Study Guide: Heart Anatomy, Physiology, and Pathology (Chapter 20)

Heart Anatomy and Physiology

Mediastinum and Position of the Heart in the Thorax

The heart is located in the mediastinum, a central compartment of the thoracic cavity. It lies between the lungs, posterior to the sternum, and anterior to the vertebral column. - Mediastinum: The space containing the heart, great vessels, thymus, esophagus, and trachea. - Position: The heart is slightly left of the midline, with its apex pointing downward and to the left.

Pericardium: Structure and Function

The pericardium is a double-walled sac that surrounds the heart, providing protection and anchoring it within the thorax. - Fibrous Pericardium: Tough outer layer that prevents overexpansion. - Serous Pericardium: Inner layer divided into parietal and visceral (epicardium) layers, with pericardial fluid reducing friction.

Pericarditis: Definition and Etiology

- Pericarditis: Inflammation of the pericardium, often caused by infection, autoimmune disorders, or trauma. - Etiology: Viral, bacterial, or idiopathic causes; can lead to chest pain and pericardial effusion.

Structure and Function of Heart Wall Layers

The heart wall consists of three layers, each with distinct functions. - Epicardium: Outer layer, also known as visceral pericardium. - Myocardium: Middle, muscular layer responsible for contraction. - Endocardium: Inner layer lining the chambers and valves.

Heart Muscle Histology: Intercalated Discs

Cardiac muscle cells are connected by intercalated discs, which facilitate synchronized contraction. - Intercalated Discs: Specialized junctions containing gap junctions and desmosomes. - Function: Allow rapid transmission of electrical impulses and strong mechanical attachment.

Cardiac Hypertrophy: Definition, Causes, and Risk Factors

- Cardiac Hypertrophy: Thickening of the heart muscle, usually the left ventricle. - Causes: Chronic hypertension, valvular disease, athletic training. - Risk Factors: High blood pressure, genetic predisposition, heart valve disorders.

Heart Anatomy and Blood Flow

Internal and External Anatomy of the Heart

The heart has four chambers (right/left atria, right/left ventricles) and major vessels (aorta, pulmonary arteries/veins, vena cavae). - External Features: Coronary arteries, auricles, sulci. - Internal Features: Valves (tricuspid, mitral, pulmonary, aortic), septa.

Blood Flow Through the Heart

Blood flows in a specific sequence through the heart chambers and valves. - Sequence: Vena cavae → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary artery → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta.

Heart Sounds and Valve Disorders

Heart Sounds: S1 and S2

Heart sounds are produced by the closing of heart valves. - S1 (Lub): Closure of AV valves (mitral and tricuspid). - S2 (Dub): Closure of semilunar valves (aortic and pulmonary).

Valve Disorders: MVP and AVS

- Mitral Valve Prolapse (MVP): Mitral valve leaflets bulge into the left atrium during systole; may cause regurgitation. - Aortic Valve Stenosis (AVS): Narrowing of the aortic valve, impeding blood flow from the left ventricle. - Etiology: MVP is often genetic or due to connective tissue disorders; AVS is commonly caused by age-related calcification.

Coronary Artery Disease and Myocardial Infarction

Coronary Artery Disease (CAD)

- Definition: Narrowing or blockage of coronary arteries due to atherosclerosis. - Effects: Reduced blood flow to myocardium, risk of angina and MI.

Blood Tests for Myocardial Infarction (MI)

Several blood tests are used to diagnose MI by detecting cardiac biomarkers.

Test	Purpose
Troponin	Highly specific for cardiac injury; rises within hours of MI
CK-MB	Creatine kinase isoenzyme; indicates myocardial damage
Myoglobin	Early marker, but less specific

Cardiac Conduction and ECG Interpretation

Conduction System Pathway

The heart's electrical system coordinates contraction. - Pathway: SA node → AV node → Bundle of His → bundle branches → Purkinje fibers.

ECG Waves: P, QRS, T

- P wave: Atrial depolarization. - QRS complex: Ventricular depolarization. - T wave: Ventricular repolarization.

Importance of Slow Calcium Channels

- Myocardium: Slow calcium channels prolong action potential, allowing sustained contraction. - Skeletal Muscle: Relies mainly on fast sodium channels; shorter action potential.

ST Elevation in MI

- ST Elevation: Indicates acute myocardial injury; seen in ECG during MI.

Cardiovascular Physiology

Blood Pressure: Diastole and Systole

- Systole: Ventricular contraction; highest pressure. - Diastole: Ventricular relaxation; lowest pressure.

ANP/BNP Hormones: Origin and Actions

- Atrial Natriuretic Peptide (ANP): Released from atria; promotes sodium excretion, reduces blood volume. - Brain Natriuretic Peptide (BNP): Released from ventricles; similar effects, used as a marker for heart failure.

Cardio-Dynamics: CO, SV, Preload, Afterload

Cardio-dynamics refers to the mechanics of heart function. - Cardiac Output (CO): Volume of blood pumped per minute. $CO = HR \times SV$ - Stroke Volume (SV): Volume of blood ejected per beat. - Preload: Degree of stretch of cardiac muscle before contraction. - Afterload: Resistance the heart must overcome to eject blood.

Ejection Fraction and Congestive Heart Failure (CHF)

- Ejection Fraction (EF): Percentage of blood ejected from ventricle per beat. $EF = \frac{SV}{EDV} \times 100\%$ - Normal EF: 55-70%. - CHF: EF < 40% indicates heart failure; heart cannot pump effectively.

Example Calculation:

If EDV = 120 mL, SV = 70 mL: $EF = \frac{70}{120} \times 100\% = 58.3\%$

Summary Table: Key Heart Concepts

Concept	Definition	Normal Value/Range
Cardiac Output (CO)	Blood pumped per minute	4-8 L/min
Stroke Volume (SV)	Blood pumped per beat	60-100 mL
Ejection Fraction (EF)	% blood ejected per beat	55-70%
Blood Pressure	Force of blood on vessel walls	120/80 mmHg