I. Male Reproductive System.

    A. Purpose: produce sperm and deliver them into the female body.

    B. Sperm.
        1. Head.
            a. Acrosome.
                i. Tip
                ii. Contains enzymes, apparently to dissolve the membrane of the ovum.
            b. Haploid nucleus.
        2. Midpiece.
            a. Many mitochondria wrapped into a tight coil.
            b. Provide the energy for swimming.
        3. Tail.
            a. Modified flagellum.
            b. Propels the sperm.

    C. Testes.
        1. The organs that produce sperm.
        2. Located in the scrotum.
            a. A pouch below the penis.
            b. Sperm production requires a temperature 2° C cooler than the abdomen.
        3. Shaped like a flattened egg, 4 cm long.
        4. Consists of seminiferous tubules where sperm is produced.
        5. Between these are clusters of cells that secrete male sex hormones.
        6. Cells lining the seminiferous tubules produce sperm.
        7. Sperm production is continuous from puberty until death.
        8. Other cells in the seminiferous tubules produce jelly-like substances to nourish the sperm.
        9. This sperm-jelly mixture is carried to the epididymis.

    D. Accessory organs.
        1. Produce 95% of the semen and carry the sperm outside the body.
        2. Epididymis.
            a. A thin, coiled 6 m long tube tightly packed on the testes inside the scrotum.
            b. Stores sperm until mature.
            c. After 18 h in the epididymis the sperm can become mature.
        3. Vas deferens.
            a. Straight tube from the epididymis, around the bladder, and to the urethra.
            b. Carries sperm by muscular contractions.
        4. Seminal vesicle: secretes a fluid into the vas deferens.
        5. Prostate gland: secretes most of the seminal fluid.
        6. Urethra.
            a. Passage outside the body through the penis.
            b. Used by both urine and semen.
            c. Muscles prevent urine and semen mixing.
        7. Bulbourethral glands (Cowper’s glands).
            a. Open into the urethra.
            b. Secrete a clear, sticky, alkaline fluid.
            c. Neutralizes the normal acids in the urethra.
        8. Penis: penetrates the female body and delivers semen into the vagina during sexual intercourse.

    E. Semen.
        1. The fluid that contains the sperm when it exits the body.
        2. Composed of fluids secreted by the testes, epididymis, seminal vesicles, prostate gland, and bulbourethral glands.
        3. Contains nutrition for the sperm.
        4. Its alkalinity activates the sperm and protects them from the acidity of the female’s body.

II. Female Reproductive System.

    A. Purpose: produce ova, receive sperm, protect and nourish the developing embryo.

    B. Ovaries.
        1. Almond-shaped organs that contain ova (eggs).
        2. At birth, a girl’s ovaries are supplied with 200,000 immature ova.
        3. New ova are not produced during a woman’s life.
        4. From puberty until menopause a few ova mature each month.
        5. The ovaries ordinarily alternate in releasing an ovum .
        6. Each immature ovum with its surrounding cells is a follicle.
        7. At puberty, the anterior pituitary gland secretes follicle stimulating hormone (FSH).
        8. FSH stimulates several follicles to develop each month.
        9. Meiosis (which had been arrested) continues in the ova.
        10. One or two ova mature; the rest degenerate.
        11. The follicle enlarges and forms a cavity with a clear fluid which nourishes and protects the ovum.
        12. After 2 weeks, the follicle bursts open and releases the ovum outside the ovary.
        13. This is ovulation.
        14. The follicle cells secrete a gelatinous coating which protects the ovum.

    C. Accessory organs.
        1. Oviduct (Fallopian tube).
            a. A tube connected to the uterus with a funnel-like opening next to the ovary.
            b. The opening has finger-like projections which partially enclose the ovary.
            c. The inner surface is lined with a ciliated mucous membrane.
            d. The cilia beat and create a current which pulls the ovum into the tube.
            e. The cilia and peristaltic contractions of the oviduct move the ovum toward the uterus.
            f. Fertilization occurs in the oviduct.
            g. The zygote begins to divide and develop on its way to the uterus.
            h. If fertilization does not occur, the ovum degenerates.
        2. Uterus.
            a. A pear-shaped organ.
            b. Wall of muscle tissue, but lined with ciliated epithelial cells.
            c. The lining thickens to receive the embryo.
            d. If an embryo lodges in the uterine lining, the uterus serves as the womb.
        3. Cervix: where the uterus joins the vagina.
        4. Vagina.
            a. Short, elastic canal leading from the uterus outside the body.
            b. Receives semen from the penis.
            c. Is the birth canal.

    D. Female reproductive cycles.
        1. Ovarian cycle: the ovary prepares and releases an ovum.
            a. A large amount of FSH is released by the anterior pituitary gland to start the development of a follicle.
            b. The amount of FSH diminishes over a 2-week period until ovulation occurs.
            c. During this same 2 weeks, the pituitary gland increases secretion of luteinizing hormone.
            d. After ovulation the luteinizing hormone causes the follicle to develop into a yellow structure called the corpus luteum.
            e. During the next 2 weeks, the amount of luteinizing hormone decreases, causing the corpus luteum to degenerate.
        2. Menstrual cycle: the uterus prepares its lining to receive an embryo.
            a. The follicle produces estrogens which cause the uterine lining to thicken.
            b. Just before ovulation the follicle begins to produce progesterone.
            c. Progesterone causes the uterus to prepare to receive an embryo.
                i. Stimulates growth of blood vessels in the uterine wall.
                ii. Stimulates glands of the uterine wall to secrete other substances.
            d. After ovulation the corpus luteum produces large quantities of progesterone.
            e. 7 days after ovulation progesterone is at its peak.
            f. 10 days after ovulation the uterine wall is thickest.
            g. A fertilized ovum embeds in the uterine lining and a placenta forms.
            h. If there is no embryo, as the corpus luteum decreases its production of progesterone the uterine lining shrinks.
            i. 14 days after ovulation the uterine lining is shed from the body.

III. Fertilization and Development.

    A. “Any fool can devise an experiment in developmental biology – but no one can interpret it.” Dr. Roth

    B. Fertilization.
        1. Occurs in the oviduct a few hours to a few days after ovulation.
        2. Semen is deposited in the vagina during sexual relations.
        3. Sperm travel through the uterus into the oviduct within a few minutes.
        4. They pass through the follicular cells and the gel surrounding the ovum.
        5. An enzyme in the acrosome may assist in this.
        6. Many sperm may reach the ovum, but after one penetrates the membrane there is a change in the membrane which prevents other sperm from entering.
        7. The sperm loses its tail and its head swells.
        8. The ovum nucleus divides, completing meiosis.
        9. The sperm and ovum nuclei fuse.

    C. Development.
        1. Rapid cell division at first (cleavage).
        2. There is little growth, so each new cell is smaller than its parent.
        3. In 3 days the embryo reaches the uterus – then a mass of 16 cells.
        4. Division continues for 3 more days, forming a sphere called a blastocyst.
        5. The blastocyst is implanted in the thick uterine lining.
        6. The outer layer of embryonic cells form the placenta

    D. Placental membranes.
        1. Amnion.
            a. Surrounds the embryo.
            b. Filled with amniotic fluid.
            c. Protects the embryo.
        2. Yolk sac: forms blood cells.
        3. Allantois.
            a. Numerous blood vessels that converge to form the umbilical cord.
            b. Carry fetal blood to the placenta where food, waste, O2, and CO2 are exchanged.
        4. Chorion: forms part of the placenta.

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