10 Reproductive System

Transcription

1 Chapter 10 Reproductive System Male Reproductive System -The male reproductive system consists of the penis, testes, scrotum, a series of ducts (epididymis, vas deferens, ejaculatory ducts, and urethra), and accessory sex glands (seminal vesicles, prostate gland, and bulbourethral glands) (Figure 28.1, Tortora). 1. scrotum -a sac that surrounds the testes -Structure -The scrotum consists of 2 major layers (Figure 28.2, Tortora): a. skin -the outer layer b. dartos muscle -the inner layer -a type of smooth muscle that is attached to the skin of the scrotum via connective tissue -In addition, the scrotum is associated with the testes and the cremaster muscle. testes -singular is testis -There are 2 testes within the scrotum. 218 cremaster muscle -a type of skeletal muscle that attaches to each testis -an extension of the internal oblique muscle -Functions a. The scrotum supports the testes. b. The scrotum protects the testes. c. The scrotum regulates the temperature of the testes. -The testes are in the scrotum (and not in the pelvic cavity) in order to keep the temperature of the testes around 34 o C, which is 3 degrees below the normal body temperature. -The testes produce sperm. - Normal sperm production requires a temperature around 34 o C; higher temperatures kill sperm. -The scrotum maintains the temperature of the testes at 34 o C by contracting or relaxing the cremaster muscle and the dartos muscle. -When the temperature of the testes drops below 34 o C (example: a man jumps into a cold swimming pool), the cremaster muscle and the dartos muscle contract.

2 219 Contraction of the cremaster muscle brings the testes closer to the body, which allows the testes to absorb body heat. Contraction of the dartos muscle causes the scrotum to become tight (i.e. wrinkled in appearance), which reduces heat loss. The net effect of these muscles contracting is to increase the temperature of the testes back to 34 o C. -When the temperature of the testes becomes higher than 34 o C (example: a man takes a hot shower), the cremaster muscle and the dartos muscle relax. Relaxation of the cremaster muscle moves the testes further away from the body, which reduces exposure to body heat. Relaxation of the dartos muscle causes the scrotum to become loose, which increase heat loss. The net effect of the relaxation of these muscles is to decrease the temperature of the testes down to 34 o C. 2. testes -also called testicles or male gonads A gonad is a reproductive organ that produces gametes (sex cells such as sperm or eggs. -The testes are male gonads because they produce sperm, while the ovaries are the female gonads because they produce ova (eggs). -Structure -Each testis consists of a tunica vaginalis, tunica albuginea, seminiferous tubules, and Leydig cells (Figure 28.3, Tortora): a. tunica vaginalis -a layer of white connective tissue that surrounds the testis. b. tunica albuginea -an additional layer of white connective tissue that is deep to the tunica vaginalis -divides the testis into sections called lobules c. seminiferous tubules -The lobules of the testis contain coiled structures called seminiferous tubules, which produce sperm cells. -Each seminiferous tubule contains sperm cells at various stages of development that are surrounded by a basement membrane (connective tissue) on one side and by a lumen on the other side (Figure 28.4, Tortora). -The sperm cells are given different names as they develop in the seminiferous tubule; these names sequentially include the spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid, and spermatozoon.

3 220 spermatogenesis -the production of sperm in the seminiferous tubules of the testes -It takes about 2½ months ( 75 days) for this process to occur. -Sandwiched between the developing sperm cells in the seminiferous tubules are Sertoli cells. Sertoli cells -also called sustentacular cells -nourish, protect, and stimulate the development of sperm cells Hence, Sertoli cells are vital to the process of spermatogenesis. -In addition, Sertoli cells secrete a fluid that transports sperm from the seminiferous tubules to the epididymis. This transport function of the Sertoli cells is necessary because sperm produced in the testes are immature, which means that they are nonmotile (unable to move) and, therefore, are incapable of fertilizing an ovum. -Sperm do not become motile until they mature in the epididymis. -Sperm cell -also called spermatozoon (the plural form is sperm cells or spermatozoa) -A sperm cell consists of the following components (Figure 28.6, Tortora): 1. head -The head is divided into 2 regions: a. acrosome -a sac that contains enzymes that penetrate the ovum during fertilization b. nucleus -contains the DNA, which is haploid (i.e. consists of 23 total chromosomes: 22 autosomes and 1 X or Y sex chromosome). 2.tail -a flagellum that moves the sperm in a whiplike fashion -further divided into 4 regions: neck, middle piece (which contains mitochondria that produce energy/atp), principal piece, and end piece

