The heart is a hollow, muscular organ about the size of a closed fist. Located between the lungs in the mediastinum, it’s about 12.5 cm (5”) long and 9 cm (3½”) in diameter at its widest point. It weighs between 250 and 285 g (8.8 and 10 oz).
Where’s your heart?
The heart spans the area from the second to the fifth intercostal space. The right border of the heart lines up with the right border of the sternum. The left border lines up with the left midclavicular line. The exact position of the heart may vary slightly with each patient. Leading into and out of the heart are the great vessels:
• inferior vena cava
• superior vena cava
• pulmonary artery
• four pulmonary veins.
Slip and slide
A thin sac called the pericardium protects the heart. It has an inner, or visceral, layer that forms the epicardium and an outer, or parietal, layer. The space between the two layers contains 10 to 30 ml of serous fluid, which prevents friction between the layers as the heart pumps.
The heart has four chambers - two atria and two ventricles - separated by a cardiac septum. The upper atria have thin walls and serve as reservoirs for blood. They also boost the amount of blood moving into the lower ventricles, which fill primarily by gravity.
Blood moves to and from the heart through specific pathways. Deoxygenated venous blood returns to the right atrium through three vessels:
superior vena cava - returning blood from the upper body
inferior vena cava - returning blood from the lower body
coronary sinus - returning blood from the heart muscle
Get some fresh air
Blood in the right atrium empties into the right ventricle and is then ejected through the pulmonary valve into the pulmonary artery when the ventricle contracts. The blood then travels to the lungs to be oxygenated.
Share the wealth
From the lungs, blood travels to the left atrium through the pulmonary veins. The left atrium empties the blood into the left ventricle, which then pumps the blood through the aortic valve into the aorta and throughout the body with each contraction. Because the left ventricle pumps blood against a much higher pressure than the right ventricle, its wall is three times thicker.
Valves in the heart keep blood fl owing in only one direction through the heart. Think of the valves as traffic police at the entrances to one-way streets, preventing blood from travelling the wrong way despite great pressure to do so. Healthy valves open and close as a result of pressure changes within the four heart chambers.
The heart has two sets of valves:.
atrioventricular (AV) (between atria and ventricles) – tricuspid valve on the heart’s right side and mitral valve on its left
semilunar – pulmonary valve (between the right ventricle and pulmonary artery) and aortic valve (between the left ventricle and aorta).
On the cusp
Each valve has cusps (leaflets), which are anchored to the heart wall by cords of fibrous tissue (chordae tendineae). The cusps of the valves act to maintain tight closure. The tricuspid valve has three cusps, the mitral valve has two cusps and each of the semilunar valves has three cusps
Excerpted from Medical-Surgical Nursing Made Incredibly Easy UK Edition