The human circulatory system consists of:
1. Muscular pump; the heart
2. A transport medium; blood
3. Conduits for transporting blood; blood vessels
A circulatory system is required to transport useful substances to where they are needed and waste material to where they can be excreted. Oxygen is transported to all the cells of the body as all cells require oxygen to produce energy in the form of ATP from glucose.
The Heart
External Structure of the Heart
Internal Structure of The Heart
The heart is a four chambered muscular pump which is located behind the sternum in the thoracic cavity. Your heart is the size of your fist and usually extends from the 2nd to the 6th rib. The apex of the heart is slightly shifted to the left and thus a heart beat can be detected there. The heart is made up of cardiac muscle which contracts to force blood through blood vessels. The right side of the heart deals with deoxygenated blood and the left side deals with oxygenated blood.
Structure of the Heart
1. Atria
· The two upper thin walled chambers are called atria.
· The right atrium receives deoxygenated blood from the inferior and superior vena cava and then pumps it into the right ventricle.
· The left atrium receives oxygenated blood from the pulmonary veins which carry blood from the lungs to the heart.
· The right atrium is larger than the left atrium. Why?
2. Ventricles
· The two lower, larger thick walled chambers are called ventricles.
· The right ventricles receive blood from the right atrium and then pump it into the pulmonary artery which carries blood from the heart to the right and left lungs.
· The left ventricles receive blood from the left atrium and then pumps it into the aorta which transports oxygenated blood to the rest of the body.
· The left ventricle is thicker than the right ventricle as it needs more cardiac muscle to pump blood to the entire body under great pressure as opposed to the right ventricles that pumps blood the delicate lungs nearby.
3. Valves-ensure that blood flows in one direction.
Structure of Valves
· The atrioventricular valves (tricuspid and bicuspid valves) separate the atria from the ventricles.
· The right atrioventricular valve is called the tricuspid valves and it closes when the right ventricle contract to prevent back flow of blood into the right atrium.
· The tricuspid valves consist of three cup like flaps which shut tight when the papillary muscles contract.
· The bicuspid valve (mitral valve) which consists of two cup like flaps is between the left atrium and the left ventricle. It closes when the left ventricle contracts to prevent back flow of blood into the left atrium.
· The semi lunar valves are located in the aorta and the pulmonary artery. These are two half moon shaped valves that prevents backflow of blood when the ventricles relax right after contracting.
· The chordinae tendinae connects valves to walls of the heart and work with papillary muscles to open and close valves.
4. Associated blood vessels
· There are two large veins (superior and inferior vena cava) and small pulmonary veins associated with the heart.
· The inferior vena cava empties deoxygenated blood from the brain and upper limbs into the right atrium.
· The superior vena cava empties deoxygenated blood from the lower body into the right atrium
· The pulmonary veins empty oxygenated blood coming from the lungs into the left atrium.
· The arteries associated with the heart include the aorta and pulmonary artery.
· The pulmonary artery transport deoxygenated blood from the right ventricle to the left and right lungs to be oxygenated.
· The aorta is the largest artery in the body and transports oxygenated blood under great pressure from the left ventricle to the rest of the body.
· The coronary arteries branches from the aorta and they supply the walls or cardiac muscle with oxygenated blood.
· The coronary veins carry deoxygenated blood from the cardiac muscle to the right atrium.
· The septum separates the left side from the right side of the heart
