Human Reproduction ❮ 209If a blastocyst does not implant, production of estrogen or progesterone from the corpus
luteum will cease, causing the destruction of the endometrium.
This cycle of hormonal activity is known as the menstrual cycle.A woman repeats this
cycle, on an average, every 28 days. This cycle is disrupted when a sperm fertilizes the egg
and successful implantation occurs. During pregnancy, hormone levels in the body change
as a result of the presence of the corpus luteum, which maintains constant levels of estro-
gen and progesterone. This halts ovulation for the remainder of the pregnancy. If a sperm
does not fertilize the egg, however, negative feedback reduces the levels of LH and FSH and
leads to the deterioration of the endometrium, which then sloughs off during the menstrual
cycle. When the levels of hormones circulating in the blood drop low enough, the cycle will
begin again with the release of LH and FSH, culminating in the next menstrual cycle.
In males, as in females, GnRH causes the pituitary to release LH and FSH. The LH
causes the continual production of testosterone in men. FSH and testosterone work
together to assist the maturation of sperm produced during spermatogenesis. The baseline
levels of testosterone are vital to the development of secondary sex characteristics in men.For questions 1–4, please use the following answer
selections:
A. Blastula
B. Morula
C. Somite
D. Trophoblast
E. Hypoblast- After the fourth cleavage division, the one cell
has become 16 cells and is now given this name. - Gives rise to the yolk sac of the developing embryo.
- Forms the placenta for the developing fetus.
- Gives rise to the muscles and vertebrae in
mammals. - Which of the following is not a structure involved
in the ejaculation of sperm?
A. Epididymis
B. Seminal vesicles
C. Cervix
D. Vas deferens
E. Interstitial cells - Which of the following hormones feeds back to
cause the LH surge of the menstrual cycle?
A. Estrogen
B. Progesterone
C. FSH
D. LH
E. GnRH
7. Which of the following structures is notderived
from the endoderm of a developing embryo?
A. Liver
B. Thyroid
C. Heart
D. Bladder
E. Lungs
For questions 8–11, please use the following answer
selections:
A. FSH
B. LH
C. Testosterone
D. Estrogen
E. hCG
8. This hormone ultimately triggers ovulation in
females.
9. This hormone is produced in the interstitial cells.
10.This hormone is responsible for maintenance of
the corpus luteum during early pregnancy.
11.This hormone works with testosterone to assist
in maturation of the sperm produced during
spermatogenesis.
Review Questions
http://www.ebook3000.com