Heart - Blood, The Multiform Heart, The Human Heart, Regulation Of The Heart, Embryonic Development Of The Human Heart
vessel hearts body lower
A heart is a means to circulate blood through the body of an animal. Among the lower species such as insects, arachnids, and others, the heart may simply be an expanded area in a blood vessel and may occur a number of times. The earthworm, for example, has 10 such "hearts." These areas contract rhythmically to force the blood through the aorta, or blood vessel.
Not until the evolution of the higher vertebrates does the heart achieve its ultimate form, that of a chambered organ with differentiated purposes. Even the lower chordates, such as amphioxus, possess hearts not more advanced than those in the earthworm. It is simply a pulsating blood vessel that moves blood through the body.
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The heart is a pulsating organ that pushes a liquid medium throughout the body. It may be as simple as one chamber or as complex as four chambers, as in the higher mammals. In all animals, however, it is an organ that must function day after day without pause to keep the blood moving. In general, blood that returns from the body or from the oxygen exchanging structures returns to an atrium, which …
Located in the thoracic cavity, the heart is a four-chambered muscular organ that serves as the primary pump or driving force within the circulatory system. The heart contains a special form of muscle, appropriately named cardiac muscle, that has intrinsic contractility (i.e., is able to beat on its own, without nervous system control). The Chinese were aware more than 2,000 years ago that the hea…
Various intrinsic, neural, and hormonal factors act to influence the rhythm control and impulse conduction within the heart. The rhythmic control of the cardiac cycle and its accompanying heartbeat relies on the regulation of impulses generated and conducted within the heart. Regulation of the cardiac cycle is also achieved via the autonomic nervous system. The sympathetic and parasympathetic divi…
The developing fetal heart accounts for a large percentage of the volume of the early thorax. About 20 days after fertilization, the heart develops from the fusion of paired endothelial tubes into a single tube. Heart growth subsequently involves the growth, expansion, and partitioning of this tube into four chambers separated by thickened septa of cardiac muscle and valves. Atrial development is …
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