HEART
The heart is a powerful muscle that pumps blood throughout the body by means of a coordinated contraction. It is the organ that controls the flow of blood in the body, or the center of human emotion.
What are the functions of the heart?
Right-Hand Side of the Heart
The right-hand side of the heart receives de-oxygenated blood from the body tissues (from the upper- and lower-body via the superior vena cava and the inferior vena cava, respectively) into the right atrium. This de-oxygenated blood passes through the tricuspid valve into the right ventricle. This blood is then pumped under higher pressure from the right ventricle to the lungs via the pulmonary artery.
Left-Hand Side of the Heart
The left-hand side of the heart receives oxygenated blood from the lungs (via the pulmonary veins) into the left atrium. This oxygenated blood then passes through the bicuspid valve into the left ventricle. It is then pumped to the aorta under greater pressure (as explained below). This higher pressure ensures that the oxygenated blood leaving the heart via the aorta is effectively delivered to other parts of the body via the vascular system of blood vessels (incl. arteries, arterioles, and capillaries).
The heart structure
The heart consists of four chambers, right and left atria above right and left ventricles. The functions of each part are as follows.
• The right atrium links to the right ventricle by the tricuspid valve. This valve prevents back flow of the blood into the atrium above, when the ventricle contracts.
• The left atrium links to the left ventricle by the bicuspid valve (mitral valve). This also prevents back flow of the blood into the atrium above.
• The chordae tendonae attach each ventricle to its atrioventricular valve. Contractions of the ventricles have a tendency to force these valves up into the atria. Back flow of blood would be dangerous, so the chordae tendonae hold each valve firmly to prevent this from occurring.
• Semi-lunar (pocket) valves are found in the blood vessels leaving the heart (pulmonary artery and aorta). They only allow exit of blood from the heart through these vessels following ventricular contractions. Elastic recoil of these arteries and relaxation of the ventricles closes each semi-lunar valve.
• Ventricles have thicker muscular walls than atria. When each atrium contracts it only needs to propel the blood a short distance into each ventricle.
• The left ventricle has even thicker muscular walls than the right ventricle. The left ventricle needs a more powerful contraction to propel blood to the systemic circulation (all of the body apart from the lungs). The right ventricle propels blood to the nearby lungs. The contraction does not need to be so powerful.
HOMEWORK
On your own try to label the diagram bellow and compare with the images above.
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