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Reproductive Systems Reproductive Organs • Primary sex organs: Produce and house sex cells • Secondary sex organs: Provide the route by which sex cells unite Reproductive Organs • Primary sex organs (called gonads) include testes in males and ovaries in females. • The gonads produce sex cells (gametes); these include: sperm in males, and eggs (ova) in females. • Secondary sex organs encompass all other organs necessary for reproduction. • In males, this includes a system of ducts, glands, and the penis, all of which are charged with storing and transporting sperm. • In females, the secondary sex organs provide a location for the uniting of egg and sperm as well as the environment for nourishing a fertilized egg. Male Reproductive System Serves to produce, transport, and introduce mature sperm into the female reproductive tract Testes Spermatic cord Cremaster muscle Testis Median septum Testes • The penis and the scrotum are the external portions of the male reproductive system. Inside the scrotum reside two testes, the organs that manufacture sperm and produce the male hormone testosterone. • Extending from the abdomen to each testicle is a strand of connective tissue called the spermatic cord; the sperm duct (vas deferens) as well as blood and lymphatic vessels and nerves lie within the cord. • Two small, oval testes lie suspended in a sac of tissue called the scrotum. • The median septum divides the scrotum. • The cremaster muscle surrounds the spermatic cord and testis. In cold weather, it contracts to draw the testes closer to the body for warmth. Inside the Testes Rete testis Efferent ductules Spermatic ducts Lobule Epididymis Seminiferous tubules Vas deferens Inside the Testes • Inside the testes, a series of spermatic ducts carry sperm away from the testis and out of the body. • Fibrous tissue separates each testis into over 200 lobules. Coiled within each lobule are one to three seminiferous tubules, where sperm are produced. Also in the wall of the tubule are sustentacular (Sertoli) cells. These cells promote the development of sperm by supplying nutrients, removing waste, and secreting the hormone inhibin, which plays a role in the maturation and release of sperm. • Lying between the seminiferous tubules are clusters of interstitial cells—called Leydig cells—that produce testosterone. Inside the Testes • A network of vessels called the Rete testis lead away from the seminiferous tubules; these vessels provide a location in which sperm partially mature. • Efferent ductules conduct immature sperm away from the testis to the epididymis. Sperm move from the head of the epididymis to the tail, maturing as they go. They are then stored in the tail of the epididymis, where they remain fertile for 40 to 60 days. After that, unless they are released, they disintegrate and are reabsorbed by the epididymis. • Sperm leave the tail of the epididymis and pass into the vas deferens. Vas Deferens Vas deferens Ejaculatory duct Vas Deferens • The vas deferens travels up through the spermatic cord, into the pelvic cavity, over the ureter to the prostate, and behind the bladder. • As the vas deferens turns downward, it joins the seminal vesicle to form the ejaculatory duct. The ejaculatory ducts pass through the prostate and empty into the urethra. Question Where is testosterone produced? A. B. C. D. Seminiferous tubules Interstitial cells of the testes Epididymis Sustentacular (Sertoli) cells Accessory Glands Accessory Glands • Located at the base of the bladder, a pair of seminal vesicles secretes a thick, yellowish fluid into the ejaculatory duct. The fluid comprises about 60% of semen; it contains fructose (an energy source for sperm motility) and substances that nourish and ensure sperm motility. • The prostate gland encircles both the urethra and ejaculatory duct. It secretes a thin, milky, alkaline fluid into the urethra; besides adding volume to the semen (it comprises about 30% of the fluid portion of semen), the fluid enhances sperm motility. • Two pea-shaped bulbourethral glands (also called Cowper’s glands) secrete a clear fluid into the penile portion of the urethra during sexual arousal. Besides serving as a lubricant for sexual intercourse, the fluid also neutralizes the acidity of residual urine in the urethra, which would harm the sperm. Penis • Body is called the shaft. • Head is the glans penis. • Loose skin covering is the prepuce. Interior of the Penis Corpus cavernosa Corpus spongiosum Interior of the Penis • Three cylinders of erectile tissue fill the shaft of the penis. During sexual arousal, the tissues fill with blood, causing the penis to enlarge and become erect. • The two larger cylinders of tissue are called the corpus cavernosa (singular: corpus cavernosum). • The smaller cylinder of tissue, called the corpus spongiosum, encircles the urethra. Spermatogenesis Spermatogenesis 1. Sperm begin as spermatogonia, primitive sex cells located in the walls of the seminiferous tubules. 