Cardiovascular System - Comprehensive Study Notes

The Pulmonary and Systemic Circuits

• The heart pumps 7{,}000 liters of blood through the body each day.
• The heart contracts 2.5\times 10^9 times in an average lifetime.
• The heart and all blood vessels make up the cardiovascular system.
• The blood vessels form two circuits: • Pulmonary circuit • Systemic circuit.

The Pulmonary and Systemic Circuits (Functional Overview)

• The heart acts as two side-by-side pumps: the right side and the left side.
• Right side receives oxygen-poor blood from tissues and pumps to the lungs to remove CO₂ and pick up O₂ via the pulmonary circuit.
• Left side receives oxygenated blood from the lungs and pumps to body tissues via the systemic circuit.
• Receiving chambers:
  • Right atrium receives blood returning from the systemic circuit.
  • Left atrium receives blood returning from the pulmonary circuit.
• Pumping chambers:
  • Right ventricle pumps blood through the pulmonary circuit.
  • Left ventricle pumps blood through the systemic circuit.

Blood Vessels Overview

• Three types of vessels:
  • Arteries: Carry blood away from the heart.
  • Veins: Carry blood to the heart.
  • Capillaries: Networks between arteries and veins that exchange materials.
• Capillaries (exchange vessels): Exchange dissolved gases, nutrients, wastes between blood and tissues.

Capillaries and Gas Exchange

• Capillaries are also called exchange vessels because they enable material exchange between blood and tissues.
• Exchange involves dissolved gases (O₂ and CO₂), nutrients, and waste products.
• In the lungs (alveoli), oxygenated blood (O₂) is gained, and CO₂ is expelled during pulmonary gas exchange.

Pulmonary Gas Exchange and Systemic Flow (Illustrative Pathways)

• Systemic circuit delivers oxygen to all body cells and carries away wastes.
• Oxygenated blood is pumped to body tissues via the aorta; deoxygenated blood is pumped to the lungs via the pulmonary arteries.
• The pulmonary circuit eliminates CO₂ via the lungs and oxygenates the blood.
• Oxygenated blood returns to the heart via the pulmonary veins. Deoxygenated blood returns to the heart via the venae cavae.
• Alveolus: site of gas exchange where O₂ enters blood and CO₂ exits blood.

Four Chambers of the Heart

• Right atrium: collects blood from systemic circuit.
• Right ventricle: pumps blood to the pulmonary circuit.
• Left atrium: collects blood from pulmonary veins.
• Left ventricle: pumps blood to the systemic circuit.

Structure of the Heart

• The heart is a hollow, cone-shaped muscular pump.
• Four chambers: two atria (blood storage) and two ventricles (pumps).
• Right ventricle is a low-pressure pump; left ventricle is a high-pressure pump.

Size and Location of the Heart

• The heart size varies with body size.
• Average size: 14\text{ cm} long and 9\text{ cm} wide.
• Location: lies in the thoracic cavity; posterior to the sternum; medial to the lungs; anterior to the vertebral column.
• The base lies beneath the 2nd rib; the apex at the 5th intercostal space; the heart sits just above the diaphragm.

Heart Walls and Pericardium

• The heart wall has three layers:
  • Endocardium (inner)
  • Myocardium (middle; contracts to pump)
  • Epicardium (visceral pericardium; outer)
• Pericardial cavity between parietal and visceral layers contains pericardial fluid.
• Pericardial sac is fibrous tissue surrounding and stabilizing the heart.

The Pericardium and Pericardial Space

• The pericardial cavity lies between the parietal and visceral pericardium and contains pericardial fluid.
• The pericardial sac is fibrous tissue that surrounds and stabilizes the heart.
• The heart sits in relation to surrounding anatomy with the base near the 2nd rib and the apex near the 5th intercostal space.

Heart Wall and Positioning (Anatomical Relationships)

• Diaphragm below the heart; base oriented toward the right shoulder; apex toward the left hip region.

Homeostatic Imbalance: Pericardium

• Pericarditis: inflammation of the pericardium, roughens membrane surfaces, causing a pericardial friction rub heard with a stethoscope.
• Cardiac tamponade: excess fluid in pericardial space can compress the heart and limit pumping ability.

