E

chap 7

Chapter Overview

The Cardiovascular System and Its Control

  • Overview of key components:

    • The heart

    • The vascular system

    • Blood

Major Functions of the Cardiovascular System

  • Delivers:

    • O2 and nutrients to tissues

  • Removes:

    • CO2 and metabolic wastes

  • Transports:

    • Hormones and other biological molecules

  • Supports:

    • Temperature balance and fluid regulation

  • Maintains:

    • Acid-base balance

  • Regulates:

    • Immune function

Components of the Cardiovascular System

Major Elements

  • Three major circulatory elements:

    1. Pump (Heart):

    • Responsible for generating pressure to drive blood through vessels

    1. Channels or tubes (Blood Vessels):

    • Include arteries, veins, and capillaries

    1. Fluid medium (Blood):

    • Carries nutrients, gases, and wastes

  • Blood Flow must meet metabolic demands of tissues.

The Heart and Its Anatomy

General Structure

  • Four Chambers:

    • Right Atrium (RA): Receives deoxygenated blood

    • Left Atrium (LA): Receives oxygenated blood

    • Right Ventricle (RV): Pumps deoxygenated blood to the lungs

    • Left Ventricle (LV): Pumps oxygenated blood to the body

  • Pericardium:

    • Protective sac surrounding the heart

  • Pericardial Cavity:

    • Contains pericardial fluid to reduce friction

Heart Flow Pathway
Blood Flow Through the Heart

  • Right Heart (Pulmonary Circulation):

    • Deoxygenated blood pathway:

    • Superior, inferior venae cavae → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve → Pulmonary Arteries → Lungs

  • Left Heart (Systemic Circulation):

    • Oxygenated blood pathway:

    • Lungs → Pulmonary Veins → Left Atrium → Mitral Valve → Left Ventricle → Aortic Valve → Aorta

Myocardium Function and Structure

Characteristics

  • Myocardium: Cardiac muscle tissue responsible for heart contractions

  • Left Ventricle: Has the most myocardium due to requirement of pumping blood to the entire body.

    • Walls are thick (hypertrophy) due to increased workload.

    • Hypertrophy can occur with both exercise and disease, but adaptations vary.

Cardiac Muscle Fiber Types

  • Type and Structure:

    • Similar to Type I fibers (endurance)

    • Highly oxidative, high capillary density, and numerous mitochondria present.

    • Striated muscle fibers

  • Intercalated Disks:

    • Connect cardiac muscle fibers through desmosomes and gap junctions for coordinated contractions.

Comparison Between Myocardium and Skeletal Muscle

Structural Differences

  • Skeletal Muscle:

    • Large, long, unbranched, multinucleated

    • Associated with voluntary contractions

    • Calcium released through sarcoplasmic reticulum (SR)

  • Myocardial Cells:

    • Small, short, branched, with one nucleus

    • Continuous, involuntary, rhythmic contractions

    • Utilizes calcium-induced calcium release mechanism for contraction

Cardiac Blood Supply

Coronary Arteries

  • Right Coronary Artery:

    • Supplies blood to the right side of the heart

    • Divides into marginal and posterior interventricular arteries

  • Left Coronary Artery:

    • Supplies blood to the left side of the heart

    • Divides into circumflex and anterior descending arteries

  • Pathophysiology:

    • Atherosclerosis leads to coronary artery disease

Cardiac Conduction System

Intrinsic Control of Heart Activity

  • Components:

    • Special heart cells generate and transmit electrical signals.

    • Key parts:

    1. Sinoatrial (SA) Node: Primary pacemaker

    2. Atrioventricular (AV) Node: Delays signal transmission

    3. AV Bundle (Bundle of His): Facilitates signal to ventricles

    4. Purkinje Fibers: Spread the signal throughout the ventricles

  • Intrinsic Heart Rate = 100 beats/min (measured in heart transplant patients)

Extrinsic Control of Heart Activity
Parasympathetic Nervous System

  • Via the vagus nerve (Cranial Nerve X)

  • Effects:

    • Decreases heart rate (HR) and force of contraction

    • Normal resting HR ranges: 60 - 100 beats/min

    • Elite endurance athletes may have resting HR as low as 35 beats/min

Sympathetic Nervous System

  • Opposite effects of parasympathetic system

  • Effects:

    • Increases heart rate and contraction force

    • Involves norepinephrine release

    • Maximum possible HR = 250 beats/min

  • Hormonal influences such as epinephrine and norepinephrine have similar effects on HR

Electrocardiogram (ECG)

Overview

  • ECG records the heart's electrical activity using 10 electrodes and produces 12 leads

  • Diagnostic tool for coronary artery disease.

