Video Transcript
The figure shows changes in the
endometrium of the uterus during a 28-day menstrual cycle. Which hormone stimulates the
thickening of the uterine lining, endometrium, from day 19 to 28? (A) Testosterone, (B) progesterone,
(C) glucagon, (D) thyroid hormone, or (E) growth hormone.
The pituitary gland is an endocrine
gland that’s located just under the brain. It’s sometimes called the master
gland as it can secrete hormones that have effects on other endocrine glands. In biological females, one of these
endocrine glands that the pituitary gland hormones can target are the ovaries. The pituitary gland secretes
hormones called gonadotropins. In biological females,
gonadotropins regulate the production of the hormones estrogen and progesterone in
the ovaries. Estrogen is involved in the
development of secondary sex characteristics when a person reaches puberty.
In females, this might include the
development of breasts and starting the menstrual cycle. Estrogen also plays a part in
regulating the menstrual cycle, which is shown in the diagram as provided to us by
the question. During the menstrual cycle, an egg
cell is released from one of the ovaries in a process called ovulation. During this time, the uterine
lining, which is otherwise known as the endometrium, thickens to be prepared if an
egg cell is fertilized by a sperm cell. This is because a resulting embryo
if this fertilization occurs will implant into the endometrium. Progesterone is the hormone that’s
responsible for thickening this endometrium layer from day 19 to approximately day
28 of the menstrual cycle.
If pregnancy occurs, progesterone
levels remain high, so the endometrium layer remains thick to support the
development of the baby. However, if fertilization, and
therefore pregnancy, does not occur, then the endometrium is shed through a process
called menstruation or sometimes a period. This begins the menstrual cycle
again, and then the uterine lining will thicken once more as the levels of
progesterone start to increase again. Therefore, we’ve worked out that
the hormone that stimulates the thickening of the uterine lining or the endometrium
during the menstrual cycle is progesterone.