4 221 -Note that during fetal development and childhood, the testes do not produce any sperm. -Once, the male reaches puberty, however, the testes start making sperm and continue to do so for most of the male s life. d. Leydig cells -also called interstitial cells -located between the seminiferous tubules -secrete testosterone into the blood -Functions a. The testes produce sperm. b. The testes produce testosterone. 3. male duct system -The fluid secreted by the Sertoli cells transports sperm from the seminiferous tubules to the epididymis, which is the beginning of the male duct system (Figure 28.1, Tortora). The male duct system consists of a series of tubes that are continuous with one another; it sequentially consists of the epididymis, vas deferens, ejaculatory ducts, and the urethra. a. epididymis -The epididymis is a coiled tube located above each testis (Figure 28.3, Tortora). -Structure -The epididymis consists of a layer of epithelial cells that line a lumen and an underlying layer of smooth muscle. -Functions 1. The epididymis is the site of sperm maturation. -Recall that sperm entering the epididymis are immature (nonmotile) and, therefore, are incapable of fertilizing an ovum. The epididymis matures sperm by making them motile, which enables them to fertilize an ovum. This maturation process requires about 2 weeks. 2. The epididymis propels sperm. -During ejaculation, the smooth muscle in the wall of the epididymis contracts. -This causes sperm to be propelled into the vas deferens. 3. The epididymis stores sperm. -Sperm can be stored in the epididymis for several months.

5 222 If the man does not ejaculate the stored sperm during this window of time, then they are destroyed to make room for newer sperm. b. vas deferens -also called the ductus deferens -Each vas deferens is a long tube that extends off of the epididymis, ascends the scrotum, enters the pelvic cavity, courses past the urinary bladder, and then ends as an expanded region called the ampulla (Figure 28.1, Tortora). -Structure -The vas deferens consists of a layer of epithelial cells that line a lumen and an underlying layer of smooth muscle. -Functions 1. The vas deferens propels sperm. -During ejaculation, the smooth muscle in the wall of the vas deferens contracts. -This causes sperm to be propelled into the ejaculatory duct and then into the urethra. 2. The vas deferens stores sperm. -The vas deferens can also store sperm for several months. -After that, they are destroyed to make room for newer sperm. -Spermatic Cord -a collective term that refers to various structures in the scrotum that are bundled together into a cord by connective tissue (Figure 28.2, Tortora) -includes the following: vas deferens testicular artery -supplies blood to the testes pampiniform plexus of testicular veins -drains blood from the testes lymphatic vessels nerves cremaster muscle c. ejaculatory ducts -Structure -There are 2 ejaculatory ducts; each is formed by the union a seminal vesicle with the ampulla of the vas deferens (Figure 28.1, Tortora). -Function -During ejaculation, the ejaculatory ducts allow sperm to move from the vas deferens into the urethra.

6 223 d. urethra -the terminal part of the male duct system -Structure -The male urethra consists of 3 anatomical regions (Figure 28.1, Tortora): 1. prostatic urethra -the part of the urethra that runs through the prostate gland 2. membranous (intermediate) urethra -the part of the urethra located between the prostate gland and the penis 3. penile urethra -also called the spongy urethra -the part of the urethra that runs through the corpus spongiosum of the penis At the tip of the penis, the penile urethra opens to the outside environment as the external urethral orifice. -The various regions of the urethra have a similar histology: a layer of epithelium that lines a lumen and an underlying layer of connective tissue. -Function -The urethra conveys sperm (in the form of semen) and urine out of the body. However, the semen and urine do not pass through the urethra at the same time. During ejaculation, the urinary sphincter at the base of the urinary bladder is closed, thereby preventing urine from entering the urethra. 4. accessory sex glands -The accessory sex glands add secretions to sperm during ejaculation to form semen. The accessory sex glands include the seminal vesicles, prostate gland, and bulbourethral glands (Figures 28.1 and 28.9, Tortora): a. seminal vesicles -paired glands that secrete fructose, an alkaline fluid containing bicarbonate (HCO3 - ) ions, and prostaglandins into the ejaculatory duct during ejaculation. Recall that each seminal vesicle unites with ampulla of the vas deferens to form the ejaculatory duct. b. prostate gland -a single gland that is about the size and shape of a chestnut -secretes citric acid and seminalplasmin into the urethra during ejaculation

