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.
Confidence votes 25.5K. Smiling begins at birth; yet it is more out of natural instinct than to show an outward sign of pleasure. It has been found that this generally occurs at around 2 months of age. Babies smile in the womb, probably just to flex the facial muscles. Smiling to indicate pleasure starts generally around 6-8 weeks. Smiling begins at birth; yet it is more out of natural instinct than to show an outward sign of pleasure. It has been found that this generally occurs at around 2 months of age.  Smiling to indicate pleasure starts generally around 6-8 weeks.