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The heart is a muscular organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek ?a?d??, kardia, for "heart." The heart of a vertebrate is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during a lifetime (about 66 years). The mammalian heart is derived from embryonic mesoderm germ-layer cells that differentiate after gastrulation into mesothelium, endothelium, and myocardium. Mesothelial pericardium forms the inner lining of the heart. The outer lining of the heart, lymphatic and blood vessels develop from endothelium. Myocardium develops into heart muscle.[1] From splachnopleuric mesoderm tissue, the cardiogenic plate develops cranially and laterally to the neural plate. In the cardiogenic plate, two separate angiogenic cell clusters form on either side of the embryo. Each cell cluster coalesces to form an endocardial tube continuous with a dorsal aorta and a vitteloumbilical vein. As embryonic tissue continues to fold, the two endocardial tubes are pushed into the thoracic cavity and begin to fuse together and are completely fused at approximately 21 days.[2]
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Heart Subcategories
Heart Articles
Home is Where the Heart is
by Wedding Star
Nov 07, 2008
Heralding the ultimate in charm and romance, as well as a practical money saving solution, the search for the perfect wedding venue can sometimes end outside your own front door.
Whether you choose the home you currently live in, your family ...
Tips for Selecting Wedding Musicians
by Gail Leino
Jan 31, 2006
Planning a wedding celebration can be crazy, fun, and overwhelming all at once! So many decisions, so little time. Menu? Decorations? Flowers? Wedding Invitations? Bridal Showers? Music? Lets focus on the music and share suggestions to ensure a succe...
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