heart

Chapter 14: The Heart and Heart Disease

This chapter covers various aspects of the heart's anatomy, physiology, and diseases associated with it.

Objectives

  • Identify structures on a heart diagram.

  • Describe basic facts about the heart.

  • Describe three tissue layers of the heart wall.

  • Describe the pericardium.

  • Differentiate the right and left sides of the heart.

  • Identify the four chambers of the heart and their functions.

  • Identify heart valves and their functions.

  • Describe the path of blood as it passes through the body.

  • Describe the blood flow to the myocardium.

  • Identify the major coronary arteries.

  • Describe the cardiac cycle and heart sounds.

  • Calculate cardiac output.

Heart Facts

  1. The heart consists of two sides:
       - Right Side: Responsible for deoxygenated blood.
       - Left Side: Responsible for oxygenated blood.

  2. Weight: Weighs less than 1 pound.

  3. Size: Approximately the size of the human fist.

  4. Location: Situated in the mediastinum (between the lungs in the thoracic cavity) and slightly left of the midline of the body.

  5. Apex: The pointed tip of the heart, which is directed toward the left side of the body.

Structure: Heart Wall (Three Layers)

The heart wall comprises three distinct layers:

  1. Endocardium:
       - Definition: The innermost layer that lines the heart's interior.
       - Function: Provides a smooth surface for blood flow and is continuous with the lining of major blood vessels.

  2. Myocardium:
       - Definition: Derived from “myo,” meaning muscle; this is the thickest layer of the heart.
       - Function: Composed of cardiac muscle tissue that contracts to pump blood through the heart.

  3. Epicardium:
       - Definition: Derived from “epi,” meaning upon; this layer is very thin and serves as the outermost layer of the heart.
       - Function: Provides protection and serves a functional role in linking the heart to surrounding structures.
       

Structure of the Heart: Pericardium

  • The pericardium consists of several layers that collectively serve multiple functions:
      1. Fibrous Pericardium:
         - Function: Anchors the heart to surrounding structures and absorbs shock to prevent damage.
      2. Serous Membrane:
         - Function: Provides lubrication to reduce friction between heart movements.
         - Composed of two layers:
           - Parietal Layer: Lines the walls of the pericardial cavity.
           - Visceral Layer (Epicardium): Attached to the myocardium.
      3. Pericardial Cavity:
         - Contains pericardial fluid, serving as a lubricant to reduce friction as the heart beats.

Divisions of the Heart

The heart consists of four chambers, each with distinct functions:

  1. Right Atrium:
       - Function: Receives deoxygenated blood from the body via superior and inferior vena cavae.

  2. Right Ventricle:
       - Function: Pumps deoxygenated blood to the lungs for oxygenation via the pulmonary arteries.

  3. Left Atrium:
       - Function: Receives oxygenated blood from the lungs via pulmonary veins.

  4. Left Ventricle:
       - Function: Pumps oxygenated blood to the rest of the body through the aorta.

Heart Valves

  1. Tricuspid (Right AV) Valve: Located between the right atrium and right ventricle.

  2. Pulmonary Semilunar Valve: Found between the right ventricle and pulmonary artery.

  3. Bicuspid (Mitral) Valve: Positioned between the left atrium and left ventricle.

  4. Aortic Semilunar Valve: Located between the left ventricle and aorta.
       
    The valves ensure unidirectional blood flow and prevent backflow during different phases of the cardiac cycle.

Pathway of Blood Through the Heart

  1. Blood enters the right atrium from the superior and inferior vena cavae.

  2. It flows through the tricuspid valve into the right ventricle.

  3. Contraction of the right ventricle forces the pulmonary valve open.

  4. Blood flows through the pulmonary valve into the pulmonary trunk, distributed to the lungs where it unloads carbon dioxide and loads oxygen.

  5. Oxygen-rich blood returns to the left atrium via pulmonary veins.

  6. Blood from the left atrium flows through the mitral valve into the left ventricle.

  7. Contraction of the left ventricle forces the aortic valve open.

  8. Blood flows through the aortic valve into the ascending aorta, supplying oxygen to the body tissues.

  9. Deoxygenated blood returns to the heart via vena cavae, completing the circuit.

Cardiac Cycle

  • Refers to the sequence of events that occur in the heart during a single heartbeat, including:
      1. Systole (Contraction phase):
         - Atrial Systole: Atria contract to push blood into ventricles.
         - Ventricular Systole: Ventricles contract to pump blood into the pulmonary artery and aorta.
      2. Diastole (Resting phase):
         - When heart chambers fill with blood.

