which wall of the uterus is made of smooth muscle
Myometrium The myometrium is the middle layer of the uterine wall, consisting mainly of uterine smooth muscle cells (also called uterine myocytes[1]), but also of supporting stromal and vascular tissue.[2] Its main function is to induce uterine contractions.
Relaxin In females, relaxin is produced mainly by the corpus luteum, in both pregnant [1] and nonpregnant[1] females; it rises to a peak within approximately 14 days of ovulation, and then declines in the absence of pregnancy, resulting in menstruation[citation needed]). During the first trimester of pregnancy, levels rise and additional relaxin is produced by the decidua. Relaxin's peak is reached during the 14 weeks of the first trimester and at delivery. It is known to mediate the hemodynamic changes that occur during pregnancy, such as increased cardiac output, increased renal blood flow, and increased arterial compliance. It also relaxes other pelvic ligaments.[6] It is believed to soften the pubic symphysis.