2. Spermatogonia divide by mitosis to produce two daughter cells, each with 46 chromosomes. 3. These cells then differentiate into slightly larger cells called primary spermatocytes, which move toward the lumen of the seminiferous tubule. 4.Through meiosis, the primary spermatocyte yields two genetically unique secondary spermatocytes, each with 23 chromosomes. 5. Each secondary spermatocyte divides again to form two spermatids. 6.Spermatids differentiate to form heads and tails and eventually transform into mature spermatozoa (sperm), each with 23 chromosomes. Spermatozoa Head Middle piece Tail Spermatozoa • The head contains the nucleus, which is packed with genetic material. A cap called an acrosome contains enzymes that help the sperm penetrate the egg during fertilization. • The middle piece contains numerous mitochondria that supply the sperm with energy. • The tail is a flagellum whose beating, whip-like movements propel the sperm forward. Semen 65% of volume comes from seminal vesicles 30% comes from prostate gland 5% comes from bulbourethral gland Semen • Semen is a whitish fluid containing both sperm and the fluid secretions of the accessory glands. Each ejaculation expels between 2 and 5 ml of semen containing between 40 and 100 million sperm. • Immediately after ejaculation, semen becomes sticky and jelly-like. This promotes fertilization by allowing the semen to stick to the walls of the vagina and cervix instead of immediately draining out. The alkalinity of semen counteracts the acidity of the vagina; this is important because sperm become immobile in an acidic environment. Question Where do sperm begin development? A. Seminiferous tubules B. Seminal vesicles C. Vas deferens D. Epididymis Male Sexual Response Excitement Plateau Orgasm Resolution Female Reproductive System Female Reproductive System • The organs of the female reproductive system are housed within the abdominal cavity. • The female’s primary reproductive organs (gonads) are the ovaries. The ovaries produce ova, the female gametes. • The accessory organs—which include the fallopian tubes, uterus, and vagina—extend from near the ovary to outside the body. Ovaries Ovaries • Two ovaries—about the size and shape of almonds—sit on each side of the uterus where they produce both egg cells (ova) and sex hormones. • Each ovary contains thousands of immature eggs. During a menstrual cycle, hormones cause one egg to begin to develop. Enclosed inside a bubble-like follicle, the egg develops until, at a certain point, the follicle bursts and releases the egg. This figure shows the stages of a single egg and follicle development. (The ovary does not contain eggs in multiple stages of development.) Internal Genitalia Isthmus Fundus Ampulla Body Infundibulum Cervix Vagina Fornices Internal Genitalia • The fallopian tubes are about 4 inches (10 cm) long and extend from the ovary to the uterus. A narrow isthmus is the portion closest to the uterus. The middle portion (the ampulla) is the usual site of egg fertilization. Cilia lining the inside beat to help propel the egg toward the uterus. The distal end is the infundibulum. The fallopian tube does not attach directly to the ovary; finger-like projections called fimbriae fan over the ovary. • The vagina is a muscular tube about 3 inches (8 cm) long; it is a receptacle for the penis and sperm, a route for the discharge of menstrual blood, and the passageway for the birth of a baby. The smooth muscle walls can expand greatly, such as during childbirth. The vagina extends slightly beyond the cervix, creating pockets called fornices. Internal Genitalia • The uterus is a muscular chamber that houses and nurtures a growing embryo. It sits between the urinary bladder and the rectum, held in place by the broad ligament. It tilts forward over the bladder. The curved, upper portion is the fundus. The upper two corners connect with the fallopian tubes. The central region is the body. The inferior end is the cervix. A passageway through the cervix, called the cervical canal, links the uterus to the vagina. Glands within the cervical canal secrete thick mucus; during ovulation, the mucus thins to allow sperm to pass. External Genitalia Mons pubis Prepuce Clitoris Labia majora Labia minora Lesser vestibular gland Greater vestibular gland External Genitalia • The mons pubis is a mound of hair-covered adipose tissue overlying the symphysis pubis. • The labia majora (singular: labium majus) are thick folds of skin and adipose tissue; hair grows on the lateral surfaces of the labia majora while the inner surfaces are hairless. • The labia minora (singular: labium minus) are two thinner, hairless folds of skin just inside the labia majora. • The area inside the labia is called the vestibule; it contains the urethral and vaginal openings. External Genitalia • The labia minora meet to form a hood of tissue called the prepuce over the clitoris. The clitoris is a small mound of erectile tissue that resembles a penis. Its role is strictly