralizes the acidic environment of the urethra and mucus that lubricates the lining of the urethra and the tip of the penis during sexual intercourse. Urinary bladder Right ductus (vas) deferens View Left ureter Hip bone (cut) Ampulla of ductus Prostate (vas) deferens Seminal vesicle Prostatic urethra Seminal vesicle duct Membranous Ejaculatory (intermediate) duct urethra Deep muscles of perineum Crus of penis Bulbourethral (Cowper’s) gland Bulb of penis Corpora cavernosa penis Corpus spongiosum penis Spongy (penile) urethra (a) Posterior view of male accessory organs of reproduction F I G U R E 28.9 CO N T I N U E S 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1092 epg EPG-9:Desktop Folder:Totora_2568T_209: 1092 CHAPTER 28 THE REPRODUCTIVE SYSTEMS F I G U R E 2 8.9 CO N T I N U E D Hip bone Urinary bladder Left ureter Pelvic diaphragm Right ductus (vas) deferens Obturator internus Seminal vesicle muscle Ampulla of ductus (vas) deferens Prostate Deep muscles of perineum Bulbospongiosus muscle (b) Posterior view of male accessory organs of reproduction ? What accessory sex gland contributes the majority of the seminal fluid? Ejaculatory Ducts deep muscles of the perineum, where it is known as the mem- Each ejaculatory duct (e-JAK-ū-la-tō-rē; ejacul-  to expel) is branous urethra. The membranous urethra is about 1 cm (0.5 in.) about 2 cm (1 in.) long and is formed by the union of the duct in length. As this duct passes through the corpus spongiosum of from the seminal vesicle and the ampulla of the ductus (vas) def- the penis, it is known as the spongy (penile) urethra, which is erens (Figure 28.9). The ejaculatory ducts form just superior to about 15–20 cm (6–8 in.) long. The spongy urethra ends at the the base (superior portion) of the prostate and pass inferiorly and external urethral orifice. The histology of the male urethra may anteriorly through the prostate. They terminate in the prostatic be reviewed on page 1052 of Chapter 26. urethra, where they eject sperm and seminal vesicle secretions  CHECKPOINT just before the release of semen from the urethra to the exterior. 6. Which ducts transport sperm within the testes? 7. Describe the location, structure, and functions of the Urethra ductus epididymis, ductus (vas) deferens, and In males, the urethra is the shared terminal duct of the repro- ejaculatory duct. ductive and urinary systems; it serves as a passageway for both 8. Give the locations of the three subdivisions of the male semen and urine. About 20 cm (8 in.) long, it passes through the urethra. prostate, the deep muscles of the perineum, and the penis, and is 9. Trace the course of sperm through the system of ducts subdivided into three parts (see Figures 28.1 and 26.22). The from the seminiferous tubules to the urethra. prostatic urethra is 2–3 cm (1 in.) long and passes through the 10. List the structures within the spermatic cord. prostate. As this duct continues inferiorly, it passes through the 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1093 epg EPG-9:Desktop Folder:Totora_2568T_209: MALE REPRODUCTIVE SYSTEM 1093 Accessory Sex Glands bulbourethral glands secrete an alkaline fluid into the urethra that protects the passing sperm by neutralizing acids from urine The ducts of the male reproductive system store and transport in the urethra. They also secrete mucus that lubricates the end of sperm cells, but the accessory sex glands secrete most of the the penis and the lining of the urethra, decreasing the number of liquid portion of semen. The accessory sex glands include the sperm damaged during ejaculation. seminal vesicles, the prostate, and the bulbourethral glands. Seminal Vesicles Semen The paired seminal vesicles (VES-i-kuls) or seminal glands are Semen ( seed) is a mixture of sperm and seminal fluid, a liq- convoluted pouchlike structures, about 5 cm (2 in.) in length, ly- uid that consists of the secretions of the seminiferous tubules, ing posterior to the base of the urinary bladder and anterior to seminal vesicles, prostate, and bulbourethral glands. The volume the rectum (Figure 28.9). Through the seminal vesicle ducts