Heart Chambers and Valves: A Quick Layout

• The heart has four chambers:
  • Right atrium receives blood from the inferior vena cava, superior vena cava, and coronary sinus.
  • Right ventricle pumps blood into the pulmonary trunk.
  • Left atrium receives blood from the four pulmonary veins.
  • Left ventricle pumps blood into the aorta.
• Valves ensure unidirectional blood flow and open/close with pressure changes.
• Two atrioventricular (AV) valves: Tricuspid (right) and Mitral (left, bicuspid).
  • AV valves are anchored by chordae tendineae to papillary muscles and prevent valve flaps from everting into atria when ventricles contract.
• Two semilunar (SL) valves: Aortic and Pulmonary.
• Fibrous skeleton of the heart provides structural support for valves and septa.

Atrioventricular Valves (AV Valves) – Functioning Details

• Blood returning to the heart fills the atria, pressing against AV valves; pressure forces AV valves open.
• As ventricles fill, AV valve flaps hang limply into ventricles.
• Atria contract, forcing additional blood into ventricles.
• Ventricles contract, pushing blood against AV valve cusps; AV valves close.
• Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria.
• AV valves open when atrial pressure is greater than ventricular pressure; AV valves close when atrial pressure is less than ventricular pressure.

Semilunar Valves

• Two SL valves: Aortic semilunar valve and Pulmonary semilunar valve.
• They prevent backflow into the ventricles when ventricles relax.
• Open and close in response to pressure changes.
• When intraventricular pressure rises above arterial pressure, SL valves open; when ventricular pressure falls and blood flows back from the arteries, the cusps fill and SL valves close.
• Illustrative flow: Aorta and Pulmonary trunk carry blood away from ventricles; SL valves ensure one-way flow back toward ventricles.

The Fibrous Skeleton and Cardiac Valves

• The fibrous rings and dense connective tissue in the interventricular septum form the skeleton of the heart.
• This structure anchors the valves and maintains proper annulus shape during contraction.

Homeostatic Imbalance: Valvular Problems

• Incompetent valve: backflow of blood, heart repumps the same blood.
• Valvular stenosis: stiff flaps constrict the opening, forcing the heart to work harder.
• Valve replacement options: mechanical, animal, or cadaver valve.

Atria and Ventricles: Receiving vs Discharging Chambers

• Atria are small, thin-walled, and contribute little to propulsion of blood.
• The ventricles are thicker and are the actual pumps.
• Right ventricle: pumps blood into the pulmonary trunk.
• Left ventricle: pumps blood into the aorta (largest artery in the body).

Gross Anatomy: The Heart and Major Vessels

• Major vessels visible include:
  • Superior and inferior vena cavae
  • Coronary sinus
  • Right and left coronary arteries
  • Aorta and pulmonary trunk
  • Pulmonary and aortic valves
• The heart sits atop the diaphragm and lies within the thoracic cavity.

Coronary Circulation: The Blood Supply to the Heart

• The heart receives blood via coronary circulation, supplied by coronary arteries and drained by cardiac veins.
• Left and right coronary arteries originate from the aortic sinuses and supply oxygenated blood to the myocardium.
• Coronary veins drain deoxygenated blood into the coronary sinus, which empties into the right atrium.
• Great cardiac vein, anterior cardiac veins, posterior cardiac vein, middle cardiac vein, and small cardiac vein are part of the system.
• The coronary circulation is particularly affected by atherosclerosis, thrombus formation, and vasospasm.

The Cardiac Cycle: A Coordinated Rhythm

• The Cardiac Cycle is the period between the start of one heartbeat and the beginning of the next and includes both contraction and relaxation.
• The cycle comprises systole (contraction) and diastole (relaxation) for both atria and ventricles in a coordinated sequence.
• Phases of the cardiac cycle (in order): atrial systole, atrial diastole, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular relaxation, and ventricular diastole with passive atrial filling.

