The Logistics of Childbirth: Understanding the Uterine Muscle
The uterus is an incredible organ! It is capable of not only making a baby, but then birthing a baby! After is completes the child birthing process, it then returns to its usual state and waits to see if you want to do it all over again. No big deal, right?
For today, let's focus on how the uterus decides it's time to birth the baby and how it is able to initiate the process of labor.
The uterus is composed of smooth muscle tissue. Smooth muscle tissue contains cells called myocytes. These cells are what help facilitate movement, otherwise known as contractility, of the muscle.
Most muscle tissue relies on interaction with the central nervous system in order to begin moving the muscle but the uterus is special! The uterus does not contract as one large muscle, it is the individual myocytes within the uterus that contract independently of eachother other. They are individually triggered by hormones and by other forms of communication that happen more centralized to the uterine muscle.
In order for labor to progress, the uterus does need to eventually contract as one whole muscle. You may now be wondering how do the myocytes within the uterus communicate with each other to make this happen?
For example’s sake, let's say you make incredible chocolate chip cookies. It's your friend’s birthday and you decide to make them cookies. They love your cookies so much that they ask for the recipe. They make their friend cookies using your recipe and the same thing repeats. This cycle repeats itself, and before you know it the whole town has your recipe in their recipe book.
Myocytes operate in a similar fashion. Once one myocyte decides to begin contracting, it will signal to the surrounding myocytes in the uterine muscle and they too may decide to start contracting.
As pregnancy progresses, hormone production increases and adjusts and by week 40, the body is producing a concoction of hormones that encourage myocyte activity. When this happens, it can easily excite all of the myocytes within the uterus and before you know it, they are all contracting simultaneously and labor has commenced.
Young, K. A., Wise, J. A., DeSaix, P., Kruse, D. H., Poe, B., Johnson, E., Johnson, J. E., Korol, O., Betts, G. J., & Womble, M. (2013). Anatomy and Physiology by OpenStax (hardcover version, full color) (1st ed.). XanEdu Publishing Inc.
Young, R. (1997). Paracrine and Intracellular Signaling Mechanisms of Calcium Waves in Cultured Human Uterine Myocytes. Obstetrics & Gynecology, 90(6), 928–932. https://doi.org/10.1016/s0029-7844(97)00498-5
Photo Credit: C, T. (2018, September 20). Uterus during Pregnancy. FirstCry Parenting. https://parenting.firstcry.com/articles/uterus-during-pregnancy-everything-you-need-to-know/