🚀 Understanding Words

• angio-: vessel

  • angiotensin—substance that constricts blood vessels.

• ather-: porridge

  • atherosclerosis—deposits of plaque in arteries.

• brady-: slow

  • bradycardia—abnormally slow heartbeat.

• diastol-: dilation

  • diastolic pressure—blood pressure when the ventricle of the heart is relaxed.

• edem-: swelling

  • edema—accumulation of fluids in the tissues that causes them to swell.

• -gram: something written

  • electrocardiogram—recording of the electrical changes in the myocardium during a cardiac cycle.

• lun-: moon

  • semilunar valve—valve with crescent-shaped flaps.

• myo-: muscle

  • myocardium—muscle tissue within the wall of the heart.

• papill-: nipple

  • papillary muscle—small mound of muscle projecting into a ventricle of the heart.

• phleb-: vein

  • phlebitis—inflammation of a vein.

• scler-: hard

  • arteriosclerosis—loss of elasticity and hardening of a blood vessel wall.

• syn-: together

  • syncytium—mass of merging cells that act together.

• systol-: contraction

  • systolic pressure—blood pressure resulting from a single-ventricular contraction.

• tachy-: rapid

  • tachycardia—abnormally fast heartbeat.

©2019 McGraw-Hill Education.

💓 Introduction

• The heart pumps 7,000 liters of blood through the body each day.

• The heart contracts 2.5 billion times during an average lifetime.

• Blood travels through the blood vessels in this sequence:

  • arteries → arterioles → capillaries → venules → veins → back to heart.

• The cardiovascular system comprises the heart and all blood vessels.

🌐 Overview of the Cardiovascular System

• Cardiovascular refers to both the heart and blood vessels.

• The heart's pumping action circulates blood through blood vessels.

• Blood vessels form two circuits:

  • Pulmonary Circuit:

    • Transports oxygen-poor blood from the heart to the lungs and back to the heart.

    • In the lungs, blood picks up O₂ and drops off CO₂.

  • Systemic Circuit:

    • Transports oxygen-rich blood from the heart to body cells and back to the heart.

    • Blood delivers nutrients to cells and removes wastes.

🧭 The Heart

• The heart is a hollow, cone-shaped, muscular pump.

• Located in the mediastinum of the thoracic cavity, above the diaphragm.

• Structure:

  • 4 chambers:

    • 2 atria (upper chambers)

    • 2 ventricles (lower chambers for pumping action)

Location and Size

• 14 cm long and 9 cm wide.

• Positioned:

  • Posterior to the sternum

  • Medial to the lungs

  • Anterior to the vertebral column

  • Base lies beneath the 2nd rib

  • Apex lies at the 5th intercostal space

Coverings of the Heart:

• Pericardium:

  • Fibrous pericardium: Outer layer enclosing double-layered serous membrane.

  • Parietal pericardium: Deep to fibrous, outer serous membrane.

  • Visceral pericardium (epicardium): Inner serous layer, attached to the heart’s surface.

🎨 Structure of the Heart Wall

The heart wall has 3 layers:

• Epicardium:

  • Outer layer also called the visceral pericardium.

  • Thin serous membrane.

• Myocardium:

  • Middle layer made of cardiac muscle tissue.

  • Thickest layer, responsible for contraction.

• Endocardium:

  • Inner layer lining all heart chambers.

  • Thin, endothelial layer.

Table: Comparison of Heart Wall Layers

💉 Heart Chambers and Valves

Chambers:

• Atria: Upper, thin-walled chambers receiving blood.

• Ventricles: Lower, thick-walled chambers pumping blood into arteries.

Right Atrium:

• Receives systemic circuit blood (from the superior and inferior vena cavae and coronary sinus).

• Pumps blood to the right ventricle.

Right Ventricle:

• Receives blood from the right atrium.

• Pumps blood to the lungs.

Left Atrium:

• Receives blood from pulmonary veins.

• Pumps blood to left ventricle.

Left Ventricle:

• Receives blood from the left atrium.

• Pumps blood to systemic circuit.

Table: Heart Valves

🔄 Cardiac Cycle

• The heart's rhythmic contraction and relaxation represent a cardiac cycle.

• Coordinated function of heart chambers.

• Atrial systole (atria contract) and ventricular diastole (ventricles relax), followed by ventricular systole (ventricles contract) and atrial diastole (atria relax).

Heart Sounds

• “Lubb”: First heart sound, during ventricular systole, caused by AV valves closing.

• “Dupp”: Second heart sound, during ventricular diastole, caused by pulmonary and aortic semilunar valves closing.

• Murmur: Abnormal sound from incomplete valve closure.

📉 Cardiac Conduction System

Components:

• SA Node (Sinoatrial Node): Pacemaker, initiates heart contractions.

• Internodal Atrial Muscle: Carries impulses from SA node to atria.

• Junctional Fibers: Transmit impulses from SA node to AV node.

• AV Node (Atrioventricular Node): Delays impulses before passing to AV Bundle.

• AV Bundle (Bundle of His): Transmits impulses quickly to bundle branches.

• Left and Right Bundle Branches: Carry impulses to Purkinje fibers.

• Purkinje Fibers: Conduct impulses to ventricular myocardium, causing contraction.

Electrocardiogram (ECG, EKG)

• Recording electrical changes in the myocardium during the cardiac cycle.

• ECG Waves:

  • P Wave: Atrial depolarization (just before atrial contraction).

  • QRS Complex: Ventricular depolarization (just before ventricular contraction).

  • T Wave: Ventricular repolarization (just before ventricular relaxation).

🔍 Detailed Sections

Regulation of the Cardiac Cycle

• The SA node modulates heart rate.

• The autonomic nervous system influences the heart rate through sympathetic and parasympathetic fibers.

• Factors affecting heart rate include physical exercise, body temperature, and concentrations of ions (like K⁺ and Ca²⁺).

Arrhythmias

Types:

• Fibrillation: Uncoordinated contractions.

• Tachycardia: Fast heartbeat (>100 beats/min at rest).

• Bradycardia: Slow heartbeat (<60 beats/min at rest).

• Flutter: Rapid, regular contractions (250-350 beats/min).

💡 Additional Insights and Clinical Applications

Exercise and Cardiovascular System

• Regular aerobic exercise enhances cardiovascular efficiency.

• Benefits include increased blood volume, hemoglobin concentration, and cardiac muscle size.

• Recommendations:

  • Heart rate at 70-85% of max rate.

  • Duration: 30 to 60 minutes, 3 to 4 times a week.

Overview of Blood Vessels

Types:

• Arteries and Arterioles: Carry blood away from the heart.

• Capillaries: Sites of substance exchange between blood and body cells.

• Venules and Veins: Transport blood back to the heart