they of semen in a typical ejaculation is 2.5–5 milliliter (mL), with secrete an alkaline, viscous fluid that contains fructose (a mono- 50–150 million sperm per mL. When the number falls below saccharide sugar), prostaglandins, and clotting proteins that are 20 million/mL, the male is likely to be infertile. A very large different from those in blood. The alkaline nature of the seminal number of sperm is required for successful fertilization because fluid helps to neutralize the acidic environment of the male ure- only a tiny fraction ever reaches the secondary oocyte. thra and female reproductive tract that otherwise would inacti- Despite the slight acidity of prostatic fluid, semen has a vate and kill sperm. The fructose is used for ATP production by slightly alkaline pH of 7.2–7.7 due to the higher pH and larger sperm. Prostaglandins contribute to sperm motility and viability volume of fluid from the seminal vesicles. The prostatic secre- and may stimulate smooth muscle contractions within the female tion gives semen a milky appearance, and fluids from the semi- reproductive tract. The clotting proteins help semen coagulate nal vesicles and bulbourethral glands give it a sticky consistency. after ejaculation. Fluid secreted by the seminal vesicles normally Seminal fluid provides sperm with a transportation medium, nu- constitutes about 60% of the volume of semen. trients, and protection from the hostile acidic environment of the Prostate male’s urethra and the female’s vagina. Once ejaculated, liquid semen coagulates within 5 minutes The prostate (PROS-tāt) is a single, doughnut-shaped gland due to the presence of clotting proteins from the seminal vesi- about the size of a golf ball. It measures about 4 cm (1.6 in.) cles. The functional role of semen coagulation is not known, but from side to side, about 3 cm (1.2 in.) from top to bottom, and the proteins involved are different from those that cause blood about 2 cm (0.8 in.) from front to back. It is inferior to the urinary coagulation. After about 10 to 20 minutes, semen reliquefies be- bladder and surrounds the prostatic urethra (Figure 28.9). The cause prostate-specific antigen (PSA) and other proteolytic en- prostate slowly increases in size from birth to puberty. It then ex- zymes produced by the prostate break down the clot. Abnormal pands rapidly until about age 30, after which time its size typi- or delayed liquefaction of clotted semen may cause complete or cally remains stable until about age 45, when further enlarge- partial immobilization of sperm, thereby inhibiting their move- ment may occur. ment through the cervix of the uterus. The presence of blood in The prostate secretes a milky, slightly acidic fluid (pH about semen is called hemospermia (hē-mō-SPER-mē-a; hemo-  6.5) that contains several substances. (1) Citric acid in prostatic blood; -sperma  seed). In most cases, it is caused by inflamma- fluid is used by sperm for ATP production via the Krebs cycle. tion of the blood vessels lining the seminal vesicles; it is usually (2) Several proteolytic enzymes, such as prostate-specific antigen treated with antibiotics. (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase, eventually break down the clotting proteins from the seminal vesicles. (3) The function of the acid phosphatase secreted by Penis the prostate is unknown. (4) Seminalplasmin in prostatic fluid is The penis contains the urethra and is a passageway for the ejac- an antibiotic that can destroy bacteria. Seminalplasmin may help ulation of semen and the excretion of urine (Figure 28.10). It is decrease the number of naturally occurring bacteria in semen cylindrical in shape and consists of a body, glans penis, and a and in the lower female reproductive tract. Secretions of the root. The body of the penis is composed of three cylindrical prostate enter the prostatic urethra through many prostatic ducts. masses of tissue, each surrounded by fibrous tissue called the Prostatic secretions make up about 25% of the volume of semen tunica albuginea (Figure 28.10). The two dorsolateral masses and contribute to sperm motility and viability. are