<span>The ventricles are the part of the heart that are responsible for the pumping action to move blood throughout the body. Therefore, the muscles in the ventricles are much larger and thicker to do their job properly. The atrium only has to pump blood through an open valve (the tricuspid valve) into the right ventricle. There is much less resistance to this flow of blood so much less muscle is needed. </span>
The process that is responsible for causing menstruation is called menstrual cycle. Menstrual cycle is the natural change that occurs specifically in the ovaries and uterus or in the female reproductive system that gives possibility to pregnancy. This process is required for the ovocytes to be produced, and also for the uterus to be prepared for pregnancy.
Maintenance of homeostasis usually involves negative feedback loops. These loops act to oppose the stimulus, or cue, that triggers them.