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.
Early in your first trimester, perhaps as early as eight weeks, you may feel dizzy and nauseous, because of low blood pressure. This happens because the pregnancy hormone progesterone relaxes the walls of your blood vessels, causing your blood pressure to fall (Bothamley and Boyle 2009). In the second and third trimesters, your growing uterus (womb) tends to put pressure on your blood vessels. This can also make you feel dizzy.