7 224 c. bulbourethral glands -also called Cowper s glands -paired glands that are about the size and shape of a pea -secrete mucus and an alkaline fluid containing bicarbonate (HCO3 - ) ions into the urethra during ejaculation -Semen -a mixture of sperm and the secretions of the accessory sex glands -ph -Semen has a slightly alkaline ph of about Appearance -Semen looks milky white. -Composition sperm alkaline fluid containing bicarbonate (HCO3 - ) ions -causes semen to have a slightly alkaline ph -neutralizes the acidic environment in the female vagina so that sperm can survive in this area fructose -serves as a nutrient that sperm use to produce energy (ATP) via cellular respiration citric acid -serves as a nutrient that sperm use to enter the Krebs Cycle in order to produce energy (ATP). Note that there are more bicarbonate ions in semen than citric acid; therefore, the ph of semen is overall slightly alkaline. prostaglandins -chemicals that eventually stimulate the contraction of smooth muscle in the female reproductive tract, which helps to move sperm towards the ovum to cause fertilization mucus -lubricates the urethra during ejaculation seminalplasmin -a chemical that kills bacteria that may be present in the male urethra and/or female reproductive tract 5. penis -Structure -The penis consists of 3 regions (Figure 28.10, Tortora): a. glans -the tips of the penis -shaped like an acorn -In an uncircumcised male, loose skin called prepuce (foreskin) surrounds the glans.

8 225 b. body -also called the shaft -the middle and longest part of the penis c. root -the part of the penis that attaches to the rest of the male s body -surrounded by the bulbospongiosus muscle, which is a type of skeletal muscle (Figure 11.13, Tortora) -The various regions of the penis are composed of erectile tissue covered by skin. erectile tissue -connective tissue that is organized into a spongelike network of spaces that fill with blood to cause an erection -supplied with blood via penile arteries and drained of blood via penile veins -In the body of the penis, there are 3 cylindrical columns of erectile tissue: 2 corpora cavernosa (singular is corpus cavernosum), which are fused together, and 1 corpus spongiosum. Note that the penile (spongy) urethra passes through the corpus spongiosum. -In the root, the corpus spongiosum enlarges, forming the bulb of the penis; in addition, the corpora cavernosa spread apart, forming the crura of the penis (singular is crus). -In the glans, only the corpus spongiosum is present and it is expanded. -Function The penis is the male organ of sexual intercourse. -During a sexual activity, the penis undergoes an erection and then an ejaculation. erection -a state of hardness that is characteristic of the penis when sexually aroused -a reflex that is coordinated by the spinal cord (Figure 28.10d, Tortora) -This involves parasympathetic nerves that extend from the sacral spinal cord to the smooth muscle of penile arteries. -Mechanism During sexual excitement, the parasympathetic nerves from the sacral spinal cord release nitric oxide (NO).

9 226 The NO causes the smooth muscle in the walls of the penile arteries to relax, resulting in vasodilation. Vasodilation of the penile arteries brings a large amount of blood to the erectile tissue of the penis, which expands as it fills up with this blood. Expansion of the erectile tissue compresses (closes) nearby penile veins, which prevents blood from leaving the erectile tissue. The net result of the vasodilation of penile arteries and the compression of penile veins is that a large volume of blood stays in the erectile tissue, which makes the penis erect. -Note that depression, a bad mood, worrying about a problem, and/or performance anxiety can cause the brain to inhibit the erection reflex, and the penis remains flaccid (nonerect) even when sexual stimuli are present. ejaculation -the expulsion of semen from the penis -occurs when the penis becomes extremely excited by sexual stimuli -a reflex that is coordinated by the spinal cord (Figure 10.1, Derrickson) -This involves the following: sympathetic nerves that extend from the upper lumbar spinal cord to the smooth muscle of the epididymis, vas deferens, and ejaculatory ducts and to the secretory cells of the accessory sex glands somatic nerves that extend from the lower lumbar spinal cord to the bulbospongiosus muscle around the root of the penis

