Blood: Structure, Function, and Disorders – Study Notes for Human Anatomy & Physiology II

Blood: Structure, Function, and Disorders

Cardiovascular System: Functions and Major Components

The cardiovascular system is responsible for transporting substances throughout the body, maintaining homeostasis, and protecting against disease. Its major components include the heart, blood vessels (arteries, veins, capillaries), and blood.

• Functions:

  • Transport of oxygen, nutrients, hormones, and waste products

  • Regulation of body temperature, pH, and fluid volume

  • Protection against blood loss (hemostasis) and infection (immune response)

• Major Components: Heart, blood vessels, and blood

Whole Blood: Composition, Volume, and Physical Characteristics

Whole blood is a specialized connective tissue composed of plasma and formed elements. The average adult has about 5 liters of blood.

• Composition: 55% plasma, 45% formed elements (erythrocytes, leukocytes, platelets)

• Physical Characteristics: Sticky, opaque fluid; color varies with oxygen content (scarlet to dark red); denser than water; slightly alkaline (pH 7.35–7.45)

Plasma: Composition, pH, and Functions

Plasma is the liquid matrix of blood, making up about 55% of its volume.

• Composition: 90% water, 8% plasma proteins (albumin, globulins, fibrinogen), 2% other solutes (nutrients, electrolytes, gases, hormones, waste products)

• pH: 7.35–7.45

• Functions: Transports substances, maintains osmotic pressure, buffers pH, and supports immune and clotting functions

Erythrocytes (Red Blood Cells): Structure, Function, and Normal Values

Erythrocytes are biconcave, anucleate cells specialized for oxygen transport.

• Structure: Biconcave disc, no nucleus or organelles, filled with hemoglobin

• Function: Transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs

• Normal Values: 4.7–6.1 million/μL (males), 4.2–5.4 million/μL (females)

Hemoglobin: Structure, Function, and Normal Values

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

• Structure: Four polypeptide chains (globins), each with a heme group containing iron

• Function: Reversibly binds oxygen and carbon dioxide for transport

• Normal Values: 13–18 g/dL (males), 12–16 g/dL (females)

Erythropoiesis: Process, Regulation, and Dietary Requirements

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

• Process: Hematopoietic stem cell → proerythroblast → erythroblast → reticulocyte → erythrocyte

• Regulation: Controlled by erythropoietin (EPO), a hormone from the kidneys in response to hypoxia

• Dietary Requirements: Iron, vitamin B12, folic acid, proteins, and other nutrients

Equation for Erythropoiesis Regulation:

$\text{Hypoxia} \rightarrow \text{Kidneys release EPO} \rightarrow \text{Red bone marrow increases RBC production}$

Erythrocyte Degradation

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

• Hemoglobin is broken down into heme and globin

• Iron is recycled; heme is converted to bilirubin and excreted in bile

Red Blood Cell Disorders

Several disorders affect erythrocyte number or function:

• Hemorrhagic anemia: Blood loss

• Hemolytic anemia: Premature RBC destruction

• Aplastic anemia: Bone marrow failure

• Iron deficiency anemia: Inadequate iron

• Pernicious anemia: Vitamin B12 deficiency

• Thalassemia: Genetic defect in globin synthesis

• Sickle cell anemia: Abnormal hemoglobin S causes RBC sickling

• Polycythemia vera: Excess RBCs due to bone marrow disorder

• Secondary polycythemia: Increased RBCs due to hypoxia or other causes

Leukocytes (White Blood Cells): Structure, Function, and Normal Values

Leukocytes are immune cells that defend the body against pathogens. They are classified as granulocytes or agranulocytes.

• Granulocytes: Neutrophils, eosinophils, basophils (contain granules in cytoplasm)

• Agranulocytes: Monocytes, lymphocytes (lack visible granules)

• Site of Formation: Red bone marrow

• Leukopoiesis: Production of WBCs, stimulated by interleukins and colony-stimulating factors

• Life Span: Hours to years, depending on type

• Normal Values: 4,800–10,800/μL

White Blood Cell Disorders

• Leukopenia: Low WBC count

• Leukocytosis: High WBC count (often infection)

• 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 blood clotting.

• Structure: Small, anucleate cytoplasmic fragments

• Function: Form platelet plugs and release clotting factors

• Production: Derived from megakaryocytes in bone marrow

• Normal Values: 150,000–400,000/μL

Hemostasis: Mechanisms

Hemostasis is the process of stopping bleeding through a series of steps:

• Vascular spasm: Vasoconstriction of damaged vessel

• Platelet plug formation: Platelets adhere to exposed collagen and aggregate

• Coagulation: Formation of fibrin mesh via intrinsic and extrinsic pathways

• Clot retraction: Platelets contract to tighten clot

• Vessel repair: Growth factors stimulate healing

• Fibrinolysis: Clot is dissolved by plasmin

Coagulation Pathways Equation:

$\text{Intrinsic/Extrinsic Pathway} \rightarrow \text{Prothrombinase} \rightarrow \text{Prothrombin} \rightarrow \text{Thrombin} \rightarrow \text{Fibrinogen} \rightarrow \text{Fibrin (clot)}$

Factors Limiting Clot Formation and Preventing Undesirable Clotting

• Endogenous factors: Smooth endothelium, antithrombin III, protein C, heparin

• Exogenous agents: Anticoagulant drugs (e.g., warfarin, aspirin)

Hemostasis Disorders

• Thrombus: Stationary clot in unbroken vessel

• Embolus: Free-floating clot

• Disseminated intravascular coagulation (DIC): Widespread clotting and bleeding

• Thrombocytopenia: Low platelet count

• Hemophilias: Genetic clotting factor deficiencies

Blood Groups: Agglutinogens, Agglutinins, and Compatibility

Agglutinogens (antigens) are surface markers on RBCs; agglutinins (antibodies) are found in plasma. The ABO and Rh systems determine blood type compatibility.

Blood Type	Agglutinogens (Antigens)	Agglutinins (Antibodies)	Can Receive From	Can Donate To
A	A	Anti-B	A, O	A, AB
B	B	Anti-A	B, O	B, AB
AB	A, B	None	A, B, AB, O	AB
O	None	Anti-A, Anti-B	O	A, B, AB, O

Rh System: Rh+ has D antigen; Rh– lacks D antigen. Rh– individuals produce anti-D antibodies if exposed to Rh+ blood.

Blood Group Incompatibility Disorders

• Erythroblastosis fetalis (hemolytic disease of the newborn): Occurs when Rh– mother carries Rh+ fetus; maternal antibodies attack fetal RBCs

• Transfusion reactions: Occur when incompatible blood is transfused, leading to agglutination and hemolysis

Example: A person with type O– blood is a universal donor but can only receive O– blood.

Additional info: Academic context and explanations have been expanded for clarity and completeness.