Exercise 30 Review Sheet Anatomy Of The Heart

Let's delve into the intricate world of the heart's anatomy, systematically reviewing the key components and their functions as typically covered in an anatomy exercise. This comprehensive examination will serve as an invaluable tool for students, healthcare professionals, and anyone with a keen interest in understanding the remarkable organ that sustains life.

Anatomy of the Heart: A Detailed Review

The heart, a muscular pump roughly the size of a fist, resides in the chest cavity, specifically within the mediastinum. Its primary function is to circulate blood throughout the body, delivering oxygen and nutrients to cells while removing waste products. Understanding the heart's anatomical structures is crucial to comprehending its complex physiology.

External Anatomy

• Size and Location: As mentioned, the heart is about the size of a fist. It sits obliquely in the mediastinum, with approximately two-thirds of its mass lying to the left of the midline.

• Apex: The pointed, inferior portion of the heart.

• Base: The broader, superior aspect where major blood vessels attach.

• Surfaces:

  • Anterior (Sternocostal) Surface: Formed primarily by the right ventricle.
  • Inferior (Diaphragmatic) Surface: Rests upon the diaphragm and is formed mainly by the left ventricle and partly by the right ventricle.
  • Left Pulmonary Surface: Faces the left lung and is formed mainly by the left ventricle.
  • Right Pulmonary Surface: Faces the right lung and is formed mainly by the right atrium.

• Borders:

  • Superior Border: Formed by the atria and great vessels.
  • Right Border: Formed by the right atrium.
  • Inferior Border: Formed by the right ventricle and a small portion of the left ventricle.
  • Left Border: Formed by the left ventricle and a small portion of the left atrium.

• Pericardium: A double-layered sac that surrounds and protects the heart. It consists of two main parts:

  • Fibrous Pericardium: The tough, outer layer that anchors the heart within the mediastinum and prevents overfilling.
  • Serous Pericardium: A thinner, double-layered membrane:
    • Parietal Layer: Fused to the fibrous pericardium.
    • Visceral Layer (Epicardium): Adheres directly to the heart's surface.
  • Pericardial Cavity: The space between the parietal and visceral layers, containing a small amount of serous fluid that reduces friction during heartbeats.

Internal Anatomy: Chambers and Valves

The heart is divided into four chambers: two atria (right and left) and two ventricles (right and left). These chambers work in a coordinated fashion to receive and pump blood. Valves ensure unidirectional blood flow.

• Atria: The superior, receiving chambers.

  • Right Atrium: Receives deoxygenated blood from the superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus.
    • Pectinate Muscles: Muscular ridges on the anterior wall of the right atrium.
    • Fossa Ovalis: A shallow depression in the interatrial septum, representing the remnant of the foramen ovale in the fetal heart.
  • Left Atrium: Receives oxygenated blood from the four pulmonary veins.
    • The left atrium has a smooth wall, except for the auricle, which contains pectinate muscles.

• Ventricles: The inferior, pumping chambers.

  • Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary trunk.
    • Trabeculae Carneae: Irregular muscular ridges on the inner surface of the ventricles.
    • Papillary Muscles: Cone-shaped muscles that project from the ventricular walls and attach to the chordae tendineae.
    • Chordae Tendineae: Tendon-like cords that connect the papillary muscles to the cusps of the tricuspid valve.
  • Left Ventricle: Pumps oxygenated blood to the entire body via the aorta.
    • The left ventricle has thicker walls than the right ventricle because it needs to generate higher pressure to pump blood to the systemic circulation.
    • It also contains trabeculae carneae and papillary muscles attached to chordae tendineae.

• Valves: Ensure unidirectional blood flow through the heart.

  • Atrioventricular (AV) Valves: Located between the atria and ventricles.
    • Tricuspid Valve (Right AV Valve): Located between the right atrium and right ventricle; has three cusps.
    • Mitral Valve (Bicuspid Valve, Left AV Valve): Located between the left atrium and left ventricle; has two cusps.
    • The chordae tendineae and papillary muscles prevent the AV valves from everting (bulging back into the atria) during ventricular contraction.
  • Semilunar Valves: Located at the exit of each ventricle.
    • Pulmonary Valve: Located between the right ventricle and the pulmonary trunk; has three cusps.
    • Aortic Valve: Located between the left ventricle and the aorta; has three cusps.
    • These valves do not have chordae tendineae or papillary muscles.

