Blood: Structure, Function, and Disorders – ANP College Study Guide

Blood – Physical Characteristics

Overview of Blood Properties

Blood is a specialized connective tissue with unique physical and chemical properties that are essential for its functions in the human body.

• Volume: Adult males contain 5-6L; adult females contain 4-5L.

• Temperature: Approximately 100.4°F, slightly higher than normal body temperature.

• Viscosity: Blood is five times as viscous as water, making it more resistant to flow due to the presence of cells and plasma proteins.

• pH: Ranges from 7.35 to 7.45, making it slightly alkaline.

• Color: Varies from scarlet (oxygenated) to deep red (deoxygenated).

Components of Blood

Whole Blood Composition

Blood consists of plasma and formed elements, each with distinct roles.

• Plasma: 46-63% of blood volume; contains water (92%), plasma proteins (7%), and other solutes (1%).

• Formed Elements: 37-54% of blood volume; includes red blood cells (RBCs, 99.9%), white blood cells (WBCs), and platelets (0.1%).

Functions of Blood

Transportation

Blood is the primary medium for transporting substances throughout the body.

• Gases: Oxygen and carbon dioxide are carried by hemoglobin and dissolved in plasma.

• Nutrients: Absorbed from the GI tract and distributed to tissues.

• Hormones: Transported from endocrine glands to target organs.

• Metabolic Wastes: Carried to kidneys for excretion.

Regulation

Blood helps maintain homeostasis by regulating temperature, pH, and electrolyte balance.

• Heat Distribution: Absorbs heat from muscles and distributes it to other tissues.

• Acid-Base Balance: Neutralizes acids generated by active tissues.

• Electrolyte Reservoir: Maintains levels of Na+, Ca2+, and other ions.

• Volume Regulation: Adjusts in response to body water levels.

Protection

Blood provides defense against pathogens and restricts fluid loss.

• White Blood Cells: Migrate to tissues to fight infections and remove debris.

• Antibodies: Attack invading organisms and foreign compounds.

• Clotting: Enzymes form clots to restrict fluid loss.

Red Blood Cells (Erythrocytes)

Structure and Function

Red blood cells are the most abundant formed elements and are specialized for oxygen transport.

• Abundance: 4.5-6.3 million/µL in males; 4.2-5.5 million/µL in females.

• Shape: Biconcave disc (diameter ≈ 8µm, thickness ≈ 2.5µm) increases surface area for gas exchange and flexibility.

• Organelles: Lack nucleus and most organelles; are membranous bags of hemoglobin.

• Hemoglobin: Binds and transports O2 and CO2.

Hemoglobin Structure

Hemoglobin is a large protein responsible for oxygen transport.

• Composition: Four polypeptide chains (2 α, 2 β), each with a heme group containing iron.

• Oxygen Binding: Each iron ion binds one O2 molecule; thus, each hemoglobin can carry four O2 molecules.

Red Blood Cell Formation (Erythropoiesis)

Process and Regulation

Erythropoiesis is the process of RBC formation, occurring in the red bone marrow.

• Stem Cells: All blood cells develop from hemocytoblasts.

• Pathways: Hemocytoblasts differentiate into myeloid and lymphoid stem cells, which give rise to RBCs, WBCs, and platelets.

• Regulation: Erythropoietin (EPO), produced by kidneys, stimulates RBC production in response to hypoxia.

Lifecycle and Fate of RBCs

Destruction and Recycling

RBCs have a lifespan of about 120 days and are subjected to mechanical stress.

• Senescence: Old or damaged RBCs are engulfed by macrophages.

• Hemolysis: RBCs rupture, and hemoglobin is broken down.

• Fate of Components: Globin proteins are metabolized; heme is converted to bilirubin, which is transported to the liver and excreted in bile.

• Bilirubin: Excess bilirubin causes jaundice; its breakdown products color urine and feces.

Complete Blood Count (CBC) and Hematocrit

Clinical Importance

CBC is a routine test to determine the number and proportion of blood cells.

• Hematocrit: Percentage of blood occupied by RBCs; average is 46% in males, 42% in females.

• Clinical Significance: Low hematocrit indicates anemia; high values indicate polycythemia.

Blood Disorders

Polycythemia

Polycythemia is an elevated hematocrit with normal blood volume, often due to increased erythropoietin or bone marrow cancer.

