Heart Structure and Function: APHY102 Exam Review Study Notes

Heart Structure and Function

Layers of the Heart Wall

The heart wall consists of three main layers, each with distinct functions and characteristics essential for cardiac physiology.

• Epicardium: The outermost layer, also known as the visceral pericardium. It provides protection and contains blood vessels that supply the heart.

• Myocardium: The thick, muscular middle layer responsible for the contractile force needed to pump blood.

• Endocardium: The innermost layer lining the heart chambers and valves, providing a smooth surface for blood flow.

Example: Damage to the myocardium, such as in myocardial infarction, impairs the heart's ability to contract effectively.

Pericardium

The pericardium is a double-walled sac that surrounds and protects the heart, consisting of the fibrous and serous pericardium.

• Fibrous Pericardium: Tough outer layer that anchors the heart and prevents overfilling.

• Serous Pericardium: Inner layer divided into parietal and visceral layers, with pericardial fluid reducing friction during heartbeats.

Blood Flow Through the Heart

Understanding the pathway of blood through the heart is crucial for grasping cardiac physiology and the oxygenation process.

• Right Atrium: Receives deoxygenated blood from the body via the superior and inferior vena cava.

• Right Ventricle: Pumps blood to the lungs through the pulmonary artery for oxygenation.

• Left Atrium: Receives oxygenated blood from the lungs via the pulmonary veins.

• Left Ventricle: Pumps oxygenated blood to the body through the aorta.

Key Questions:

• Where does blood enter the right atrium from?

• How does blood get to the lungs?

• How is oxygenated blood returned to the heart?

• Which chamber sends blood to the body?

Example: Blood flows from the right atrium to the right ventricle, then to the lungs, returns to the left atrium, and is pumped out by the left ventricle.

Major Heart Vessels

The heart is connected to several major vessels that facilitate blood flow to and from the heart.

• Superior/Inferior Vena Cava: Bring deoxygenated blood from the body to the right atrium.

• Pulmonary Arteries: Carry deoxygenated blood from the right ventricle to the lungs.

• Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.

• Aorta: Distributes oxygenated blood from the left ventricle to the body.

Heart Valves

Valves ensure unidirectional blood flow and prevent backflow within the heart.

• Tricuspid Valve: Between right atrium and right ventricle.

• Pulmonary Valve: Between right ventricle and pulmonary artery.

• Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

• Aortic Valve: Between left ventricle and aorta.

Example: The mitral valve prevents backflow of blood into the left atrium during ventricular contraction.

Coronary Circulation

The heart muscle itself requires a dedicated blood supply, provided by the coronary arteries and veins.

• Coronary Arteries: Branch from the aorta and supply oxygenated blood to the myocardium.

• Coronary Veins: Collect deoxygenated blood from the myocardium and drain into the right atrium via the coronary sinus.

Cardiac Conduction System

The heart's electrical system coordinates contraction and maintains rhythmic heartbeat.

• Sinoatrial (SA) Node: The primary pacemaker, initiates electrical impulses.

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

• Bundle of His, Bundle Branches, Purkinje Fibers: Distribute impulses throughout the ventricles.

Example: Damage to the SA node can result in arrhythmias and require artificial pacemakers.

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including contraction (systole) and relaxation (diastole).

• Systole: Contraction phase, blood is ejected from the chambers.

• Diastole: Relaxation phase, chambers fill with blood.

Equation:

$\text{Cardiac Output} = \text{Heart Rate} \times \text{Stroke Volume}$

Example: Increased heart rate or stroke volume raises cardiac output, important during exercise.

Heart Sounds

Heart sounds are produced by the closing of valves and can be used to diagnose cardiac function.

• "Lub" (S1): Closure of AV valves (tricuspid and mitral).

• "Dub" (S2): Closure of semilunar valves (aortic and pulmonary).

Common Heart Conditions

Several conditions can affect heart function and structure.

• Myocardial Infarction: Blockage of coronary arteries leading to heart muscle death.

• Arrhythmias: Abnormal heart rhythms due to conduction system defects.

• Valve Disorders: Stenosis or regurgitation affecting blood flow.

Definitions and Key Terms

• Systole: Contraction phase of the cardiac cycle.

• Diastole: Relaxation phase of the cardiac cycle.

• Stroke Volume: Amount of blood pumped by a ventricle per beat.

• Cardiac Output: Total volume of blood pumped by the heart per minute.

Table: Heart Chambers and Associated Vessels

Chamber	Receives Blood From	Sends Blood To	Main Vessel
Right Atrium	Body (via vena cavae)	Right Ventricle	Tricuspid Valve
Right Ventricle	Right Atrium	Lungs	Pulmonary Artery
Left Atrium	Lungs (via pulmonary veins)	Left Ventricle	Bicuspid (Mitral) Valve
Left Ventricle	Left Atrium	Body	Aorta

Additional info:

• Definitions for terms such as "systole," "diastole," "cardiac cycle," and "stroke volume" were added for completeness.

• Table summarizing heart chambers and associated vessels was inferred from standard anatomy knowledge.