Video Transcript
The diagram provided shows the changes in the concentrations of the pituitary gland
hormones over a typical 28-day menstrual cycle. What hormone is indicated by the purple line?
This question is asking us about the menstrual cycle. The menstrual cycle is a process that releases a mature egg and prepares the female
body for pregnancy. This 28-day cycle can be broken up into different stages. Let’s discuss each of these stages to answer our question.
The menstrual cycle begins with menstruation on cycle days zero to five. This is when the uterine lining from the previous cycle is shed. During menstruation, the pituitary gland begins secreting follicle-stimulating
hormone, also known as FSH, which stimulates the development of a follicle from the
ovaries. This follicle contains an egg cell. The green line in this graph represents FSH levels over the course of the menstrual
cycle.
The next stage is called the proliferative phase and occurs between cycle days six to
14. During the proliferative phase, the developing follicle begins to secrete
estrogen. Estrogen has two roles. It stimulates the cells of the uterine lining to proliferate and thicken, which is
why this phase is called the proliferative phase. And it stimulates the secretion of another hormone called luteinizing hormone, or LH,
from the pituitary gland. The purple line indicated on the graph is LH, and you can see it peak around day
14. This LH surge causes the follicle to release the egg during a process called
ovulation. This occurs around day 14.
The final stage is called the secretory phase and occurs between cycle days 14 to
28. During the secretory phase, the leftover follicle that once contained the egg becomes
a structure called the corpus luteum. The corpus luteum secretes progesterone, which is a hormone that maintains a thick
uterine lining. If an embryo doesn’t implant and pregnancy doesn’t occur, then the corpus luteum
degrades and progesterone levels fall. This causes the lining to shed and the cycle to repeat.
So, to answer our question, the purple line indicated in the graph represents
luteinizing hormone, or LH.