Internal Anatomy: Septa

• Interatrial Septum: Separates the right and left atria.
• Interventricular Septum: Separates the right and left ventricles. This septum is a substantial muscular wall.

Blood Flow Through the Heart

Understanding the sequence of blood flow is crucial for comprehending cardiac function.

1. Deoxygenated blood enters the right atrium through the superior vena cava, inferior vena cava, and coronary sinus.
2. The blood passes through the tricuspid valve into the right ventricle.
3. The right ventricle contracts, pumping blood through the pulmonary valve into the pulmonary trunk.
4. The pulmonary trunk divides into the right and left pulmonary arteries, which carry deoxygenated blood to the lungs.
5. In the lungs, blood releases carbon dioxide and picks up oxygen.
6. Oxygenated blood returns to the left atrium via the four pulmonary veins.
7. The blood passes through the mitral valve into the left ventricle.
8. The left ventricle contracts, pumping blood through the aortic valve into the aorta.
9. The aorta distributes oxygenated blood to the entire body.

Histology of the Heart Wall

The heart wall is composed of three layers:

• Epicardium (Visceral Pericardium): The outermost layer, composed of a single layer of squamous epithelial cells and underlying connective tissue. This layer contains blood vessels, lymphatic vessels, and nerves that supply the heart.

• Myocardium: The middle and thickest layer, composed of cardiac muscle tissue. This layer is responsible for the heart's pumping action. The cardiac muscle cells are arranged in spiral or circular bundles, allowing the heart to contract efficiently.

• Endocardium: The innermost layer, composed of a thin layer of squamous epithelial cells (endothelium) and underlying connective tissue. This layer lines the heart chambers and covers the heart valves, providing a smooth surface for blood flow. It is continuous with the endothelium of the blood vessels entering and leaving the heart.

Cardiac Muscle Tissue

• Cardiomyocytes: Short, branched cells with one or two centrally located nuclei.
• Striations: Like skeletal muscle, cardiac muscle exhibits striations due to the arrangement of actin and myosin filaments.
• Intercalated Discs: Unique structures that connect cardiac muscle cells. They contain:
  • Desmosomes: Provide strong adhesion between cells.
  • Gap Junctions: Allow for rapid spread of electrical signals, enabling coordinated contraction.
• Autorhythmicity: Cardiac muscle cells have the ability to generate their own electrical impulses, allowing the heart to beat independently. This is facilitated by specialized cells within the sinoatrial (SA) node.

Cardiac Skeleton

A framework of dense connective tissue that:

• Surrounds and supports the heart valves.
• Provides points of attachment for cardiac muscle.
• Electrically insulates the atria from the ventricles, preventing simultaneous contraction.

Coronary Circulation

The heart, like any other organ, requires its own blood supply. This is provided by the coronary arteries.

• Right Coronary Artery (RCA): Arises from the ascending aorta and travels in the coronary sulcus (atrioventricular groove). It typically supplies the right atrium, right ventricle, and part of the left ventricle. Branches include:

  • Right Marginal Artery: Supplies the right ventricle.
  • Posterior Interventricular Artery (Posterior Descending Artery): Runs in the posterior interventricular sulcus and supplies the posterior walls of both ventricles and the posterior portion of the interventricular septum.

• Left Coronary Artery (LCA): Arises from the ascending aorta and divides into two major branches:

  • Left Anterior Descending Artery (LAD): Runs in the anterior interventricular sulcus and supplies the anterior walls of both ventricles and the anterior portion of the interventricular septum. This artery is often referred to as the "widow maker" due to its critical role in supplying blood to a large portion of the heart.
  • Circumflex Artery: Travels in the coronary sulcus around the left side of the heart and supplies the left atrium and the posterior and lateral walls of the left ventricle.

• Coronary Veins: Drain deoxygenated blood from the myocardium and empty into the coronary sinus, which then empties into the right atrium.

  • Great Cardiac Vein: Runs alongside the anterior interventricular artery.
  • Middle Cardiac Vein: Runs alongside the posterior interventricular artery.
  • Small Cardiac Vein: Runs alongside the right marginal artery.

Innervation of the Heart

The heart is innervated by the autonomic nervous system (ANS), which regulates heart rate and contractility.

• Sympathetic Nervous System: Increases heart rate and contractility.
• Parasympathetic Nervous System: Decreases heart rate.

