Systole Reference Libraries
The heart is a part of the circulatory system, and is considered one of the most vital organs of the human body. It is about the size of a fist, has a mass of approximately 300 grams, and its main function is to contract and produce enough pressure to circulate blood throughout the body. The top of the heart where the veins and arteries all connect is called the base. The pointed lower tip of...
- Having no light.
- Of or relating to the region of a body of water that is not reached by sunlight and in which photosynthesis is unable to occur.