IO

Lecture 2 Blood Vessels

BLOOD VESSELS

  • Chapter Reference: BP - Chapter 25

  • Year: 2024

Hemodynamics of Blood Flow

  • Systemic Circuit:

    • Supplies blood to the head, upper limbs, digestive tract, kidneys, trunk, and lower limbs.

  • Pulmonary Circuit:

    • Sends blood to the lungs.

HEMODYNAMICS

  • Definition:

    • "Hemo" means blood, and "dynamic" refers to motion and forces.

    • It describes physical principles governing blood pressure, flow, and resistance in the cardiovascular system.

Components and Function of the Vascular System

  • Function:

    • Delivery of oxygen and nutrients, removal of wastes from tissues.

  • Components Include:

    • Arteries and arterioles

    • Capillaries

    • Venules and veins

Composition of Blood Vessels

  1. Tunica Externa (Adventitia):

    • Outermost covering, made of fibrous and connective tissues for support.

  2. Tunica Media:

    • Middle layer, made of smooth muscle, regulates vessel diameter through constriction.

  3. Tunica Intima:

    • Inner layer, elastic, contains endothelial cells adjacent to blood.

Lumen Structure Comparison

  • Types of Vessels:

    • Artery:

      • Enclosed by all three layers (Tunica intima, media, & externa)

    • Vein:

      • Similar to arteries, but typically larger and thinner walled.

    • Capillaries:

      • Composed of a single layer of endothelium for exchange.

Blood Vessel Structure: Arteries, Veins, and Capillaries

  • All three vessel types have layers, except for capillaries and venules.

  • Tunica Intima:

    • Smooth, slippery surface (Endothelium)

  • Tunica Media:

    • Contains smooth muscles for vasoconstriction and vasodilation.

  • Tunica Adventitia:

    • Merges with surrounding connective tissue.

Composition of the Arterial System

  • Arteries:

    • Thick-walled; elastic fibers allow stretching and recoiling.

  • Arterioles:

    • Act as resistance vessels; control blood flow into capillaries.

Effects of Peripheral Resistance and Regulation of Blood Flow

  • Blood Pressure Equation:

    • Blood Pressure (BP) = Cardiac Output (CO) × Peripheral Vascular Resistance (PVR)

  • Factors Affecting Hemodynamics:

    • Volume, Pressure, Resistance

Venous System: Characteristics and Function

  • Low-pressure system returning blood to the heart (CVP measured via catheter).

  • Valves in veins prevent retrograde flow; skeletal muscles assist blood movement.

  • Central Venous Pressure (CVP):

    • Normal reading: 8 to 12 mmHg.

Compliance in Blood Vessels

  • Compliance Formula (C):

    • C = V/P (Volume/Pressure)

  • More compliant vessels (e.g., veins) expand more easily under pressure changes.

Cardiomyopathy and Heart Failure

  1. Cardiomyopathy:

    • Causes congestive heart failure (CHF), leading to peripheral region effects.

  2. Right-Sided Heart Failure:

    • Leads to venous congestion of body organs.

    • Symptoms include peripheral edema, hepatomegaly, ascites.

Microcirculation and Capillary Function

  • Microcirculation: Includes arterioles, capillaries, and venules.

  • Capillaries:

    • Exchange nutrients, gases, and waste via diffusion and filtration.

Blood Flow Principles

  • Pressure and Volume Relationships:

    • Higher pressure differences result in greater flow rates.

    • Poiseuille’s Law:

      • F = ΔP/R (Flow = Pressure Difference / Resistance)

Resistance Factors Affecting Blood Flow

  • Three Factors:

    1. Vessel Radius (major determinant).

    2. Blood Viscosity.

    3. Vessel Length (total).

  • Resistance Sensitivity to Radius:

    • Inversely proportional to the fourth power of the radius (R = 1/r^4).

Capillary Exchange Dynamics

  • Hydrostatic pressure (HBP) pushes fluids out; osmotic pressure pulls fluids back in.

  • Lymphatic vessels collect excess interstitial fluid.

Autonomic Control of Cardiac Function and Blood Pressure

  • Cardiac Function Centers: Located in the medulla oblongata.

  • Baroreceptors:

    • Stretch-sensitive receptors monitoring blood pressure.

  • Chemoreceptors: Monitor O2, CO2, and pH levels.

Edema

  • Definition: Excess interstitial fluid accumulation in tissues.

  • Causes: Imbalance in fluid movement between vascular compartments leading to increased capillary pressure.

Review Questions

Summary and Key Terms

  • Essential interactions of blood dynamics affecting heart function and structure.

  • Cardiomyopathy impacts overall circulation efficiency leading to symptoms like edema and congestion.