Final answer:
The type of contractions Mary is experiencing in her uterus are caused by the involuntary smooth muscle called the myometrium and are controlled by the nervous system. These contractions are part of the natural childbirth process to help deliver the baby.
Step-by-step explanation:
Mary is pregnant and the contractions she is experiencing are an important part of the childbirth process. The uterus consists of smooth muscle, which is involuntary. The nervous system controls its contraction. These contractions are critical for moving the baby through the cervix and vagina during labor. The myometrium is the layer of the uterus that contains the muscle fibers responsible for these contractions. These muscle fibers run in various directions, allowing for the powerful contractions needed for both labor and menstrual periods.
The stages of childbirth include cervical dilation, expulsion of the newborn, and afterbirth. The contractions are known as true labor, which gets more powerful and frequent over time. These contractions are stimulated by the stretching of the myometrium and cervix when the baby is in a head-down position, triggering the labor process.