Chapter 26: The Reproductive System

13. Briefly describe the process of oogenesis.

1. Primary germ cells in embryo differentiates into oogonia (ovary-specific stem cells( 2. Oogonium multiplies by mitosis and begins at meiosis but stops at Prophase I 3. The cells suspended in Prophase I are called primary oocytes; they remain here until puberty 4. At puberty, FSH periodically stimulates a follicle to grow and induces its primary oocyte (2n) to complete meiosis I and start meiosis II 5. Meiosis then arrests the SECONDARY oocytes (n) at metaphase II; they are released at ovulation when the follicle breaks open 6. Only one oocyte matures and is released each month; meiosis continues if a sperm penetrates the oocyte (only then is oogenesis completed to produce an ovum) 7. After meiosis is completed, the haploid nuclei of the sperm and the mature ovum fuse (fertilization)

9. Describe the hormonal regulation of male reproductive system.

Brain-testicular axis refers to the relationship and interactions between the hypothalamus, anterior pituitary gland, and the testes. •The hypothalamus releases gonadotropin-releasing hormone (GnRH), which controls the release of the anterior pituitary hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in males. •FSH indirectly stimulates spermatogenesis. •LH, also called interstitial cell-stimulating hormone (ICSH), stimulates the interstitial cells to produce testosterone. •Locally, testosterone acts as a final trigger for spermatogenesis. •Testosterone inhibits hypothalamic release of GnRH and acts directly on the anterior pituitary gland to inhibit gonadotropin release. •Inhibin is produced by the sustentacular cells and released when sperm count is high. Mechanism and Effects of Testosterone Activity •Testosterone is synthesized from cholesterol and exerts its effects by activating specific genes to be transcribed. •Testosterone targets accessory organs (ducts, glands, and penis), causing them to grow and assume adult size and function. •Testosterone induces male secondary sex characteristics: pubic, axillary, and facial hair, deepening of the voice, thickening of the skin and increase in oil production, and an increase in bone and skeletal muscle size and mass.

14. How does oogenesis differ from spermatogenesis?

Cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte (goes on to become the ovum). The smaller cells are called polar bodies. Spermatogenesis results in 4 mature sperm. Oogenesis has long resting periods

16. Summarize the effects of estrogens and progesterone on female reproductive system.

Extrauterine Effects of Estrogens and Progesterone •Rising estrogen levels promote oogenesis and follicle growth in the ovary, as well as growth and function of the female reproductive structures. •Estrogens also cause the epiphyses of the long bones to close during growth spurts in puberty. •The estrogen-induced secondary sex characteristics of females include growth of breasts, increased deposition of subcutaneous fat in the hips and breasts, widening and lightening of the pelvis, growth of pubic and axillary hair, and metabolic changes. •Progesterone works with estrogen to establish and help regulate the uterine cycle, and promotes changes in cervical mucus.

7. Distinguish between meiosis and mitosis,

Meiosis consists of two consecutive nuclear divisions and the production of four daughter cells with half as many cells as a normal body cell. •Meiosis I reduces the number of chromosomes in a cell from 46 to 23 by separating homologous chromosomes into different cells. •Meiosis II resembles mitosis in every way, except the chromatids are separated into four cells.

1. Describe the common function of the male and female reproductive system.

Produce Gamates and offspring

3. Describe the location, structure, and function of each organs of male reproductive duct (epididymis, ductus (vas) deferens and urethra).

The Male Duct System •The epididymis consists of a highly coiled tube that provides a place for immature sperm to mature and to be expelled during ejaculation. •The ductus deferens, or vas deferens, carries sperm from storage sites in the epididymis, through the inguinal canal, over the bladder, and into the ejaculatory duct. •The urethra is the terminal portion of the male duct system and carries both urine and sperm (not at the same time) to the exterior environment.

12. Describe the anatomy of the female external genitalia.

The external genitalia, also called the vulva or pudendum, include the mons pubis, labia, clitoris, and structures associated with the vestibule.

4. Describe the structure of the penis, and discuss its role in the reproductive process.

The penis is the copulatory organ, designed to deliver sperm into the female reproductive tract. •The penis is made of an attached root, and a free shaft or body that ends in the glans. •The prepuce, or foreskin, covers the penis and may be slipped back to form a cuff around the glans. •Internally the penis contains the corpus spongiosum and the corpora cavernosum, two erectile tissues.

2. Describe the structure and function of the testes, and explain the importance of their location in the scrotum.

The testes are the primary reproductive organ of the male, producing both sperm and testosterone. The testes are divided into lobules with seminiferous tubules inside, where sperm are produced. Interstitial cells are found in the connective tissue surrounding the seminiferous tubules and produce testosterone. •The scrotum is a sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis and houses the testes. It provides an environment 3° below the core body temperature. oIt responds to temperature changes.

