Heart

🫀 CARDIOVASCULAR SYSTEM — COMPREHENSIVE REVIEWER

I. Cardiovascular System

The cardiovascular system is responsible for transporting blood throughout the body.

Main components

1. Heart – muscular pump that circulates blood.

2. Blood vessels – pathways through which blood travels.

   • Arteries – carry blood away from the heart

   • Veins – carry blood toward the heart

   • Capillaries – allow exchange of gases, nutrients, and wastes

3. Blood – transports oxygen, nutrients, hormones, and wastes.

Major functions

• Delivers oxygen and nutrients to tissues

• Removes carbon dioxide and metabolic wastes

• Transports hormones

• Helps regulate temperature, pH, and fluid balance

• Contributes to immune defense

II. Position of the Heart

The heart is located in the thoracic cavity, specifically in the mediastinum, between the right and left lungs.

Important anatomical points

• Behind the sternum

• Above the diaphragm

• Between the lungs

• Slightly left of the body's midline

• The apex points downward, forward, and toward the left.

• The base is directed upward and posteriorly.

Heart orientation

• Apex → inferior and left

• Base → superior and posterior

III. Structures of the Heart and Their Functions

A. Four Chambers

Easy memory:

Right = lungs
Left = body

IV. Major Structures Inside the Heart

1. Interatrial septum

Separates the right and left atria.

2. Interventricular septum

Separates the right and left ventricles.

3. Atrioventricular (AV) valves

Prevent blood from flowing backward from the ventricles into the atria.

• Tricuspid valve → right side

• Mitral/Bicuspid valve → left side

4. Semilunar valves

Prevent blood from flowing back into the ventricles.

• Pulmonary semilunar valve → between right ventricle and pulmonary trunk

• Aortic semilunar valve → between left ventricle and aorta

5. Chordae tendineae

Strong, cord-like structures attached to the AV valves.

Function: Prevent AV valves from turning inside out during ventricular contraction.

6. Papillary muscles

Muscles attached to the chordae tendineae.

Function: Contract during ventricular systole to help stabilize the AV valves.

7. Trabeculae carneae

Irregular muscular ridges inside the ventricles.

Function: Help strengthen ventricular contraction and prevent the ventricular walls from sticking together.

V. Great Vessels

Superior Vena Cava

Carries deoxygenated blood from the upper body to the right atrium.

Inferior Vena Cava

Carries deoxygenated blood from the lower body to the right atrium.

Pulmonary Trunk

Carries deoxygenated blood from the right ventricle toward the lungs.

It divides into:

• Right pulmonary artery

• Left pulmonary artery

Pulmonary Arteries

Pulmonary arteries

Carry deoxygenated blood from the right ventricle to the lungs.

⭐ Important exception:

Pulmonary arteries carry deoxygenated blood.

This is different from most arteries.

Pulmonary Veins

Carry oxygenated blood from the lungs to the left atrium.

There are normally four pulmonary veins.

Aorta

The body's largest artery.

Carries oxygenated blood from the left ventricle to the systemic circulation.

VI. Process of Blood Circulation

There are two major circuits:

1. Pulmonary circulation

Heart → lungs → heart

Purpose: oxygenates blood and removes carbon dioxide.

2. Systemic circulation

Heart → body → heart

Purpose: delivers oxygen and nutrients to body tissues.

genui{"learning_viz":{"type_id":"BLOOD_CIRCULATION","initial_values":{"circulation":"pulmonary"}}}

Complete pathway

Body tissues
↓
Superior & Inferior Vena Cava
↓
Right Atrium
↓
Tricuspid Valve
↓
Right Ventricle
↓
Pulmonary Semilunar Valve
↓
Pulmonary Trunk
↓
Pulmonary Arteries
↓
Lungs
↓
Pulmonary Veins
↓
Left Atrium
↓
Mitral/Bicuspid Valve
↓
Left Ventricle
↓
Aortic Semilunar Valve
↓
Aorta
↓
Systemic arteries
↓
Body tissues

Remember:

Body → Right Heart → Lungs → Left Heart → Body

VII. Pericardial Cavity and Its Layers

⚠ You wrote "Parietal Cavity and Visceral layers." The anatomical term is usually pericardial cavity, with parietal and visceral layers.

The pericardial cavity is the potential space surrounding the heart.

It contains a small amount of serous fluid, which reduces friction as the heart beats.

Pericardium

The pericardium surrounds and protects the heart.

It has:

1. Fibrous pericardium

• Tough outer connective tissue

• Protects the heart

• Helps anchor the heart in the mediastinum

• Limits excessive expansion

2. Serous pericardium

Has two layers:

Parietal layer

• Lines the inner surface of the fibrous pericardium.

Visceral layer

• Directly covers the surface of the heart.

• Also called the epicardium.