  • Normal heart sounds:
      - “Lubb” during ventricular systole (contraction).
      - “Dub” during ventricular diastole (relaxation).

Cardiac Output

  • Definition: Cardiac output (CO) is the volume of blood pumped by each ventricle per minute.
      - Calculated as:
      extCardiacOutput=extHeartRateimesextStrokeVolumeext{Cardiac Output} = ext{Heart Rate} imes ext{Stroke Volume}
      - Heart Rate (HR): The number of times the heart beats in one minute (beats/min).
      - Stroke Volume (SV): The volume of blood ejected from a ventricle per heartbeat (ml/beat).

Heart's Conduction System

  • Unique since it doesn't require external nervous system stimulation to contract; it includes:
      1. Sinoatrial Node (SA Node): The natural pacemaker of the heart that initiates the electrical impulse.
      2. Atrioventricular Node (AV Node): Receives the impulse from the SA node and facilitates atrial contraction.
      3. Bundle of HIS: Transmits impulses from the AV node down the interventricular septum.
      4. Purkinje Fibers: Distribute the impulse throughout the ventricles, causing them to contract.

Variations in Heart Rates

  • Bradycardia: A slow heart rate (<60 bpm).

  • Tachycardia: A fast heart rate (>100 bpm).

  • Sinus Arrhythmia: Normal fluctuations in heart rate due to variations in breathing.

  • Premature Beat (Extrasystole): An additional beat occurring before the expected heart rhythm.

Heart Sounds and Disorders

  • Heart murmurs refer to abnormal heart sounds caused by faulty valves.

Heart Studies Techniques

  1. Stethoscope: For auscultation (listening).

  2. Electrocardiograph (ECG or EKG): Monitors electrical activity of the heart.

  3. Catheterization: A method that involves inserting a tube into the heart to measure pressures and obtain blood samples.

  4. Echocardiography: Uses ultrasound to visualize the heart's structures and actions.

Heart Diseases and Disorders

  1. Inflammation:
       - Endocarditis: Inflammation of the inner lining of the heart.
       - Myocarditis: Inflammation of the heart muscle.
       - Pericarditis: Inflammation of the pericardium.

  2. Heart Rhythm Abnormalities:
       - Arrhythmia/Dysrhythmia: Irregular heartbeat rates.
       - Fibrillation: Rapid, chaotic electrical activity.
       - Heart Block: Disruption of electrical impulses.

  3. Congenital Heart Disease: Defects present at birth affecting normal heart functions.

  4. Valve Disorders:
       - Valvular Stenosis: Narrowing of heart valves.
       - Rheumatic Heart Disease: Damage caused by rheumatic fever due to bacterial infection impacting heart muscle and valves.

  5. Coronary Artery Disease (CAD):
       - Atherosclerosis leading to decreased blood flow and potential heart attacks (myocardial infarction).

  6. Congestive Heart Failure (CHF): Inability of the heart to pump blood effectively due to other diseases.

Prevention of Heart Disease

  • Non-modifiable Risk Factors:
      - Age, Gender, Heredity, Body Type

  • Modifiable Risk Factors:
      - Smoking, Physical inactivity, Obesity, Dietary Saturated Fat Intake, Hypertension, Diabetes, Gout, Sleep Apnea.

Medical Emergency Response for Heart Events

  1. Call for help and bring assistance to the victim.

  2. Check for airway, breathing, and circulation (ABCs).

  3. Administer Cardiopulmonary Resuscitation (CPR) if necessary, following proper steps.

  4. Use an Automated External Defibrillator (AED) promptly when available.

  5. Recognize signs of life or changes in the victim's condition to know when to continue or stop CPR.

Conclusion

Understanding the heart's anatomy, function, conditions, and how to respond to heart emergencies is essential for managing heart health and handling medical emergencies effectively.