1. Puberty is the time in an adolescent s life when external sex characteristics

Transcription

1 CHAPTER 28 Answers to What Did You Learn? 1. Puberty is the time in an adolescent s life when external sex characteristics become more prominent, the gametes begin to mature, and the gonads secrete their sex hormones. 2. The urogenital triangle in both sexes is bounded by the ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles. The female triangle contains the clitoris and the urethral and vaginal orifices, while the male triangle contains the base of the penis and the scrotum. 3. The types of ovarian follicles are primordial, primary, secondary, and mature. A primordial follicle consists of a primary oocyte and a single layer of squamous follicle cells. A primary follicle forms from a maturing primordial follicle. Each primary follicle consists of a primary oocyte surrounded by one or more layers of cuboidal follicle cells, which are now called granulosa cells. A secondary follicle forms from a primary follicle. Each secondary follicle contains a primary oocyte, many layers of granulosa cells, and a fluid-filled space called an antrum. A mature follicle matures from a secondary follicle. It contains a secondary oocyte, many follicle cells, and a very large antrum. 4. Ovulation refers to the release of the secondary oocyte from a vesicular follicle and occurs on day 14 of a 28-day ovarian cycle. 28-1

2 5. Menarche is the first menstrual cycle. It is the culmination of the period of sexual development during puberty. Typically, the onset of menarche occurs at about age years. 6. The uterine tube is lined with a ciliated columnar epithelium that helps propel the oocyte toward the uterus. 7. Round ligaments of the uterus extend from the lateral sides of the uterus, through the inguinal canal, and attach to the labia major. These ligaments help keep the uterus in an anteverted position. Transverse cervical ligaments (also called cardinal ligments) run from the sides of the cervix and superior vagina laterally to the pelvic wall; they help restrict inferior movements of the uterus. The uterosacral ligaments (also called sacrocervical ligaments) connect the inferior portion of the uterus posteriorly to the sacrum. 8. The innermost uterine tunic of the uterus is a lining called the endometrium. It contains a deep basal layer and a superficial functional layer. The basal layer is adjacent to the myometrium, the thick muscular middle tunic, or the uterine wall. The superficial functional layer grows and develops in response to progesterone, and will be shed as menses. 9. The mammary glands contain lobes that are subdivided into lobules. Lobules contain secretory units termed alveoli that produce milk in the lactating female. The tiny ducts of the lobules merge and form about 10 to 20 larger channels called lactiferous ducts. A lactiferous duct drains breast milk from a single lobe. As each lactiferous duct approaches the nipple, its lumen expands to form a lactiferous sinus. Prior to release from the nipple, milk is stored in these spaces. 28-2

3 10. The scrotum is the external skin-covered sac that houses the testes. The scrotum is homologous to the labia majora in the female. 11. The interstitial cells reside in the interstitial spaces between the seminiferous tubules in the testes. The interstitial cells produce androgens under the influence of luteinizing hormone. There are several types of androgens, the most common is testosterone. 12. Spermatogenesis is the process of sperm development. This process occurs within the seminiferous tubule of the testis. Spermatogenesis does not occur until puberty, when significant levels of FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are secreted and stimulate the testis to begin its gamete development. Spermatogenesis begins when a spermatogonium divides by mitosis to produce a new spermatogonium and a primary spermatocyte. The primary spermatocyte undergoes the first meiotic division to become a secondary spermatocyte, and the secondary spermatocyte undergoes the second meiotic division to become a spermatid. The final stage of spermatogenesis is a process called spermiogenesis, where the spermatid differentiates into a sperm. 13. The ejaculatory duct is formed from the union of the ampulla of the ductus deferens and the proximal region of the seminal vesicle. 14. Semen is the combination of sperm produced in the testes and seminal fluid secreted by male accessory glands. The accessory glands are the seminal vesicles, prostate gland, and bulbourethral glands; all produce a component of the seminal fluid. 28-3

4 15. Both parasympathetic and sympathetic innervation work together to cause an erection and ejaculation. The parasympathetic innervation is necessary to achieve an erection; the sympathetic innervation promotes ejaculation. 16. Gamete maturation stops in females by their 40s or 50s, and menopause occurs. A reduction in hormone production results in some atrophy of reproductive organs and the breasts. The vaginal wall thickness decreases and there is a reduction in glandular secretions for maintaining a lubricated and moist lining. The uterus shrinks and atrophies at menopause, becoming smaller than it was before puberty. 17. The genetic sex refers to the sex of an individual based upon their type of sex chromosomes. An individual with two X chromosomes is a genetic female, while an individual with one X and one Y chromosome is a genetic male. In contrast, the phenotypic sex of an individual refers to the appearance of the internal and external genitalia. An individual with testes and/or male external genitalia is a phenotypic male, whereas an individual with ovaries and/or female external genitalia is a phenotypic female. Answers to Content Review 1. Both male and female reproductive systems have organs called gonads that produce reproductive cells called gametes. Gametes unite to form a new individual. Additionally, the gonads produce large amounts of sex hormones (estrogen and progesterone in the female, and androgens in the male) that affect and control maturation, development, and changes in the activity of reproductive system organs. 28-4

