Humans have a closed circulatory system. You may remember that in a closed system blood is contained within vessels and that the main components of a closed circulatory system are the heart, blood vessels, and blood.
The heart is a conical, hollow, musculotendinous organ. It lies in the thorax between the lungs and behind the sternum. It’s about 10cm long and weighs about 300 gram. The base of the heart is above and the apex is below. The heart lies in the thorax between the lungs and behind the sternum. Two-thirds of the heart is on the left side. It lies obliquely. It’s directed more towards the left side than on the right side. The apex of the heart lies at the level of 5th intercostals space, 9cm to the left of midline. The base extends to the level of the second rib.
The 3 Layers of Heart:
- The heart is surrounded by an outer covering called pericardium. It contains two layers called visceral pericardium and parietal pericardium. Pericardial fluid is present between these two layers.
- The middle layer is made of heart muscle fibers. It’s called as myocardium
- The inner lining is called as endocardium.
Chambers of the heart:
The Human heart has four chambers: two atria and two ventricles.
- The 2 chambers on the right side are known as Right Atrium, Right Ventricle.
- The 2 chambers on the left side are called Left Atrium, Left Ventricle.
- The 4 chambers are divided by 2 septa, the interatrial septum, and Inter-Ventricular septum.
Valves of the heart:
The heart has 4 valves: they are as follows
- The mitral valve and tricuspid valve, which controls blood flow from the atria to the ventricles.
- The aortic valve and pulmonary valve, which control blood flow out of the ventricles.
Some tendinous cords arise from the lower border of these valves. They’re called chordate tendinae. The chordate tendinae in turn attached to papillary muscle which arises from ventricular walls.
Blood vessels attached to heart:
- the right atrium receives superior vena cava vein and inferior vena cava vein. They carry venous blood to the heart.
- From the right ventricle, arise the pulmonary artery. It carries venous blood to lungs for oxygenation.
- The left atrium receives 4 pulmonary veins. They carry oxygenated blood to the heart.
- From the left ventricle. Arise the aorta. It delivers pure-blood to all parts of the body.
Blood supply to the heart:
The heart receives its blood supply through right and left coronary arteries. They’re the first branches of the aorta. Venous blood heart is collected by the coronary sinus. It opens directly into the right atrium.
Nerve supply to the heart:
The heart is supplied by sympathetic and vagus nerves. Branches from these nerves pass through the sino auricular node.