STRUCTURE AND FUNCTION OF THE FEMALE REPRODUCTIVE SYSTEM

Transcription

1 Unit 7B STRUCTURE AND FUNCTION OF THE FEMALE REPRODUCTIVE SYSTEM LEARNING OBJECTIVES 1. Learn the structures of the female reproductive tract. 2. Learn the functions of the female reproductive tract. 3. Learn how many potential eggs does a female possess at different stages in her life? 4. Learn the different tissues composing the uterus and the function of each. 5. Learn how meiosis differs in the production of sperm and eggs. INTRODUCTION The female reproductive system has four major functions: 1) produce eggs (ova), 2) produce hormones (estrogen, progesterone, and testosterone), 3) nurture and protect the embryo and fetus until the organism is capable of living outside the maternal body, and 4) receive the penis (semen). Figure 7-4 is a side view of the female reproductive system. The ovaries produce the eggs and hormones. One lies on each side of the abdominal cavity and is enclosed in a tough protective capsule of connective tissue. Each ovary contains many follicles; each follicle contains an egg (figure 7-5). Figure 7-4. A longitudinal section of the female reproductive system. 92

2 There are 2,000,000 follicles at birth but the number is reduced to 300,000 to 400,000 by puberty. The number of follicles decreases from puberty to menopause (figure 7-6). After puberty, one or rarely two or more follicles matures and releases its egg during each menstrual cycle; this is the process of ovulation. After ovulation the follicle becomes the corpus luteum. If pregnancy occurs, the corpus luteum persists for 3-6 months secreting progesterone; if pregnancy doesn t occur, the corpus luteum degenerates. As with the sperm, reduction of the number of chromosomes occurs, oogenesis. Figure 7-5. Showing x-section of ovary and development of follicles. The first division of oogenesis occurs in the ovary prior to ovulation; the second division occurs after fertilization. 93

3 Figure 7-6. Changes in the number of germ cells in the human ovary. (After Baker, 1970) Two oviducts (fallopian tubes) transport the egg to the uterus by ciliary action and rhythmic contractions. The egg is released from the ovary into the abdominal cavity near the finger-like extensions surrounding the funnel-like opening of the oviduct. The movements of these structures plus the ciliary action of the epithelium (innermost layer of the tube) draw the egg along with some fluid from the abdominal cavity into the oviduct. Some eggs do not enter the tube and usually disintegrate. If one of these eggs is fertilized, it can result in ectopic pregnancy (development of an egg outside the uterus). The uterus is about the size and shape of a pear. It consists of an endometrium (inner layer), middle layer of muscle, and an outer layer of connective tissue. The endometrium is richly supplied with blood vessels. It is the endometrium that will contribute to the placenta. The cervix of the uterus extends into the vagina. The examination referred to as a pap smear is used to detect cancerous or pre cancerous cells of the cervix. During the menstrual cycle, the endometrium builds up and sloughs off. Removal of the uterus is referred to as a hysterectomy; whereas, removal of the ovaries along with the uterus is called an ovariohysterectomy. The vagina serves as the receptacle for the penis and semen. It also serves as the birth canal. At birth its opening is covered by a hymen membrane. An active female often breaks this structure prior to sexual intercourse. In some cases it is necessary to have the structure surgically removed. 94

4 The external genitals are shown in figure 7-7). The labia minora are two small folds surrounding the opening to the vagina. The labia majora are thick, fatty ridges of tissue that surround the labia minora. The vestibule is a cleft formed within the folds Figure 7-7. External genitals of the human female. of the labia minora and contains the openings of the urethra and vagina. At the top of the vestibule is a small bulb of erectile tissue, clitoris, (the female equivalent of the male penis). 95

5 Unit 7B OBJECTIVE QUESTIONS OVER THE FEMALE REPRODUCTIVE SYSTEM 1. The number of follicles at puberty is about (A) 3,000,000 (B) 2,000,000 (C) 300,000 (D) The second division of meiosis in the formation of the egg occurs (A) prior to puberty (B) at the time of puberty (C) just prior to ovulation (D) just after fertilization. 3. The innermost layer of the uterus is the (A) muscle layer (B) connective tissue layer (C) endometrium. 4. The opening of the (A) fallopian tube (B) uterus (C) vagina is covered by the hymen at the time of birth of the female. 5. The pap smear is a method for early detection of cancer of the (A) vagina (B) ovary (C) uterus (D) fallopian tube. 6. The normal menstruation cycle occurs (A) more frequently (B) less frequently (C) with the same frequency as/than ovulation. 7. If (A) pregnancy occurs (B) pregnancy doesn t occur the corpus luteum persists for about 3-6 months. 8. The female ovary produces (A) estrogen (B) progesterone (C) testosterone (D) two of the preceding (E) all the preceding. 9. Normally sperm are deposited in the (A) vagina (B) uterus (C) oviduct. 10. The (A) vagina (B) urethra (C) both A and B (D) neither A or B open(s) into the vestibule. DISCUSSION QUESTIONS OVER FEMALE REPRODUCTIVE SYSTEM 1. What is the function of the hymen membrane? 96

6 2. What happens to the hymen membrane? 3. What is the role of menstruation? 4. Knowing the function of the uterus, what types of tissues must be included in its makeup? Explain. 5. What changes occur in the female reproductive system at puberty? 6. What is meant by referring to the female reproductive system as an open system? 7. What should be done with an ectopic pregnancy? Explain the reason. 8. What is the advantage of the egg retaining most of the cytoplasm within the egg as a result of oogenesis; whereas, in spermatogenesis the cytoplasm is split equally between the four sperm? 97