Many eukaryotes have long slender motile cytoplasmic projections, called flagella , or similar structures called cilia . Flagella and cilia are sometimes referred to as undulipodia ,  and are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin . These are entirely distinct from prokaryotic flagellae. They are supported by a bundle of microtubules arising from a centriole , characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or mastigonemes , and scales connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm .
Although gonadotropins are secreted in a pulsatile manner (as a result of pulsatile GnRH release), unlike the case of GnRH and GnRH agonists , constant/non-pulsatile activation of the gonadotropin receptors by the gonadotropins does not produce functional inhibition. This can be seen during the first 7–10 weeks of pregnancy, where constantly high and progressively-increasing levels of hCG circulate and mediate production of estrogen and progesterone by the corpus luteum until the placenta takes over the production of these hormones.