A&P ch.22 reproductive system PDF

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Chapter Summary 22.1 Meiosis and Sex Cell Production 1. Sex cells are produced by meiosis consisting of two divisions, each progressing through prophase, metaphase, anaphase, and telophase. a. In the first meiotic division, homologous, replicated chromosomes (each consisting of two chromatids held together by a centromere) separate, and their number is halved. b. In the second meiotic division, the chromatids part, producing four haploid cells. c. Meiosis leads to genetic variability because of the random alignment of maternally and paternally derived chromosomes in metaphase I and crossing over. 22.2 Organs of the Male Reproductive System The primary male sex organs are the two testes, which produce sperm cells and male sex hormones. Accessory sex organs are internal and external. 1) Testes a) Descent of the testes i) Testes originate posterior to the parietal peritoneum near the level of the developing kidneys. ii) The gubernaculum guides the descent of the testes into the lower abdominal cavity and through the inguinal canal. iii) Undescended testes cannot produce sperm cells because of the high abdominal temperature. b) Structure of the testes i) The testes are separated by connective tissue and filled with seminiferous tubules. ii) The seminiferous tubules unite to form the rete testis that joins the epididymis. iii) The seminiferous tubules contain spermatogenic cells that give rise to sperm cells. iv) The interstitial cells that produce male sex hormones are between the seminiferous tubules. c) Formation of sperm cells i) The epithelium lining the seminiferous tubules includes sustentacular cells and spermatogenic cells. (1) The sustentacular cells support and nourish the spermatogenic cells. (2) The spermatogenic cells give rise to spermatogonia. ii) Spermatogenesis produces sperm cells from spermatogonia that have differentiated to become primary spermatocytes. (1) Spermatogenesis produces four sperm cells from each primary spermatocyte.

(2) Meiosis halves the number of chromosomes in sperm cells (46 to 23). iii) Membranous processes of adjacent sustentacular cells form a barrier in the epithelium. (1) The barrier separates early and late stages of spermatogenesis. (2) It helps provide a favorable environment for differentiating cells. d) Structure of a sperm cell i) The sperm head contains a nucleus with 23 chromosomes. ii) The sperm body has many mitochondria. iii) The sperm tail propels the cell. 2) Male internal accessory reproductive organs a) Epididymides i) Each epididymis is a tightly coiled tube on the outside of the testis that leads into the ductus deferens. ii) They store and nourish immature sperm cells and promote their maturation. b) Ductus deferentia i) Each ductus deferens is a muscular tube that forms part of the spermatic cord. ii) They pass through the inguinal canal, enter the abdominal cavity, course medially into the pelvic cavity, and end behind the urinary bladder. iii) They fuse with the ducts from the seminal vesicles to form the ejaculatory ducts. c) Seminal vesicles i) Each seminal vesicle is a saclike structure attached to the ductus deferens. ii) They secrete an alkaline fluid that contains nutrients, such as fructose, and prostaglandins. iii) This secretion is added to sperm cells entering the ejaculatory ducts. d) Prostate gland i) The prostate gland surrounds the urethra just inferior to the urinary bladder. ii) It secretes a thin, milky fluid containing citrate and prostate-specific antigen. e) Bulbourethral glands i) These glands are two small structures inferior to the prostate gland. ii) They secrete a fluid that lubricates the penis in preparation for sexual intercourse. f) Semen i) Semen consists of sperm cells and secretions of the seminal vesicles, prostate gland, and bulbourethral glands. ii) This fluid is slightly alkaline and contains nutrients and prostaglandins. iii) Sperm cells in semen swim, but cannot fertilize oocytes until they enter the female reproductive tract.

3) Male external accessory reproductive organs a) Scrotum i) The scrotum is a pouch of skin and subcutaneous tissue that encloses the testes. ii) Contraction of the dartos muscle in the scrotal wall causes the scrotal skin to wrinkle and the testes to move closer to the pelvic cavity or with relaxation of the dartos muscle the scrotum hangs loosely, regulating the environmental temperature of the testes, important for sperm production and survival. b) Penis i) The penis conveys urine and semen. ii) It becomes erect for insertion into the vagina during sexual intercourse. iii) Its body is composed of three columns of erectile tissue surrounded by connective tissue. iv) The root of the penis is attached to the pelvic arch and membranes of the perineum. c) Erection, orgasm, and ejaculation i) During erection, vascular spaces in the erectile tissue become engorged with blood as arteries dilate and veins are compressed. ii) Orgasm is the culmination of sexual stimulation and is accompanied by emission and ejaculation. iii) Semen moves along the reproductive tract as smooth muscle in the walls of the tubular structures contracts by reflex. iv) Following ejaculation, the penis becomes flaccid. 22.3 Hormonal Control of Male Reproductive Functions 1) Hypothalamic and pituitary hormones 2) The male body remains reproductively immature until the hypothalamus releases GnRH, which stimulates the anterior pituitary gland to release gonadotropins. a) FSH stimulates spermatogenesis. b) LH (ICSH) stimulates the interstitial cells to produce male sex hormones. c) Inhibin prevents oversecretion of FSH. 3) Male sex hormones a) Male sex hormones are called androgens. b) Testosterone is the most important androgen. c) Testosterone is converted into dihydrotestosterone in some organs. d) Androgens that fail to become fixed in tissues are metabolized in the liver and excreted. e) Androgen production increases rapidly at puberty. 4) Actions of testosterone a) Testosterone stimulates the development of the male reproductive organs and causes the testes to descend.

