Video Transcript
What structure secretes
progesterone during the last five months of pregnancy? (A) Embryo, (B) corpus luteum, (C)
graafian follicle, (D) placenta, (E) pituitary gland.
This question is asking us to
recall the function of the hormone progesterone in pregnancy and the structure that
secretes it.
Let’s start by reviewing what we
know about the hormones involved in the maintenance of pregnancy and the structures
that produce them. After fertilization, there are
several hormones that help support the implanted embryo and the continuation of
pregnancy. These hormones include human
chorionic gonadotropin or hCG, progesterone, and estrogen.
In the early stages of pregnancy,
hCG is produced by the cells that are surrounding a growing embryo that eventually
form the placenta. hCG is partly responsible for maintaining the endometrial
thickness throughout pregnancy. hCG also ensures that the corpus luteum, a temporary
structure in the ovary, continues to secrete progesterone at the beginning of
pregnancy.
Progesterone plays an important
role during pregnancy by preventing the uterus from contracting and by increasing
blood flow to the uterus. After the fourth month of
pregnancy, the corpus luteum breaks down. And the placenta takes over the
role of secreting progesterone for the remaining months of pregnancy. The placenta also secretes
estrogen. During pregnancy, estrogen
increases vascularization, or the formation of blood vessels in the uterus, which
helps support the developing fetus. So while the corpus luteum secretes
progesterone in the first four months of pregnancy, in the later stages of
pregnancy, it is the placenta that takes over secreting progesterone.
Now that we have reviewed the
hormones involved in the maintenance of pregnancy and the structures that produce
them, we are ready to answer the question. The structure that secretes
progesterone during the last five months of pregnancy is the placenta.