10 227 -Mechanism When sexual excitement of the penis becomes extremely intense, the sympathetic nerves from the upper lumbar spinal cord stimulate the contraction of the smooth muscle of the epididymis, vas deferens, and ejaculatory ducts. This causes stored sperm to be propelled from the epididymis into the urethra. In addition, the sympathetic nerves stimulate the accessory sex glands to release their secretions into the urethra. Semen is formed as these secretions mix with sperm. Then the somatic nerves from the lower lumbar spinal cord stimulate the contraction of the bulbospongiosus muscle. This cause the semen to be propelled from the urethra to the outside environment, and the man experiences an orgasm (a sense of intense pleasure). -On average, the amount of semen ejaculated from the penis is about 3 ml and contains about 300 million sperm (i.e. 300 million sperm / 3 ml or 100 million sperm /ml). -Such a large number of sperm are released because only about 100 of them will make it to the ampulla of the fallopian tubes, which is where fertilization takes place. -The rest of the sperm die along the way in the vagina and uterus. -Therefore, a man is considered to be infertile if his sperm count is below 20 million sperm/ml) because none of the sperm will reach the ovum. -Frequent ejaculations (more than 4 per week) can lead to a low sperm count due to the fact that the testes cannot produce sperm quick enough to keep up with the fast pace by which the sperm are being released from the body. -However, this infertility is usually temporary and reverses once the frequency of ejaculation decreases and the testes have a chance to produce more sperm.

11 228 -Male Reproductive Hormones -The major male reproductive hormones are gonadotropin releasing hormone, follicle stimulating hormone, luteinizing hormone, and testosterone (Figure 10.2, Derrickson). -These hormones are secreted once the male reaches puberty, and they continue to be released for most of the male s adult life. -Note that there is some testosterone released by the testes during fetal development; however, this secretion stops soon after birth, and there isn t any significant amount of testosterone produced during childhood. 1. Gonadotropin Releasing Hormone (GnRH) -Source -GnRH is secreted by the hypothalamus in a pulsatile fashion (i.e. the hypothalamus secretes a small amount of GnRH periodically throughout the day). -Function -GnRH causes the anterior pituitary gland to secrete FSH and LH. 2. Follicle Stimulating Hormone (FSH) -Source -FSH is secreted by the anterior pituitary gland. -Function -FSH stimulates spermatogenesis. -FSH achieves this goal by activating the Sertoli cells. 3. Luteinizing Hormone (LH) -Source -LH is secreted by the anterior pituitary gland. -Function -LH stimulates the Leydig cells to secrete testosterone into the blood. 4. Testosterone -Source -Testosterone is secreted by the Leydig cells of the testes. -Functions Testosterone causes the development of male primary sex characteristics (i.e. growth of male reproductive organs). Testosterone causes the development of male secondary sex characteristics (low pitched voice, increased body hair, and increased skeletal and muscular growth). Testosterone stimulates spermatogenesis. -Sperm cells require both testosterone and FSH in order to progress through the various stages of spermatogenesis. Testosterone causes increased libido (sex drive). Testosterone causes increased aggressiveness.

12 229 -Note that in many target cells, the effects of testosterone are mediated by dihydrotestosterone (DHT). In such cases, target cells contain an enzyme called 5-alpha reductase that converts the testosterone into DHT. -Androgens -Testosterone and DHT are examples of androgens. -An androgen is a hormone that promotes masculine characteristics. -There are 3 major types of androgens: a. testosterone -secreted by the testes in men b. dihydrotestosterone (DHT) -a conversion product of testosterone found in men c. adrenal androgen -The main adrenal androgen is dehydroepiandrosterone (DHEA), which is secreted by the adrenal gland in both men and women. -In men, the effects of adrenal androgen are trivial to those of testosterone and DHT, which are much more potent. -In women, the only androgen present is adrenal androgen and its concentration is small. -Nevertheless, adrenal androgen is responsible for the following features in women: axillary hair pubic hair libido (sex drive) -In addition, some DHEA can be converted into estrogen; therefore, DHEA is a small source of estrogen in postmenopausal women. -Note that once a woman goes through menopause, the secretion of estrogen by the ovaries declines to insignificant amounts. -Regulation - Testosterone secretion is ultimately regulated by the hypothalamus via a negative feedback system. -The hypothalamus secretes GnRH in a pulsatile fashion. -The release of GnRH causes the anterior pituitary to secrete LH. -LH then acts on the testes to promote secretion of testosterone and the blood concentration of testosterone increases.

