Chapter 26 The Reproductive System Answers Part 2

98) Explain what makes homologous chromosomes similar to one another and how they may differ. Answer: Homologous chromosomes are pairs of chromosomes with the same genes. However, the matching genes on the homologous chromosomes may have different variants, or alleles. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.1.3 99) Summarize the important points of meiosis I and II. Answer: Important points about meiosis I: Pairs of homologous chromosomes, each consisting of two sister chromatids, separate to produce haploid (1n) cells with 23 chromosomes. Crossing over and independent assortment randomly "shuffle" the alleles and align the maternal and paternal chromosomes, which contributes to the genetic diversity of the offspring. Important points about meiosis II: The process separates the homologous chromosomes into individual chromatids. Potentially there are four haploid cells at the end of telophase II. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.1.3 100) Briefly explain how mitosis and meiosis differ. Answer: Mitosis occurs because new cells are needed for tissue growth or repair, and these new cells need to be genetically identical to the original cell. So, the process of mitosis occurs by first making a complete copy of the DNA and then dividing each cell into two so that each resulting cell gets one copy of the DNA. In contrast, meiosis produces sperm and ova for reproduction. These cells need to have half the chromosome number of the original cell so that when they combine to form a new cell, the chromosome number will not be doubled. Also, meiosis mixes up the possible combinations of genes that each sperm or egg cell will receive, to produce a genetically unique individual. Meiosis I includes the unique set of steps that reduce the chromosome number and shuffle the alleles. Meiosis II then completes the process to potentially form four daughter cells. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.1.2 101) Trace the pathway of sperm from the seminiferous tubules to the external urethral orifice of the penis. Answer: Sperm are made in the seminiferous tubules of each testis. Seminiferous tubules are surrounded by myoid cells, which contract to push sperm and testicular fluids through the tubules and out of the testes. The seminiferous tubules of each lobule merge into a single straight tubule that moves sperm into the rete testis, a network of tubules on the posterior side of the testis. Sperm then pass through efferent ductules and enter the first portion of the duct system, the epididymis. After leaving the epididymis, the sperm continue traveling through a system of ducts: ductus deferens, ejaculatory duct, urethra (prostatic, membranous and spongy regions) and exit the body through the external urethral orifice. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.2.2 21 102) Let's imagine a new form of birth control for males has been developed. This drug works by inhibiting capacitation of the sperm after ejaculation has occurred. Determine why capacitation is a critical step through which sperm must pass for fertilization to be successful and why this drug may work. Answer: A drug that prevents capacitation will render sperm incapable of fertilizing an immature female gamete. Under normal conditions, the alkaline pH of semen helps make the sperm fully motile, and the sperm begin the process of capacitation. By this process, sperm undergo changes that enable them to penetrate and fertilize an immature female gamete. Sperm should finish capacitation in the female reproductive tract, where secretions will prepare the sperm cell's plasma membrane to fuse with that of the female gamete. Without these changes, sperm will be unable to penetrate a female gamete. Bloom's Taxonomy: 3) Application Learning Outcome: 26.2.4 103) Summarize the processes of spermatogenesis and spermiogenesis. Answer: Spermatogenesis is the process of sperm cell development. It includes all phases of meiosis and spermiogenesis, the cytoplasmic changes required to form a mature sperm cell. Spermatogenesis occurs in the seminiferous tubules of the testes by spermatogenic cells. Spermatogonia divide to produce primary spermatocytes, which undergo the first meiotic division to form two secondary spermatocytes. Each secondary spermatocyte undergoes the second meiotic division to produce four total spermatids. Spermiogenesis is the maturation of spermatids into motile sperm cells. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.3.1 104) Explain how the hypothalamic-pituitary-gonadal (HPG) axis is involved in testosterone production in males. Answer: In the first-tier of control, the hypothalamus releases gonadotropin-releasing hormone (GnRH). In the second-tier of control, GnRH stimulates the anterior pituitary to secrete folliclestimulating hormone (FSH) and luteinizing hormone (LH). In the third-tier of control, LH and FSH target the testes. LH stimulates the interstitial cells of the testes to secrete testosterone while FSH stimulates the sustentacular cells to secrete androgen-binding protein (ABP) (to help keep testosterone levels in the testis high) and the hormone inhibin. The effect of testosterone is to stimulate spermatogenesis and the development of male characteristics. