Exercise 20 Review Sheet Anatomy Of The Heart Answers

Alright, let's dive into a comprehensive review of the anatomy of the heart, focusing on the key elements covered in Exercise 20 and providing clear answers to potential review sheet questions. This will not only help solidify your understanding but also prepare you to ace any related assessments.

Anatomy of the Heart: An In-Depth Review

The heart, a vital organ in the circulatory system, functions as a powerful pump responsible for circulating blood throughout the body. Understanding its intricate anatomy is crucial for grasping its physiological functions and potential pathologies. This review will cover the external and internal anatomy of the heart, blood supply, innervation, and common clinical considerations.

External Anatomy of the Heart

The heart, roughly the size of your fist, is located in the mediastinum, the space between the lungs in the thoracic cavity. Its orientation is slightly oblique, with the apex (pointed end) directed inferiorly and to the left, while the base (superior aspect) faces posteriorly and to the right.

Surfaces and Borders: The heart has several surfaces and borders. The anterior surface (sternocostal surface) is primarily formed by the right ventricle. The inferior surface (diaphragmatic surface) rests on the diaphragm and is formed by the left ventricle and a portion of the right ventricle. The right border is formed by the right atrium, the left border by the left ventricle and a small portion of the left atrium, the superior border by the atria and great vessels, and the inferior border by the right ventricle.
Pericardium: The heart is enclosed within a double-layered sac called the pericardium. The outer layer, the fibrous pericardium, is a tough, inelastic connective tissue layer that protects the heart, anchors it within the mediastinum, and prevents overfilling. The inner layer, the serous pericardium, is a double-layered membrane. The parietal layer of the serous pericardium is fused to the fibrous pericardium. The visceral layer (epicardium) adheres directly to the heart's surface. Between the parietal and visceral layers is the pericardial cavity, a space filled with a small amount of serous fluid that reduces friction during heartbeats.
Great Vessels: Several large blood vessels are connected to the heart. These include:
- Superior Vena Cava (SVC): Returns deoxygenated blood from the upper body to the right atrium.
- Inferior Vena Cava (IVC): Returns deoxygenated blood from the lower body to the right atrium.
- Pulmonary Trunk: Arises from the right ventricle and bifurcates into the right and left pulmonary arteries, carrying deoxygenated blood to the lungs.
- Pulmonary Veins: Four pulmonary veins (two from each lung) return oxygenated blood from the lungs to the left atrium.
- Aorta: Arises from the left ventricle and distributes oxygenated blood to the entire body. The ascending aorta gives rise to the coronary arteries.
Sulci: The heart's surface is marked by several grooves called sulci (or grooves). These sulci typically contain coronary blood vessels and fat.
- Coronary Sulcus (Atrioventricular Sulcus): Encircles the heart and separates the atria from the ventricles.
- Anterior Interventricular Sulcus: Located on the anterior surface of the heart and separates the right and left ventricles.
- Posterior Interventricular Sulcus: Located on the posterior surface of the heart and separates the right and left ventricles.

Internal Anatomy of the Heart

The heart is a four-chambered organ, consisting of two atria and two ventricles.

Atria: The atria are the superior chambers of the heart and receive blood returning to the heart.
- Right Atrium: Receives deoxygenated blood from the SVC, IVC, and coronary sinus. Features include:
  - Pectinate Muscles: Muscular ridges on the anterior wall.
  - Fossa Ovalis: A depression in the interatrial septum, representing the remnant of the foramen ovale in the fetal heart.
  - Crista Terminalis: A C-shaped ridge on the internal surface.
  - Opening of Coronary Sinus: Returns deoxygenated blood from the heart itself.
- Left Atrium: Receives oxygenated blood from the four pulmonary veins. The internal surface is smooth except for pectinate muscles in the auricle.
Ventricles: The ventricles are the inferior chambers of the heart and pump blood out of the heart.
- Right Ventricle: Pumps deoxygenated blood into the pulmonary trunk. Features include:
  - Trabeculae Carneae: Irregular muscular ridges on the internal walls.
  - Papillary Muscles: Cone-shaped muscles that project from the ventricular wall.
  - Chordae Tendineae: Tendon-like cords that attach the papillary muscles to the cusps of the tricuspid valve.
  - Pulmonary Valve (Semilunar Valve): Located at the opening of the pulmonary trunk.
- Left Ventricle: Pumps oxygenated blood into the aorta. The left ventricle has thicker walls than the right ventricle because it must generate higher pressure to pump blood throughout the systemic circulation. Features include:
  - Trabeculae Carneae: Similar to the right ventricle.
  - Papillary Muscles: Similar to the right ventricle.
  - Chordae Tendineae: Similar to the right ventricle.
  - Aortic Valve (Semilunar Valve): Located at the opening of the aorta.
Valves of the Heart: The heart has four valves that ensure unidirectional blood flow.
- Atrioventricular (AV) Valves: These valves are located between the atria and ventricles.
  - Tricuspid Valve: Located between the right atrium and right ventricle; has three cusps.
  - Mitral Valve (Bicuspid Valve): Located between the left atrium and left ventricle; has two cusps.
  - Mechanism: When the ventricles contract, the pressure increases, forcing the AV valves closed. The papillary muscles and chordae tendineae prevent the valve cusps from everting into the atria.
- Semilunar Valves: These valves are located at the exit of the ventricles into the great vessels.
  - Pulmonary Valve: Located between the right ventricle and the pulmonary trunk; has three semilunar cusps.
  - Aortic Valve: Located between the left ventricle and the aorta; has three semilunar cusps.
  - Mechanism: When the ventricles relax, blood flows backward toward the heart, filling the cusps of the semilunar valves and forcing them closed, preventing backflow into the ventricles.
Septa: The heart has two major septa that separate the chambers.
- Interatrial Septum: Separates the right and left atria.
- Interventricular Septum: Separates the right and left ventricles.