sensory, providing a source of sexual stimulation. • A pair of mucous glands, called the lesser vestibular glands (or Skene’s glands) open into the vestibule near the urinary meatus, providing lubrication. • Two pea-sized glands called greater vestibular glands (or Bartholin’s glands) sit on either side of the vaginal opening; their secretions help keep the vulva moist and provide lubrication during sexual intercourse. Question What is the curved upper portion of the uterus called? A. Infundibulum B. Fimbriae C. Vestibule D. Fundus Breasts Lobule Lactiferous duct Lactiferous sinus Acini Suspensory ligaments Areola Breasts • Each breast contains 15 to 20 lobules separated by fibrous tissue and adipose tissue. • Each lobule consists of clusters of tiny, sac-like acini that secrete milk during lactation. Minute ducts drain the acini, merging to form larger ducts. The ducts unite to form a single lactiferous duct for each lobe. Before reaching the nipple, the ducts enlarge slightly to form lactiferous sinuses. Each duct ends in a tiny opening on the surface of the areola. • A pigmented area called the areola encircles the nipple. Numerous sebaceous glands (that look like small bumps) dot the surface. Sebum from these glands lubricates the areola, helping prevent dryness and cracking during nursing. • Suspensory ligaments help support the breasts and also serve to attach the breasts to the underlying pectoralis muscles. Female Reproductive Cycle • Ovarian cycle: Centers on changes in the ovaries • Menstrual cycle: Focuses on changes in the uterus • The reproductive cycle averages 28 days in length; however, the length of the cycle can range from 20 to 45 days. Both cycles are controlled by the cyclical secretion of hormones: the ovarian cycle is governed by the hormones FSH (follicle-stimulating hormone) and LH (luteinizing hormone); the menstrual cycle is under the influence of estrogen and progesterone. Ovarian Cycle • Follicular phase: Triggered by follicle-stimulating hormone (FSH) • Ovulation: Prompted by spike in luteinizing hormone (LH) • Luteal phase: Influenced by high levels of progesterone secreted by corpus luteum View animation on “Ovarian cycle” Ovarian Cycle • Low levels of estrogen and progesterone stimulate the hypothalamus to release gonadotropin-releasing hormone (GnRH). GnRH stimulates the anterior pituitary to release FSH and LH. • FSH triggers several of the follicles to resume development, beginning the follicular phase. Only one follicle, will make it to maturity. The developing follicle secretes estrogen (which stimulates the thickening of the endometrium in the menstrual cycle) and small amounts of progesterone. The follicle migrates to the surface of the ovary. The mature follicle is called a graafian follicle. Ovarian Cycle • In the mid-point of the cycle, estrogen levels peak, triggering a spike in LH. The sudden spike in LH causes the follicle to rupture and release the ovum (ovulation). The fimbriae of the fallopian tube sweep across the top of the ovary to catch the emerging oocyte. • The remnants of the follicle remain on the ovary and form the corpus luteum, which marks the beginning of the luteal phase. The corpus luteum secretes large amounts of progesterone and small amounts of estrogen. The progesterone causes the endometrium to continue to thicken and become more vascular. High levels of progesterone and estrogen also inhibit the pituitary from producing FSH and LH so that no other follicles develop. Ovarian Cycle • If fertilization doesn’t occur, the corpus luteum degenerates into inactive scar tissue called the corpus albicans. • Estrogen and progesterone levels plummet, causing the endometrium to slough off, resulting in menstruation. With the decline in ovarian hormones, the pituitary is no longer inhibited; FSH levels begin to rise and a new cycle begins. Menstrual Cycle 1. 2. 3. 4. 5. Menstrual phase Proliferative phase: ↑ estrogen → growth of blood vessels Ovulation Secretory phase: ↑ progesterone → ↑ endometrial thickening Premenstrual phase: ↓ progesterone → ischemic endometrium Menstrual Cycle • Estrogen and progesterone drive the menstrual cycle. • Menstrual phase: The first day of bleeding is the first day of the menstrual cycle; it lasts 3 to 5 days as the endometrium sheds its functional layer. • Proliferative phase: About day 6, rising levels of estrogen (secreted by the ovaries) stimulates the repair of the base layer as well as the growth of blood vessels. • Secretory phase: The endometrium develops into a nutritious bed about 5 to 6 mm thick. • Premenstrual phase: If fertilization doesn’t occur, the corpus luteum atrophies and progesterone levels plummet. Blood vessels nourishing the endometrium spasm, interrupting blood flow. The endometrium becomes ischemic and necrotic, causing it to slough off. Female Sexual Response Excitement Plateau Orgasm Resolution Question A surge in which hormone causes ovulation? A. Follicle-stimulating hormone (FSH) B. Luteinizing hormone (LH) C. Estrogen D. Progesterone