Contraception

Medical Terms Pictures

Vas deferens

Oviduct

Medical Terms Pictures

Oviduct

FIGURE 15-4. Sterilization. (A) Vasectomy. (B) Tubal ligation.

Uterine cannula

Laparoscope and forceps

FIGURE 15-5. Laparoscopic sterilization.

FIGURE 15-5. Laparoscopic sterilization.

Tubal Ligation

Pregnancy and Birth

Fertilization and Early Development

If an ovulated egg cell is penetrated by a sperm cell, fertilization (Fig. 15-6) results. After this union, the nuclei of the sperm and egg cells fuse, restoring the chromosome number to 46 and forming a zygote. As the zygote travels through the oviduct toward the uterus, it divides rapidly. Within 6 to 7 days, the fertilized egg reaches the uterus and implants into the endometrium, and the embryo begins to develop.

During the first 8 weeks of growth, all of the major body systems are established. Embryonic tissue produces human chorionic gonadotropin (HCG), a hormone that keeps the corpus luteum functional in the ovary to maintain the endometrium. (The presence of HCG in urine is the basis for the most commonly used tests for pregnancy.) After 2 months, placental hormones take over this function and the corpus luteum degenerates. At this time the embryo becomes a fetus.

The Placenta

During development, the fetus is nourished by the placenta, an organ formed from the outermost layer of the embryo, the chorion, and the innermost layer of the uterus, the endometrium (Fig. 15-7). Here, exchanges take place between the bloodstreams of the mother and the fetus through fetal capillaries.

The umbilical cord contains the blood vessels that link the fetus to the placenta. Fetal blood is carried to the placenta in two umbilical arteries. While traveling through the placenta, the blood picks up nutrients and oxygen and gives up carbon dioxide and metabolic waste. Restored blood is carried from the placenta to the fetus in a single umbilical vein.

Ovary

Ovarian -ligament

Broad — ligament

Body of uterus -

Cervical canal -Cervix Vagina Rugae

Vaginal Rugae

Fimbriae

Ovum

FIGURE 15-6. Female reproductive system showing fertilization. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

Fimbriae

Ovum

Ovarian follicle (ruptured)

Corpus luteum Maturing follicle

Greater vestibular (Bartholin) gland

FIGURE 15-6. Female reproductive system showing fertilization. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

Although the bloodstreams of the mother and the fetus do not mix, and all exchanges take place through capillaries, some materials do manage to get through the placenta in both directions. For example, some viruses, drugs, and other harmful substances are known to pass from the mother to the fetus; fetal proteins can enter the mother's blood and cause immunologic reactions.

During gestation (the period of development), the fetus is cushioned and protected by fluid contained in the amniotic sac (amnion) (Fig. 15-8), commonly called the bag of waters. This sac ruptures at birth.

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Essentials of Human Physiology

Essentials of Human Physiology

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  • wegahta adonay
    Where human egg cells wait?
    8 years ago

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