Cardiovascular

1. Introduction to the Cardiovascular System

The cardiovascular system, also known as the circulatory system, is a vital organ system responsible for transporting substances throughout the body. It consists of the heart, blood vessels, and blood. Its primary functions include:

  • Transport of Oxygen and Nutrients: Delivers oxygen from the lungs to tissues and nutrients from the digestive system to cells.

  • Removal of Waste Products: Carries carbon dioxide from tissues to the lungs for exhalation and metabolic wastes to the kidneys for excretion.

  • Hormone Transport: Distributes hormones throughout the body to regulate various bodily functions.

  • Immune Response: Transports immune cells (white blood cells) and antibodies to fight infections.

  • Temperature Regulation: Helps maintain body temperature by distributing heat.

2. Components of the Cardiovascular System

2.1 The Heart

The heart is a muscular, four-chambered organ located in the chest cavity between the lungs, slightly to the left. It acts as a pump, propelling blood through the circulatory system.

  • Structure:

    • Chambers:

      • Atria (upper chambers): Receive blood. Right atrium receives deoxygenated blood from the body; left atrium receives oxygenated blood from the lungs.

      • Ventricles (lower chambers): Pump blood out of the heart. Right ventricle pumps deoxygenated blood to the lungs; left ventricle pumps oxygenated blood to the rest of the body.

    • Valves: Prevent backflow of blood.

      • Atrioventricular (AV) valves: Tricuspid (between right atrium and ventricle) and Mitral/Bicuspid (between left atrium and ventricle).

      • Semilunar valves: Pulmonary (between right ventricle and pulmonary artery) and Aortic (between left ventricle and aorta).

  • Cardiac Cycle:

    • Diastole: Relaxation phase, when the heart chambers fill with blood.

    • Systole: Contraction phase, when the heart chambers pump blood out.

  • Electrical Activity: The heart's rhythm is controlled by an intrinsic electrical conduction system, starting with the sinoatrial (SA) node ($\$SA\text{ }node), the natural pacemaker.

2.2 Blood Vessels

Blood vessels are a network of tubes that carry blood throughout the body.

  • Arteries: Carry oxygenated blood away from the heart to the body's tissues (except for the pulmonary artery, which carries deoxygenated blood to the lungs).

    • Have thick, muscular walls to withstand high pressure.

    • Branch into smaller arterioles.

  • Capillaries: Microscopic vessels that form a network between arterioles and venules.

    • Site of exchange: Oxygen, nutrients, and waste products are exchanged between blood and tissues through their thin, permeable walls.

  • Veins: Carry deoxygenated blood back to the heart from the body's tissues (except for the pulmonary veins, which carry oxygenated blood from the lungs to the heart).

    • Have thinner walls and larger lumens than arteries.

    • Contain valves to prevent backflow of blood, especially against gravity.

    • Small venules merge to form larger veins.

2.3 Blood

Blood is a specialized connective tissue composed of plasma and formed elements.

  • Plasma (approx. 55\% of blood volume):

    • Mainly water, but also contains proteins (e.g., albumin, globulins, fibrinogen), electrolytes, hormones, nutrients, and waste products.

  • Formed Elements (approx. 45\% of blood volume):

    • Red Blood Cells (Erythrocytes):

      • Contain hemoglobin, which binds to oxygen for transport.

      • Lack a nucleus and mitochondria in mature form.

    • White Blood Cells (Leukocytes):

      • Part of the immune system, defending the body against infection and disease.

      • Types include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

    • Platelets (Thrombocytes):

      • Cell fragments involved in blood clotting (hemostasis).

3. Blood Circulation

The cardiovascular system operates on two main circuits:

  • Pulmonary Circuit:

    • Carries deoxygenated blood from the right side of the heart to the lungs.

    • In the lungs, blood releases carbon dioxide and picks up oxygen.

    • Oxygenated blood then returns to the left side of the heart.

  • Systemic Circuit:

    • Carries oxygenated blood from the left side of the heart to the rest of the body's tissues.

    • In the tissues, oxygen is delivered, and carbon dioxide and other waste products are picked up.

    • Deoxygenated blood then returns to the right side of the heart.

4. Key Physiological Parameters

  • Blood Pressure (BP): The pressure exerted by circulating blood against the walls of blood vessels.

    • Measured as systolic pressure (during ventricular contraction) over diastolic pressure (during ventricular relaxation).

    • Normal resting BP is often around 120/80\text{ }mmHg.

  • Heart Rate (HR): The number of times the heart beats per minute.

    • Average resting HR for adults is 60-100\text{ }beats/minute.

  • Cardiac Output (CO): The volume of blood pumped by the heart per minute.

    • Calculated as CO = HR \times SV$$ (Stroke Volume, the volume of blood pumped per beat).

5. Common Cardiovascular Conditions

  • Hypertension (High Blood Pressure): Chronically elevated blood pressure.

  • Atherosclerosis: Hardening and narrowing of arteries due to plaque buildup.

  • Coronary Artery Disease (CAD): Narrowing of the coronary arteries, leading to reduced blood flow to the heart muscle.

  • Myocardial Infarction (Heart Attack): Occurs when blood flow to a part of the heart is blocked, causing heart muscle damage.

  • Stroke: Occurs when blood flow to a part of the brain is interrupted, leading to brain cell death.