Blood Components and Functions

Plasma

Plasma is the liquid portion of blood, making up about 55% of its volume. It serves as a transport medium for nutrients, hormones, and waste products.

• Definition: Plasma is a pale yellow fluid composed mainly of water, proteins (albumin, globulins, fibrinogen), electrolytes, and dissolved gases.

• Function: Maintains blood pressure, transports substances, and assists in clotting and immune responses.

Platelets

Platelets, or thrombocytes, are small cell fragments crucial for blood clotting.

• Function: Initiate clot formation to prevent blood loss after injury.

Erythrocytes (Red Blood Cells, RBCs)

Erythrocytes are specialized cells responsible for oxygen transport.

• Hemoglobin: The protein in RBCs that binds oxygen for transport.

• Sickle Cell Erythrocytes: Abnormally shaped RBCs due to genetic mutation, leading to impaired oxygen delivery.

Leukocytes (White Blood Cells, WBCs)

Leukocytes are immune cells that protect the body against infection and foreign substances.

• Granulocytes: WBCs with granules in their cytoplasm.

  • Neutrophils: Most abundant, phagocytize bacteria.

  • Eosinophils: Combat parasites and mediate allergic responses.

  • Basophils: Release histamine in inflammatory reactions.

• Agranulocytes: WBCs without visible granules.

  • Lymphocytes: Include B cells and T cells, central to adaptive immunity.

  • Monocytes: Differentiate into macrophages for phagocytosis.

Blood Typing and Transfusion

ABO Blood Groups

The ABO system classifies blood based on the presence of antigens and antibodies.

• Antigens: Surface markers on RBCs for A, B, AB, and O types.

• Antibodies: Plasma proteins that react against incompatible antigens.

• Universal Donor: Type O blood (no A/B antigens).

• Universal Recipient: Type AB blood (no anti-A/B antibodies).

• Rh Factors: Additional antigen; Rh+ or Rh- status affects compatibility.

Whole Blood Centrifugation

Centrifugation separates blood into its components for analysis.

• Formed Elements: Cellular components (RBCs, WBCs, platelets).

• Buffy Coat: Thin layer containing leukocytes and platelets.

• Hematocrit: Percentage of blood volume occupied by RBCs.

Miscellaneous Blood Topics

• Hemolytic Disease of the Newborn (Erythroblastosis Fetalis): Occurs when maternal antibodies attack fetal RBCs, often due to Rh incompatibility.

• RhogAM: Medication to prevent Rh sensitization in mothers.

• Transfusion Reaction: Immune response to incompatible blood transfusion.

• Agglutination: Clumping of RBCs due to antibody-antigen reaction.

Heart Anatomy and Physiology

Heart Coverings

The heart is enclosed by protective layers collectively called the pericardium.

• Pericardium: Double-walled sac surrounding the heart.

• Fibrous Pericardium: Tough outer layer for protection and anchoring.

• Serous Pericardium: Inner layer with two parts:

  • Parietal Layer: Lines the fibrous pericardium.

  • Visceral Layer (Epicardium): Covers the heart surface.

  • Pericardial Cavity: Space between layers containing serous fluid to reduce friction.

Layers of the Heart

The heart wall consists of three layers, each with distinct functions.

• Epicardium: Outer protective layer.

• Myocardium: Middle muscular layer responsible for contraction.

• Endocardium: Inner lining of the heart chambers and valves.

Chambers and Great Vessels

The heart contains four chambers and is connected to major blood vessels.

• Atria: Upper chambers receiving blood.

  • Auricles: Ear-like extensions increasing atrial volume.

  • Pectinate Muscles: Ridges in atrial walls.

  • Fossa Ovalis: Remnant of fetal foramen ovale.

  • Superior/Inferior Vena Cava: Major veins returning blood to right atrium.

  • Coronary Sinus: Drains blood from heart muscle into right atrium.

  • Pulmonary Veins: Carry oxygenated blood from lungs to left atrium.

• Interatrial Septum: Wall separating atria.

• Ventricles: Lower chambers pumping blood out of the heart.

  • Trabeculae Carneae: Muscular ridges in ventricles.

  • Papillary Muscles: Anchor chordae tendineae to valves.

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

  • Pulmonary Arteries: Transport deoxygenated blood to lungs.

  • Aorta: Main artery carrying oxygenated blood to body.

    • Ascending Aorta

    • Aortic Arch

    • Descending Aorta

    • Thoracic Aorta

  • Interventricular Septum: Wall separating ventricles.

Heart Valves and Blood Flow

Valves of the Heart

Heart valves ensure unidirectional blood flow and prevent backflow.

• Tricuspid Valve: Between right atrium and right ventricle.

• Mitral Valve (Bicuspid Valve): Between left atrium and left ventricle.

• Chordae Tendineae: Tendinous cords connecting valves to papillary muscles.

• Semilunar Valves:

  • Aortic Semilunar Valve: Between left ventricle and aorta.

  • Pulmonary Semilunar Valve: Between right ventricle and pulmonary trunk.

Note: Know the path that blood flows through the heart and the mechanism for how valves open and close.

Coronary Circulation

Coronary Arteries and Veins

The heart receives its own blood supply via the coronary circulation.

• Coronary Arteries:

  • Left Coronary Artery

    • Anterior Interventricular Artery (Left Anterior Descending Artery)

    • Circumflex Artery

  • Right Coronary Artery

• Coronary Veins:

  • Great Cardiac Vein

  • Coronary Sinus

Cardiac Conduction System

Electrical Pathways

The heart's rhythmic contractions are controlled by its conduction system.

• Sinoatrial (SA) Node: Pacemaker initiating each heartbeat.

• Atrioventricular (AV) Node: Delays impulse before passing to ventricles.

• Atrioventricular (AV) Bundle (Bundle of His): Conducts impulses from AV node to bundle branches.

• Right and Left Bundle Branches: Carry impulses through interventricular septum.

• Apex: Tip of the heart where impulses travel before ascending.

• Purkinje Fibers: Distribute impulse throughout ventricular myocardium.

Electrocardiogram (ECG)

An ECG records the electrical activity of the heart.

• QRS Complex: Represents ventricular depolarization.

• T Wave: Represents ventricular repolarization.

Note: ECG will be covered in detail in Unit 2.

Cardiac Histology

Intercalated Discs and Nucleation

Cardiac muscle cells are connected by specialized structures for efficient contraction.

• Intercalated Discs: Junctions between cardiac cells allowing rapid electrical communication.

• Nucleation: Cardiac muscle cells are typically uninucleate but may be binucleate.

Cardiac Tissue Structure

Cardiac muscle is striated, involuntary, and highly vascularized, supporting continuous rhythmic contractions.

Summary Table: Blood Cell Types

Key Equations

• Hematocrit Calculation:

• Blood Flow Equation (for reference):

Where is the pressure difference and is resistance.

Additional info: Some details, such as the structure of cardiac tissue and the blood flow equation, were inferred to provide academic completeness.