Reproductive Physiology Beth was a 22-year-old woman who thought she might be pr

Question

Reproductive Physiology

Beth was a 22-year-old woman who thought she might be pregnant. Although her menstrual periods were often irregular, this one was several weeks late. She made an appointment with her doctor, but while she waited, she decided to try a home pregnancy test. At the drugstore, she found several brands of home pregnancy tests, all of which appeared similar in content. They contained a plastic dipstick to be immersed in urine. An indicator dot changed color if the woman was pregnant. Beth took a kit home, and followed the simple directions. There was no color change, indicating that she was not pregnant.

Although she was confident she had used the test exactly according to directions, Beth decided to keep her doctor's appointment anyway. Perhaps a more sensitive test would show an early pregnancy her home kit missed. The doctor sent her to a small clinical laboratory where she was asked to collect another urine specimen. Curious about the whole process, Beth asked the lab technologist how she planned to test the specimen. The technologist explained that pregnancy tests are based on the presence or absence of a hormone found only in pregnant women. The test, she explained, contains a monoclonal antibody linked to an enzyme and a dye system. If the hormone is present in the urine, it binds to the antibody and the enzyme causing the dye to change color. In fact, she told Beth, the clinical lab test is just like the home pregnancy tests. The lab test confirmed the home result—no color change, no pregnancy.

1. By mid-pregnancy, hCG levels decline. What other hormone mechanism takes over to maintain the pregnancy?

2. Describe the hormonal influences that lead to ovulation. What are the feedback pathways?

3. Create a theoretical timeline, referring to the days in the ovarian cycle, in which it is possible for a sperm to fertilize an ovum. Give rationale.

4. How is lactation suppressed during pregnancy? How does this change after parturition?

Explanation / Answer

Answer 1. Hormones that maintain the pregnancy are:

1. Estrogen

2. Progesterone : It is regarded as the hormone which sustains pregnancy. The growth of the breasts during pregnancy is under the influence of both oestrogena nd progesterone. Oetrogen stimulates the proliferation of the duct system, growth and pigmentation of the nipples and areola,the development of the alveoli and the lobules is influenced by progesterone.

3. Human placental lactogen: also known as Human Chorionic somatomamotrophin (hCS). there is a close relation between its production and the placental weight throughout pregnancy.

4. Oxytocin produces uterine contraction and produces ejection of milk during lactation.

Answer 2. Luteinizing Hormone (LH) triggers ovulation in response to the oestrogen mediated feedback from negative to positive creating a LH-mid cycle surge. This activates an inflammatory response in the dominant follicle and leads to the breakdown of the follicular boundary and escape of the oocyte.

Other hormones include

1. Gonadotropin releasing hormone (GnRH)

2. Follicle stimulating Hormone (FSH)

FSH and LH induces the production of oestrogen and progesterone from te ovary which through a feedback mechanism influence the release of GnRH from the hypothalamus.

Feedback pathways (see diagram)

Answer 3. During the ovulation phase (14th day of cycle), oestrogen levels peak causing a LH and FSH surge resulting in the rupture of the follicles and the release of the oocyte from the ovary. This lasts for 24-36 hours. If no fertilization occurs, the egg (oocyte) will degenerate between 12-24 hours of ovulation.

Answer 4. Oestrogen and Progesterone in the breast prevent the production of milk during pregnancy. During the postpartum period, their effect is withdrawn and prolactin (Anterior pituitary hormone) dominates and milk secretion is stimulated and maintained. Milk ejection is accomplished by oxytocin (Posterior pituitary hormone).

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