• Effects: Increases blood viscosity, reducing flow.

• Treatment: Blood dilution with isotonic saline.

• Application: Endurance athletes may induce polycythemia to enhance performance.

Anemia

Anemia is a condition of abnormally low oxygen-carrying capacity in the blood.

• Symptoms: Shortness of breath, fatigue, chills.

• Types: Hemorrhagic (blood loss), hemolytic (RBC rupture), aplastic (bone marrow destruction), iron-deficiency, pernicious (B12 deficiency), thalassemia, sickle cell.

Sickle Cell Anemia

Sickle cell anemia is caused by a mutation in the β chain of hemoglobin, resulting in sickle-shaped RBCs that block blood vessels.

• Genetic Basis: Single mutation in the globin gene.

• Clinical Effects: Blockage of small vessels, pain, and organ damage.

Erythroblastosis Fetalis

A type of hemolytic anemia affecting newborns when an Rh- mother produces antibodies against an Rh+ fetus.

• Mechanism: Maternal antibodies attack fetal RBCs, causing anemia and hypoxia.

• Prevention: Blood transfusions and Rh immunoglobulin therapy.

White Blood Cells (Leukocytes)

Functions and Types

White blood cells defend the body against pathogens and remove toxins, wastes, and abnormal cells.

• Abundance: 6000-9000/µL of blood.

• Location: Most are in connective tissues and lymphatic organs.

• Classification: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).

Granulocytes

• Neutrophils: 50-70% of WBCs; first responders to infection; attack bacteria.

• Eosinophils: 2-4% of WBCs; defend against parasites and participate in allergic reactions.

• Basophils: <1% of WBCs; release histamine and heparin at injury sites.

Agranulocytes

• Monocytes: 2-8% of WBCs; become macrophages in tissues and are aggressive phagocytes.

• Lymphocytes: 20-30% of WBCs; include T cells (cellular immunity), B cells (antibody production), and NK cells (immune surveillance).

Platelets and Hemostasis

Platelet Function

Platelets are cell fragments involved in blood clotting and tissue repair.

• Production: Released from megakaryocytes in bone marrow.

• Lifespan: 9-12 days; removed by splenic phagocytes.

• Abundance: 350,000/µL of blood.

Hemostasis (Blood Clotting)

Hemostasis prevents blood loss and establishes a framework for tissue repair.

• Vascular Phase: Endothelial cells contract, release chemicals, and become sticky; vascular spasm reduces blood loss.

• Platelet Phase: Platelets adhere to exposed surfaces and become activated, forming a platelet plug.

• Coagulation Phase: Fibrinogen is converted to fibrin, trapping RBCs and platelets to form a clot.

Clot Retraction and Manipulation

Clot retraction stabilizes the injury site and facilitates tissue repair. Anticoagulant drugs manipulate hemostasis to prevent unwanted clotting.

• Clot Retraction: Platelets contract, pulling vessel edges together.

• Anticoagulants: Heparin, Coumadin, Streptokinase, and Aspirin inhibit various steps in clot formation.

Thrombi, Emboli, and Hemophilia

Thrombi are clots that form in intact vessels; emboli are clots that travel in the bloodstream. Hemophilia is a hereditary bleeding disorder due to deficiency of clotting factors.

• Thrombus: Can obstruct blood flow and cause tissue damage.

• Embolus: Can cause blockages in critical vessels, leading to stroke or pulmonary embolism.

• Hemophilia: Most commonly due to lack of Factor VIII (Hemophilia A); X-linked inheritance.

Blood Type Compatibility

Blood Types and Transfusion

Blood type compatibility is crucial for safe transfusions.

• Type O negative: Universal donor.

• Type AB positive: Universal recipient.

• Rh factor: Important in pregnancy and transfusion reactions.

Summary Table: Blood Cell Types and Functions

Cell Type	Abundance	Function
Red Blood Cells	99.9% of formed elements	Oxygen and carbon dioxide transport
Neutrophils	50-70% of WBCs	Bacterial defense
Lymphocytes	20-30% of WBCs	Immune response
Monocytes	2-8% of WBCs	Phagocytosis
Eosinophils	2-4% of WBCs	Parasite defense, allergy
Basophils	<1% of WBCs	Histamine and heparin release
Platelets	350,000/µL	Clotting