13 230 -A high blood concentration of testosterone, however, inhibits GnRH secretion from the hypothalamus and LH secretion from the anterior pituitary. -Without the release of LH, the testes are not stimulated to secrete any more testosterone and the blood concentration of testosterone decreases. -Therefore, a person who takes anabolic steroids (testosteronelike drugs) for body building will have a lowered blood concentration of natural testosterone, which results in infertility (testosterone is required for spermatogenesis), atrophy of the testes (the testes shrink due to lack of stimulation from LH and testosterone), and violent mood swings (due to the effects of testosterone on behavior). Female Reproductive System -The female reproductive system consists of the ovaries, fallopian tubes, uterus, vagina, vulva, and mammary glands (Figures 28.11, 28.16, and 28.20, and 28.22, Tortora). 1. ovaries -the female gonads -paired glands that are shaped like almonds -The ovaries are held in place by various ligaments (Figure 28.16, Tortora). -Functions a. The ovaries produce ova (eggs). -Each ovum is actually produced as part of a larger structure called an ovarian follicle. -An ovarian follicle is given different names as it develops in the ovary; these names sequentially include the primordial follicle, primary follicle, secondary follicle, and mature (Graafian) follicle (Figure 10.3, Derrickson). 1. primordial follicle -consists of an ovum that is surrounded by a layer of granulosa cells -Note that the ovum contains a nucleus, which is haploid (i.e. it has 23 total chromosomes: 22 autosomes and 1 X sex chromosome) 2. primary follicle -develops from the primordial follicle -consists of an ovum that is surrounded by several layers of granulosa cells and two layers of theca cells -larger than the primordial follicle due to proliferation of the granulosa cells and the presence of the theca cells -The primary follicle also contains a glycoprotein layer called the zona pellucida that surrounds the ovum.

14 secondary follicle -develops from the primary follicle -consists of the following: a. ovum b. antrum -a fluid-filled cavity that forms within the secondary follicle c. granulosa cells -There are several layers of granulosa cells found within the secondary follicle. -The closest layer of granulosa cells that surrounds the ovum is now called the corona radiata. Additional layers of granulosa cells line the antrum of the secondary follicle. d. theca cells - forms the outer wall of the secondary follicle. 4. mature (Graafian) follicle -develops from the secondary follicle -The mature (Graafian) follicle is structurally similar to the secondary follicle; the only major difference is that the mature (Graafian) follicle is larger due to cell growth. oogenesis -the production of ova in the ovaries -Oogenesis starts before birth, comes to a halt during childhood, resumes at puberty, and continues until menopause. -Before birth, the ovaries produce all of the ovarian follicles that a woman will ever have during her life. -About 2 million ovarian follicles are formed in each ovary of a female fetus. -However, all of these ovarian follicles are primordial follicles, which are immature. -The primordial follicles remain undeveloped for the duration of fetal development and throughout childhood. -The primordial follicles continue to develop once a female reaches puberty and thereafter until menopause. Once a month starting at puberty, one of the primordial follicles develop into a primary follicle.

15 232 The primary follicle then develops into a secondary follicle. The secondary follicle subsequently develops into a mature (Graafian) follicle. The mature (Graafian) follicle then splits open and releases its ovum (with surrounding zona pellucida and corona radiata) from the ovary; this process is called ovulation. The ovum is then swept into the fallopian tube. The remainder of the mature (Graafian) follicle (i.e. the granulosa cells and theca cells that lined the antrum) stays in the ovary and is now called the corpus hemorrhagicum. The corpus hemorrhagicum expands and then turns into the corpus luteum, which is yellow in color. The corpus luteum subsequently degenerates, forming a whitish mass of scar tissue called corpus albicans. The corpus albicans eventually disappears due to cells in the ovary that absorb it. -Even though 2 million ovarian follicles are produced in each ovary, only about 450 total ova are actually ovulated throughout a woman s entire reproductive life (1 ovum released every month from age 13 to about age 50).

16 233 -The rest of the ovarian follicles gradually undergo atresia (degradation). -By the time a woman reaches age 45 to 55, there are no more ovarian follicles left and she enters menopause. b. The ovaries produce estrogen and progesterone. -This function of the ovaries occurs in 2 ways: 1. The ovarian follicle secretes estrogen as it develops in the ovary. -This process involves both the theca cells and the granulosa cells of the secondary follicle and the mature (Graafian) follicle. As a secondary follicle is developing into a mature (Graafian) follicle, the theca cells produce a steroid called androstenedione. The granulosa cells then take up the androstenedione, convert it to estrogen, and then secrete the estrogen into the blood. 2. After ovulation has occurred, the corpus luteum also secretes estrogen and progesterone into the blood. 2. Fallopian tubes -also called uterine tubes or oviducts -A woman has 2 fallopian tubes; each extends laterally from the uterus and comes close to (but does not actually touch) an ovary. -Structure -External Anatomy -A fallopian tube consists of 3 major external regions (Figure 28.16, Tortora): a. infundibulum -the part of the fallopian tube that is closest to the ovary -contains fingerlike projections called fimbriae that sweep the ovulated ovum into the fallopian tube b. ampulla -the part of the fallopian tube that is between the infundibulum and the isthmus -Fertilization normally occurs here. c. isthmus -the narrow part of the fallopian tube that connects with the uterus