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.3.2 22 105) Explain the roles of the parasympathetic and sympathetic nervous systems in the basic phases of the male sexual response, erection and ejaculation. Answer: Although erection is under parasympathetic control, ejaculation is under sympathetic control. During sexual arousal, a parasympathetic reflex triggers the release of nitric oxide (NO) from blood vessel endothelial cells. This relaxes smooth muscle in the walls of the arterioles of the penis, dilating them, and within the blood sinuses in erectile tissue, which allows large amounts of blood to enter the tissue. The combination of increased blood flow and widening blood sinuses results in an erection. Ejaculation, the process by which semen is expelled from the penis, actually occurs in two stages, emission and expulsion. Emission is the movement of sperm and testicular fluid, as well as secretions from the prostate gland and seminal vesicle, into the urethra. Rhythmic contractions of skeletal muscles at the base of the erectile columns of the penis result in the expulsion of semen from the urethra. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.3.4 106) List the two main functions of the ovaries. Answer: The ovaries have two main functions: 1) produce ova, and 2) secrete several hormones such as estrogens, progesterone, inhibin, and relaxin. Bloom's Taxonomy: 1) Knowledge Learning Outcome: 26.4.1 107) List and describe the three ligaments that support the ovary, and the structures to which they are attached. Answer: Each ovary is held in place by three ligaments: First is the broad ligament that attaches to the ovaries, uterine tubes, and uterus and connects them to the bony pelvis. Next is the ovarian ligament, which connects the medial surface of the ovary to the uterus, near the attachment of the uterine tube. Finally, the suspensory ligament (or infundibulopelvic ligament) connects the lateral surface of the ovary to the pelvic wall. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.4.1 108) Describe the histology of the three layers of the uterus. Answer: The perimetrium is the outermost serous layer of the uterus and is an extension of the parietal peritoneum. The myometrium is the thick middle layer, composed of bundles of smooth muscle. The innermost endometrium lines the uterine cavity and is a mucous membrane composed of simple columnar epithelium on a layer of connective tissue called the lamina propria. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.4.2 109) Upon its release from the ovary, trace the pathway of an oocyte from the ovary to the uterus. Answer: From the ovary, the oocyte travels into the uterine tube due to the sweeping action of the fimbriae. The oocyte moves through the infundibulum, ampulla, and the isthmus of the uterine tube, and then enters the uterus. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.4.3 23 110) Summarize the three phases of the female's ovarian cycle. Answer: In the follicular phase, several primary follicles (with primary oocytes) begin to mature into secondary follicles. Usually only one secondary follicle with a primary oocyte will develop into a vesicular (tertiary) follicle, and the primary oocyte inside will become a secondary oocyte after the LH surge. Ovulation releases the secondary oocyte into the peritoneal cavity. In the luteal phase, the ruptured follicle forms the corpus luteum, which secretes progesterone and estrogens for the rest of the cycle. If fertilization does not occur, the corpus luteum degenerates into the corpus albicans. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.5.2 111) Explain the changes in progesterone production that occur when fertilization does occur and when fertilization does not occur. Answer: If fertilization occurs, progesterone from the corpus luteum inhibits the release of gonadotropins and will continue to do this. If fertilization does not occur, the corpus luteum degenerates into the corpus albicans and estrogen, progesterone, and inhibin levels drop. With ovarian hormones no longer inhibiting secretion of GnRH, its levels rise and the cycle begins again. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.5.3 112) Summarize the female secondary sex characteristics. Answer: Female secondary sex characteristics include changes in bone structure, such as a widening pelvis; an increase in adipose tissue in general and particularly in the breasts and around the hips and thighs; hair in the pubic and axillary areas; and development of female libido. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.5.5 113) Outline the main events of the phases of the uterine (menstrual) cycle. Answer: The uterine cycle, the series of cyclic changes in the endometrium that occur each month in response to fluctuating ovarian hormones, includes the following phases, regulated by the HPG axis. In the menstrual phase, the uterus sheds the stratum functionalis of the endometrium through the vagina. This phase results from rising follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels and normal/low levels of estrogens and progesterone. In the proliferative phase, a new stratum functionalis grows and thickens as estrogen levels rise. Ovulation occurs in the ovary at the end of this phase. In the secretory phase, the endometrium prepares for implantation of an embryo by continuing to grow, increasing vasculature, and secreting nutrients into the uterine cavity. This phase occurs as rising progesterone levels from the corpus luteum stimulate continued growth of the endometrium and inhibit LH release. If pregnancy does not occur, the menstrual phase will follow. