Chapter 18: The Heart and Cardiovascular Function – Study Guide

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Heart: Location & Orientation

Mediastinum

The mediastinum is the central compartment of the thoracic cavity, where the heart is located. It lies between the lungs, posterior to the sternum, and anterior to the vertebral column.

Base: The broad superior portion of the heart, where major vessels attach.
Apex: The pointed inferior tip of the heart, directed downward and to the left.

External Gross Anatomy

Major Structures

Right & Left Atrium: Superior chambers that receive blood.
Right & Left Ventricles: Inferior chambers that pump blood out of the heart.
Coronary Sulcus: Groove separating atria from ventricles; contains coronary vessels.
Interventricular Sulcus: Groove marking the boundary between the right and left ventricles.
Pericardium: Double-layered membrane surrounding the heart, providing protection and reducing friction.

Internal Anatomy

Chambers

Left & Right Atrium: Receive blood from systemic and pulmonary circuits.
Left & Right Ventricle: Pump blood into systemic and pulmonary circuits.

Valves

Left & Right Atrioventricular (AV) Valves: Prevent backflow from ventricles to atria. Right AV is the tricuspid valve; Left AV is the bicuspid (mitral) valve.
Pulmonary Semilunar Valve: Prevents backflow from pulmonary artery to right ventricle.
Aortic Semilunar Valve: Prevents backflow from aorta to left ventricle.

Additional Structures

Chordae Tendineae: Tendinous cords anchoring AV valves to papillary muscles.
Trabeculae Carneae: Irregular muscular ridges in ventricular walls.
Papillary Muscles: Contract to prevent AV valve prolapse during ventricular contraction.
Fossa Ovalis: Remnant of fetal foramen ovale, found in the right atrium.

Tracing Blood Flow Through the Heart

Blood flow from vena cava to aorta:

Superior/Inferior Vena Cava
Right Atrium
Tricuspid Valve (Right AV)
Right Ventricle
Pulmonary Semilunar Valve
Pulmonary Trunk
Pulmonary Arteries
Lungs (gas exchange)
Pulmonary Veins
Left Atrium
Bicuspid (Mitral) Valve (Left AV)
Left Ventricle
Aortic Semilunar Valve
Aorta

Coronary Circulation

The heart's own blood supply is provided by the coronary arteries and veins.

Left & Right Coronary Arteries: Originate from the base of the aorta.
Right Marginal Artery: Supplies right ventricle.
Left Anterior Descending (LAD) Artery: Supplies anterior interventricular septum and left ventricle.
Circumflex Artery: Supplies left atrium and posterior left ventricle.
Right Posterior Descending Artery: Supplies posterior interventricular septum.
Left Marginal Artery: Supplies left ventricle.
Coronary Sulcus: Houses major coronary vessels.
Great Cardiac Vein: Drains blood from heart muscle into the coronary sinus.

Pulmonary & Systemic Circuits

The heart pumps blood through two main circuits:

Pulmonary Circuit: Right side of heart pumps deoxygenated blood to lungs.
Systemic Circuit: Left side of heart pumps oxygenated blood to body tissues.

Cardiac Cycle

Systole vs. Diastole

Systole: Contraction phase; chambers eject blood.
Diastole: Relaxation phase; chambers fill with blood.

Conduction System (Nodes & Pathways)

Sinoatrial (SA) Node: Pacemaker; initiates electrical impulse.
Atrioventricular (AV) Node: Delays impulse, allowing atrial contraction.
AV Bundle (Bundle of His): Conducts impulse to ventricles.
Bundle Branches & Purkinje Fibers: Distribute impulse throughout ventricles.

Heart Sounds (S1, S2)

S1 ("lub"): Closure of AV valves at start of ventricular systole.
S2 ("dub"): Closure of semilunar valves at start of ventricular diastole.

Cardiac Muscle Tissue

Intercalated Discs: Specialized junctions for rapid electrical communication and mechanical strength.
Depolarization (Na-channels): Rapid influx of sodium ions initiates action potential.
Plateau (Ca-channels): Calcium influx prolongs depolarization, allowing sustained contraction.
Repolarization (K-channels): Potassium efflux restores resting membrane potential.

Cardiac Output (CO)

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

Formula:

HR: Heart Rate (beats per minute)
SV: Stroke Volume (volume per beat)

Electrocardiogram (ECG)

Waves & Intervals

P wave: Atrial depolarization
QRS complex: Ventricular depolarization
T wave: Ventricular repolarization
PR interval: Time from atrial to ventricular depolarization
QT interval: Duration of ventricular depolarization and repolarization

Autonomic Heart Rate Effects

Bradycardia: Slow heart rate (<60 bpm)
Tachycardia: Fast heart rate (>100 bpm)
Cardioinhibitory Center: Parasympathetic control; decreases heart rate.
Cardioregulatory Center: Sympathetic control; increases heart rate.

Stroke Volume

Preload: Degree of stretch of cardiac muscle before contraction.
Afterload: Resistance the heart must overcome to eject blood.
Isovolumetric Contraction: Ventricles contract with all valves closed; pressure rises but no blood is ejected.
Isovolumetric Relaxation: Ventricles relax with all valves closed; pressure falls but no blood enters.
Ejection: Blood is pumped out of the left ventricle into the aorta.

Summary Table: Heart Valves and Their Functions

Valve	Location	Function
Tricuspid (Right AV)	Between right atrium & right ventricle	Prevents backflow to right atrium
Bicuspid (Mitral, Left AV)	Between left atrium & left ventricle	Prevents backflow to left atrium
Pulmonary Semilunar	Between right ventricle & pulmonary trunk	Prevents backflow to right ventricle
Aortic Semilunar	Between left ventricle & aorta	Prevents backflow to left ventricle

Example: Tracing a Drop of Blood

For exam preparation, be able to trace a drop of blood from the vena cava through the heart, lungs, and back to the aorta, naming each chamber, valve, and vessel it passes.

Additional info: Academic context and definitions were added to expand brief study guide points into full explanations suitable for exam review.