Heart Actions During the Cardiac Cycle (A Working Sequence)

• Phase 1: Atria contract (atrial systole); AV valves open; ventricles begin filling; semilunar valves closed.
• Phase 2: Atria relax (atrial diastole); ventricles continue filling; ventricular pressure remains low.
• Phase 3: Isovolumetric ventricular contraction; ventricles begin to contract; AV valves snap shut; no blood ejected yet; all valves closed.
• Phase 4: Ventricular ejection; ventricular pressure rises above arterial pressure; semilunar valves open; blood is ejected to pulmonary trunk and aorta.
• Phase 5: Isovolumetric ventricular relaxation; ventricles relax; blood flows back toward valves; semilunar valves close; AV valves remain closed briefly.
• Phase 6: Late ventricular diastole; all chambers relax; passive filling of ventricles continues; atria may actively contract to complete filling (atrial systole).
• Visual cue: Isovolumetric relaxation occurs when all valves are closed and ventricular pressure falls with no volume change.

Blood Pressure and the Cardiac Cycle

• Blood pressure rises during systole and falls during diastole.
• Blood flows from areas of high pressure to low pressure.
• The regulatory timing of contractions and one-way valves control the cycle.

Heart Rate and Cardiac Cycle Timing

• At a heart rate of 75\ \text{bpm}, the cardiac cycle lasts about 800\ \text{ms}.
• When heart rate increases, all phases shorten, with diastole shortening more markedly.

Heart Sounds and Murmurs

• The normal heartbeat sounds like “lubb-dupp.”
• The first heart sound (lubb) occurs during ventricular systole and corresponds to AV valve closure.
• The second heart sound (dupp) occurs during ventricular diastole and corresponds to the closure of the aortic and pulmonary semilunar valves.
• Murmurs are abnormal sounds produced when valve cusps do not close completely.

Cardiac Conduction System: Coordinating the Heartbeat

• The cardiac conduction system initiates and distributes impulses to coordinate the cardiac cycle.
• Key components:
  • Sinoatrial (SA) node: the natural pacemaker that generates impulses.
  • Atrioventricular (AV) node: conducts impulses from atria to ventricles; there is a brief delay (pause of about 0.1\ \text{s}) allowing atrial contraction to complete.
  • AV bundle (Bundle of His): connects atria to ventricles.
  • Bundle branches: conduct impulses through the interventricular septum.
  • Subendocardial conducting network (Purkinje fibers): depolarize contractile cells of both ventricles.
• Internodal pathways connect the SA node to the AV node.

Electrocardiogram (ECG or EKG)

• An ECG records electrical changes during the cardiac cycle.
• Key waves/segments:
  • P wave: atrial depolarization.
  • QRS complex: ventricular depolarization.
  • T wave: ventricular repolarization.
• Additional features: PR segment (conduction through AV node and AV bundle) and ST segment (ventricular repolarization context).

Regulation of the Cardiac Cycle and Heart Rate

• The SA node controls inherent heart rate; autonomic nervous system modifies rate via sympathetic and parasympathetic inputs.
• Regulatory reflex centers influence heart rate; physical activity, body temperature, and ionic concentrations (notably potassium and calcium) also affect rate.
• Parasympathetic impulses decrease heart action; sympathetic impulses increase heart action.

Clinical Applications: Arrhythmias and Pacemakers

• Arrhythmias are abnormal electrical activity; can be tachycardia (>100 BPM at rest) or bradycardia (<60 BPM at rest).
• Can lead to fainting, cardiac arrest, or palpitations; fibrillation involves chaotic, uncoordinated contraction.
• Types:
  • Atrial fibrillation (not usually life-threatening).
  • Ventricular fibrillation (often deadly).
• Pacemakers:
  • Single-chamber pacemaker (one lead in either atrium or ventricle).
  • Dual-chamber pacemaker (one lead in each of the atrium and ventricle).
  • Biventricular pacemaker (three leads, in right atrium, right ventricle, and left ventricle via the coronary sinus).
  • The pulse generator provides power; leads deliver impulses and sense electrical activity.

Other Factors Influencing Heart Rate

• Age: fetus has the fastest HR; different age groups have different baselines.
• Gender: females typically have faster HR than males.
• Exercise: increases HR.
• Body temperature: increases HR with higher temperatures.

