Cardiovascular System: Heart Anatomy and Function

Pulmonary and Systemic Circuits

Overview of Heart Function as Two Muscular Pumps

The heart functions as two separate muscular pumps that supply blood to two distinct circuits: the pulmonary circuit and the systemic circuit.

• Pulmonary Circuit: The right side of the heart receives deoxygenated blood from body tissues and pumps it to the lungs for oxygenation.

• Systemic Circuit: The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body.

• Key Pathway: Right Atrium → Right Ventricle → Pulmonary Circuit; Left Atrium → Left Ventricle → Systemic Circuit

Example: Blood low in oxygen returns from the body to the right atrium, is pumped to the lungs via the right ventricle, returns oxygenated to the left atrium, and is pumped to the body via the left ventricle.

Heart Anatomy

Location of the Heart in the Mediastinum

The heart is located in the mediastinum, the central compartment of the thoracic cavity, between the lungs and behind the sternum.

• Position: Sits superior to the diaphragm, posterior to the sternum, and anterior to the vertebral column.

• Apex: Points to the left of the midline, typically at the level of the 5th intercostal space.

• Base: Located at the top, where the great vessels attach.

Example: The heart's apex is found at the 2nd rib to the middle of the 5th and 6th ribs.

Coverings of the Heart

Pericardium: Structure and Function

The heart is enclosed by a double-walled sac called the pericardium, which protects and anchors the heart within the mediastinum.

• Fibrous Pericardium: The tough, outer layer made of dense connective tissue. It prevents overfilling and anchors the heart.

• Serous Pericardium: The inner layer, consisting of two parts:

  • Parietal Layer: Lines the inner surface of the fibrous pericardium.

  • Visceral Layer (Epicardium): Covers the heart surface.

• Pericardial Cavity: The space between the parietal and visceral layers, filled with serous fluid to reduce friction during heartbeats.

Clinical Note: Pericarditis is inflammation of the pericardium, which can lead to pericardial effusion and cardiac tamponade (compression of the heart due to fluid accumulation).

Layers of the Heart Wall

Three Distinct Layers

The heart wall consists of three layers, each with specific functions and structures.

• Epicardium: The outermost layer, also known as the visceral layer of the serous pericardium.

• Myocardium: The thick, middle layer composed of cardiac muscle tissue. Responsible for the contractile force of the heart.

• Endocardium: The innermost layer, made of simple squamous epithelium (endothelium). Lines the heart chambers and covers the heart valves.

Example: The myocardium is organized in spiral bundles, allowing efficient contraction and blood ejection.

Heart Chambers and Septa

Internal Structure of the Heart

The heart contains four chambers separated by septa:

• Right Atrium and Left Atrium: Superior chambers that receive blood.

• Right Ventricle and Left Ventricle: Inferior chambers that pump blood out of the heart.

• Interatrial Septum: Separates the right and left atria. Contains the fossa ovalis, a remnant of the fetal foramen ovale.

• Interventricular Septum: Separates the right and left ventricles.

Example: The interatrial septum prevents mixing of oxygenated and deoxygenated blood between the atria.

Heart Chambers and Surface Grooves

External Landmarks of the Heart

Surface grooves mark the boundaries between the heart's chambers and serve as pathways for coronary vessels.

• Coronary Sulcus (Atrioventricular Groove): Runs between the atria and ventricles.

• Anterior and Posterior Interventricular Sulci: Run between the ventricles on the anterior and posterior surfaces.

Example: The coronary sulcus contains the major coronary arteries and veins supplying the heart muscle.

Heart Chambers: Atria

Structure and Function of the Atria

The atria are thin-walled chambers that receive blood returning to the heart.

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

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

• Auricles: Small, ear-like extensions that increase atrial volume.

• Pectinate Muscles: Muscular ridges found in the atrial walls, especially in the right atrium.

• Fossa Ovalis: A shallow depression in the interatrial septum, marking the site of the fetal foramen ovale.

Example: The right atrium collects blood from the systemic circuit, while the left atrium collects blood from the pulmonary circuit.

Summary Table: Heart Wall Layers

Layer	Location	Main Function
Epicardium	Outer surface	Protection, reduces friction
Myocardium	Middle layer	Contraction, pumps blood
Endocardium	Inner surface	Lines chambers, covers valves

Summary Table: Heart Chambers and Blood Flow

Chamber	Receives Blood From	Pumps Blood To	Type of Blood
Right Atrium	Body (systemic veins)	Right Ventricle	Deoxygenated
Right Ventricle	Right Atrium	Lungs (pulmonary artery)	Deoxygenated
Left Atrium	Lungs (pulmonary veins)	Left Ventricle	Oxygenated
Left Ventricle	Left Atrium	Body (aorta)	Oxygenated

Key Equations

• Cardiac Output: The amount of blood pumped by each ventricle per minute.

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

$\text{Stroke Volume} = \text{End Diastolic Volume} - \text{End Systolic Volume}$

Additional info:

• Some anatomical details and clinical notes were inferred for completeness and clarity.

• Tables were constructed to summarize key structural and functional relationships.