The Uterine Cycle: Proliferative Phase

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  • 0:07 Uterine Cycle Review
  • 1:24 Endometrial Zones
  • 2:18 Proliferative Phase
  • 5:58 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

A woman's body goes through many changes as it prepares for the possibility of pregnancy. Learn about how the uterus prepares for pregnancy by building up its inner lining during this lesson on the proliferative phase of the uterine cycle.

Uterine Cycle Review

Ever hear the expression 'start with a clean slate'? Well, that's kind of like what the female's uterus is doing during the proliferative phase of the uterine cycle. If you're new to learning about the uterine cycle, let's run through a brief review. The uterine (or menstrual) cycle is a series of monthly changes in the lining of the uterine wall. The uterus undergoes these changes in preparation for the potential of pregnancy. And, like many other cycles, it's split up into different parts. The part we're covering in this lesson is the second of the three phases in the cycle.

The cycle begins with menses. That's when the uterus sheds all of its old tissue from the previous month. This shedding is what creates what I meant by a 'clean slate.' Once all the old tissue is gone, the slate has been wiped clean; it's like new again, ready to be re-used. That brings us to the second phase, the proliferative phase. This is when a new lining of tissue is built back up. This is followed by the last phase, the secretory phase, which just kind of puts on the finishing touches. All of these phases involve only one of the many layers in the uterus - the innermost layer, the endometrium.

Endometrial Zones

The basilar zone is like the foundation of the endometrium.
Basilar Zone

The endometrium is further divided into layers of its own, the functional and basilar zones. The basilar zone is like the anchor; it attaches the endometrium to the layer beneath it. This is where all the resources for the rebuilding of the uterine lining come from. You can think of it like the foundation, on top of which is built the next layer of the endometrium, the functional zone. This is the part of the endometrium that changes the most during the uterine cycle. This is the layer that is shed during menses and rebuilt during the proliferative phase.

While the functional zone undergoes all those changes, the basilar zone stays pretty much the same, but that doesn't mean it's not important. Like I said, it's the foundation, and from the foundation comes all the things needed for the rebuilding of the functional zone.

Proliferative Phase

So, let's talk about that rebuilding. First, the functional zone from the previous month is shed during menses, leaving the basilar zone underneath exposed. Then the rebuilding process begins. You can think of it like the building of a house. All houses are built on a foundation, right? Well, that's our basilar zone. It's the foundation that anchors the house to the ground. And, the ground? Well, that's kind of like the myometrium.

The early stages of rebuilding begin with estrogen from the ovaries. And, just like construction workers have a lot of different jobs while building a house, estrogen also has a couple different jobs. Estrogen stimulates:

  • repair of the functional zone
  • growth of the functional zone
  • increased vascularization (that's just increased numbers of arteries or veins) in the functional zone
  • increased number of mucus and uterine glands

Rebuilding starts with the multiplication of uterine glands within the basilar zone. Then, the functional zone increases in thickness, like walls being added to a house. It becomes highly vascularized as arteries from the basilar zone grow into the functional zone. These arteries are going to provide nutrition and blood supply to the functional zone tissue.

By the later stages of the proliferative phase, the functional zone is several millimeters thick thanks to the addition of various glands within the tissue. Mucous glands form and extend downward toward its border with the basilar zone, while uterine glands enlarge and start to coil. They also secrete a mucus substance rich in the carbohydrate glycogen. Glycogen is needed just in case a fertilized egg implants in the uterus. Glycogen stores the sugar glucose, so it provides a good source of energy for the developing egg, also called an embryo.

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