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.