Heart and Conduction Flashcards

Heart and Conduction

Learning Objectives

• List the major functions of the heart.
• Describe the size, shape, and location of the heart.
• Describe the morphology of the heart, including chambers, valves, and adjoining blood vessels.
• List the components of the heart wall and the structure and function of each component.
• Explain the structure and function of the conduction system of the heart.
• Describe the events in the cardiac cycle, including contraction and relaxation of heart chambers, opening and closing of heart valves, and the pathway of blood through the heart.

Relevance for Nurses

• Taking blood pressure.
• Listening to patients' heartbeat.
• Setting up ECG leads.
• Understanding cardiovascular disease symptoms, complications, and treatment, given it's the leading cause of death worldwide (nearly 18 million deaths per year).

Components of the Cardiovascular System

• Pump (heart).
• Conducting tubes (blood vessels).
• Fluid (blood).

The Heart

• Size: About the size of a large fist.
• Weight:
  • Males: 280 - 340 grams.
  • Females: 230 - 280 grams.
• Function: Pumps blood to the lungs and around the body.
• Muscle: Cardiac muscle (myocardium), contracts repeatedly without tiring.
• Right Heart: Pumps deoxygenated blood to the lungs.
• Left Heart: Pumps oxygenated blood to the rest of the body.

Heart Chambers and Valves

• Four chambers: Left and right atria, left and right ventricles.
• Four valves separate the chambers.
• Pericardium: Protective covering around the heart.

Layers of the Heart Tissue

Pericardium

• Protective tissue covering the heart.
• Made up of fibrous pericardium and serous pericardium.
• Fluid between layers reduces friction during heartbeats.

Myocardium

• Muscular wall of the heart, forming the atria and ventricles.
• Under involuntary control.
• Coordinated contraction moves blood from atria to ventricles.
• Functions as a single unit, transmitting force from cell to cell.

Endocardium

• Innermost lining of the heart chambers and valves.
• Made of simple squamous endothelium.
• Continuous with blood vessels leaving the heart.

Location of the Heart

• Within the thoracic cavity, in the anterior portion of the mediastinum.
• Just left of center (midsagittal plane).
• Within the pericardial sac.
• Base: At the level of the third costal cartilage.
• Apex: Around the fifth intercostal space.
• Height: About 12.5 cm from base to apex.

Surface Landmarks

• Base: Widest part, where vessels attach.
• Apex: Pointy part at the bottom.
• Large blood vessels leaving the heart.
• Atria and ventricles.
• Blood vessels supplying the heart.
• The base of the heart is at the top, and the apex is at the bottom.

Heart Chambers

• Right Atrium: Receives deoxygenated blood from the superior and inferior vena cava and pumps it to the right ventricle.
• Right Ventricle: Receives deoxygenated blood from the right atrium and pumps it into the pulmonary artery to the lungs.
• Left Atrium: Receives oxygenated blood from the pulmonary veins and pumps it to the left ventricle.
• Left Ventricle: Receives oxygenated blood from the left atrium and pumps it into the aorta to the rest of the body.

Great Vessels of the Heart

• Superior Vena Cava: Drains blood from the head, neck, and arms into the right atrium.
• Inferior Vena Cava: Drains blood from the chest down (abdomen, legs, feet, groin) into the right atrium.
• Pulmonary Trunk: Branches into pulmonary arteries, taking blood from the right ventricle to the lungs.
  • Arteries carry blood away from the heart.
• Pulmonary Veins: Deliver oxygenated blood from the lungs to the left atrium.
  • Veins carry blood into the heart
• Aorta: Distributes blood from the left ventricle through the arterial system around the body.

Valves of the Heart

• Specialized valves separate heart chambers, controlling blood flow.
• Ensure blood moves in one direction.
• Open and close in sequence.
• Two main valve types:
  • Atrioventricular (AV) Valves: Between the atria and the ventricles.
  • Semilunar Valves: Between the ventricles and the aorta or pulmonary trunk.

Right Atrioventricular Valve

• Also called the tricuspid valve.
• Has three leaflets.
• Allows blood to flow from the right atrium to the right ventricle.

Left Atrioventricular Valve

• Also called the bicuspid or mitral valve.
• Has two cusps.
• Allows blood to flow from the left atrium to the left ventricle.

Semilunar Valves

• Left Semilunar or Aortic Valve: Allows blood to flow from the left ventricle to the aorta.
• Right Semilunar or Pulmonary Valve: Allows blood to flow from the right ventricle to the pulmonary arteries.
• Leaflets look like a semilunar moon.

Chordae Tendineae

• String-like tendons anchoring valve leaflets to the heart wall.
• Made of collagen and elastin for dynamic contraction and relaxation.
• Anchored to papillary muscles, which contract to pull valves closed.
• Prevent valves from flying open and causing regurgitation.
• Papillary muscles rupture during heart attacks, affecting blood flow.

Pulmonary and Systemic Circuits

Pulmonary Circuit

• Right side of the heart.
• Receives deoxygenated blood from the superior and inferior vena cava.
• Pumps blood to the lungs via the pulmonary trunk and arteries.
• Carries oxygen-poor, carbon dioxide-rich blood to the lungs.

Systemic Circuit

• Left side of the heart.
• Oxygenated, carbon dioxide-poor blood comes into the left atrium.
• Blood is pumped out of the left ventricle via the aorta.
• Aorta disseminates blood via the arterial system to the rest of the body.
• Requires higher pressure to pump blood to the entire body.

