The Human Circulatory System

Main Blood Vessels

The human circulatory system consists of a network of blood vessels that transport blood throughout the body. These vessels are essential for delivering oxygen, nutrients, and removing waste products.

• Arteries: Carry blood away from the heart to various parts of the body. The pulmonary artery carries deoxygenated blood from the heart to the lungs.

• Veins: Carry blood towards the heart. The pulmonary vein returns oxygenated blood from the lungs to the heart. The superior vena cava and inferior vena cava bring deoxygenated blood from the body back to the heart.

• Capillaries: Tiny blood vessels where exchange of gases, nutrients, and waste occurs between blood and tissues.

Blood acts as the transport medium, carrying essential substances throughout the body.

Structure and Function of the Human Heart

The heart is a muscular organ that pumps blood at varying speeds and pressures to meet the body's needs. Its structure is highly adapted to its function as a pump.

• Chambers: The heart is divided into four chambers: two atria (left and right) and two ventricles (left and right).

• Septum: A wall of muscle called the septum separates the left and right sides of the heart, preventing mixing of oxygenated and deoxygenated blood.

• Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.

• Left Ventricle: Pumps oxygenated blood to the rest of the body via the aorta.

• Valves: Ensure unidirectional flow of blood through the heart. The bicuspid (mitral) valve and tricuspid valve separate the atria from the ventricles.

• Atria Walls: Thin and stretchable to receive returning blood, but contract to push blood into the ventricles.

• Cardiac Muscle: Specialized muscle that contracts and relaxes continuously without fatigue.

Coronary Circulation supplies the heart muscle itself with oxygen and nutrients via coronary arteries. Blood is returned to the right atrium through coronary veins.

Coronary Heart Disease (CHD)

Coronary heart disease occurs when the coronary arteries become narrowed or blocked, often due to fatty deposits such as cholesterol. This restricts blood flow to the heart muscle, leading to oxygen and nutrient deprivation, and can result in heart attacks.

• Causes:

  • Heredity: Genetic predisposition to CHD.

  • High Blood Pressure: Increases strain on the heart.

  • Diet: High intake of saturated fats raises cholesterol levels.

  • Smoking: Raises blood pressure and increases clot formation risk.

  • Stress: Elevates blood pressure.

  • Lack of Exercise: Regular exercise lowers blood pressure and strengthens the heart.

• Effects: Reduced blood supply to heart muscle, risk of heart attack, and potentially fatal outcomes.

Summary Table: Structure and Function of the Heart

Key Terms and Definitions

• Artery: Blood vessel that carries blood away from the heart.

• Vein: Blood vessel that carries blood towards the heart.

• Capillary: Microscopic blood vessel for exchange of substances between blood and tissues.

• Cardiac Muscle: Specialized muscle tissue of the heart.

• Coronary Heart Disease (CHD): Disease caused by blockage of coronary arteries.

Example: Blood Flow Through the Heart

• Deoxygenated blood enters the right atrium via the vena cava.

• Blood moves to the right ventricle, which pumps it to the lungs through the pulmonary artery.

• Oxygenated blood returns to the left atrium via the pulmonary vein.

• Blood moves to the left ventricle, which pumps it to the rest of the body through the aorta.

Relevant Equations

• Blood Pressure:

• Cardiac Output:

Additional info: Some details about the heart's structure and disease risk factors were expanded for clarity and completeness.