Study Notes for Unit 1: Cardiovascular and Pulmonary Systems

SCIENTIFIC PRINCIPLES OF HES1823

UNIT 1

THE CARDIOVASCULAR SYSTEM

Unit 1, Section 2

LEARNING OBJECTIVES

  • Know the major components of the cardiovascular system, the major structures of the heart, and the components of the vascular system.
  • Identify specific arteries discussed in class.
  • Understand the path of blood flow through the heart.
  • Know what ECG and the QRS complex represent.
  • Understand the differences between arteries and veins.
  • Grasp the meanings of systole and diastole.
  • Comprehend cardiac output.

CARDIOVASCULAR SYSTEM COMPONENTS

  • The Heart: Distributes blood through the circulation.
  • Blood Vessels:
    • Arteries: Carry blood away from the heart.
    • Arterioles: Smaller branches of arteries leading to capillaries.
    • Veins: Carry blood back to the heart.
    • Venules: Small veins that collect blood from capillaries.
    • Capillaries: Sites of gas and nutrient exchange.
  • Blood: Carries nutrients, ions, wastes, and gases.

THE HEART

  • A muscular organ enclosed in a fibrous sac.
  • Weighs less than 0.5 kg.

ANATOMY OF THE HEART

  • Components:
    • Brachiocephalic Trunk
    • Superior Vena Cava
    • Right Pulmonary Artery
    • Ascending Aorta
    • Pulmonary Trunk
    • Right Pulmonary Veins
    • Right Atrium
    • Right Ventricle
    • Left Atrium
    • Left Ventricle
    • Left Coronary Artery
    • Great Cardiac Vein
    • Apex (the tip of the heart)
    • Coronary circulation components include various arteries and veins supplying the heart muscle.

HEART MUSCLE

  • Composition: The walls of the heart are primarily composed of striated muscle.
  • Myocytes (muscle cells) cannot contract independently like skeletal muscle.
  • Both atria contract together followed by both ventricles contracting together.

THE CARDIAC CYCLE

  • The heart goes through cycles of contraction (systole) and relaxation (diastole).
  • Approximately 40 million beats occur per year.
  • At rest, the heart pumps approximately 1,400 gallons of blood per day.

BLOOD FLOW THROUGH THE HEART

  • Right Side of the Heart:
    • Receives deoxygenated blood from systemic circulation.
    • Pumps deoxygenated blood to the lungs for oxygenation via pulmonary circulation.
  • Left Side of the Heart:
    • Receives oxygenated blood from pulmonary veins.
    • Pumps oxygenated blood to systemic circulation.

CIRCULATORY PATHWAYS

  • Pulmonary Circuit:
    • Involves the movement of blood from the right ventricle to the lungs and back to the left atrium.
    • Gas exchange occurs in capillary beds of lungs.
  • Systemic Circuit:
    • Involves the flow of blood from the left ventricle through the body and back to the right atrium.
    • Oxygen-rich blood enters the tissues, while oxygen-poor blood returns to the heart.

HEART ANATOMY

  • Interventricular Septum: A muscular wall separating the right and left sides of the heart.
  • Chambers: The heart has atrial and ventricular chambers.
  • Atrioventricular (AV) Valves:
    • Separate the atria from the ventricles, allowing one-way blood flow.
    • Prevent backflow during the cardiac cycle.

ATRIA AND VENTRICLES

  • Atria:
    • Receive and store blood while ventricles contract.
    • Thin-walled and sac-like; approximately 70% of returning blood flows directly into ventricles before contraction.
  • Ventricles:
    • Produce the pressure necessary to drive blood through the pulmonary and systemic vascular systems.
    • Contain spiral and circular arrangements of cardiac muscle.

VALVES IN THE HEART

  • Two sets of valves:
    1. Atrioventricular (AV) valves:
    • Separate atria from ventricles (e.g., tricuspid and mitral valves).
    1. Semilunar valves:
    • Separate right and left ventricles from the circulation.
    • Prevent blood from flowing in reverse during the cardiac cycle.

VALVE MOVEMENT DURING CARDIAC CYCLE

  • Atrioventricular Valves:
    • Open when the ventricles fill with blood.
    • Close during ventricular contraction (systole).
  • Semilunar Valves:
    • Open when the ventricles contract to expel blood.
    • Close during ventricular relaxation (diastole).

HEARTBEAT COORDINATION

  • Efficient pumping requires the atria to contract first, followed by the ventricles.
  • Contraction is triggered by an electrical impulse starting at the SA node (sinoatrial node) in the right atrium.

CONDUCTION SYSTEM OF THE HEART

  • Components:
    • Sinoatrial (SA) Node: Primary pacemaker of the heart.
    • Atrioventricular (AV) Node: Receives impulse from SA Node.
    • Bundle of His, Right and Left Bundle Branches, Purkinje Fibres: Conduct impulse throughout ventricles.

ELECTROCARDIOGRAM (ECG or EKG)

  • A diagnostic tool for evaluating the electrical activity of the heart.
  • Changes in heart defects can alter the shape and timing of ECG waves such as P wave, QRS complex, and T wave.

SUMMARY OF CARDIAC CYCLE PHASES

  1. Ventricular Filling:
    • Atria fill and open AV valves.
  2. Isovolumetric Contraction:
    • Ventricles contract with closed valves.
  3. Ventricular Ejection:
    • Blood is expelled into arteries.
  4. Isovolumetric Relaxation:
    • Ventricles relax with closed valves.