Blood Supply to the Heart

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

Coronary Arteries: These arteries arise from the ascending aorta, just above the aortic valve.
- Right Coronary Artery (RCA): Arises from the right aortic sinus. It typically supplies the right atrium, right ventricle, posterior portion of the left ventricle, and the sinoatrial (SA) and atrioventricular (AV) nodes in most individuals. Branches include:
  - Right Marginal Artery: Supplies the right ventricle.
  - Posterior Interventricular Artery (Posterior Descending Artery - PDA): Runs in the posterior interventricular sulcus and supplies the posterior portions of the ventricles and the posterior interventricular septum. (In approximately 85% of people, the PDA arises from the RCA – "right dominant" circulation).
- Left Coronary Artery (LCA): Arises from the left aortic sinus. It typically supplies the left atrium, left ventricle, and most of the interventricular septum. Branches include:
  - Left Anterior Descending Artery (LAD): Runs in the anterior interventricular sulcus and supplies the anterior portions of the ventricles and the anterior interventricular septum. Often referred to as the "widow maker" due to its critical role in supplying the left ventricle.
  - Circumflex Artery: Runs in the coronary sulcus around the left side of the heart and supplies the left atrium and posterior and lateral walls of the left ventricle.
Coronary Veins: After circulating through the heart tissue, deoxygenated blood is collected by the coronary veins, which drain into the coronary sinus.
- Coronary Sinus: A large venous channel located on the posterior surface of the heart in the coronary sulcus. It empties into the right atrium.
- Great Cardiac Vein: Runs alongside the LAD in the anterior interventricular sulcus.
- Middle Cardiac Vein: Runs alongside the PDA in the posterior interventricular sulcus.
- Small Cardiac Vein: Runs along the right marginal artery.

Innervation of the Heart

The heart is innervated by the autonomic nervous system (both sympathetic and parasympathetic fibers), which regulates heart rate and contractility.

Sympathetic Innervation: Increases heart rate and contractility. Sympathetic fibers arise from the thoracic spinal cord and synapse in the cervical and upper thoracic ganglia. Postganglionic fibers travel to the heart via the cardiac nerves.
Parasympathetic Innervation: Decreases heart rate. Parasympathetic fibers are carried by the vagus nerve (CN X). Vagal fibers synapse in ganglia located near the heart.

Cardiac Conduction System

The heart possesses a specialized conduction system that generates and distributes electrical impulses, coordinating the contraction of the atria and ventricles.

Sinoatrial (SA) Node: Located in the right atrium near the SVC opening. It is the heart's primary pacemaker, initiating electrical impulses that spread throughout the atria, causing them to contract.
Atrioventricular (AV) Node: Located in the interatrial septum near the tricuspid valve. The AV node delays the impulse, allowing the atria to finish contracting before the ventricles contract.
Atrioventricular (AV) Bundle (Bundle of His): Originates from the AV node and passes through the fibrous skeleton of the heart into 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: Terminal fibers that extend from the bundle branches and spread throughout the ventricular myocardium, causing the ventricles to contract.

Clinical Considerations

Understanding the anatomy of the heart is crucial for diagnosing and treating various cardiovascular conditions.

Myocardial Infarction (Heart Attack): Typically caused by a blockage in a coronary artery, leading to ischemia (lack of blood supply) and damage to the heart muscle. The location and extent of the infarction depend on which artery is affected. LAD occlusion is particularly dangerous due to the large area of the left ventricle it supplies.
Angina Pectoris: Chest pain caused by temporary ischemia of the heart muscle, often due to narrowing of the coronary arteries (e.g., atherosclerosis).
Valve Stenosis: Narrowing of a heart valve, restricting blood flow.
Valve Insufficiency (Regurgitation): Failure of a heart valve to close properly, allowing blood to leak backward.
Congenital Heart Defects: Structural abnormalities present at birth, such as septal defects (e.g., atrial septal defect, ventricular septal defect) or valve abnormalities.
Cardiac Arrhythmias: Irregular heart rhythms caused by disturbances in the electrical conduction system. Examples include atrial fibrillation, ventricular tachycardia, and heart block.
Pericarditis: Inflammation of the pericardium, causing chest pain.

