Human Physiology, 14th edition (2016)

752 Chapter 20

1. Androgens, primarily DHEAS, secreted by the fetal
   adrenal cortex are converted into estrogen by the
   placenta.


2. Estrogen secreted by the placenta induces oxytocin
   synthesis, enhances uterine sensitivity to oxytocin, and
   promotes prostaglandin synthesis in the uterus. These
   events culminate in labor and delivery.
   E. The high levels of estrogen during pregnancy, acting
   synergistically with other hormones, stimulate growth and
   development of the mammary glands.

1. Prolactin (and the prolactin-like effects of hCS) can

stimulate the production of milk proteins. Prolactin

secretion and action, however, are blocked during

pregnancy by the high levels of estrogen secreted by the

placenta.

2. After delivery, when estrogen levels fall, prolactin

stimulates milk production.

3. The milk-ejection reflex is a neuroendocrine reflex. The

stimulus of suckling causes reflex secretion of oxytocin.

This stimulates contractions of the lactiferous ducts and

the ejection of milk from the nipple.

Test Your Knowledge

Match these:

1. Menstrual phase


2. Follicular phase


3. Luteal phase


4. Ovulation


5. A person with the genotype XO has

a. ovaries. c. both ovaries and testes.

b. testes. d. neither ovaries nor testes.

6. An embryo with the genotype XX develops female
   accessory sex organs because of
   a. androgens. c. lack of androgens.
   b. estrogens. d. lack of estrogens.


7. In the male,

a. FSH is not secreted by the pituitary.

b. FSH receptors are located in the Leydig cells.

c. FSH receptors are located in the spermatogonia.

d. FSH receptors are located in the Sertoli cells.

8. The secretion of FSH in a male is inhibited by negative
   feedback effects of
   a. inhibin secreted from the tubules.
   b. inhibin secreted from the Leydig cells.
   c. testosterone secreted from the tubules.
   d. testosterone secreted from the Leydig cells.


9. Which of these statements is true?

a. Sperm are not motile until they pass through the

epididymis.

b. Sperm require capacitation in the female reproductive

tract before they can fertilize an ovum.

c. A secondary oocyte does not complete meiotic division

until it has been fertilized.

d. All of these are true.

a. High estrogen and

progesterone; low FSH and

LH

b. Low estrogen and

progesterone

c. LH surge

d. Increasing estrogen; low LH

and low progesterone

REVIEW ACTIVITIES

10. The corpus luteum is maintained for the first 10 weeks of
    pregnancy by
    a. hCG. c. estrogen.
    b. LH. d. progesterone.


11. Fertilization normally occurs in
    a. the ovaries.
    b. the uterine tubes.
    c. the uterus.
    d. the vagina.


12. The placenta is formed from
    a. the fetal chorion frondosum.
    b. the maternal decidua basalis.
    c. both a and b.
    d. neither a nor b.


13. Uterine contractions are stimulated by
    a. oxytocin. d. both a and b.
    b. prostaglandins. e. both b and c.
    c. prolactin.


14. Contraction of the mammary glands and ducts during the
    milk-ejection reflex is stimulated by
    a. prolactin. c. estrogen.
    b. oxytocin. d. progesterone.


15. If GnRH were secreted in large amounts and at a constant
    rate rather than in a pulsatile fashion, which of these
    statements would be true?
    a. LH secretion will increase at first and then decrease.
    b. LH secretion will increase indefinitely.
    c. Testosterone secretion in a male will be continuously high.
    d. Estradiol secretion in a woman will be continuously high.


16. The contents of the birth control pill
    a. inhibit secretion of gonadotropins.
    b. exert negative feedback on the hypothalamus.
    c. prevent ovulation.
    d. maintain the endometrium.
    e. All of these.