The cardiac plexus, located near the base of the heart, contains both sympathetic and parasympathetic fibers.

Conduction System of the Heart

The heart's coordinated contraction is controlled by an intrinsic conduction system.

• Sinoatrial (SA) Node: Located in the right atrial wall near the superior vena cava opening. It is the pacemaker of the heart, initiating electrical impulses that trigger each heartbeat.

• Atrioventricular (AV) Node: Located in the interatrial septum near the tricuspid valve. It receives impulses from the SA node and delays them slightly to allow the atria to contract before the ventricles.

• Atrioventricular (AV) Bundle (Bundle of His): Located in the upper part of the interventricular septum. It receives impulses from the AV node and transmits them down the interventricular septum.

• Right and Left Bundle Branches: The AV bundle divides into right and left bundle branches, which run along the interventricular septum toward the apex of the heart.

• Purkinje Fibers: Branch extensively throughout the ventricular myocardium. They rapidly conduct the impulses, causing the ventricles to contract in a coordinated manner.

Clinical Significance

Understanding the anatomy of the heart is essential for diagnosing and treating various cardiac conditions.

• Myocardial Infarction (Heart Attack): Blockage of a coronary artery, leading to ischemia (lack of blood flow) and damage to the myocardium. The location and extent of the damage depend on which coronary artery is affected.

• Valve Disorders: Stenosis (narrowing) or insufficiency (leakage) of heart valves, which can impair blood flow and lead to heart failure.

• Congenital Heart Defects: Structural abnormalities present at birth, such as septal defects or valve abnormalities.

• Arrhythmias: Irregular heart rhythms caused by abnormalities in the heart's conduction system.

• Cardiomyopathy: Disease of the heart muscle, leading to impaired contractility and heart failure.

Exercise 30 Review Sheet: Key Structures to Identify

A typical "Exercise 30 Review Sheet" might ask you to identify the following structures on a heart model or diagram:

• External Structures: Apex, base, atria, ventricles, pulmonary trunk, aorta, superior vena cava, inferior vena cava, pulmonary veins.

• Internal Structures: Right atrium, left atrium, right ventricle, left ventricle, tricuspid valve, mitral valve, pulmonary valve, aortic valve, interatrial septum, interventricular septum, chordae tendineae, papillary muscles, trabeculae carneae, fossa ovalis, pectinate muscles.

• Coronary Circulation: Right coronary artery, left coronary artery, left anterior descending artery, circumflex artery, right marginal artery, posterior interventricular artery, great cardiac vein, middle cardiac vein, small cardiac vein, coronary sinus.

• Conduction System: SA node, AV node, AV bundle, right and left bundle branches, Purkinje fibers.

In addition to identification, you may also be asked to describe the function of each structure and trace the flow of blood through the heart.

Frequently Asked Questions (FAQ)

• What is the difference between the pulmonary and systemic circulations? The pulmonary circulation involves the flow of blood from the right ventricle to the lungs for oxygenation and back to the left atrium. The systemic circulation involves the flow of oxygenated blood from the left ventricle to the rest of the body and back to the right atrium.

• Why is the left ventricle thicker than the right ventricle? The left ventricle pumps blood to the entire systemic circulation, requiring it to generate much higher pressure than the right ventricle, which only pumps blood to the lungs.

• What is the function of the chordae tendineae and papillary muscles? They prevent the atrioventricular valves (tricuspid and mitral) from everting (bulging back into the atria) during ventricular contraction, ensuring unidirectional blood flow.

• What is the pacemaker of the heart? The sinoatrial (SA) node, located in the right atrium, is the pacemaker of the heart. It initiates the electrical impulses that trigger each heartbeat.

• What is the coronary sinus? A large vein on the posterior surface of the heart that collects deoxygenated blood from the coronary veins and empties into the right atrium.

Conclusion

A thorough understanding of the heart's anatomy is fundamental to comprehending its physiological function and diagnosing and treating cardiac diseases. By meticulously reviewing the external and internal structures, blood flow pathways, histological components, coronary circulation, and conduction system, we gain invaluable insights into this vital organ. Utilizing tools like the "Exercise 30 Review Sheet" can solidify your knowledge and prepare you for success in anatomy studies and related healthcare fields. The heart, a marvel of biological engineering, deserves our deepest appreciation and continued study.