Gross Anatomy Of The Heart Review Sheet Exercise 21 Answers

Gross Anatomy of the Heart: Review Sheet Exercise 21 Answers

This comprehensive guide provides detailed answers and explanations for a typical Exercise 21 focusing on the gross anatomy of the heart. It's designed to help students solidify their understanding of cardiac structure and function, preparing them for exams and furthering their knowledge of this vital organ. Remember to always consult your specific textbook and lecture notes as variations may exist.

I. External Anatomy: A Closer Look

1. Locate and identify the following external features:

a. Apex: The inferior, pointed end of the heart; typically located at the 5th intercostal space, midclavicular line. This is the point of maximal impulse (PMI) felt during auscultation.

b. Base: The superior, broad portion of the heart, primarily formed by the atria. Major vessels like the aorta and pulmonary trunk emerge from the base.

c. Superior Vena Cava: Returns deoxygenated blood from the upper body to the right atrium. It's a large, superiorly positioned vein.

d. Inferior Vena Cava: Returns deoxygenated blood from the lower body to the right atrium. It's positioned inferiorly to the superior vena cava.

e. Pulmonary Trunk: Carries deoxygenated blood from the right ventricle to the pulmonary arteries. Divides into left and right pulmonary arteries. It's a large artery arising from the right ventricle.

f. Pulmonary Veins (4): Return oxygenated blood from the lungs to the left atrium. There are typically two from each lung.

g. Aorta: Carries oxygenated blood from the left ventricle to the systemic circulation. The largest artery in the body, arising from the left ventricle.

h. Coronary Sulcus (Atrioventricular Groove): Separates the atria from the ventricles. It contains the coronary arteries and veins.

i. Anterior Interventricular Sulcus: Separates the right and left ventricles anteriorly. Contains the anterior interventricular artery.

j. Posterior Interventricular Sulcus: Separates the right and left ventricles posteriorly. Contains the posterior interventricular artery (a branch of the right coronary artery in most individuals).

2. Differentiate between the auricles and the atria:

The atria are the two superior chambers of the heart receiving blood. The auricles are the ear-like appendages extending from each atrium, slightly increasing atrial capacity. They are not critical to the main function of the atria but serve as small reservoirs.

II. Internal Anatomy: A Journey Through Chambers and Valves

1. Describe the internal structure of each chamber:

• Right Atrium: Receives deoxygenated blood from the superior and inferior vena cava and coronary sinus. Features the fossa ovalis (remnant of the foramen ovale) and pectinate muscles (muscular ridges).

• Right Ventricle: Receives deoxygenated blood from the right atrium. It has thicker walls than the right atrium, and features trabeculae carneae (irregular muscular ridges), papillary muscles (cone-shaped muscles), and chordae tendineae (tendinous cords connecting papillary muscles to the cusps of the tricuspid valve). The pulmonary valve is found at its outflow.

• Left Atrium: Receives oxygenated blood from the four pulmonary veins. The walls are thinner than the left ventricle's. Smooth internal surface, relatively few trabeculae.

• Left Ventricle: Receives oxygenated blood from the left atrium. It is the thickest-walled chamber because it pumps blood throughout the systemic circulation. The interior features trabeculae carneae, papillary muscles, and chordae tendineae associated with the mitral valve. The aortic valve is found at its outflow.

2. Identify and describe the function of each heart valve:

• Tricuspid Valve (Right Atrioventricular Valve): Located between the right atrium and right ventricle, it has three cusps (leaflets). It prevents backflow of blood from the ventricle to the atrium during ventricular contraction.

• Pulmonary Valve (Pulmonary Semilunar Valve): Located at the outflow of the right ventricle, preventing backflow of blood from the pulmonary trunk into the right ventricle. It has three semilunar cusps.

• Mitral Valve (Left Atrioventricular Valve/Bicuspid Valve): Located between the left atrium and left ventricle, it has two cusps. It prevents backflow from the ventricle to the atrium during ventricular contraction.

• Aortic Valve (Aortic Semilunar Valve): Located at the outflow of the left ventricle, preventing backflow of blood from the aorta into the left ventricle. It has three semilunar cusps.