THE VASCULAR SYSTEM

  • Arteries: Low-resistance vessels that transport blood to organs.
  • Arterioles: Regulate blood flow to organs.
  • Capillaries: Sites of nutrient and fluid exchange.
  • Veins: Low-resistance conduits returning blood to the heart.

ARTERIAL SYSTEM COMPONENTS

  • Includes arteries such as:
    • Aorta, Common Carotid Arteries, Subclavian Artery, Brachiocephalic Trunk, Renal Arteries, Femoral Artery, and many others.

VENOUS SYSTEM COMPONENTS

  • Includes veins such as:
    • Superior Vena Cava, Inferior Vena Cava, Hepatic Portal Vein, and various jugular and saphenous veins.

VASCULAR STRUCTURE

  • All blood vessels have a common structural feature, a smooth layer of endothelial cells known as endothelium that lines their inner surfaces.
  • Endothelium participates in the regulation of blood flow and blood pressure.

DISTRIBUTION OF TOTAL BLOOD VOLUME

  • Volume Distribution (Total: 5,000 mL):
    • Heart: 360 mL (7.2%)
    • Lungs: 130 mL (2.6%)
    • Arteries: 130 mL (2.6%)
    • Capillaries: 110 mL (2.2%)
    • Veins: 2,300 mL (46.0%)…
    • Aorta, large arteries: 300 mL (6.0%)…

PULMONARY ANATOMY & PHYSIOLOGY

LEARNING OBJECTIVES

  • Understand the anatomy of the lungs and the two airway zones.
  • Know the characteristics of alveoli.
  • Understand the four components of respiratory function.
  • Understand how air moves in and out of the lungs, including the involved muscles.
  • Know definitions of lung volumes and capacities.

ORGANIZATION OF THE RESPIRATORY SYSTEM

  • Two lungs divided into lobes with a branching network of airways leading to the alveoli where gas exchange occurs.
  • Main functions include providing oxygen and eliminating carbon dioxide from blood.

THE AIRWAYS

  • Divided into two zones:
    • Conducting Zone: From trachea to the bronchioles without gas exchange.
    • Respiratory Zone: From respiratory bronchioles to alveolar sacs (gas exchange occurs).
  • Air travels through:
    • Trachea → Primary bronchi → Secondary bronchi → Tertiary bronchi → Bronchioles → Alveolar ducts → Alveoli.

THE ALVEOLI

  • Sac-like structures at the end of bronchioles, over 300 million present.
  • Highly capillarized, facilitating gas exchange with a thin blood-gas barrier.

GAS EXCHANGE AT ALVEOLI

  • Exchange process:
    • O₂ in and CO₂ out across alveolar membranes.

OXYGEN AND CARBON DIOXIDE TRANSPORT IN BLOOD

  • Oxygen:
    • 3% dissolved in plasma, 97% bound to hemoglobin.
  • Carbon Dioxide:
    • 10% dissolved in plasma, 20% bound to globin part of hemoglobin, 70% in bicarbonate form.

FOUR COMPONENTS OF RESPIRATORY FUNCTION

  1. Pulmonary Ventilation: Movement of air in and out of lungs.
  2. External Respiration: O₂ and CO₂ exchange between lungs and blood.
  3. Gas Transport: Movement of gases from lungs to tissues via the circulatory system.

PULMONARY VENTILATION

  • Defined as the process of air moving in and out of the lungs.
  • Inspiration: Air flows from environment into alveoli.
  • Expiration: Air flows from alveoli back to environment.
  • Dead Space Ventilation: Air that does not reach the alveoli; contributes to anatomical dead space.

ALVEOLAR VENTILATION

  • For example, if John’s ventilation rate is 500 mL/min and his dead space is 150 mL, his alveolar ventilation rate would be 350 mL/min.

AIRWAY MECHANICS

  • Airflow is determined by a pressure gradient, moving from high to low pressure.
    • Inhalation: Lung pressure < outside pressure.
    • Exhalation: Lung pressure > outside pressure.

MECHANICS OF VENTILATION

  • Inhalation: Muscles (diaphragm and intercostals) contract, expanding thoracic cavity and lowering intrathoracic pressure.
  • Expiration: Muscles relax, thoracic cavity size decreases, causing pressure to increase.

PULMONARY PROPERTIES

  • Elasticity: Ability of lungs to return to original shape after inhalation.
  • Compliance: How easily lungs stretch; it defines the volume change for a given pressure change.
  • High compliance means easy inflation, low if high pressure is required for inflation.

EXCHANGE OF GASES

  • Occurs via diffusion depending on partial pressure gradients, e.g., O₂ travels from high (160 mmHg) to lower pressures (40 mmHg in cells).
  • CO₂ has a reverse gradient: highest in cells (46 mmHg) to lowest in atmosphere (0.3 mmHg).

LUNG VOLUMES AND CAPACITIES

  • Tidal Volume (TV): Volume of air per breath.
  • Residual Volume (RV): Volume remaining after forced exhalation.
  • Total Lung Capacity (TLC): Maximal lung volume.
  • Vital Capacity (VC): Max volume exhaled after maximal inhalation.
  • Minute Ventilation (VE): Rate at which air is moved through lungs in 1 minute defined as: VE = TV imes ext{Respiratory Rate}

FORCED EXPIRATORY VOLUME (FEV)

  • Defined as the volume of air expired forcefully in a given unit of time after a deep inspiration.
  • Example metrics:
    • FEV1 = volume expired in 1 second.
    • FEV3 = volume expired in 3 seconds.
  • Expressed as a percentage of vital capacity (normal FEV1 is 80% of VC).
  • Used to diagnose respiratory conditions.