5 Both reproductive systems have a duct system to convey gametes away from the gonads toward the site of fertilization (in females) or simply to the outside of the body (in males). Both reproductive systems are primarily nonfunctional and dormant until a time period known as puberty. Homologues are (female to male): clitoris to penis, labia majora to scrotum, and vestibular glands to bulbourethral glands. 2. GnRH (gonadotropin releasing hormone) is released by the hypothalamus to stimulate FSH (follicle-stimulating hormone) and LH (luteinizing hormone) release from the anterior pituitary. At the beginning of the follicular phase, FSH and LH stimulate the maturation of some primordial follicles into primary, secondary, and mature follicles. Ovulation is induced when there is a peak in luteinizing hormone (LH) levels. The corpus luteum secretes estrogen and progesterone that function to stabilize and build up the uterine lining, and prepare the uterus for possible implantation of a fertilized oocyte. When a woman is pregnant, the levels of estrogen, progesterone, and prolactin rise dramatically. While prolactin is responsible for breast milk production, it is the hormone oxytocin that is responsible for milk ejection. 3. The uterine tubes consist of the infundibulum, ampulla, isthmus, and uterine part. The infundibulum is the free, funnel-shaped lateral portion that contains fimbriae to capture the ovulated oocyte. The ampulla is the expanded region medial to the infundibulum; fertilization of the oocyte usually occurs here. The isthmus extends medially from the infundibulum, and forms about one-third of the length of the uterine tube, while the uterine part extends medially from the isthmus and 28-5

6 is continuous with the uterine wall. 4. The uterine wall is composed of three concentric tunics (layers): the perimetrium, myometrium, and endometrium. The outer tunic of most of the uterus is a serous membrane called the perimetrium. It becomes continuous with the broad ligament. The myometrium is the thick, middle muscular tunic of the uterine wall. It is formed from three intertwining layers of smooth muscle. The innermost tunic of the uterus is a lining called the endometrium. It is an intricate mucosa that is composed of a simple columnar epithelium and an underlying lamina propria. The lamina propria is filled with compound tubular glands that enlarge during the menstrual cycle. 5. The ovarian cycle typically lasts 28 days and contains the follicular phase, ovulation, and the luteal phase. The follicular phase occurs from days 1 13 of an approximate 28-day ovarian cycle. FSH and LH stimulate some primordial follicles to mature into primary follicles. One primary follicle matures into a secondary follicle that matures into a mature follicle. Division of the primary oocyte produces a secondary oocyte. Ovulation occurs on day 14 of a 28-day ovarian cycle; it is the release of the secondary oocyte from a mature follicle. The luteal phase is from day and occurs when the remaining follicle cells in the ruptured mature follicle turn into a corpus luteum. The corpus luteum secretes large amounts of progesterone and some estrogen to stabilize and build up the uterine lining, and prepare the uterus for possible implantation of a fertilized oocyte. The uterine cycle also typically lasts 28 days, but it contains a menstrual phase, proliferative phase, and secretory phase. The menstrual phase occurs 28-6

7 during days 1 5 (approximately) of the cycle when the functional layer is sloughed off. The proliferative phase occurs from (approximately) days The initial growth and development of the functional layer of the endometrium overlaps the time of follicle growth and estrogen secretion. The last phase is the secretory phase from (approximately) days During the secretory phase, there is an increase in vascularization and development of uterine glands as a result of an increase in progesterone secretion from the corpus luteum. 6. Externally, the mammary gland has a nipple, which is a cylindrical projection on the center of the breast. It contains multiple tiny openings of the excretory ducts. The areola is the pigmented rosy or brownish ring of skin around the nipple. Its surface often appears uneven and grainy as a result of the numerous sebaceous glands immediately internal to the surface. Internally, the mammary glands are subdivided into lobes. Lobes are subdivided into smaller compartments called lobules that contain secretory units termed alveoli. Alveoli produce milk in the lactating female. Alveoli become more numerous and larger during pregnancy. 7. Sustentacular cells (also called nurse or Sertoli cells) are located throughout the seminiferous tubule. The sustentacular cells are so named because they provide a protective environment for the developing sperm cells, and their cytoplasm helps nourish these developing sperm. The sustentacular cells are secured together by tight junctions, which form a blood-testis barrier and help protect developing sperm cells from the male immune system. 8. Spermatogenesis is the process of sperm development with the seminiferous tubules. It begins when spermatogonia divide by mitosis; one cell produced is a 28-7

8 new spermatogonium, the other cell is a diploid primary spermatocyte. A primary spermatocyte undergoes meiosis I; the two haploid cells that are produced are called secondary spermatocytes. Secondary spermatocytes complete meiosis (go through meiosis II) to form haploid spermatids. Spermatids undergo the last stage of spermatogenesis, called spermiogenesis, to become mature spermatozoa, or sperm. 9. Seminal vesicles produce a viscous, whitish-yellow fluid, containing both fructose and prostaglandins. The fructose is a sugar that nourishes the sperm as they travel through the female reproductive tract, while the prostaglandins promote the widening and slight dilation of the external os of the cervix. The prostatic secretion is a slightly acidic, milky fluid that is rich in citric acid, seminalplasmin, and prostate-specific antigen [PSA]. The citric acid is a nutrient for sperm health, the seminalplasmin is an antibiotic that combats urinary tract infections, and the PSA helps liquefy semen following ejaculation. The secretory product of the bulbourethral glands is a clear, viscous mucin that forms mucus when mixed with water. This mucin is the final component of the seminal fluid. It acts to protect the urethra and serve as a lubricant for the insertion of the penis into the vagina during sexual intercourse. 10. The erectile bodies in the penis are composed of a complex network of venous spaces surrounded by a central artery. During sexual excitement, blood enters the erectile bodies via the central artery and fills in the venous spaces. As these venous spaces become engorged with blood, the erectile bodies becomes rigid, a process called erection. As the erectile bodies become rigid, they compress the 28-8

9 veins that drain blood away from the venous spaces. Thus, the spaces fill with blood, but blood will not leave the erectile bodies until the sexual excitement ceases. Parasympathetic innervation is responsible for erection of the penis. 28-9