3. Explain the role of the papillary muscles and chordae tendineae:

The papillary muscles are cone-shaped muscles projecting into the ventricular cavities. The chordae tendineae are tendinous cords connecting the papillary muscles to the cusps of the atrioventricular valves (tricuspid and mitral). Their coordinated action prevents the valve cusps from inverting (prolapsing) into the atria during ventricular contraction. This ensures unidirectional blood flow.

III. Coronary Circulation: Nourishing the Heart

1. Trace the path of blood flow through the coronary arteries:

The coronary arteries arise from the base of the aorta, just beyond the aortic valve.

• Right Coronary Artery (RCA): Supplies blood to the right atrium, right ventricle, part of the left ventricle, and the posterior portion of the interventricular septum. Major branches include the marginal artery and the posterior interventricular artery.

• Left Coronary Artery (LCA): Divides into two main branches:

  • Left Anterior Descending Artery (LAD): Supplies blood to the anterior portion of the interventricular septum, the anterior wall of the left ventricle, and part of the right ventricle.

  • Circumflex Artery: Supplies blood to the left atrium and the posterior and lateral walls of the left ventricle.

2. Describe the path of blood flow through the coronary veins:

Deoxygenated blood from the myocardium drains into the coronary veins. These veins converge to form:

• Great Cardiac Vein: Runs alongside the LAD artery.

• Middle Cardiac Vein: Runs alongside the posterior interventricular artery.

• Small Cardiac Vein: Runs alongside the right marginal artery.

These veins drain into the coronary sinus, which empties into the right atrium.

IV. Cardiac Conduction System: The Heart's Electrical System

1. Describe the components and function of the cardiac conduction system:

The cardiac conduction system ensures coordinated contraction of the heart chambers.

• Sinoatrial (SA) Node: The heart's primary pacemaker, located in the right atrium near the superior vena cava. It initiates the heartbeat.

• Atrioventricular (AV) Node: Located in the interatrial septum, it delays the impulse from the SA node, allowing the atria to fully contract before the ventricles.

• Bundle of His (AV Bundle): Conducts the impulse from the AV node to the ventricles. It is located in the interventricular septum.

• Right and Left Bundle Branches: These branches conduct the impulse down the interventricular septum to the Purkinje fibers.

• Purkinje Fibers: These fibers spread the impulse throughout the ventricles, causing ventricular contraction.

2. Explain the significance of the AV nodal delay:

The AV nodal delay is crucial for ensuring efficient blood flow. It allows the atria to completely empty their blood into the ventricles before ventricular contraction begins. Without this delay, the atria and ventricles would contract simultaneously, reducing the effectiveness of the heart pump.

V. Clinical Correlations: Understanding Heart Conditions

1. Explain the consequences of a blockage in the coronary arteries:

Blockages in the coronary arteries, often due to atherosclerosis (plaque buildup), reduce blood flow to the myocardium. This can lead to angina pectoris (chest pain) or myocardial infarction (heart attack). The severity depends on the location and extent of the blockage.

2. Describe the effects of valvular heart disease:

Valvular heart disease can involve stenosis (narrowing) or regurgitation (leakage) of a heart valve. Stenosis increases the workload of the heart, while regurgitation reduces the effectiveness of the heart's pumping action. Both can lead to heart failure. Examples include mitral valve prolapse, aortic stenosis, and tricuspid regurgitation.

3. Discuss the impact of congenital heart defects:

Congenital heart defects are structural abnormalities of the heart present at birth. These defects can affect blood flow through the heart and lungs, leading to various complications. Examples include atrial septal defects, ventricular septal defects, and tetralogy of Fallot.

This detailed review provides a thorough understanding of the gross anatomy of the heart. By understanding the structure and function of each component – from chambers and valves to the coronary circulation and conduction system – a strong foundation for further study in cardiovascular physiology and pathology is established. Remember to actively review diagrams and models to solidify your understanding of the three-dimensional relationships within the heart. Continuous review and active recall will significantly improve retention and comprehension.