b) It is responsible for the development and maintenance of male secondary sex characteristics. 5) Regulation of male sex hormones a) A negative feedback mechanism regulates testosterone concentration. i) As the concentration of testosterone rises, the hypothalamus is inhibited, and the anterior pituitary gland secretion of gonadotropins is reduced. ii) As the concentration of testosterone falls, the hypothalamus signals the anterior pituitary gland to secrete gonadotropins. b) The concentration of testosterone remains relatively stable from day to day. 22.4 Organs of the Female Reproductive System The primary female sex organs are the two ovaries, which produce female sex cells and sex hormones. Accessory sex organs are internal and external. 1) Ovaries a) Ovary attachments i) Several ligaments hold the ovaries in position. ii) These ligaments include the broad, suspensory, and ovarian ligaments. b) Ovary descent i) The ovaries descend from posterior to the parietal peritoneum near the developing kidneys. ii) They attach to the pelvic wall just inferior to the pelvic brim. c) Ovary structure i) The ovaries are subdivided into a medulla and a cortex. ii) The medulla is composed of connective tissue, blood vessels, lymphatic vessels, and nerves. iii) The cortex contains ovarian follicles and is covered by cuboidal epithelium. d) Primordial follicles i) During prenatal development, oogonia divide by mitosis to produce more oogonia that develop into primary oocytes. ii) Each primordial follicle contains a primary oocyte and a layer of flattened epithelial cells. iii) The primary oocyte begins to undergo meiosis, but the process soon halts and does not resume until puberty. iv) The number of oocytes steadily declines throughout the life of a female. e) Oogenesis i) Beginning at puberty, some primary oocytes are stimulated to continue meiosis. ii) When a primary oocyte undergoes oogenesis, it gives rise to a secondary oocyte in which the original chromosome number is halved (from 46 to 23). iii) If fertilization occurs, the secondary oocyte undergoes a second meiotic division which produces an ovum.

iv) The chromosomes of the sperm cell combine with the chromosomes of the

ovum, producing a zygote. f) Follicle maturation i) At puberty, FSH initiates follicle maturation. ii) During maturation of the follicle, the primary oocyte enlarges, the follicular cells proliferate, and a fluid-filled cavity (atrum) appears. iii) Ovarian cells surrounding the follicle form two layers. iv) A mature antral follicle contains a secondary oocyte surrounded by a zona pellucida and corona radiata. v) Usually only one dominant follicle fully develops in preparation for ovulation per menstrual cycle. g) Ovulation i) Ovulation is the release of a secondary oocyte and first polar body from an ovary. ii) A rupturing follicle releases the secondary oocyte. iii) After ovulation, the secondary oocyte is drawn into the opening of the uterine tube. 2) Female internal accessory reproductive organs a) Uterine tubes i) These tubes convey oocytes toward the uterus. ii) The end of each uterine tube is expanded, and its margin bears irregular extensions. iii) Ciliated cells that line the tube and peristaltic contractions in the wall of the tube move an oocyte into the tubes opening. iv) Fertilization of the oocyte occurs here. b) Uterus i) The uterus receives the embryo and sustains it during development. ii) The uterine wall includes the endometrium, myometrium, and perimetrium. c) Vagina i) The vagina connects the uterus to the vestibule. ii) It receives the erect penis, conveys uterine secretions to the outside, and provides a passageway for the fetus during birth. iii) A thin membrane, the hymen, partially closes the vaginal orifice. iv) The vaginal wall consists of a mucosal layer, muscular layer, and outer fibrous layer. 3) Female external accessory reproductive organs a) Labia majora i) The labia majora are rounded folds of adipose tissue and skin that enclose and protect the other external reproductive parts. ii) The anterior ends form a rounded elevation over the pubic symphysis, called the mons pubis. b) Labia minora