Homeostatic Imbalances: Heart Failure and Congestion

• Tachycardia: abnormally fast heart rate (> 100\ \text{BPM}) at rest.
• Bradycardia: slower heart rate (< 60\ \text{BPM}) which can impair circulation in nonathletes but may be desirable in endurance athletes.
• Congestive heart failure (CHF): CO is so low that circulation cannot meet tissue needs; caused by weakened myocardium due to
  • coronary atherosclerosis (clogged arteries),
  • persistent high blood pressure,
  • multiple myocardial infarcts,
  • dilated cardiomyopathy (DCM).
• Left-sided failure leads to pulmonary congestion (blood backs up in the lungs); right-sided failure leads to peripheral congestion (edema in body tissues).
• Treatments focus on reducing fluid, decreasing afterload, and increasing contractility.

Exercise and the Heart

• Aerobic exercise benefits:
  • increased cardiac output (CO),
  • increased HDL and decreased triglycerides,
  • improved lung function,
  • decreased blood pressure,
  • weight control.

Lifespan Changes in the Cardiovascular System

• Cholesterol deposition in vessels; heart enlargement; death of cardiac muscle cells; increased fibrous tissue; increased adipose tissue in the heart; increased blood pressure; potential decrease in resting heart rate.
• A comparison of mammalian lifespans: about 1 billion heartbeats for most mammals; rabbits reach a billion quickly due to high HR; elephants exceed 80 years with slow HR; humans uniquely surpass ~2 billion heartbeats thanks to modern medicine and improved living conditions.

Historical and Contemporary Notes

• Julio Macias Gonzalez (17) died after a hickey caused a thrombus that traveled to the brain causing a stroke.
• René Leannec, a physician, invented the stethoscope after feeling uncomfortable placing his ear to a woman’s chest.

Coronary Artery Disease (CAD) and Interventions

• CAD entails partial or complete blockage of coronary circulation; cardiac muscle requires a constant oxygen and nutrient supply.
• Causes include atherosclerotic plaque buildup, thrombus formation, and vessel spasms.
• Angina pectoris is an early symptom of CAD, caused by ischemia during increased workload or stress.
• Myocardial infarction (MI, heart attack): blockage leads to tissue death (infarct); MI is commonly related to severe CAD.
• Treatments and risk reduction: stop smoking, manage blood pressure, modify diet to lower cholesterol and promote weight loss, reduce stress, increase physical activity where appropriate.
• CAD management options include drugs, bypass grafts (CABG), angioplasty, and stents. CABG involves using a blood vessel from elsewhere to bypass the blockage.

Coronary Circulation Details (Anatomy)

• Coronary arteries originate at the aortic sinuses and are subject to elastic rebound in systole, driving blood through between contractions.
• The major vessels include the left and right coronary arteries, great cardiac vein, coronary sinus, and several smaller veins (marginal, middle, posterior veins, etc.).
• The cardiac veins drain into the coronary sinus, which empties into the right atrium.

The Cardiac Cycle in Brief

• Definition: The period between the start of one heartbeat and the beginning of the next; it includes phases of contraction and relaxation.
• The cycle’s timing is closely linked to electrical conduction, valve function, and pressure changes within chambers.

Appendix: Anatomy of the Heart Structures (Recap)

• Endocardium, Myocardium, Epicardium form the heart wall.
• Pericardium provides lubrication and protection; pericardial cavity contains fluid.
• Valves: AV valves (tricuspid, mitral) and SL valves (aortic, pulmonary).
• Cardiac Skeleton anchors valves and maintains structural integrity during contraction.
• Conduction system coordinates the heartbeat via SA node, AV node, AV bundle, bundle branches, Purkinje fibers, and interneuronal pathways.

Quick Reference: Key Numbers and Concepts

• Cardiac output (CO) varies with HR and stroke volume; baseline measurements differ by individual.
• Typical resting HR: around 60$-$100\ \text{bpm} in adults; exercise increases HR.
• Cardiac cycle duration at 75\ \text{bpm}: 800\ \text{ms}.
• Normal valve function relies on pressure changes to open/close; AV valves handle atrial-to-ventricular flow; SL valves handle ventricular-to-arterial flow.
• Blood flows: systemic capillaries → body tissues (O₂ delivery) → systemic veins → SVC/IVC → right atrium → right ventricle → pulmonary trunk → lungs (gas exchange) → pulmonary veins → left atrium → left ventricle → aorta → systemic capillaries (O₂ delivery).

End of Notes