The Circulatory System and Heart Structure

• The circulatory system is an organ system responsible for transporting oxygen and nutrients throughout the body
• The circulatory system relies on the blood, blood vessels, and the heart to move oxygen and nutients around the body
• The circulatory system operates as a double circulatory system, with two distinct loops
• One loop carries deoxygenated blood from the heart to the lungs for oxygenation and then back to the heart
• The second loop carries oxygenated blood from the heart to the rest of the body, where it delivers oxygen

Heart Structure

• The heart comprises four chambers with thick muscular walls
• Veins and arteries are connected to the heart chambers for blood flow
• When viewing a diagram of the heart, the left appears on the right and vice versa, as if viewing another person
• The top two chambers of the heart are called atria (singular: atrium)
• The bottom two chambers of the heart are called ventricles
• Valves are located between the chambers and vessels to prevent backflow of blood

Blood Flow

• Blood enters the heart via the vena cava and the pulmonary vein
• The right atrium receives blood from the vena cava, which carries deoxygenated blood from the body
• The left atrium receives blood from the pulmonary vein, which carries oxygenated blood from the lungs
• As the atria contract, they push blood into the ventricles
• The ventricles then contract and push blood out into the pulmonary artery
• Blood that is pushed into the pulmonary artery, travels to the lungs
• The ventricles also push blood into the aorta, which feeds the rest of the body
• As the ventricles push blood, the atria refill, and the cycle repeats approximately 70 times a minute
• The cycle repeats over 100,000 times each day

Pacemaker Cells

• A cluster of cells in the right atrium act as a pacemaker, which keeps a steady heart beat
• Pacemaker cells create electrical impulses that cause the heart muscles to contract
• In cases of pacemaker cell malfunction, an artificial pacemaker can be implanted
• An artificial pacemaker sends electrical currents to the heart to ensure regular contractions

Arteries vs Veins

• Arteries carry blood away from the heart
• Veins carry blood to the heart
• The pulmonary artery carries deoxygenated blood away from the heart to the lungs
• Although the pulmonary artery carries deoxygenated blood, it is still an artery
• The pulmonary vein carries oxygenated blood to the heart from the lungs
• Even though the pulmonary vein carries oxygenated blood, it is still a vein

Coronary Arteries

• The heart receives its own supply of oxygenated blood via coronary arteries
• Coronary arteries branch off the aorta and encircle the heart
• This ensures the heart muscle tissue receives the oxygen and nutrients it needs

The circulatory system transports essential substances throughout the body. It includes blood, blood vessels, and the heart, operating as a double circulatory system. The heart has four chambers: atria and ventricles connected to veins and arteries.