Fimbriae (common pili) and flagella on the surface of bacterial cells. Left: dividing Shigella enclosed in fimbriae. The structures are probably involved in the bacterium's ability to adhere to the intestinal surface. Right: dividing pair of Salmonella displaying both its peritrichous flagella and its fimbriae.
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.
As estrogen begins to stimulate uterine contractions, the uterus also produces hormones called prostaglandins. These also contribute to a decrease in progesterone levels. The release of prostaglandins helps initiate labor and, along with another hormone called relaxin, relaxes the muscles of the cervix.ut once labor is complete and the baby is no longer in the birth canal, the cervix is not being stretched anymore. This lack of the physical signal of stretching is what stops the positive feedback loop, and labor comes to an end.