17 234 -Internal Anatomy -The fallopian tube consists of 3 internal layers: a. mucosa -inner layer -consists of a layer of epithelial cells that line a lumen and an underlying layer of connective tissue b. muscularis -middle layer -consists of smooth muscle c. serosa -outer layer -consists of epithelial cells and connective tissue -Functions a. Fertilization normally occurs in the fallopian tubes. Recall that sperm are released into the vagina during sexual intercourse. From the vagina, sperm move into the uterus and then into the isthmus of the fallopian tube. From the isthmus, sperm move into the ampulla of the fallopian tube. While in the ampulla, the sperm encounter the ovulated egg. Consequently, the ovum is fertilized by one of the sperm cells. b. The fallopian tubes transport the ovum into the uterus. -Contraction of the muscularis of the fallopian tube moves the ovum (whether fertilized or not) down the fallopian tube and into the uterus.

18 uterus -also called the womb -a pear-shaped organ located between the fallopian tube and the vagina (Figures and 28.19, Tortora) -Structure -External Anatomy -The uterus consists of 3 external regions: a. fundus -the superior part of the uterus b. body -the middle and largest part of the uterus c. cervix -the inferior part of the uterus -Note that the cervix is continuous with the vagina. -Like the ovaries, the uterus is also held in place by ligaments. -Internal Anatomy -The uterus consists of 3 internal layers: a. endometrium -inner layer of the uterus -further subdivided into 2 strata (sublayers): 1. stratum functionalis -the layer of the endometrium that lines the uterine cavity -In an unpregnant woman, the stratum functionalis sheds (i.e. detaches from the rest of the uterus) every month as a part of a process called menstruation. In a pregnant woman, the stratum functionalis remains attached to the rest of the uterus and serves as the location where the fertilized ovum implants and develops into a fetus. 2. stratum basalis -the layer of the endometrium that is below the stratum functionalis -a permanent layer whose cells can proliferate (divide) to form a new stratum functionalis every month after menstruation occurs -Both the stratum functionalis and the stratum basalis consist of epithelial cells, heavily vascularized connective tissue, and endometrial glands. b. myometrium -middle layer of the uterus -consists of smooth muscle -During childbirth, the posterior pituitary gland secretes oxytocin, which causes the myometrium of the uterus to contract.

19 236 -Consequently, the fetus moves from the uterus into the vagina and then out of the body. c. perimetrium -outer layer of the uterus -consists of epithelial cells and connective tissue -Functions a. In an unpregnant woman, menstruation occurs in the uterus. b. In a pregnant woman, the uterus is the location where the fertilized ovum implants and develops into a fetus. c. During childbirth, the uterus contracts in order to push the fetus out of the woman s body. 4. vagina -a tube-shaped organ that extends inferiorly from the uterus -Structure -Externally, the vagina opens up to the exterior of a woman s body at a region called the vaginal orifice (Figure 28.20, Tortora). In a virgin woman, the vaginal orifice is partially covered by vascularized connective tissue called hymen. -After a woman s first sexual intercourse, the hymen is usually torn and is no longer present from that point on. -Internally, the vagina consists of 3 internal layers: a. mucosa -inner layer -consists of a layer of epithelial cells that line a lumen and an underlying layer of connective tissue -The epithelial cells of the mucosa are involved in the formation of vaginal fluid, which is released into the vaginal lumen. This vaginal fluid is acidic and, consequently, reduces the growth of microbes in the vagina. b. muscularis -middle layer -consists of smooth muscle -The relaxation of this smooth muscle allows the vagina to stretch tremendously during sexual intercourse and during childbirth. c. adventitia -outer layer -consists of connective tissue -Functions a. The vagina is the female organ of sexual intercourse. b. The vagina is a passageway for the release of menstrual fluid from the uterus to the outside environment during menstruation. c. The vagina serves as the birth canal, allowing the fetus to move from the uterus to the outside environment during childbirth.