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.5.2 24 114) List the five methods of birth control and provide at least one example of each method. Answer: The five methods of birth control include (1) behavioral modification such as abstinence; (2) barrier methods, such as condoms; (3) hormonal methods, such as oral contraceptives; (4) intrauterine methods such as intrauterine devices (IUDs); and (5) permanent methods, such as vasectomy, tubal ligation, and tubal implants. Bloom's Taxonomy: 1) Knowledge Learning Outcome: 26.6.2 115) What are sexually transmitted infections (STIs) and what impact can they have on the reproductive systems of those who have one? Answer: A sexually transmitted infection (STI) is an infectious disease spread through sexual contact. STIs are the most important cause of reproductive disorders and often cause infertility in adults. Bloom's Taxonomy: 1) Knowledge Learning Outcome: 26.7.2 116) Jane has genital warts caused by human papillomavirus (HPV). Determine the form of contraception that will help her prevent the spread of this sexually transmitted infection (STI) to her sexual partner. Answer: Barrier methods of birth control prevent sperm from moving beyond the vagina. These methods include condoms, diaphragms, cervical caps, and the sponge. Jane should select a condom for its ability to reduce STIs. Most condoms are made of synthetic materials or latex, although some are made from animal membranes (lamb intestine). Male condoms, worn on the penis, are the most common type of condom in use. Female condoms are inserted into the vagina and include a flexible ring that covers the cervix and an outer ring that covers the external genitalia. In addition to reducing the risk of pregnancy, synthetic and latex condoms lower the risk of sexually transmitted infections, such as genital warts. Bloom's Taxonomy: 3) Application Learning Outcome: 26.6.2, 26.7.1 117) During a vasectomy, the ductus deferens is cut and then either ligated (tied off) or cauterized (burned) at the ends. Determine the effect of a vasectomy on the passage of sperm from the male's body and the impact on testosterone production. Answer: A vasectomy prevents sperm from leaving the man's body with the semen during ejaculation. Sperm are still produced, but they degenerate and are destroyed by phagocytosis. Semen is also still produced because the vas deferens is cut below the area where the accessory structures secrete the other components of semen. Testosterone production is unhampered because the blood vessels are unaffected. Thus, blood testosterone levels remain normal. For these reasons, a vasectomy has no effect on sexual desire or performance. Bloom's Taxonomy: 3) Application Learning Outcome: 26.2.2, 26.6.2 25 118) Chris wears a testosterone patch to increase his testosterone levels. Determine the effects on gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). Answer: Testosterone inhibits gonadotropin-releasing hormone (GnRH) levels through a negative feedback loop. Since GnRH is inhibited by testosterone, secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) will also be inhibited. Bloom's Taxonomy: 3) Application Learning Outcome: 26.3.2 119) Summarize the secondary male sex characteristics that develop primarily at puberty. Answer: The male secondary sex characteristics include the growth of pubic, axillary, and facial hair; enhanced hair growth on the chest or other body areas in some men; an enlarged larynx and thicker vocal cords, resulting in a noticeable "Adam's apple" and deepening voice; and thickened skin and increased secretions of sebaceous glands (the oilier skin often results in acne). Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.3.5 120) After a chlamydia infection, Mrs. Jones developed scar tissue in her uterine tubes. Determine why she is at a higher risk for an ectopic (tubal) pregnancy in her uterine tubes. Answer: During the process of ovulation, when an oocyte is expelled from the ovary, the fimbriae sweep the ovarian surface and "catch" the oocyte. The oocyte is then carried into the uterine tube. A combination of muscular peristalsis and the beating of the cilia moves the oocyte toward the uterus. Fertilization, which begins when a sperm cell binds to and penetrates the plasma membrane of an oocyte, occurs in the uterine tubes, usually in the ampulla. Implantation should occur in the uterus, but in Mrs. Jones' situation, the fertilized ovum will have more difficulty making its way from the uterine tube to the uterus due to the scar tissue and inflammation of the uterine tubes. Thus, the fertilized ovum has a higher chance of implanting in the uterine tube causing an ectopic (tubal) pregnancy. Bloom's Taxonomy: 3) Application Learning Outcome: 26.4.1, 26.4.3, 26.7.2 121) Some forms of hormonal birth control, such as the Depo-Provera shot, contain progesterone only. Explain how these types of birth control prevent pregnancy. Answer: Normally, progesterone is necessary to maintain pregnancy, and is secreted by the corpus luteum until the third month of pregnancy. However, if pregnancy prevention is desired, the elevated levels of progesterone that come from the hormonal birth control will prevent ovulation. Progesterone inhibits the release of gonadotropins and will continue to do this as long as progesterone injections are provided at proper intervals. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.5.3, 26.6.2 26 122) Forty year old Amy had a tubal ligation to permanently prevent pregnancies. She is concerned the tubal ligation will affect her libido (sex drive). Explain what effect, if any, the tubal ligation will have on her libido. Answer: During tubal ligation, a surgeon makes an insertion into the wall of the body cavity, cuts through the uterine tubes, and either ligates or cauterizes their ends. This prevents the oocyte from passing through the uterine tubes and the sperm from reaching the oocyte. This procedure will not affect her libido (sex drive) as estrogens and progesterone will still be able to travel from the ovaries into the blood stream. The blood supply to the reproductive organs is not interrupted through a tubal ligation. Bloom's Taxonomy: 2) Comprehension Learning Outcome: 26.6.2 27