called the corpora cavernosa penis (corpora  main bod- ies; cavernosa  hollow). The smaller midventral mass, the Bulbourethral Glands - corpus spongiosum penis, contains the spongy urethra and The paired bulbourethral glands (bul-bō-ū-RE -thral), or keeps it open during ejaculation. Skin and a subcutaneous layer Cowper’s glands, are about the size of peas. They are located enclose all three masses, which consist of erectile tissue. Erectile inferior to the prostate on either side of the membranous urethra tissue is composed of numerous blood sinuses (vascular spaces) within the deep muscles of the perineum, and their ducts open lined by endothelial cells and surrounded by smooth muscle and into the spongy urethra (Figure 28.9). During sexual arousal, the elastic connective tissue. 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1094 epg EPG-9:Desktop Folder:Totora_2568T_209: 1094 CHAPTER 28 THE REPRODUCTIVE SYSTEMS Figure 28.10 Internal structure of the penis. The inset in (b) shows details of the skin and fasciae. (See Tortora, A Photographic Atlas of the Human Body, Second Edition, Figure 14.6.) The penis contains the urethra, a common pathway for semen and urine. Urinary bladder Internal urethral orifice Transverse Prostatic urethra Prostate plane Orifice of ejaculatory duct Bulbourethral (Cowper’s) gland Membranous urethra Deep muscles of perineum ROOT OF PENIS: Bulb of penis Crus of penis Skin Deep dorsal Superficial (subcutaneous) vein dorsal vein BODY OF PENIS: Corpora cavernosa penis Dorsal Subcutaneous layer artery Fascia Corpus spongiosum penis Dorsal Corpora cavernosa penis Spongy (penile) urethra Tunica albuginea of corpora cavernosum Deep artery of penis Corona Corpus spongiosum Frontal penis GLANS PENIS plane Spongy (penile) urethra Prepuce Ventral Tunica albuginea of (foreskin) corpus spongiosum External urethral orifice penis (a) Frontal section (b) Transverse section Superficial dorsal vein Skin Deep dorsal vein Transverse plane Dorsal artery Subcutaneous layer Corpora cavernosa penis Tunica albuginea of corpora cavernosa Deep artery of penis Spongy (penile) urethra Corpus spongiosum penis Tunica albuginea of corpus spongiosum penis (c) Transverse section ? Which tissue masses form the erectile tissue in the penis, and why do they become rigid during sexual arousal? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1095 epg EPG-9:Desktop Folder:Totora_2568T_209: FEMALE REPRODUCTIVE SYSTEM 1095 The distal end of the corpus spongiosum penis is a slightly cannot attain them. Other causes include a spinal cord disorder, enlarged, acorn-shaped region called the glans penis; its margin leukemia, sickle-cell disease, or a pelvic tumor. is the corona. The distal urethra enlarges within the glans penis Ejaculation (ē-jak-ū-LĀ-shun; ejectus-  to throw out), the and forms a terminal slitlike opening, the external urethral ori- powerful release of semen from the urethra to the exterior, is a fice. Covering the glans in an uncircumcised penis is the loosely sympathetic reflex coordinated by the lumbar portion of the fitting prepuce (PRĒ-poos), or foreskin. spinal cord. As part of the reflex, the smooth muscle sphincter at The root of the penis is the attached portion (proximal por- the base of the urinary bladder closes, preventing urine from be- tion). It consists of the bulb of the penis, the expanded portion ing expelled during ejaculation, and semen from entering the of the base of the corpus spongiosum penis, and the crura of the urinary bladder. Even before ejaculation occurs, peristaltic con- penis (singular is crus  resembling a leg), the two separated tractions in the epididymis, ductus (vas) deferens, seminal vesi- and tapered portions of the corpora cavernosa penis. The bulb of cles, ejaculatory ducts, and prostate propel semen into the penile the penis is attached to the inferior surface of the deep muscles portion of the urethra (spongy urethra). Typically, this leads to of the perineum and is enclosed by the bulbospongiosus muscle, emission (e- -MISH-un), the discharge of a small volume of se- a muscle that aids ejaculation. Each