Cardiovascular System: Anatomy & Physiology Study Guide

Cardiovascular System

Heart Structure and Function

The heart is a muscular organ responsible for pumping blood throughout the body. Its structure is closely related to its function, with each part playing a specific role in circulation.

• Chambers: The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle. The left ventricle has a thicker wall because it pumps blood to the entire body, requiring more force than the right ventricle, which only pumps to the lungs.

• Valves: The heart contains atrioventricular (tricuspid and mitral) and semilunar (pulmonary and aortic) valves to prevent backflow and ensure unidirectional blood flow.

• Septum: The interventricular septum divides the left and right sides of the heart, preventing mixing of oxygenated and deoxygenated blood.

• Fibrous Skeleton: A dense connective tissue structure that supports the heart, anchors valves, and insulates electrical impulses between atria and ventricles.

• Pericardium: The heart is enclosed in a double-walled sac. The fibrous pericardium is the outer layer, and the serous pericardium (with parietal and visceral layers) is the inner layer.

Example: The left ventricle's thick wall allows it to generate higher pressure to circulate blood through the systemic circuit.

Blood Flow Through the Heart

Blood flows through the heart in a specific sequence, passing through valves and chambers to ensure efficient circulation.

• Deoxygenated blood enters the right atrium from the superior and inferior vena cava.

• It passes through the tricuspid valve into the right ventricle.

• From the right ventricle, blood is pumped through the pulmonary valve into the pulmonary arteries and to the lungs.

• Oxygenated blood returns via pulmonary veins to the left atrium.

• It passes through the mitral (bicuspid) valve into the left ventricle.

• The left ventricle pumps blood through the aortic valve into the aorta and systemic circulation.

Key Point: Valves ensure blood flows in one direction and prevent backflow.

Cardiac Conduction System

The heart's electrical system coordinates contraction and relaxation, ensuring efficient pumping.

• Sinoatrial (SA) Node: The heart's natural pacemaker, initiates electrical impulses.

• Atrioventricular (AV) Node: Delays the impulse, allowing atria to contract before ventricles.

• Bundle of His, Bundle Branches, Purkinje Fibers: Conduct impulses rapidly through the ventricles.

Example: Damage to the SA node can result in arrhythmias; damage to the AV node can cause heart block.

Action Potentials and Cardiac Muscle

Cardiac muscle cells generate action potentials that trigger contraction. These differ from skeletal muscle action potentials in duration and ion involvement.

• Phases: Rapid depolarization (Na+ influx), plateau (Ca2+ influx), repolarization (K+ efflux).

• Refractory Period: Longer in cardiac muscle, preventing tetanus and allowing relaxation between beats.

• AP Transmission: Action potentials spread from cell to cell via gap junctions in intercalated discs.

Comparison: Cardiac muscle has a longer refractory period than skeletal muscle, preventing sustained contractions.

Electrocardiogram (ECG/EKG)

An ECG records the electrical activity of the heart, providing information about heart rate, rhythm, and conduction.

• P wave: Atrial depolarization

• QRS complex: Ventricular depolarization

• T wave: Ventricular repolarization

Example: Abnormalities in the QRS complex can indicate ventricular problems.

Cardiac Cycle and Heart Sounds

The cardiac cycle consists of systole (contraction) and diastole (relaxation) phases, with associated heart sounds.

• S1 ("lub"): Closure of AV valves at the start of ventricular systole.

• S2 ("dub"): Closure of semilunar valves at the start of ventricular diastole.

Example: Heart murmurs are abnormal sounds caused by turbulent blood flow, often due to valve defects.

Stroke Volume and Cardiac Output

Stroke volume (SV) and cardiac output (CO) are key measures of heart function.

• Stroke Volume (SV): The amount of blood ejected by a ventricle in one contraction.

• Cardiac Output (CO): The volume of blood pumped by each ventricle per minute.

Formulas:

• $SV = EDV - ESV$

• $CO = SV \times HR$

Where EDV = end-diastolic volume, ESV = end-systolic volume, HR = heart rate.

Frank-Starling Law of the Heart

The Frank-Starling law states that the strength of the heart's contraction increases with greater filling (preload).

• Increased EDV stretches cardiac muscle fibers, resulting in a more forceful contraction.

• This mechanism helps balance output between the right and left sides of the heart.

Example: During exercise, increased venous return raises EDV and thus increases stroke volume.

Regulation of Heart Function

Heart function is regulated by neural, hormonal, and intrinsic mechanisms.

• Sympathetic Stimulation: Increases heart rate and contractility.

• Parasympathetic Stimulation: Decreases heart rate.

• Hormones: Epinephrine and norepinephrine increase heart rate and force.

Example: Stress activates the sympathetic nervous system, increasing cardiac output.

Coronary Circulation

The heart receives its own blood supply via the coronary arteries, which branch from the aorta.

• Coronary blood flow is greatest during diastole, when the heart muscle is relaxed.

• Blockage of coronary arteries can lead to myocardial infarction (heart attack).

Example: Coronary artery disease is the leading cause of death in the US but is preventable through lifestyle changes and medical management.

Table: Comparison of Cardiac and Skeletal Muscle

Feature	Cardiac Muscle	Skeletal Muscle
Cell Shape	Branched, interconnected	Long, cylindrical
Control	Involuntary	Voluntary
Action Potential Duration	Long (200-400 ms)	Short (1-5 ms)
Refractory Period	Long	Short
Gap Junctions	Present (intercalated discs)	Absent

Clinical Relevance: Coronary Artery Disease

Coronary artery disease (CAD) is caused by the buildup of plaque in the coronary arteries, reducing blood flow to the heart muscle.

• Risk Factors: High cholesterol, hypertension, smoking, diabetes, obesity, sedentary lifestyle.

• Prevention: Healthy diet, regular exercise, controlling blood pressure and cholesterol, avoiding tobacco.

Example: CAD can lead to angina or myocardial infarction if untreated.

Additional info: Some explanations and context were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.