5. Describe the location, structure, and function of the accessory glands of the male reproductive system (seminal vesicles, prostate gland and bulbourethral glands).

Accessory Glands •The seminal vesicles lie on the posterior bladder wall and their alkaline secretion accounts for 60% of the volume of semen consisting of fructose, ascorbic acid, a coagulating enzyme (vesiculase), and prostaglandins. •The prostate gland is responsible for producing a milky, slightly acidic fluid containing citrate, several enzymes, and prostate-specific antigen, making up about one-third of the semen. •The bulbourethral glands, or Cowper's glands, produce a thick, clear mucus prior to ejaculation that neutralizes any acidic urine in the urethra.

15. Describe the phases and the regulation of ovarian and menstrual cycles.

Hormonal Regulation of the Ovarian Cycle •During childhood, the ovaries grow and secrete small amounts of estrogen that inhibit the release of GnRH until puberty, when the hypothalamus becomes less sensitive to estrogen and begins to release GnRH in a rhythmic manner. Hormonal Interactions During the Ovarian Cycle •On day 1 of the cycle, levels of GnRH rise and stimulate increased production and release of FSH and LH. •FSH and LH stimulate follicle growth and maturation, and estrogen secretion. •Rising levels of estrogen in the plasma exert negative feedback on the anterior pituitary, inhibiting release of FSH and LH. •Estrogen exerts positive feedback on the anterior pituitary, resulting in a burst of LH triggering ovulation and transforming the ruptured follicle into the corpus luteum. •Rising plasma levels of progesterone and estrogen exert negative feedback on LH and FSH release. •LH levels fall and luteal activity ends; the corpus luteum degenerates, dropping the levels of estrogen and progesterone, and the cycle starts again. The uterine (menstrual) cycle is a series of cyclic changes that the uterine endometrium goes through each month in response to changing levels of ovarian hormones in the blood •The menstrual phase takes place on days 1-5 typically, and is the time when the endometrium is shed from the uterus. •The proliferation phase (days 6-14) is the time in which the endometrium is rebuilt, once again becoming velvety, thick, and well vascularized. •The secretory phase (days 15-28) is the phase in which the endometrium prepares for implantation of an embryo.

6. Discuss the sources, components, and functions of semen.

Semen is a milky white, somewhat sticky mixture of sperm and accessory gland secretions that provides a transport medium for sperm.

8. Briefly outline the events of spermatogenesis.

Spermatogenesis is the series of events in the seminiferous tubules that produce male gametes (sperm or spermatozoa). Spermatogenesis begins when the spermatogonia divide to produce type A daughter cells that maintain the stem cell line, and type B daughter cells that get pushed toward the lumen to become primary spermatocytes and ultimately sperm. •Each primary spermatocyte undergoes meiosis I to produce two secondary spermatocytes, which then undergo meiosis II to form spermatids. •Spermiogenesis is a streamlining process that strips the spermatid of excess cytoplasm and forms a tail, resulting in a sperm with a head, a midpiece, and a tail. •The sustentacular cells, or Sertoli cells, form a blood-testis barrier that prevents membrane-bound antigens from escaping into the bloodstream.

10. Describe the location, structure, and function of the ovaries.

The ovaries produce the female gametes (ova, or eggs) and the sex hormones (estrogens and progesterone). •The paired ovaries are found on either side of the uterus and are held in place by several ligaments. •Saclike structures called ovarian follicles consist of an immature egg, called an oocyte, encased by one or more layers of different cells. •Follicles at different stages are distinguished by their structure as primordial follicles, primary follicles, secondary follicles, and Graafian or vesicular follicles. •Ovulation occurs each month in adult women when one of the maturing follicles ejects its oocyte from the ovary. •The ruptured follicle transforms into a glandular structure called the corpus luteum, which eventually degenerates.

11. Describe the location, structure, and function of each organs of female reproductive duct (uterine tubes, uterus and vagina).

The uterine tubes, or fallopian tubes or oviducts, form the beginning of the female duct system, receive the ovulated oocyte, and provide a site for fertilization to take place. •The uterus is a hollow, thick-walled muscular organ that functions to receive, retain, and nourish a fertilized ovum. •The uterus is supported by the mesometrium, the lateral cervical ligaments, the uterosacral ligaments, and the round ligaments. •The wall of the uterus is composed of three layers: the perimetrium, the myometrium, and the endometrium. •The vagina provides a passageway for delivery of an infant and for menstrual blood, and also receives the penis and semen during sexual intercourse.