Blood: Structure, Function, and Disorders (Human Anatomy & Physiology II)

Blood: Structure, Function, and Disorders

Cardiovascular System: Functions and Major Components

The cardiovascular system is responsible for transporting nutrients, gases, hormones, and waste products throughout the body. It consists of the heart, blood vessels (arteries, veins, capillaries), and blood.

• Functions: Transport, regulation (temperature, pH, fluid balance), protection (immune response, clotting).

• Major Components: Heart (pump), blood vessels (conduits), blood (transport medium).

• Example: Oxygen is carried from the lungs to tissues via blood.

Composition, Volume, and Physical Characteristics of Whole Blood

Whole blood is a specialized connective tissue with unique physical and chemical properties.

• Composition: Plasma (~55%), formed elements (~45%) including erythrocytes, leukocytes, and platelets.

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

• Physical Characteristics: Viscous, slightly alkaline (pH 7.35–7.45), temperature ~38°C.

Plasma: Composition, pH, and Functions

Plasma is the liquid component of blood, serving as a transport medium for nutrients, hormones, and waste.

• Composition: Water (~90%), proteins (albumin, globulins, fibrinogen), electrolytes, nutrients, gases, waste products.

• pH: 7.35–7.45 (slightly alkaline).

• Functions: Maintains osmotic pressure, transports substances, aids in clotting and immune defense.

Erythrocytes: Structure, Function, and Normal Values

Erythrocytes (red blood cells) are biconcave, anucleate cells specialized for oxygen transport.

• Structure: Biconcave shape increases surface area; lacks nucleus and organelles.

• Function: Transport oxygen (via hemoglobin) and carbon dioxide.

• Normal Values: Males: 4.7–6.1 million/µL; females: 4.2–5.4 million/µL.

Hemoglobin: Structure, Function, and Normal Values

Hemoglobin is a protein in erythrocytes that binds oxygen and carbon dioxide.

• Structure: Four polypeptide chains (globin) each with a heme group containing iron.

• Function: Oxygen transport; each molecule binds up to four O2 molecules.

• Normal Values: Males: 13–18 g/dL; females: 12–16 g/dL.

• Equation: $\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2$

Erythropoiesis: Process, Regulation, and Dietary Requirements

Erythropoiesis is the formation of erythrocytes in the red bone marrow.

• Process: Stem cells differentiate into erythrocytes under the influence of erythropoietin (EPO).

• Regulation: EPO released by kidneys in response to hypoxia.

• Dietary Requirements: Iron, vitamin B12, folic acid, proteins.

• Equation: $\text{Hypoxia} \rightarrow \text{EPO release} \rightarrow \text{Increased erythropoiesis}$

Erythrocyte Degradation

Old erythrocytes are removed by macrophages in the spleen, liver, and bone marrow.

• Process: Hemoglobin is broken down into heme and globin; heme is converted to bilirubin and excreted.

• Example: Bilirubin gives bile its yellow color.

Red Blood Cell Disorders

Various disorders affect erythrocyte number and function.

• Hemorrhagic Anemia: Blood loss.

• Hemolytic Anemia: RBC destruction.

• Aplastic Anemia: Bone marrow failure.

• Iron Deficiency Anemia: Low iron.

• Pernicious Anemia: Vitamin B12 deficiency.

• Thalassemia: Genetic globin defect.

• Sickle Cell Anemia: Abnormal hemoglobin causes sickling.

• Polycythemia Vera: Excess RBCs.

• Secondary Polycythemia: Increased RBCs due to hypoxia.

Leukocytes: Structure, Function, and Normal Values

Leukocytes (white blood cells) are immune cells classified as granulocytes or agranulocytes.

• Granulocytes: Neutrophils, eosinophils, basophils; contain granules, formed in bone marrow.

• Agranulocytes: Monocytes, lymphocytes; lack granules, formed in bone marrow and lymphatic tissue.

• Functions: Defense against pathogens, immune regulation.

• Normal Values: 4,000–11,000/µL.

• Leukopoiesis: Formation of WBCs.

White Blood Cell Disorders

Disorders affect leukocyte number and function.

• Leukopenia: Low WBC count.

• Leukocytosis: High WBC count.

• Leukemia: Cancer of WBCs.

• Infectious Mononucleosis: Viral infection (Epstein-Barr virus).

Platelets: Structure, Function, Production, and Normal Values

Platelets (thrombocytes) are cell fragments essential for clotting.

• Structure: Small, anucleate fragments from megakaryocytes.

• Function: Initiate clotting by forming platelet plugs.

• Production: Thrombopoiesis in bone marrow.

• Normal Values: 150,000–400,000/µL.

Hemostasis: Mechanisms

Hemostasis is the process of stopping bleeding via several mechanisms.

• Vascular Spasm: Vasoconstriction reduces blood flow.

• Platelet Plug Formation: Platelets adhere to injury site.

• Coagulation: Cascade of reactions forms fibrin clot (intrinsic and extrinsic pathways).

• Clot Retraction: Clot tightens to reduce bleeding.

• Vessel Repair: Growth factors stimulate healing.

• Fibrinolysis: Clot is dissolved by plasmin.

• Equation: $\text{Prothrombin} \xrightarrow{\text{Thrombin}} \text{Fibrinogen} \rightarrow \text{Fibrin}$

Factors Limiting Clot Formation and Agents Preventing Undesirable Clotting

Clot formation is regulated to prevent excessive or inappropriate clotting.

• Endogenous Factors: Antithrombin, protein C, heparin.

• Exogenous Agents: Aspirin, warfarin, heparin (medications).

Hemostasis Disorders

Disorders can disrupt normal clotting.

• Thrombus: Stationary clot.

• Embolus: Traveling clot.

• Disseminated Intravascular Coagulation (DIC): Widespread clotting and bleeding.

• Thrombocytopenia: Low platelet count.

• Hemophilias: Genetic clotting factor deficiencies.

Blood Groups: Agglutinogens, Agglutinins, and Compatibility

Blood types are determined by antigens (agglutinogens) and antibodies (agglutinins).

• Agglutinogen: Antigen on RBC surface (A, B, Rh).

• Agglutinin: Antibody in plasma (anti-A, anti-B, anti-Rh).

• Compatibility: Donor-recipient matching based on ABO/Rh system.

Blood Type	Agglutinogens	Agglutinins	Can Receive From
A	A	Anti-B	A, O
B	B	Anti-A	B, O
AB	A, B	None	A, B, AB, O
O	None	Anti-A, Anti-B	O
Rh+	Rh	None	Rh+, Rh-
Rh-	None	Anti-Rh (if sensitized)	Rh-

Blood Group Incompatibilities: Erythroblastosis Fetalis and Transfusion Reactions

Incompatibilities can cause serious clinical conditions.

• Erythroblastosis Fetalis: Hemolytic disease of the newborn due to Rh incompatibility.

• Transfusion Reactions: Immune response to incompatible blood.

• Example: Rh-negative mother with Rh-positive fetus may develop anti-Rh antibodies.