heart
The heart is a hollow muscular organ. ... The heart is protected in the front by the ribs and in the back by the vertebrae. The average adults heart is about the same size or a little bigger than their fist weighing about nine to eleven ounces. A newborn baby’s heart weighs about two thirds an ounce. Three layers of tissue make up the heart. A membrane called the pericardium is the covering of the of the heart it surrounds the epicardium. ... It is also the thickest layer of tissue in the heart. The inner layer of the heart is called the endocardium. ... The inside of the heart consists of four major chambers. ... The heart has four valves. ... The steady pumping of the heart supports life by moving blood through the body. Transportation of nutrients and oxygen from the heart to the cells is the main function of the heart. The heart also helps waste to be eliminated. The heart is used as a muscular pumping device for distributing blood to all parts of the body. When the heart is pumping or beating this means it is working. ... When the heart is relaxing or not working it is called diastole.