It may be a straight tube, as in spiders and annelid worms, or a somewhat more elaborate structure with one or more receiving chambers (atria) and a main pumping chamber (ventricle), as in mollusks. Heart, organ that serves as a pump to circulate the blood. The two distinct sounds are heard, a low, slightly prolonged “lub” (first sound) occurring at the beginning of ventricular contraction or systole and a sharper, higher-pitched “dup” (second sound), caused by the closure of aortic and pulmonary valves at the end of systole. The rhythmic noises accompanying the heartbeat are called heart sounds. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!. ![]() Learn about the major environmental problems facing our planet and what can be done about them!
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |