A 25-year-old woman stated that it had been six weeks since her last menses. Her

Question

A 25-year-old woman stated that it had been six weeks since her last menses. Her pregnancy test was positive. By the sixth month of pregnancy, she felt irregular contractions of the uterus but no complications were present. After nine months, a healthy, 7 lb., 3 oz girl was delivered with no complications. Breast feeding was planned.

1. What hormonal component is the basis of pregnancy tests?

2. Following the positive pregnancy test, what hormonal mechanism prevented spontaneous abortion of the implanted embryo?

3. What prevented the uterus from initiating labor before the designated delivery time?

4. Describe the positive feedback systems that occur during labor and delivery.

5. What maintains milk production after birth?

6. Is it possible to get pregnant during the time of breast feeding? Explain your answer.

Explanation / Answer

Human chorionic gonadotropic hormone (HCG) which is produced by the trophoblasts and embryo. The uterine lining is preserved by progesterone and thus the endometrium is prevented from shedding and spontaneous abortion is prevented. The levels of progesterone are high till delivery time and this hormone inhibits contractions and prevents the onset of labor. Positive feedback is as following: Contraction of uterus Action potentials are increased in the cervix Cerical dilation due to high levels of oxytocin being released from posterior pituitary Plasma oxytocin increased Uterine contractions are increased 5. The following process maintains milk production after birth: Baby’s suckling Mechanoreceptors to hypothalamus are stimulated This reduces dopamine levels Plasma dopamine levels are reduced Anterior pituitary gland increases the secretion of prolactin Prolactin stimulates milk production Oxytocin stimulates milk ejection 6. Usually no, even if it occurs, it quite rare. Lactase inhibits GnRH and as a result the uterus is not ready to receive an ovum. The follicles don’t develop and implantation does not occur.

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