i) The labia minora are flattened, longitudinal folds between the labia majora. ii) They are well supplied with blood vessels. c) Clitoris i) The clitoris is a small projection at the anterior end of the vulva; it is homologous to the male penis. ii) It is composed of two columns of erectile tissue. iii) Its root is attached to the sides of the pubic arch. d) Vestibule i) The vestibule is the space between the labia minora that encloses the vaginal and urethral openings. ii) The vestibular glands secrete mucus into the vestibule during sexual stimulation. e) Erection, lubrication, and orgasm i) During periods of sexual stimulation, the erectile tissues of the clitoris and vestibular bulbs become engorged with blood and swollen. ii) The vestibular glands secrete mucus into the vestibule and vagina. iii) During orgasm, the muscles of the perineum, uterine wall, and uterine tubes contract rhythmically. 22.5 Hormonal Control of Female Reproductive Functions Hormones from the hypothalamus, anterior pituitary gland, and ovaries play important roles in the control of sex cell maturation, the development and maintenance of female secondary sex characteristics, and changes that occur during each menstrual cycle. 1) Female sex hormones a) A female body remains reproductively immature until about ten years of age, when gonadotropin secretion increases. b) The most important female sex hormones are estrogens and progesterone. i) Estrogens are responsible for the development and maintenance of most female secondary sex characteristics. ii) Progesterone prepares the uterus for pregnancy. 2) Menstrual cycle a) The menstrual cycle is characterized by regularly recurring changes in the uterine lining culminating in menstrual flow. b) Menarche is the females first menstrual cycle. c) FSH stimulates maturation of ovarian follicles. d) Granulosa cells of maturing follicles secrete estrogens, responsible for maintaining the secondary sex traits and thickening the uterine lining. e) In response to the secretion of a relatively large amount of LH (an “LH surge”), just prior to ovulation, the primary oocyte completes meiosis I to give rise to a secondary oocyte and first polar body. f) Ovulation occurs when LH along with FSH induce complex interactions which weaken and rupture the antral follicle, releasing the secondary oocyte.

g) After ovulation, follicle remnants form the corpus luteum.

i) The corpus luteum secretes estrogens and progesterone, which cause the uterine lining to become more vascular and glandular. ii) If a secondary oocyte is not fertilized, the corpus luteum begins to degenerate. iii) As the concentrations of estrogens and progesterone decline, the uterine lining disintegrates, causing menstrual flow. h) During this cycle, estrogens and progesterone inhibit the release of LH and FSH (except for the large increase at mid-cycle). As the concentrations of estrogens and progesterone decline, the anterior pituitary gland secretes FSH and LH again, stimulating the next menstrual cycle. 3) Menopause a) Menopause is cessation of menstrual cycles. Less estrogens and progesterone are produced. b) The female reproductive organs decrease in size. 22.6 Mammary Glands 1) Location of the glands a) The mammary glands are located in the subcutaneous tissue of the anterior thorax within the breasts. b) The breasts extend between the second and sixth ribs and from sternum to axillae. 2) Structure of the glands a) The mammary glands are composed of lobes that contain tubular glands. b) Dense connective and adipose tissues separate the lobes. c) Ducts connect the mammary glands to the nipple. 3) Development of the breasts a) Breasts of males do not develop. b) Estrogens stimulate breast development in females. i) Alveolar glands and ducts enlarge. ii) Fat is deposited in the breasts. 22.7 Birth Control Birth control is the voluntary regulation of the number of children produced and the time they are conceived. This usually involves some method of contraception. 1) Coitus interruptus a) Coitus interruptus is withdrawal of the penis from the vagina before ejaculation. b) Some semen may be expelled from the penis before ejaculation. 2) Rhythm method a) Abstinence from sexual intercourse two days before and one day after ovulation is the rhythm method. b) It is difficult to predict the time of ovulation. 3) Mechanical barriers a) Males and females can use condoms.

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b) Condoms may also protect the user from contracting or spreading infections. Chemical barriers a) Spermicidal film, sponges, suppositories, foams, and gels are chemical barriers to conception. b) These provide an unfavorable environment in the vagina for sperm survival. Combined hormone contraceptives a) A flexible ring inserted deep into the vagina, a plastic patch, or a pill can deliver estrogen and progestin to prevent pregnancy. b) They disrupt the normal pattern of gonadotropin secretion which prevents follicle maturation and ovulation, and they thicken cervical mucus to prevent the sperm from joining the oocyte. c) When used correctly, combined hormone contraceptives are almost 100% effective. d) d. Some women develop undesirable side effects. e) A minipill contains only progestin and must be taken at the same time daily. Other hormone contraceptives a) Intramuscular injection with medroxyprogesterone acetate every three months prevents pregnancy. b) An implantable rod containing progestin may prevent pregnancy for up to three years. Intrauterine devices a) An IUD is a solid object inserted in the uterine cavity. b) An IUD thickens cervical mucus to prevent sperm from entering the uterus, creates an inhospitable environment for the sperm, and inhibits endometrial growth necessary for implantation of a blastocyst. c) A hormone-releasing IUD can effectively prevent pregnancy for up to five years. d) An IUD may be expelled spontaneously or produce undesirable side effects. Sterilization methods a) These are surgical procedures. i) Vasectomy is performed in males. ii) Tubal ligation is performed in females. b) A nonsurgical method inserts a tiny coil into each uterine tube, causing scarring that blocks fertilization. c) Sterilization methods are the most reliable contraception.

22.8 Sexually Transmitted Infections 1. Sexually transmitted infections are passed during sexual contact and may go undetected for years. 2. Many of the diseases associated with sexually transmitted infections share symptoms....