Review: Anatomy of the Heart

Functions of the Cardiovascular System

The cardiovascular system is responsible for transporting blood, nutrients, gases, and waste products throughout the body. It plays a vital role in maintaining homeostasis and supporting cellular function.

• Transport: Delivers oxygen and nutrients to tissues and removes carbon dioxide and metabolic wastes.

• Protection: Circulates immune cells and antibodies to defend against pathogens.

• Regulation: Maintains body temperature, pH balance, and fluid balance.

• Example: Blood flow from the heart to the lungs (pulmonary circulation) and to the rest of the body (systemic circulation).

Organization of the Cardiovascular System

The cardiovascular system consists of the heart, blood vessels, and blood. Blood flows through a network of arteries, veins, and capillaries, starting and ending in the aorta.

• Key structures: Capillaries, arteries, veins, septum, atria, ventricles, pulmonary arteries and veins, pulmonary valves, pulmonary circulation, systemic circulation, aorta, superior vena cava, inferior vena cava.

• Example: The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava.

Flow of Circulation

Blood circulates through two main circuits: pulmonary (to the lungs) and systemic (to the body).

• Pulmonary circulation: Right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium.

• Systemic circulation: Left ventricle → aorta → body tissues → veins → right atrium.

Internal and External Anatomy of the Heart

The heart is a muscular organ with four chambers and several key anatomical features.

• Internal anatomy: Pericardium, myocardium, endocardium, atria, ventricles, septum, valves (tricuspid, bicuspid/mitral, pulmonary, aortic), papillary muscles, chordae tendineae.

• External anatomy: Coronary arteries, coronary veins, coronary sinus.

• Example: The left ventricle has the thickest myocardium to pump blood throughout the body.

Heart Valves

Valves ensure unidirectional blood flow and prevent backflow.

• Atrioventricular valves: Tricuspid (right), bicuspid/mitral (left).

• Semilunar valves: Pulmonary (right), aortic (left).

Importance of Heart Valves

Valves maintain efficient circulation and prevent regurgitation of blood.

• Example: Mitral valve prolapse can lead to inefficient blood flow and heart murmurs.

14.3 Cardiac Muscle and the Heart

Types of Myocardial Cells

The heart contains two main types of cells: contractile cells and autorhythmic cells.

• Contractile cells: Responsible for generating force during contraction.

• Autorhythmic cells: Generate and conduct electrical impulses; include pacemaker cells.

• Example: Pacemaker cells in the SA node initiate the heartbeat.

Pacemaker Cells and Action Potentials

Pacemaker cells initiate action potentials without neural stimulation, allowing the heart to beat autonomously.

• Key mechanism: Spontaneous depolarization due to ion channel activity.

• Example: The SA node sets the pace for the heart rate.

Excitation-Contraction Coupling (EC-Coupling)

EC-coupling links electrical signals to muscle contraction in cardiac cells.

• Process: Action potential triggers Ca2+ release from the sarcoplasmic reticulum, leading to contraction.

• Equation: -induced release (CICR)

Membrane Proteins in Cardiac Muscle

Several membrane proteins are involved in excitation-contraction coupling and relaxation.

• Na+-Ca2+ antiporter (NCX): Exchanges sodium and calcium ions across the membrane.

• Sodium-potassium pump (Na+-K+-ATPase): Maintains ionic gradients necessary for action potentials.

Phases of Cardiac Action Potential

Cardiac contractile cells undergo a distinct action potential with several phases.

• Phase 0: Rapid depolarization (Na+ influx).

• Phase 1: Initial repolarization.

• Phase 2: Plateau (Ca2+ influx balances K+ efflux).

• Phase 3: Rapid repolarization (K+ efflux).

• Phase 4: Resting membrane potential.

• Example: The plateau phase allows sustained contraction for effective blood ejection.

Refractory Period

The refractory period prevents tetanus in cardiac muscle, ensuring rhythmic contractions.

• Absolute refractory period: No new action potential can be initiated.

• Relative refractory period: A stronger stimulus may initiate an action potential.

Summation in Cardiac Muscle

Summation is limited in cardiac muscle due to the long refractory period, preventing sustained contractions.

• Example: Cardiac muscle cannot undergo tetanus, unlike skeletal muscle.

Action Potentials in Autorhythmic Cells

Autorhythmic cells have unique action potentials due to specialized ion channels.

• Key channels: Pacemaker potential, If channels, funny current, HCN channels.

• Example: The funny current (If) contributes to spontaneous depolarization in pacemaker cells.

14.4 The Heart as a Pump

Electrical Signals Through the Heart

The heart's electrical system coordinates contraction and ensures efficient pumping.

• Key components: Sinoatrial (SA) node, internodal pathways, atrioventricular (AV) node, Purkinje fibers, AV bundle (bundle of His), bundle branches.

• Example: The SA node initiates the electrical impulse that spreads through the atria.

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including contraction and relaxation phases.

• Phases: Systole (contraction), diastole (relaxation).

• Steps: Atrial systole, ventricular systole, isovolumic contraction, ventricular ejection, isovolumic relaxation, ventricular filling.

• Example: During ventricular systole, blood is ejected into the aorta and pulmonary artery.

End-Diastolic and End-Systolic Volume

EDV and ESV are key measures of heart function.

• EDV (End-Diastolic Volume): Volume of blood in the ventricle at the end of diastole.

• ESV (End-Systolic Volume): Volume of blood remaining after systole.

• Stroke Volume (SV): Amount of blood ejected per beat.

• Equation:

Electrocardiogram (ECG/EKG)

An ECG records the electrical activity of the heart and is used to diagnose cardiac conditions.

• Key waves: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

• Segments: PR segment, ST segment.

• Example: A prolonged QRS complex may indicate a conduction abnormality.

Pressure Changes During the Cardiac Cycle

Pressure changes drive blood flow through the heart and vessels.

• During systole: Ventricular pressure rises, opening semilunar valves.

• During diastole: Ventricular pressure falls, AV valves open for filling.

Heart Rate, Cardiac Output, and Stroke Volume

Cardiac output is the volume of blood pumped by the heart per minute.

• Equation:

• HR: Heart rate (beats per minute).

• SV: Stroke volume (mL per beat).

• Example: If HR = 70 bpm and SV = 70 mL, then CO = 4900 mL/min.

Autonomic Division and Heart Rate Regulation

The autonomic nervous system regulates heart rate via sympathetic and parasympathetic pathways.

• Sympathetic stimulation: Increases heart rate and contractility.

• Parasympathetic stimulation: Decreases heart rate.

• Example: During exercise, sympathetic activity increases cardiac output.

Table: Key Cardiac Volumes and Equations

Additional info: These notes expand on the original bullet points with academic context, definitions, and examples for clarity and completeness.