Pericardial cavity

Located between the parietal and visceral layers.

Contains serous fluid for lubrication.

Easy sequence:

Fibrous pericardium → Parietal layer → Pericardial cavity → Visceral layer → Heart

VIII. Layers of the Heart Wall

The heart wall has three layers:

1. Epicardium

• Outer layer

• Also the visceral layer of the serous pericardium

• Protects the heart surface

2. Myocardium

• Middle and thickest layer

• Made mainly of cardiac muscle

• Responsible for contraction and pumping blood

⭐ Myocardium = muscle

3. Endocardium

• Inner lining of the heart chambers

• Smooth surface

• Continuous with the lining of blood vessels

Memory trick:

E-M-E

Epicardium → Myocardium → Endocardium

IX. Coronary Circulation

The heart itself needs oxygen and nutrients.

These are supplied by the coronary arteries.

Coronary arteries

Arise from the beginning of the ascending aorta.

The two main coronary arteries are:

• Right coronary artery (RCA)

• Left coronary artery (LCA)

They branch across the heart and supply the myocardium.

X. Major Branches of the Coronary Arteries

Right Coronary Artery (RCA)

Major branches include:

1. Right marginal artery

Supplies portions of the right ventricle.

2. Posterior interventricular artery

Also called the posterior descending artery (PDA).

Supplies portions of the ventricles and interventricular septum.

Left Coronary Artery (LCA)

The LCA typically divides into:

1. Anterior interventricular artery

Also called the left anterior descending (LAD) artery.

Supplies much of the anterior ventricular walls and interventricular septum.

2. Circumflex artery

Runs around the left side of the heart.

Supplies portions of the left atrium and left ventricle.

Simple memory:

LCA → LAD + Circumflex

XI. Cardiac Veins

Cardiac veins drain deoxygenated blood from the myocardium.

Major cardiac veins include:

1. Great cardiac vein

Runs alongside the anterior interventricular artery.

2. Middle cardiac vein

Runs alongside the posterior interventricular artery.

3. Small cardiac vein

Drains portions of the right side of the heart.

Most cardiac veins ultimately drain into the:

Coronary Sinus

XII. Coronary Sinus

The coronary sinus is a large venous channel located on the posterior surface of the heart.

Function

Collects most of the deoxygenated blood from the heart muscle.

It empties into the:

Right atrium

Pathway:

Cardiac veins → Coronary sinus → Right atrium

⭐ Important distinction:

Coronary arteries = bring oxygenated blood TO heart muscle

Cardiac veins = take deoxygenated blood AWAY from heart muscle

Coronary sinus = collects cardiac venous blood and empties into right atrium

XIII. Disruptions in the Structure of the Heart

Structural abnormalities can interfere with normal blood flow.

1. Septal defects

A hole or abnormal opening in the septum.

Atrial septal defect (ASD)

Abnormal opening between the atria.

Ventricular septal defect (VSD)

Abnormal opening between the ventricles.

These can allow blood to pass between chambers in an abnormal manner.

2. Valve disorders

Stenosis

A valve becomes narrowed, making it harder for blood to pass through.

Regurgitation/insufficiency

A valve does not close properly, allowing blood to flow backward.

3. Congenital structural abnormalities

These are abnormalities present from birth.

Examples include:

• Septal defects

• Abnormal valve formation

• Abnormal development of major vessels

XIV. Blood Vessel Structure

Arteries

• Carry blood away from the heart

• Thick, elastic walls

• Usually carry oxygenated blood

Veins

• Carry blood toward the heart

• Thinner walls

• Many contain valves

• Usually carry deoxygenated blood

Capillaries

• Microscopic vessels

• Walls are only about one cell thick

• Main site of exchange between blood and tissues

⭐ Don't memorize arteries and veins based only on oxygen.

The key rule is:

Artery = away

Vein = toward

XV. High-Yield Comparison

🧠 MUST-MEMORIZE CONCEPTS

The 4 chambers

RA → RV → LA → LV

Blood flow

Body → RA → RV → Lungs → LA → LV → Body

Heart wall

Epicardium → Myocardium → Endocardium

Pericardial layers

Parietal → Cavity → Visceral

Coronary circulation

Coronary arteries → Heart muscle → Cardiac veins → Coronary sinus → Right atrium

Great vessels

Vena cava → Pulmonary trunk → Pulmonary arteries → Pulmonary veins → Aorta

Most important exceptions

🫁 Pulmonary arteries = deoxygenated

🫁 Pulmonary veins = oxygenated

❤ Coronary arteries = supply the heart

❤ Coronary sinus = drains the heart

One-line master pathway:

BODY → VENA CAVA → RIGHT HEART → PULMONARY ARTERIES → LUNGS → PULMONARY VEINS → LEFT HEART → AORTA → BODY