  • Phases:

    • P wave: Atrial depolarization

    • QRS Complex: Ventricular depolarization

    • T wave: Ventricular repolarization

Cardiac Cycle

Phases of the Cardiac Cycle

  • All electrical and mechanical events during a heartbeat

  • Diastole:

    • Relaxation phase, lasts twice as long as systole

    • Chambers fill with blood

  • Systole:

    • Contraction phase resulting in blood ejection

Events in Ventricular Systole

  • From QRS complex to T wave

    • Increases ventricular pressure leads to closure of atrioventricular (AV) valves

    • Heart sound 1 (“lub”) is produced

    • Blood is ejected, resulting in end-systolic volume (ESV)

Events in Ventricular Diastole

  • From T wave to next QRS complex

    • Drop in pressure causes closure of semilunar valves (heart sound 2 “dub”)

    • 70% of chamber filling is passive, while 30% occurs through atrial contraction

    • End-diastolic volume (EDV) represents the volume before contraction

Stroke Volume and Cardiac Output

Key Definitions

  • Stroke Volume (SV):

    • The volume of blood pumped during a single heartbeat

    • Calculated as: SV = EDV - ESV

    • Example: SV = 100 mL - 40 mL = 60 mL

  • Ejection Fraction (EF):

    • Percentage of EDV that is pumped out

    • Calculated as: EF = rac{SV}{EDV} where SV = 60 mL, EDV = 100 mL

    • Result: EF = 0.6 = 60\%

  • Cardiac Output (Q̇): Total volume of blood pumped per minute, calculated as: Q̇ = HR imes SV

    • Example at resting conditions: Q̇ = 70 ext{ beats/min} imes 70 ext{ mL/beat} = 4,900 ext{ mL/min} = 4.9 ext{ L/min}

Vascular System

Structure and Function

  • Arteries: Carry blood away from the heart

  • Arterioles: Control blood flow and feed into capillaries

  • Capillaries: Site of nutrient and waste exchange

  • Venules: Collect blood from capillaries

  • Veins: Return blood back to the heart

Blood Pressure and Hemodynamics

Blood Pressure Definitions

  • Systolic Blood Pressure (SBP): Highest pressure during systole, typically 110-120 ext{ mmHg}

  • Diastolic Blood Pressure (DBP): Lowest pressure during diastole, typically 70-80 ext{ mmHg}

  • Mean Arterial Pressure (MAP): Average pressure during the cardiac cycle, calculated as:
    MAP ext{ approximates } rac{2}{3} DBP + rac{1}{3} SBP

General Hemodynamics

  • Blood flow is necessary for all tissues, driven by the pressure gradient created by heart contraction.

  • Flow occurs from regions of high pressure (LV, arteries) to low pressure (veins, RA).

  • Resistance (R): The opposing force to blood flow, significantly influenced by the diameter of blood vessels.

    • Resistance formula: R = rac{hL}{r^4} where vessel radius (r) is the most crucial factor affecting resistance.

Intrinsic Control of Blood Flow

Mechanisms

  • Tissues can constrict or dilate their arterioles based on their local needs.

  • Types of Intrinsic Control:

    1. Metabolic: Responds to local metabolic byproducts (high CO2, H+, lactic acid) causing vasodilation.

    2. Endothelial: Factors released from endothelium promote vasodilation (NO, prostaglandins).

    3. Myogenic: Local pressure changes mediate vessel contraction or dilation in response to changes in perfusion pressure.

Extrinsic Neural Control

  • Sympathetic nervous system regulates overall vascular tone and blood distribution in response to systemic needs.

  • Changes in sympathetic activity lead to vasoconstriction (increase in resistance) or vasodilation (passive due to decreased sympathetic tone).

Blood Volume and Composition

Blood Volume Information

  • Average blood volume: 5-6 L in males, 4-5 L in females

  • Components:

    • Whole Blood = Plasma + Formed Elements

  • Plasma Composition:

    • Comprises 55%-60% of blood volume, with a composition of:

    • 90% water

    • 7% protein

    • 3% nutrients, ions, etc.

Formed Elements

  • Comprises 40%-45% of blood volume:

    • 99% Red blood cells (erythrocytes)

    • Less than 1% White blood cells (leukocytes)

    • Platelets (less than 1%)

  • Hematocrit: Percentage of blood volume composed of formed elements.

Red Blood Cells (RBCs)

Characteristics

  • Lacks nucleus and cannot reproduce

  • Lifespan of approximately 4 months

  • Produced and destroyed at equal rates through a process called hematopoiesis.

  • Hemoglobin: Oxygen-carrying protein that can transport up to 4 O2 molecules.

    • Composed of heme (iron-containing pigment) and globin (protein structure).

    • Each RBC contains approximately 250 million hemoglobin molecules, facilitating oxygen transport of about 20 mL O2 per 100 mL blood.

Conclusion

Importance of the Cardiovascular System

  • Essential for maintaining homeostasis across various body functions, including nutrient transport, waste removal, temperature regulation, and immune response.

  • Understanding the cardiovascular system is crucial for diagnosing and treating diseases related to blood flow and heart function.