Overview of the Cardiovascular System

Overview of the Cardiovascular System

  • Components:

    • Heart: Functions as a muscular pump.

    • Blood Vessels: Consist of arteries, arterioles, veins, venules, capillaries, which carry blood through the body.

    • Blood: Circulates through the body, is responsible for transporting materials between cells, and supports communication between organs, tissues, and cells.

Importance of Blood

  • Communication Role: Carries chemical messengers, including hormones and neurotransmitters, facilitating signaling between different parts of the body.

Lymphatic System

  • Components: Includes lymph nodes, lymphatic vessels, spleen, tonsils, thymus.

  • Function: Maintains fluid balance, filters harmful substances, and supports the immune system by transporting white blood cells.

  • Relationship to Cardiovascular System: Together, the cardiovascular and lymphatic systems form the circulatory system.

Blood Flow Process

  • Blood flows through a continuous loop involving deoxygenated and oxygenated blood.

  • Deoxygenated Blood Route:

    • Returns to the right atrium from the body.

    • Moves to the right ventricle through the AV valve.

    • Travels through the semilunar valve into the pulmonary artery.

    • Exchange of oxygen and CO₂ occurs in the lungs.

  • Oxygenated Blood Route:

    • Returns from the lungs via the pulmonary vein to the left atrium.

    • Enters the left ventricle through the AV valve.

    • Exits through the semilunar valve at the aorta into systemic circulation.

Structure and Function of Blood Vessels

  • Types of Blood Vessels:

    • Arteries: Thick muscular walls for high pressure. Largest diameter.

    • Veins: Also large diameter but under lower pressure, contain musculature.

  • Blood Flow Velocity:

    • Velocity is highest in arteries and veins; decreases significantly in capillaries, which allows for nutrient exchange.

  • Diameter and Surface Area:

    • Smaller diameter vessels have more branching, which increases total surface area beneficial for nutrient exchange.

  • Blood Volume Distribution:

    • Approximately 60% of blood in systemic veins and venules, 8% in the heart, and 5% in capillaries.

Key Vessel Characteristic Comparisons

  • Arteries: Thick walls, large diameter, high velocity of blood flow; involved in high-pressure transport.

  • Veins: Thinner walls, larger diameter than most vessels; have valves that prevent backflow.

  • Capillaries: Small diameter, very low velocity; ideal for nutrient and gas exchange due to high surface area and slow flow.

Control of Blood Flow

  • Organ-Specific Blood Flow:

    • Varies according to the metabolic needs of tissues (e.g., more blood flow to skeletal muscles during exercise).

  • Cardiac Output: Amount of blood pumped by the heart per minute, calculated as
    CO = HR imes SV where ( HR ) is heart rate and ( SV ) is stroke volume.

Factors Affecting Blood Movement in Veins

  • Mechanisms to help blood flow against gravity:

    • Thoracic pressure gradient during breathing.

    • Skeletal muscle contraction (muscle pump).

    • One-way valves in veins to prevent backflow.

  • Varicose Veins: Caused by malfunction of valves leading to blood pooling in superficial veins, more common as people age.

Heart Structure and Function

  • Cardiac Muscle (Myocardium):

    • Involuntary, contracts autonomously without conscious thought.

    • High mitochondrial content (35% of volume) provides high oxidative capacity and resistance to fatigue.

  • Heart Sounds (Lub-Dub):

    • Lub: Closing of AV valves at the start of ventricular contraction.

    • Dub: Closing of semilunar valves at the end of ventricular contraction.

Cardiovascular Diseases

  • Coronary Artery Disease: Narrowing or blockage of arteries supplying blood to the heart.

  • Stroke: Interruption of blood flow to the brain, can be due to blockage or bleeding.

  • Myocardial Infarction (Heart Attack): Blockage of blood flow to the heart muscle.

  • Heart Failure: Heart can't pump blood effectively, leading to decreased output.

  • Hypertension (High Blood Pressure): Elevated pressure within arteries can damage blood vessels.

  • Dyslipidemia: Abnormal lipid levels, particularly elevated LDL cholesterol which can lead to plaque buildup in arteries.

    • Normal artery vs. plaque buildup at varying levels of LDL cholesterol.

Application: Framingham Risk Score

  • A tool used clinically to assess an individual’s cardiovascular risk.

  • Factors include:

    • Age (e.g., Mr. PH, 63-year-old male).

    • HDL and LDL cholesterol levels.

    • Systolic blood pressure.

    • Smoking status.

    • Diabetes status.

  • Scoring: Higher points correlate with increased risk for cardiovascular disease, including a ten-year risk percentage.

  • Case Study Analysis: Patient risk assessment considering lifestyle factors can predict health outcomes (e.g., Mr. PH's heart age compared to biological age reveals accelerated aging due to health factors).