Coronary Circulation

• Supplies blood to the heart itself.
• Right and left coronary arteries (RCA and LCA) branch off the ascending aorta.
• Coronary veins drain into the coronary sinus, which drains into the right atrium.
• Partial or total blockage of coronary arteries can occur, compromising blood flow to the heart (angina, heart attack).

Pathway of Blood Flow Through the Heart

1. Superior and Inferior Vena Cava: Drain blood into the right atrium.
2. Right Atrium: Receives blood from the vena cava.
3. Tricuspid Valve: Blood flows through the open tricuspid valve into the right ventricle.
4. Pulmonary Valve: Blood is pumped from the right ventricle through the pulmonary valve into the pulmonary trunk.
5. Pulmonary Arteries: Deoxygenated blood is carried to the lungs.
6. Pulmonary Veins: Oxygen-rich blood is pumped back into the heart.
7. Left Atrium: Receives blood from the pulmonary veins.
8. Mitral Valve: Blood passes through the mitral valve into the left ventricle.
9. Left Ventricle: Contracts to push blood through the aortic valve into the aorta.
10. Aorta: Blood is disseminated throughout the body.

Cardiac Cycle

• Coordinated contraction and relaxation of the heart.
• Electrical impulses synchronize contraction of heart muscle.
• Ensures blood flows in one direction.
• Atria contract first, then ventricles.
• Brief resting phase before cycle repeats.

Systole

• Heart chamber contracts, decreasing volume.
• Increases pressure, pushing the valve open.
• Blood is ejected into the adjacent chamber or artery.

Diastole

• Heart chamber relaxes, increasing volume.
• Decreases pressure, allowing filling.
• Valve closes after filling.

Phases

1. Relaxation
2. Atrial Contraction (Atrial Systole) / Ventricular Relaxation (Ventricular Diastole)
3. AV Valves Close
4. Atria Relax
5. Ventricles Contract
6. Semilunar Valves Open
7. Relaxation and repeat

• Fluid moves from high to low pressure.

Key Definitions

• End Diastolic Volume (EDV): Volume of blood in the ventricle at the end of diastole (filling).
• End Systolic Volume (ESV): Volume of blood remaining in the ventricle after contraction.
• Stroke Volume (SV): Amount of blood ejected per heartbeat from each ventricle.
  • SV = EDV - ESV

Heart Sounds

• Turbulence in blood flow caused by valve closure.
• Two main sounds: "Lub" and "Dub"
  • Lub: Closure of atrioventricular valves (loudest), best heard at apex of the heart.
  • Dub: Closure of semilunar valves (softer, shorter), best heard at base of the heart.
• Bicuspid valve best heard at the apex of the heart.
• Tricuspid valve best heard at the left sternal border.
• Aortic valve best heard between the 2nd and 3rd right intercostal space.
• Pulmonary valve best heard between the 2nd and 3rd left intercostal space.

Electrical Activity of the Heart

• Heart generates its own electrical rhythm.
• Self-excitable (automaticity) and autorhythmic (sets own pace).
• Can be modulated by neural input (speeds up or slows down).
• SA node (sinoatrial node): Group of specialized pacemaker cells in the right atrium that generate the sinus rhythm (normal rhythm of 70-80 bpm).
• Electrical activity spreads through specialized network of tracts.

Conduction System

1. SA Node: Triggers normal heart rhythm (sinus rhythm).
2. AV Node: Present between atria and ventricles.
3. Bundle of His: Travels down the interventricular septum towards the apex.
4. Bundle Branches: Travel up right and left sides of the heart.
5. Purkinje Fibers: Innervate the myocardium from the apex up, ensuring contraction happens in one direction.

The ventricles contract from the bottom up

Electrocardiogram (ECG)

• Measures electrical activity of the heart.
• Electrical changes aligned with phases of contraction and relaxation.
• Used in diagnostics to detect problems with the heart.
• Electrodes placed on the surface of the body.

Waves

• P Wave: Atrial depolarization.
• QRS Complex: Ventricular depolarization (atria repolarize).
• T Wave: Ventricular repolarization.

Heart Rate

• Influenced by sympathetic and parasympathetic nervous systems
• Bradycardia: Slow heart rate (under 60 bpm)
• Tachycardia: Fast heart rate (more than 100 bpm)

Fibrillation

• Uncoordinated contraction of atria or ventricles.
• Loss of sequential depolarization.
• Atrial Fibrillation: Inappropriate contraction of the atria.
• Ventricular Fibrillation: Inconsistent and inappropriate contraction of the ventricles, impairs pumping, and decreases cardiac output.
• Atrial fibrillation is a risk factor for embolic stroke.

Lecture Summary

• Heart is located in the mediastinum enclosed within the pericardial sac.
• Heart wall has three layers.
• Four chambers: right and left atria, right and left ventricles.
• Blood enters atria from veins and is ejected into arteries by contraction of the ventricles.
• Direction of blood flow is only in one direction through the heart due to atrioventricular and semilunar valves.
• Coronary circulation supplies the myocardium.
• Circuits: Pulmonary (pumps to the lungs) and systemic (pumps to the rest of the body).
• Cardiac cycle: Coordinated contraction and relaxation of the atria and ventricles.
• Valve closure can be heard at specific sites on the chest and is due to the turbulence of blood flow.
• Heartbeat initiated at SA node and propagated by conduction system.
• Deviations in heart contraction in the context of fibrillation.