Cardiovascular Physiology

Cardiovascular System Physiology

Overview of Cardiovascular Physiology

  • Definition: The study of the function of the heart, blood vessels, and blood.

  • Primary Functions:

    • Supply and transport essential substances for life and health including:

    • Oxygen

    • Nutrients:

      • Glucose

      • Amino acids

      • Fatty acids

      • Lipids

    • Removal of waste products:

      • Carbon dioxide

      • Lactic acid

      • Nitrogenous wastes from protein metabolism

      • Heat

    • Transport of hormones, water, and essential electrolytes.

Importance of Blood Flow

  • Consequences of Heart Failure:

    • Stopping the heart for 30 seconds leads to unconsciousness.

    • Irreversible damage to brain and sensitive tissues occurs within minutes.

  • Impact of Blood Volume Loss:

    • Loss of 10% of normal blood volume can impair exercise performance.

  • Tissue Function Dependence:

    • Normal function relies on adequate blood flow delivery.

    • Higher metabolic rates increase blood flow requirements.

  • Ischemia:

    • Definition: Inadequate blood supply to a tissue.

    • Transient ischemia: Leads to dysfunction.

    • Persistent ischemia: Causes permanent tissue damage (infarction) and cell death (necrosis).

Anatomy of Veins and Arteries

Major Veins and Their Functions

  • Intracranial Veins:

    • Internal Jugular Vein

    • External Jugular Vein

    • Inferior Thyroid Vein

  • Caval Veins:

    • Superior Vena Cava

    • Inferior Vena Cava

  • Other Important Veins:

    • Subclavian Vein

    • Azygos Vein

    • Axillary Vein

    • Hepatic Vein

    • Renal Veins

    • Great Saphenous Vein

  • Miscellaneous Veins:

    • Brachial Vein

    • Cephalic Vein

    • Median Cubital Vein

    • Basilic Vein

    • Inferior Mesenteric Vein

    • etc.

Major Arteries and Their Functions

  • Aorta: Emanates from the left ventricle of the heart

  • Key Arteries:

    • Brachiocephalic Trunk

    • Common Carotid Artery

    • Subclavian Artery

    • Renal Artery

    • Femoral Artery

  • Other Important Arteries:

    • Anterior Tibial Artery

    • Posterior Tibial Artery

    • etc.

Vascular Circulation

Categories of Circulation

  • Systemic Circulation:

    • Blood vessels between the aorta and vena cava excluding the lungs.

  • Pulmonary Circulation:

    • Involves blood vessels in the lungs (pulmonary arteries and veins).

  • Central Circulation:

    • Pulmonary circulation and heart.

Portal Systems

  • Definition: Blood passages by capillaries to veins then to a second set of capillaries before returning to the heart.

  • Examples of Portal Systems:

    • Splenic Portal System:

    • Supplies blood to digestive organs.

    • Blood from gastric, splenic, or mesenteric capillaries enters the portal vein to the liver.

    • Renal Portal System

    • Hypothalamic-Hypophyseal Portal System

Modes of Transport in Cardiovascular System

Bulk Flow

  • Definition: Rapid movement of blood through the heart and vessels.

  • Characteristics:

    • Blood from the heart reaches distant body parts within 10 seconds.

    • Requires energy from hydrostatic pressure differences (perfusion pressure).

  • Perfusion Pressure:

    • Definition: Difference in pressure between two points in a blood vessel.

    • Created by the heart's pumping action.

Transmural Pressure

  • Definition: Difference between blood pressure inside a vessel and tissue fluid pressure outside the vessel.

  • Importance of Transmural Pressure:

    • Determines blood flow out of a vessel if a hole is made in the wall.

Blood Pressure Dynamics

  • Systolic Pressure: Pressure in the aorta during left ventricle contraction; approximately 120 mm Hg.

  • Diastolic Pressure: Pressure in aorta between heartbeats; approximately 80 mm Hg.

  • Mean Aortic Pressure: Average pressure; roughly 98 mm Hg; crucial for driving blood through systemic circulation.

  • Final Blood Pressure in Vena Cava: Approximately 3 mm Hg.

  • Pulmonary Artery Pressure: 20/8 mm Hg (systolic/diastolic).

  • Pulmonary Vein Pressure: Approximately 5 mm Hg.

  • Differences in pressure due to lower resistance in pulmonary blood vessels.

Blood Flow and Capillary Dynamics

Flow Characteristics

  • Blood flow is rapid in large arteries, decreases in capillaries, then increases again in veins.

  • Volume flow rate remains constant through arteries, capillaries, and veins.

  • Capillary Characteristics:

    • Large cross-sectional area and surface area for effective exchange.

    • Total surface area of capillaries in systemic circulation: approximately 20 m² in a large dog (30 times greater than the dog's body surface area).

Diffusion as a Transport Mechanism

  • Definition: Movement of dissolved substances across blood vessel walls from bloodstream to interstitial fluid.

  • Energy Source for Diffusion: Concentration differences.

  • Characteristics of Diffusion:

    • Considered slow transport; cells must be within 100 µm of a capillary.

  • Example: Diffusion of oxygen from alveolar sacs to alveolar capillaries is facilitated by being within 1 mm of each other.

Blood Composition

Components of Blood

  • Blood consists of:

    • Cells (hematocrit) suspended in plasma.

    • Plasma Composition:

    • 93% Water

    • 5-7% Proteins (e.g., globulin, albumin, fibrinogen).

    • Electrolytes (dominant cation: sodium; predominant anions: chloride, bicarbonate).

Importance of Plasma Electrolytes

  • Electrolytes must be kept within narrow limits for homeostasis.

  • Plasma electrolytes can diffuse across capillary walls, equilibrating concentrations between plasma and interstitial fluid.

Effects of Abnormal Hematocrit Levels

  • Higher Hematocrit (Polycythemia):

    • Increases blood viscosity, burdening the heart with extra workload, leading to potential heart failure.

  • Lower Hematocrit (Anemia):

    • Causes increased cardiac output needed to deliver sufficient O₂; elevates heart workload, risking heart failure in diseased hearts.