crus of the penis bends lat- men before ejaculation. Emission may also occur during sleep erally away from the bulb of the penis to attach to the ischial and (nocturnal emission). The musculature of the penis (bulbospon- inferior pubic rami and is surrounded by the ischiocavernosus giosus, ischiocavernosus, and superficial transverse perineus muscle (see Figure 11.13 on page 369). The weight of the penis muscles), which is supplied by the pudendal nerve, also con- is supported by two ligaments that are continuous with the fascia tracts at ejaculation (see Figure 11.13 on page 369). of the penis. (1) The fundiform ligament arises from the infe- Once sexual stimulation of the penis has ended, the arterioles rior part of the linea alba. (2) The suspensory ligament of the supplying the erectile tissue of the penis constrict and the penis arises from the pubic symphysis. smooth muscle within erectile tissue contracts, making the blood sinuses smaller. This relieves pressure on the veins supplying the penis and allows the blood to drain through them. Consequently, CLINICAL CONNECTION Circumcision the penis returns to its flaccid (relaxed) state. Circumcision ( to cut around) is a surgical procedure in which part of or the entire prepuce is removed. It is usually performed just after deliv- ery, 3 to 4 days after birth, or on the eighth day as part of a Jewish reli- CLINICAL CONNECTION Premature Ejaculation gious rite. Although most health-care professionals find no medical jus- A premature ejaculation is ejaculation that occurs too early, for exam- tification for circumcision, some feel that it has benefits, such as a ple, during foreplay or upon or shortly after penetration. It is usually lower risk of urinary tract infections, protection against penile cancer, caused by anxiety, other psychological causes, or an unusually sensi- and possibly a lower risk for sexually transmitted diseases. Indeed, tive foreskin or glans penis. For most males, premature ejaculation can studies in several African villages have found lower rates of HIV infec- be overcome by various techniques (such as squeezing the penis be- tion among circumcised men. tween the glans penis and shaft as ejaculation approaches), behavioral therapy, or medication. Upon sexual stimulation (visual, tactile, auditory, olfactory, or imagined), parasympathetic fibers from the sacral portion of  CHECKPOINT the spinal cord initiate and maintain an erection, the enlarge- 11. Briefly explain the locations and functions of the seminal ment and stiffening of the penis. The parasympathetic fibers vesicles, the prostate, and the bulbourethral (Cowper’s) release and cause local production of nitric oxide (NO). The NO glands. causes smooth muscle in the walls of arterioles supplying erec- 12. What is semen? What is its function? tile tissue to relax, which allows these blood vessels to dilate. 13. Explain the physiological processes involved in erection This in turn causes large amounts of blood to enter the erectile and ejaculation. tissue of the penis. NO also causes the smooth muscle within the erectile tissue to relax, resulting in widening of the blood si- nuses. The combination of increased blood flow and widening of the blood sinuses results in an erection. Expansion of the blood FEMALE REPRODUCTIVE SYSTEM sinuses also compresses the veins that drain the penis; the slow-  OBJECTIVES ing of blood outflow helps to maintain the erection. Describe the location, structure, and functions of the The term priapism (PRĪ-a-pizm) refers to a persistent and organs of the female reproductive system. usually painful erection of the penis that does not involve sexual Discuss the process of oogenesis in the ovaries. desire or excitement. The condition may last up to several hours and is accompanied by pain and tenderness. It results from ab- The organs of the female reproductive system (Figure 28.11) normalities of blood vessels and nerves, usually in response to include the ovaries (female gonads); the uterine (fallopian) medication used to produce erections in males who otherwise tubes, or oviducts; the uterus; the vagina; and external organs, 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1096 epg EPG-9:Desktop Folder:Totora_2568T_209: 1096 CHAPTER 28 THE REPRODUCTIVE SYSTEMS Functions of the Female Reproductive System 1. The ovaries produce secondary oocytes and hormones, including Figure 28.11 Female organs of reproduction and surrounding progesterone and estrogens (female sex hormones), inhibin, and relaxin. structures. 