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Breast changes during the menstrual cycle
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The breast is not a static tissue. The mammary gland, which is the part that makes milk, changes across the menstrual cycle and also during pregnancy, and it does so to prepare for lactation.
In the first half of the cycle, the follicular phase, estrogen is in charge. Its high levels make the cells multiply in the ducts, the small tubes that carry milk toward the nipple.
In the second half, midway through the luteal phase, progesterone takes over. The epithelial cells, meaning the cells that line these structures, become larger and taller, and high progesterone triggers the appearance of alveolar buds, the sprouts that will become the sacs where milk is stored.
Think of a pantry that gets stocked before it is needed. After menopause those hormones fall, involution begins, and the breast decreases in size.
In brief
The mammary gland changes across the menstrual cycle and pregnancy, preparing for lactation.
A pantry stocked before it is needed.
In the follicular phase, high estrogen levels stimulate proliferation of the ducts.
Midway through the luteal phase, epithelial cells grow larger and taller, and high progesterone triggers the formation of alveolar buds.
After menopause, the fall in these hormones initiates involution and the breast decreases in size.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingHistology, Mammary Glands, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Thorax: Mammary Gland, StatPearlsPublished
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