Uterine contractions in non-pregnant and pregnant state

70  Abstract— Uterine contractions are important in many reproductive functions including the transport of sperms and embryo, menstruation, pregnancy and parturition. Improper or irregular uterine activity may underlie the common pathological disorders such as infertility, improper implantation, preterm labor, and weak uterine contraction during labor. In addition, successful labor is controlled by the coordinated activity and harmony between the uterine smooth muscle cells. If however, this activity becomes too weak or strong, normal labor may not be progressed which could lead to fetal morbidity and mortality. Uterine contraction is generated by shortening of uterine smooth muscle cells. Calcium ion is the key regulatory factor for this contraction to occur and its influx into the cell is initiated predominantly by depolarization of myometrial cell membrane. The transient increase in intracellular calcium concentration initiates cycles of myometrial contraction and relaxation. Basically, uterine contraction depends heavily on intracellular calcium concentration and any alteration of this concentration could affect the strength of uterine activity. This review presents an overview of the physiology of myometrial contraction and the role of calcium ions during contraction and relaxation.