2. The uterine tubes transport a secondary oocyte to the uterus and normally are the sites where fertilization occurs. The organs of reproduction in females include the 3. The uterus is the site of implantation of a fertilized ovum, development ovaries, uterine (fallopian) tubes, uterus, vagina, of the fetus during pregnancy, and labor. vulva, and mammary glands. 4. The vagina receives the penis during sexual intercourse and is a passageway for childbirth. 5. The mammary glands synthesize, secrete, and eject milk for nourishment of the newborn. Sagittal plane Uterine (fallopian) tube Fimbriae Sacrum Ovary Uterus Uterosacral ligament Round ligament Posterior fornix of vagina of uterus Rectouterine pouch (pouch of Douglas) Cervix Vesicouterine pouch Urinary bladder Coccyx Pubic symphysis Rectum Mons pubis Clitoris Vagina Urethra Labium majus Anus External urethral orifice Labium minus (a) Sagittal section Fimbriae Ovary Uterine (fallopian) tube Rectouterine Fundus of uterus pouch (pouch of Douglas) Body of uterus Vesicouterine Cervix of uterus pouch Urinary bladder Vagina Pubic symphysis Rectum Mons pubis Urethra Clitoris Labium minus Labium majus (b) Sagittal section ? Which structures in males are homologous to the ovaries, the clitoris, the paraurethral glands, and the greater vestibular glands? 2568T_c28_1081-1132.qxd 2/14/08 0:11 AM Page 1097 epg EPG-9:Desktop Folder:Totora_2568T_209: FEMALE REPRODUCTIVE SYSTEM 1097 which are collectively called the vulva, or pudendum. The mam- Histology of the Ovary mary glands are considered part of both the integumentary sys- Each ovary consists of the following parts (Figure 28.13): tem and the female reproductive system. The germinal epithelium (germen  sprout or bud) is a Ovaries layer of simple epithelium (low cuboidal or squamous) that covers the surface of the ovary. We now know that the term The ovaries ( egg receptacles), which are the female gonads, germinal epithelium in humans is not accurate because it are paired glands that resemble unshelled almonds in size and does not give rise to ova; the name came about because, at shape; they are homologous to the testes. (Here homologous one time, people believed that it did. We have since learned means that two organs have the same embryonic origin.) The that the cells that produce ova arise from the yolk sac and ovaries produce (1) gametes, secondary oocytes that develop migrate to the ovaries during embryonic development. into mature ova (eggs) after fertilization, and (2) hormones, in- The tunica albuginea is a whitish capsule of dense irregular cluding progesterone and estrogens (the female sex hormones), connective tissue located immediately deep to the germinal inhibin, and relaxin. epithelium. The ovaries, one on either side of the uterus, descend to the brim of the superior portion of the pelvic cavity during the third The ovarian cortex is a region just deep to the tunica al- month of development. A series of ligaments holds them in posi- buginea. It consists of ovarian follicles (described shortly) tion (Figure 28.12). The broad ligament of the uterus (see also surrounded by dense irregular connective tissue that con- Figure 28.11b), which is itself part of the parietal peritoneum, tains collagen fibers and fibroblast-like cells called stromal attaches to the ovaries by a double-layered fold of peritoneum cells. called the mesovarium. The ovarian ligament anchors the The ovarian medulla is deep to the ovarian cortex. The bor- ovaries to the uterus, and the suspensory ligament attaches der between the cortex and medulla is indistinct, but the them to the pelvic wall. Each ovary contains a hilum, the point medulla consists of more loosely arranged connective tissue