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| UNDERSTANDING CONCEPTION |
| Human Reproduction and Development |
Human reproduction employs internal fertilization, and depends on the integrated action of hormones, the nervous system, and the reproductive system. Gonads are sex organs that produce gametes. Male gonads are the testes, which produce sperm and male sex hormones. Female gonads are the ovaries, which produce eggs (ova) and female sex hormones.
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| Female Reproduc tive System |
The main female reproductive organs are the uterus, ovaries, fallopian tubes, and vagina. The uterus, a hollow muscular organ about 3 inches long located deep inside the pelvic cavity is home to the developing fetus. The neck of the uterus (cervix) projects into the vagina, a muscular tube about 4 inches long that receives the penis and sperm and serves as the birth canal.
The fallopian tubes, a pair of structures each about 4 inches long, join the uterus near the top. Their flared ends lie near the ovaries, paired almond-shaped glands that produce ova (eggs) and female hormones. After an ovum is expelled into the pelvic cavity, it passes through a fallopian tube into the uterus. If the egg has been fertilized by a sperm, it implants in the uterus and gestation begins. |
| The Female Reproductive System |
| The female gonads, ovaries, are located within the lower abdominal cavity. |
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The female reporoductive system.
The ovary contains many follicles composed of a developing egg surrounded by an outer layer of follicle cells. Each egg begins oogenesis as a primary oocyte. At birth each female carries a lifetime supply of developing oocytes, each of which is in Prophase I. A developing egg (secondary oocyte) is released each month from puberty until menopause, a total of 400-500 eggs.
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| Ovarian Cycles |
After puberty the ovary cycles between a follicular phase (maturing follicles) and a luteal phase (presence of the corpus luteum). These cyclic phases are interrupted only by pregnancy and continue until menopause, when reproductive capability ends. The ovarian cycle lasts usually 28 days. During the first phase, the oocyte matures within a follicle. At midpoint of the cycle, the oocyte is released from the ovary in a process known as ovulation. Following ovulation the follicle forms a corpus luteum which synthesizes and prepares hormones to prepare the uterus for pregnancy.
The secondary oocyte passes into the oviduct (fallopian tube or uterine tube). The oviduct is connected to the uterus.
| The relationship of ovary and Fallopian tube. |
The uterus has an inner layer, the endometrium, in which a fertilized egg implants. At the lower end of the uterus the cervix connects the uterus to the vagina. The vagina receives the penis during intercourse and serves as the birth canal.
The female external genitals are collectively known as the vulva. The labia minora is a thin membrane of folded skin just outside the vaginal opening. The labia majora cover and protect the genital area. A clitoris, important in arousal, is a short shaft with a sensitive tip covered by a fold of skin. |
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