Exercise 20 Review Sheet: Sample Questions and Answers

Let's anticipate some common questions you might find on an Exercise 20 review sheet focusing on the anatomy of the heart, along with detailed answers.

Question 1: Describe the location of the heart within the thoracic cavity.

Answer: The heart is located in the mediastinum, the space between the lungs in the thoracic cavity. It is positioned obliquely, with the apex directed inferiorly and to the left, and the base facing posteriorly and to the right.

Question 2: What are the layers of the pericardium, and what is their function?

Answer: The pericardium consists of two layers: the fibrous pericardium and the serous pericardium. The fibrous pericardium is the outer, tough connective tissue layer that protects the heart, anchors it within the mediastinum, and prevents overfilling. The serous pericardium has two layers: the parietal layer, which is fused to the fibrous pericardium, and the visceral layer (epicardium), which adheres to the heart's surface. The pericardial cavity between these layers contains serous fluid that reduces friction during heartbeats.

Question 3: Name the four chambers of the heart and describe their primary functions.

Answer: The four chambers of the heart are:

Right Atrium: Receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
Right Ventricle: Pumps deoxygenated blood into the pulmonary trunk.
Left Atrium: Receives oxygenated blood from the pulmonary veins.
Left Ventricle: Pumps oxygenated blood into the aorta.

Question 4: Describe the function of the atrioventricular (AV) valves and semilunar valves.

Answer: Atrioventricular (AV) valves (tricuspid and mitral valves) prevent backflow of blood from the ventricles into the atria during ventricular contraction. They are anchored by chordae tendineae and papillary muscles. Semilunar valves (pulmonary and aortic valves) prevent backflow of blood from the pulmonary trunk and aorta into the ventricles during ventricular relaxation.

Question 5: Trace the pathway of blood flow through the heart, starting with deoxygenated blood entering the right atrium.

Answer: The pathway of blood flow is as follows:

Deoxygenated blood enters the right atrium from the superior vena cava, inferior vena cava, and coronary sinus.
Blood passes through the tricuspid valve into the right ventricle.
The right ventricle pumps blood through the pulmonary valve into the pulmonary trunk.
The pulmonary trunk divides into the right and left pulmonary arteries, which carry blood to the lungs.
In the lungs, blood becomes oxygenated.
Oxygenated blood returns to the left atrium via the pulmonary veins.
Blood passes through the mitral (bicuspid) valve into the left ventricle.
The left ventricle pumps blood through the aortic valve into the aorta.
The aorta distributes oxygenated blood to the entire body.

Question 6: Name the major branches of the right and left coronary arteries and describe the regions of the heart they supply.

Answer:

Right Coronary Artery (RCA):
- Right Marginal Artery: Supplies the right ventricle.
- Posterior Interventricular Artery (PDA): Supplies the posterior portions of the ventricles and the posterior interventricular septum (in most individuals).
Left Coronary Artery (LCA):
- Left Anterior Descending Artery (LAD): Supplies the anterior portions of the ventricles and the anterior interventricular septum.
- Circumflex Artery: Supplies the left atrium and posterior and lateral walls of the left ventricle.

Question 7: Describe the components of the cardiac conduction system and their roles in initiating and coordinating heart contractions.

Answer: The cardiac conduction system includes:

Sinoatrial (SA) Node: The heart's primary pacemaker, initiating electrical impulses that spread throughout the atria.
Atrioventricular (AV) Node: Delays the impulse, allowing the atria to finish contracting before the ventricles contract.
Atrioventricular (AV) Bundle (Bundle of His): Transmits the impulse from the AV node to the ventricles.
Right and Left Bundle Branches: Carry the impulse along the interventricular septum.
Purkinje Fibers: Distribute the impulse throughout the ventricular myocardium, causing the ventricles to contract.

Question 8: What is the coronary sinus, and where does it drain?

Answer: The coronary sinus is a large venous channel located on the posterior surface of the heart in the coronary sulcus. It receives deoxygenated blood from the major cardiac veins (great, middle, and small cardiac veins) and drains into the right atrium.

Question 9: Explain the significance of the left anterior descending (LAD) artery in the context of myocardial infarction.

Answer: The left anterior descending (LAD) artery is often referred to as the "widow maker" because it supplies a significant portion of the left ventricle, which is the main pumping chamber of the heart. Occlusion of the LAD can lead to a large myocardial infarction, resulting in severe heart damage and potentially life-threatening consequences.

Question 10: Differentiate between the functions of the sympathetic and parasympathetic nervous systems on heart rate.

Answer: The sympathetic nervous system increases heart rate and contractility. The parasympathetic nervous system, via the vagus nerve, decreases heart rate.

Conclusion

Mastering the anatomy of the heart is fundamental for understanding its function and associated clinical conditions. By thoroughly reviewing the external and internal structures, blood supply, innervation, and conduction system, you'll be well-prepared to tackle any questions related to Exercise 20 and gain a deeper appreciation for this remarkable organ. Good luck with your studies!