an organ that pumps blood around the body. In spiders and annelid worms, it is a straight tube. In mollusks, it is a slightly more complex structure with one or more receiving chambers (atria) and a primary pumping chamber (ventricle).
The heart of fish is a folded tube with three or four enlarged regions that resemble the chambers in the heart of a mammal. In amphibians, reptiles, birds, and mammals that have lungs, the heart has undergone several phases of evolution from a single pump to a double pump that circulates blood both to the lungs and throughout the body.
The heart, a four-chambered double pump that is at the center of the circulatory system in humans, other mammals, and birds. In humans, it rests on the diaphragm, the muscle wall separating the chest from the abdomen, which is located between the two lungs and somewhat to the left of center, behind the breastbone.
The myocardial, a thick muscular wall, is made up of numerous layers in the heart. The endocardium lines the inside, and the pericardium, a thin layer of tissue, covers the exterior. The right and left hearts, which are further separated into two chambers, are located on either side of the cavity of the heart.
Komentar