Blood and Heart: Key Structures and Terminology

Blood

Blood is a specialized connective tissue that plays a vital role in transport, regulation, and protection within the body. It consists of plasma and formed elements, each with distinct functions.

• Plasma: The liquid component of blood, comprising about 55% of total blood volume. It contains water, proteins (such as albumin, globulins, and fibrinogen), electrolytes, nutrients, hormones, and waste products.

• Red Blood Cells (Erythrocytes/RBCs): Biconcave cells responsible for transporting oxygen and carbon dioxide. They contain hemoglobin, a protein that binds oxygen.

• White Blood Cells (Leukocytes/WBCs): Cells involved in immune defense. There are several types:

  • Neutrophils: Most abundant WBC; phagocytize bacteria.

  • Eosinophils: Combat parasitic infections and modulate allergic responses.

  • Basophils: Release histamine and heparin during inflammatory responses.

  • Monocytes: Differentiate into macrophages; phagocytize pathogens and debris.

  • Lymphocytes: Include B cells (produce antibodies), T cells (cell-mediated immunity), and NK cells (destroy abnormal cells).

• Platelets (Thrombocytes): Cell fragments essential for blood clotting.

Example: During injury, platelets aggregate at the site to form a clot, preventing excessive blood loss.

Heart

The heart is a muscular organ responsible for pumping blood throughout the body. It is divided into four chambers and surrounded by protective layers.

• Apex: The pointed lower tip of the heart, directed toward the left hip.

• Fibrous Pericardium: Tough, outermost layer of the pericardium; protects and anchors the heart.

• Serous Pericardium: Double-layered membrane; includes the parietal layer (outer) and visceral layer (inner, also called Epicardium).

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

• Myocardium: Thick, muscular middle layer responsible for contraction.

  • Pectinate Muscles: Ridges in the atria.

  • Trabeculae Carneae: Irregular muscular columns in the ventricles.

• Endocardium: Thin, inner lining of the heart chambers.

Heart Chambers

• Right/Left Atrium (Atria): Upper chambers receiving blood.

• Right/Left Auricle: Ear-like extensions of the atria.

• Right/Left Ventricle: Lower chambers pumping blood out of the heart.

• Interventricular Septum: Wall separating the right and left ventricles.

Heart Valves

Valves ensure unidirectional blood flow through the heart.

• Atrioventricular (AV) Valves: Located between atria and ventricles.

  • Chordae Tendineae: Tendinous cords anchoring valve leaflets to papillary muscles.

  • Papillary Muscles: Contract to prevent valve prolapse.

  • Tricuspid Valve: Right AV valve; three cusps.

  • Bicuspid (Mitral) Valve: Left AV valve; two cusps.

• Semilunar Valves: Located at the base of large arteries leaving the heart.

  • Pulmonary Valve: Between right ventricle and pulmonary trunk.

  • Aortic Valve: Between left ventricle and aorta.

Heart Sulci

• Sulcus (Sulci): Grooves on the heart surface marking chamber boundaries.

  • Atrioventricular/Coronary Sulcus: Separates atria from ventricles.

  • Anterior Interventricular Sulcus: Marks the front boundary between ventricles.

  • Posterior Interventricular Sulcus: Marks the back boundary between ventricles.

Great Vessels

Great vessels are major blood vessels entering and leaving the heart.

• Superior Vena Cava: Returns deoxygenated blood from upper body to right atrium.

• Inferior Vena Cava: Returns deoxygenated blood from lower body to right atrium.

• Pulmonary Trunk: Carries deoxygenated blood from right ventricle to lungs.

  • Pulmonary Arteries (R/L): Branches of pulmonary trunk; carry blood to lungs.

  • Pulmonary Veins (R/L): Return oxygenated blood from lungs to left atrium.

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

Heart Conduction System

The heart's conduction system coordinates the heartbeat through specialized cells.

• Sinoatrial (SA) Node: Pacemaker; initiates electrical impulses.

• Atrioventricular (AV) Node: Delays impulse, allowing atria to contract before ventricles.

• AV Bundle (Bundle of His): Conducts impulses from AV node to ventricles.

• Bundle Branches (R/L): Carry impulses through interventricular septum.

• Purkinje Fibers (R/L): Distribute impulse to ventricular muscle, causing contraction.

Example: The SA node generates an action potential, leading to coordinated contraction of the heart chambers.

Coronary Vessels

Coronary vessels supply blood to the heart muscle itself.

• Right Coronary Artery: Supplies right side of heart.

  • Right Marginal Artery: Branch of right coronary artery.

  • Posterior Interventricular Artery: Supplies posterior ventricles.

• Left Coronary Artery: Supplies left side of heart.

  • Anterior Interventricular Artery (LAD): Supplies anterior ventricles.

  • Circumflex Artery: Supplies left atrium and ventricle.

• Great Cardiac Vein: Drains anterior heart.

• Middle Cardiac Vein: Drains posterior heart.

• Small Cardiac Vein: Drains right margin.

• Coronary Sinus: Collects venous blood from heart and empties into right atrium.

Other Structures

• Ligamentum Arteriosum: Remnant of fetal ductus arteriosus; connects pulmonary trunk to aorta.

• Fossa Ovalis: Remnant of fetal foramen ovale; depression in right atrium.

Summary Table: Blood Cell Types

Summary Table: Heart Valves

Additional info: The conduction system ensures rhythmic contraction, and the coronary vessels are essential for myocardial oxygenation. The ligamentum arteriosum and fossa ovalis are remnants of fetal circulation, important in developmental anatomy.