20 vulva -a collective name that refers to the external genitalia of a woman -consists of the following (Figure 28.20, Tortora): a. mons pubis -a region of adipose tissue covered by skin and pubic hair that is located anterior to the pubic bone b. labia majora -large folds of skin that are inferior to the mons pubis -usually covered by pubic hair c. labia minora -small folds of skin that are between the labia majora -lack pubic hair -The labia minora surround the vestibule, which is a space that contains the external urethral orifice and the vaginal orifice. d. clitoris -formed at the superior junction of the labia minora -consists of erectile tissue that fills with blood and becomes erect when a woman is sexually aroused -Hence, the clitoris is similar to, but much smaller than, the penis of a male. -Note that deep to the vulva is the bulbospongiosus muscle (Figure 11.12, Tortora). -During sexual intercourse, the rhythmic contraction of the bulbospongiosus muscle causes a woman to have an orgasm. -Recall that in a male, the bulbospongiosus muscle surrounds the root of the penis. -Nevertheless, the contraction of this muscle in a male also causes an orgasm. 6. mammary glands -Each breast consists of a mammary gland and surrounding adipose tissue (Figure 28.22, Tortora). -The mammary glands are modified sweat glands that produce milk (a process called lactation) in a woman that has just given birth. -Female Reproductive Hormones -The major female reproductive hormones are gonadotropin releasing hormone (GnRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone (Figure 10.4, Derrickson). -These hormones are released once the female reaches puberty. 1. Gonadotropin Releasing Hormone (GnRH) -Source -GnRH is secreted by the hypothalamus in a pulsatile fashion. -Function -GnRH causes the anterior pituitary gland to secrete FSH and LH.

21 Follicle Stimulating Hormone (FSH) -Source -FSH is secreted by the anterior pituitary gland. -Functions a. FSH stimulates the growth and development of the ovarian follicle. b. FSH stimulates the ovarian follicle to produce estrogen. -FSH achieves this goal by causing the granulosa cells of the secondary follicle and mature (Graafian) follicle to take up androstenedione from the theca cells, convert it to estrogen, and then to secrete the estrogen into the blood. 3. Luteinizing Hormone (LH) -Source -LH is secreted by the anterior pituitary gland. -Functions a. LH stimulates the growth and development of the ovarian follicle. b. LH stimulates the ovarian follicle to produce estrogen. -LH achieves this goal by causing the theca cells of the secondary follicle and the mature (Graafian) follicle to secrete androstenedione. As mentioned earlier, FSH then causes the granulosa cells to take up the androstenedione, convert it to estrogen, and then to secrete the estrogen into the blood. c. LH causes ovulation to occur. d. LH causes the corpus luteum to form. -Hence the name luteinizing hormone. e. LH stimulates the corpus luteum to secrete estrogen and progesterone into the blood. 4. Estrogen -Source -Depending on the stage of the female reproductive cycle, estrogen is secreted by the secondary follicle, mature (Graafian) follicle, or corpus luteum of the ovary. -Functions a. Estrogen causes the development of female primary sex characteristics (i.e. growth of female reproductive organs). b. Estrogen causes the development of female secondary sex characteristics (high pitched voice, fat distribution in the breasts and hips, and reduced body hair). c. Estrogen causes the stratum basale of the uterus to proliferate

22 239 in order to form a new stratum functionalis every month after menstruation occurs. -Regulation -Estrogen secretion is ultimately regulated by the hypothalamus via a negative feedback system. -The hypothalamus secretes GnRH in a pulsatile fashion. -The release of GnRH causes the anterior pituitary to secrete FSH and LH. -The FSH and the LH stimulate the development of an ovarian follicle. -While the ovarian follicle develops, estrogen is released and the blood concentration of estrogen increases. -A high blood estrogen concentration, however, inhibits the secretion of GnRH from the hypothalamus and the secretion of FSH and LH from the anterior pituitary. -Without FSH and LH, the ovarian follicle does not develop; therefore, no more estrogen is secreted and the blood concentration of estrogen decreases. 5. Progesterone -Source -Progesterone is secreted by the corpus luteum of the ovary. -Function -Progesterone causes the endometrium of the uterus to become secretory in order to prepare for the possible implantation of a fertilized ovum. -Progesterone achieves this goal by stimulating the endometrial glands to secrete various nutrients (sugars, proteins, and lipids) into the surrounding endometrial tissue and the uterine cavity. Once the fertilized ovum implants, it can feed on these nutrients until the placenta develops. -Regulation -Progesterone secretion is also regulated by a negative feedback system. -As in the case with estrogen, a high blood concentration of progesterone inhibits the secretion of GnRH, FSH, and LH. -Without FSH and LH, an ovarian follicle does not develop and the corpus luteum never forms. -Without the corpus luteum, no more progesterone is secreted, and the blood concentration of progesterone decreases.

