Menstrual Cycle 201: The Uterine Cycle

Your period is just the beginning (literally). 

Welcome to Part 2 of our Menstrual Cycle series. Last time, we took you deep into the phases of the ovarian cycle. But, that’s only half of the story. This week, we’re picking up with the Uterine Cycle, clearing up any lingering questions about menstruation you might have. 

Here’s a quick anatomy refresher to reference as we talk through what's happening during the cycle.

Remember!
On average, the normal menstrual cycle lasts 21 to 35 days, with most people’s cycles lasting an average of 28-29 days. It begins on the first day of your period and ends the day before your next period starts! Remember, though, if you’re close to menarche (your first period) or menopause (your last period), your cycle length can vary much more.

The Uterine Cycle:

The uterine cycle acts simultaneously to the ovarian cycle, mutually dependent on the other to regulate the body’s hormones, maintain the health of the reproductive system, and prepare the body for a potential pregnancy. The uterine cycle's most notable aspect is the growth and shedding of the endometrium (the lining of the uterus). 

Menstruation:

When:

The first day of your menstrual cycle is day 1 of your period. The average period lasts 5-6 days, but can last up to 8.

What:

The endometrium, has thickened to create a suitable environment for a potential fertilized egg. As estrogen and progesterone levels drop, blood flood to the endometrium dwindles, and it begins to shed and break down. This shedding makes up the period, wherein blood, mucus, and tissue from your uterus is shed through your cervix and out your vagina. Because of this the endometrium is at its thinnest during this stage.

Though menstruation can be frustrating, it is an important physical signal the body can send to us that our complex hormonal systems are functioning as they should.

Proliferative:

When:

This stage begins after the period and ends at ovulation. On average, that would be days 5-14. It is at the same time as the second half of the follicular phase. 

What: 

With the rise of estrogen in the body, the endometrium begins to renew after menstruation. It thickens and the blood flow through it increases to create the right environment for a potential fertilized egg. Granulation tissue, which helps with wound healing all over the body, also assists in the rebuilding of the endometrium.

The Secretory Phase:

When: 

The secretory phase occurs after ovulation. It continues until the day before the period begins. It occurs simultaneously with the luteal phase.

What: 

The progesterone from the corpus luteum speeds up the development of the endometrium. It becomes more glandular and vascular, with its glands secreting nutrients and mucus for a potential pregnancy. 

The cervical mucus becomes thicker to prevent sperm or pathogens from entering after the fertile window of ovulation.

When the corpus luteum breaks down and hormones dip, the endometrium starts to break down again, leading us back to the beginning of the cycle.