Cardiac Anatomy and Function Quiz

Cardiac Anatomy, Histology, and Function

• Learning Objectives: Understand the mammalian heart structure, location, and relationships; describe the pericardium, myocardium, and endocardium; understand the heart "skeleton"; identify external heart features and cardiac chambers; recognize great vessels and their blood flow; describe heart valves and coronary circulation; and describe heart innervation.

Basic Heart Structure

• Description: The heart is a four-chambered pump (two pumps in series, left and right sides). Each side has an atrium and ventricle, separated by valves.
• Right Side: Receives deoxygenated blood from systemic circulation and pumps it to the lungs.
• Left Side: Receives oxygenated blood from pulmonary circulation and pumps it into systemic circulation.
• Muscle Mass: The left ventricle's muscle mass is greater than the right's, even though they pump equal volumes.
• Shape and Location: Heart shape varies between species (more ovoid in carnivores, conical in horses/ruminants). Located in the thorax, roughly midline (but towards the left).
• Relationships: Located within the mediastinum. The thymus is cranial, lungs and phrenic nerves are lateral, and the trachea/bronchial bifurcation and esophagus are dorsal

Heart Shape and Size

• Shape: Heart shape varies with species, from more ovoid in carnivores to more conical in horses and ruminants.
• Location: In the thorax, approximately midline, though positioned slightly leftwards with the apex contacting the left thoracic wall.
• Relationships: The heart is located within the mediastinum, where it is related to other thoracic structures such as the thymus (cranial), lungs and phrenic nerves (lateral), trachea/bronchial bifurcation and the esophagus (dorsal).
• Size: Generally, the heart is roughly 1% of the bodyweight and is about 2/3 the width/height of the thoracic cavity in carnivores.

Pericardium

• Description: A double-layered sac surrounding the heart. This is referred to as "Serous" and "Fibrous."
• Function: Encloses the heart, forming a fluid-filled space that reduces friction during heartbeats.

Myocardium

• Description: The heart muscle itself, largely composed of cardiomyocytes (contractile cells), specialized pacemaker and conducting cells, interstitial connective tissue, and blood vessels/nerves.
• Arrangement: The muscle fibers arranged interconnecting layers, having a spiral/figure 8 orientation.

Endocardium

• Description: A single layer of flattened endothelial cells with a basement membrane. Forms the innermost layer of the heart and a continuous layer with the blood vessels
• Function: Smooth surface to facilitate blood flow.

Heart Valves

• Atrioventricular (AV) Valves: (Right - Tricuspid; Left - Bicuspid or Mitral) Connect the atria and ventricles.
• Semilunar Valves: (Pulmonary and Aortic) Prevent backflow from the ventricles into the atria.

Blood Vessels and Coronary Circulation

• Coronary Circulation: The arteries supply the heart itself with oxygenated blood; veins drain blood away. The left and right coronary arteries branch from the aorta. Coronary veins return blood to the right atrium through the coronary sinus.

Innervation

• Sympathetic: Largely from major sympathetic ganglia.
• Parasympathetic: Primarily from the vagus nerve (also some recurrent laryngeal branch).

External Features of the Heart

• Atria: The base of the heart, with appendages (auricles).
• Ventricles: The major lower chambers of the heart, with the left ventricle forming the apex.
• Grooves: Grooves separate the atria and ventricles.

Other Features

• Important Clinical Conditions: Fluid accumulation within the pericardial space (such as cardiac tamponade) can have serious effects.
• Skeleton of the heart: A platform of fibrous tissue, critical for proper conduction of electrical impulses.
• Terminal crest: Location of the sinoatrial node, important for initiating the heartbeat.
• Fossa ovalis: a remnant of foetal circulatory structures that closes after birth.