Heart Anatomy and Physiology: Structure, Function, and Blood Flow

Module 17.1 Overview of the Heart

The Cardiovascular System

The cardiovascular system is composed of the heart, blood vessels, and blood. Its primary function is to transport oxygen, nutrients, and waste products throughout the body.

• Heart: Pumps blood to all body tissues.

• Blood: The liquid medium carrying oxygen and nutrients.

• Blood vessels: Tubular structures that distribute blood throughout the cardiovascular system.

Location and Basic Structure of the Heart

The heart is a cone-shaped organ located slightly to the left of the midline in the thoracic cavity, posterior to the sternum and above the diaphragm.

• Apex: The pointed end, directed inferiorly and to the left.

• Base: The flattened posterior side, facing the vertebral column.

• Size: About the size of a fist, weighing 250–350 grams.

• Chambers: Four hollow chambers: right and left atria (upper chambers), right and left ventricles (lower chambers).

• Surface features:

  • Atrioventricular sulcus: Boundary between atria and ventricles.

  • Interventricular sulcus: Boundary between right and left ventricles.

• Veins and arteries: The right and left atria receive blood from veins; ventricles pump blood into arteries.

Circulation of Blood: Pulmonary and Systemic Circuits

The heart is functionally divided into right and left sides, each serving a distinct circuit:

• Pulmonary circuit: Right side pumps deoxygenated blood to the lungs for oxygenation.

• Systemic circuit: Left side pumps oxygenated blood to the rest of the body.

• Gas exchange: Occurs in the pulmonary capillaries (lungs) and systemic capillaries (body tissues).

• Pressure: Pulmonary circuit is low-pressure; systemic circuit is high-pressure.

Other Functions of the Heart

• Maintains homeostasis of blood pressure (known as blood pressure).

• Acts as an endocrine organ, producing atrial natriuretic peptide (ANP) to lower blood pressure by reducing sodium reabsorption in the kidneys.

Module 17.2 Heart Anatomy and Blood Flow Pathway

Pericardium, Heart Wall, and Heart Skeleton

The pericardium is a membranous sac surrounding the heart, providing protection and anchorage.

• Fibrous pericardium: Tough outer layer of collagen bundles, anchors heart to diaphragm and great vessels.

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

• Visceral pericardium (epicardium): Adheres directly to the heart.

• Pericardial cavity: Space between parietal and visceral layers, filled with pericardial fluid to reduce friction.

Heart Wall Structure

• Epicardium: Outermost layer, also the visceral pericardium.

• Myocardium: Middle layer, composed of cardiac muscle cells (myocytes) and a fibrous skeleton of dense irregular connective tissue.

• Endocardium: Innermost layer, composed of simple squamous epithelium (endothelium) and connective tissue.

Heart Chambers and Valves

The heart contains four chambers: two atria and two ventricles.

• Atria: Receive blood from veins.

• Ventricles: Pump blood into arteries.

• Valves: Prevent backflow of blood:

  • Atrioventricular (AV) valves: Between atria and ventricles.

  • Semilunar valves: Between ventricles and arteries.

Great Vessels of the Heart

• Aorta: Largest artery, carries oxygenated blood from left ventricle to body.

• Pulmonary trunk: Largest vessel in pulmonary circuit, carries deoxygenated blood from right ventricle to lungs.

• Superior and inferior vena cava (SVC, IVC): Major veins draining deoxygenated blood into right atrium.

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

Chambers of the Heart

• Ventricles: Larger and thicker-walled than atria; left ventricle is thicker due to higher pressure required for systemic circulation.

• Atria: Right atrium is larger and more anterior; contains pectinate muscles on its inner wall.

• Interatrial septum: Thin wall separating atria; contains fossa ovalis (remnant of fetal foramen ovale).

• Interventricular septum: Thick wall separating ventricles.

Valves of the Heart

• AV valves:

  • Tricuspid valve: Between right atrium and right ventricle (three cusps).

  • Bicuspid (mitral) valve: Between left atrium and left ventricle (two cusps).

• Semilunar valves:

  • Pulmonary valve: Between right ventricle and pulmonary trunk.

  • Aortic valve: Between left ventricle and aorta.

• Chordae tendineae: Fibrous cords attaching AV valve cusps to papillary muscles, preventing valve prolapse.

Summary Table: Heart Chambers, Valves, and Major Vessels

Chamber	Receives Blood From	Pumps Blood To	Valve	Major Vessel
Right Atrium	Superior/Inferior Vena Cava, Coronary Sinus	Right Ventricle	Tricuspid Valve	—
Right Ventricle	Right Atrium	Pulmonary Trunk	Pulmonary Valve	Pulmonary Arteries
Left Atrium	Pulmonary Veins	Left Ventricle	Bicuspid (Mitral) Valve	—
Left Ventricle	Left Atrium	Aorta	Aortic Valve	Aorta

Key Terms and Definitions

• Myocyte: Cardiac muscle cell responsible for contraction.

• Endothelium: Simple squamous epithelial lining of blood vessels and heart chambers.

• Papillary muscles: Muscles in ventricles that anchor chordae tendineae.

• Fossa ovalis: Depression in interatrial septum, remnant of fetal foramen ovale.

• Trabeculae carneae: Irregular ridges of muscle on ventricular walls.

Formulas and Equations

• Cardiac Output (CO): The amount of blood pumped by each ventricle per minute. $CO = HR \times SV$ Where HR is heart rate (beats per minute), and SV is stroke volume (mL per beat).

• Stroke Volume (SV): The amount of blood ejected by a ventricle during one contraction. $SV = EDV - ESV$ Where EDV is end-diastolic volume, and ESV is end-systolic volume.

Example: Blood Flow Through the Heart

1. Deoxygenated blood enters the right atrium via the SVC, IVC, and coronary sinus.

2. Passes through the tricuspid valve into the right ventricle.

3. Pumped through the pulmonary valve into the pulmonary trunk and arteries to the lungs.

4. Oxygenated blood returns via pulmonary veins to the left atrium.

5. Passes through the bicuspid (mitral) valve into the left ventricle.

6. Pumped through the aortic valve into the aorta and systemic circulation.

Additional info: The notes above expand on the original outline by providing definitions, examples, and formulas for cardiac output and stroke volume, as well as a summary table for heart chambers and valves. This guide is suitable for college-level Anatomy & Physiology students preparing for exams on heart anatomy and physiology.