23 240 -Female Reproductive Cycle -The female reproductive cycle (menstrual cycle) is a sequence of events that involve fluctuations of reproductive hormones as well as physical changes in the ovaries and uterus that occur on a monthly basis (Figures 28.24, Tortora). -A typical female reproductive cycle has a duration of about 28 days. -consists of 4 phases: 1. menstrual phase (days 1-5) -The stratum functionalis of the endometrium sheds (i.e. detaches from the rest of the uterus) due to a low blood concentration of estrogen and progesterone. -The detached stratum functionalis and the blood that comes along with it is called menses or menstrual fluid. -On average, a woman releases about 50 ml of menses during this phase each month. 2. preovulatory phase (days 6-13) -The hypothalamus increases its secretion of GnRH, which stimulates the anterior pituitary gland to increase its release of FSH and LH. -FSH and LH stimulate the development of a new ovarian follicle. -During this process, the ovarian follicle secretes estrogen into the blood. -Once in circulation, estrogen is transported to its target cells to promote female primary and secondary sexual characteristics. - In addition, estrogen causes the stratum basalis to proliferate in order to form a new stratum functionalis. 3. ovulation (day 14) -The anterior pituitary suddenly releases a huge amount of LH into the blood. -This LH surge causes the mature (Graafian) follicle to undergo ovulation. - The released ovum is then swept into the fallopian tube by the fimbriae. 4. postovulatory phase (days 15-28) -At the beginning of this phase, LH causes the corpus hemorrhagicum to develop into the corpus luteum. - In addition, LH stimulates the corpus luteum to secrete estrogen and progesterone into the blood. -The progesterone causes the endometrium to become secretory in order to prepare for the possible implantation of a fertilized ovum. -If the ovum has not been fertilized, then the corpus luteum degenerates into the corpus albicans, and there is no more production of estrogen and progesterone. -Consequently, the blood concentrations of estrogen and

24 241 progesterone become very low and the stratum functionalis sheds (i.e. the menstrual phase of a new female reproductive cycle occurs). -Menstruation, however, should not occur if a woman is pregnant. -If the ovum has been fertilized and subsequently implants into the stratum functionalis, then chorion surrounding the developing embryo secretes a hormone called human chorionic gonadotropin (HCG) into the blood. -HCG keeps the corpus luteum functional for about 3 months. -Consequently, estrogen and progesterone continue to be produced, which keeps the stratum functionalis attached to the stratum basalis to maintain pregnancy. -The placenta forms by the third month of pregnancy; at that point, the placenta starts to secrete progesterone and estrogen and continues to do so for the remainder of the pregnancy. -Since the corpus luteum is no longer needed, it degrades at this time. Clinical Applications and Disorders -Look up the following clinical applications and disorders in Tortora: 1. cryptorchidism p premature ejaculation p circumcision p ovarian cysts p uterine prolapse p hysterectomy p episiotomy p breast augmentation and reduction p. 1085

25 fibrocystic disease of the breasts p female athlete triad: disordered eating, amenorrhea, and premature osteoporosis p birth control methods and abortion p testicular cancer p prostate disorders p. 1098, erectile dysfunction p premenstrual syndrome p endometriosis p breast cancer p ovarian cancer p cervical cancer p vulvovaginal candidiasis p sexually transmitted diseases p castration p culdoscopy p. 1103

26 dysmenorrhea p endocervical curettage p hermaphroditism p hypospadias p leukorrhea p oophorectomy p pelvic inflammatory disease p salpingectomy p smegma p. 1103

27 Figure 10.1 Ejaculation Reflex 244

28 245 Figure 10.2 Male Reproductive Hormones Gonadotropin Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), and Testosterone Hypothalamus ( ) GnRH Anterior Pituitary ( ) high blood concentration of testosterone FSH LH Testes sperm cells FSH sperm cells (immature) (more mature) Leydig Cells LH Testosterone aggressiveness bone growth libido development of male primary and secondary sexual characteristics spermatogenesis muscular growth Note: (-) implies negative feedback.

29 Figure 10.3 Ovary and Ovarian Follicles 246

30 247 Figure 10.4 Female Reproductive Hormones Gonadotropin Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Estrogen, and Progesterone ( ) Hypothalamus ( ) high blood GnRH high blood concentration concentration of of estrogen progesterone ( ) Anterior Pituitary ( ) FSH LH Ovaries ovarian follicle FSH, LH ovarian follicle LH (immature) (mature) ovulation (ovum release) corpus luteum Estrogen Progesterone development of female primary and secondary sexual characteristics proliferation of endometrium during the menstrual cycle growth of bone Note: (-) implies a negative feedback effect. secretion of endometrial glands