Video Transcript
Which hormone, released by the pituitary gland, stimulates ovulation?
You might recall that ovulation refers to the release of a mature egg from a follicle
in the ovary. So let’s review this process and the menstrual cycle before returning to our
question.
This diagram has a lot of information in it, so let’s break it down. On the bottom, we can see the day of the menstrual cycle. A typical menstrual cycle lasts 28 days, with ovulation occurring around day 14. Above this, we see in the diagram the thickness of the uterine lining. During the menstrual cycle, the uterine lining gets thicker to create an environment
that’s suitable for the embryo to implant. During cycle days one to five, menstruation occurs. This is where the lining breaks down if an embryo does not implant.
Above the diagram of the uterine lining, we see different hormones that regulate the
menstrual cycle. We’ll talk about these in a moment. And on the top, we see the development of an egg from a follicle, which is released
at ovulation. The remaining empty follicle forms the corpus luteum, which secretes hormones that
participate in the menstrual cycle.
Now let’s focus on these hormones that regulate the menstrual cycle to answer our
question. The process begins with the secretion of follicle-stimulating hormone, or FSH, from
the anterior pituitary gland. FSH levels increase during menstruation, which causes a follicle, containing an egg
cell, within the ovary to develop. The developing follicle produces estrogen, which we can see increasing here. This causes the uterine lining to thicken or proliferate. This stage of the menstrual cycle is called the proliferation phase.
As estrogen is produced by the developing follicle, it inhibits the production of
FSH. You can see that here as the green line that represents FSH decreases while the red
line that represents estrogen increases. Estrogen also stimulates the secretion of another hormone called luteinizing hormone,
or LH, from the pituitary gland. You can see how estrogen levels, shown in red, peak at the same time as LH, shown in
yellow. When this happens, it causes the follicle to release the egg from its follicle, which
we can see here. This is called ovulation.
With the egg cell released from the follicle, the empty follicle can develop into the
corpus luteum. This structure secretes progesterone, shown in blue. The rest of the menstrual cycle is known as the secretory phase. Progesterone maintains the thickness of the uterine lining so an embryo can implant,
if one is produced from the egg that was released earlier. If an embryo implants, then pregnancy occurs and the menstrual cycle is paused until
after pregnancy. If one does not implant, then the corpus luteum degrades and progesterone levels
fall, which we can see here. Without progesterone, the thick uterine lining cannot be maintained and menstruation
occurs. FSH levels can also begin to rise again and the menstrual cycle repeats.
So, to go back to our question, the hormone that’s released by the pituitary gland
that stimulates ovulation is luteinizing hormone, or LH.
