Comprehensive Study Notes: Blood and Its Functions (Chapter 17)

Blood: The Life-Sustaining Transport Vehicle

Functions of Blood

Blood is essential for maintaining homeostasis and supporting the cardiovascular system. Its primary functions include:

• Transport: Delivers oxygen and nutrients to body cells, removes metabolic wastes, and transports hormones.

• Regulation: Maintains body temperature, pH balance, and fluid volume.

• Protection: Prevents blood loss through clotting and defends against infection via immune cells.

Physical Characteristics and Composition of Blood

Physical Characteristics

• Sticky, opaque fluid with metallic taste

• Color varies with oxygen content: scarlet (high O2), dark red (low O2)

• Average volume: 5-6L (males), 4-5L (females)

Blood Plasma

Plasma is the straw-colored, liquid portion of blood, making up about 55% of its volume.

• Composed of water, proteins (albumin, globulins, fibrinogen), nutrients, electrolytes, gases, hormones, and waste products.

• Albumin: Most abundant plasma protein, maintains osmotic pressure.

Formed Elements

• Include erythrocytes (RBCs), leukocytes (WBCs), and platelets.

• Only WBCs are complete cells; RBCs lack nuclei and organelles; platelets are cell fragments.

• Most formed elements survive in the bloodstream for only a few days.

Erythrocytes (Red Blood Cells)

Structure and Function

• Biconcave discs, 7.5 μm diameter, increase surface area for gas exchange.

• Filled with hemoglobin for oxygen transport.

• Flexible membrane allows passage through capillaries.

Hemoglobin

• Protein responsible for oxygen transport.

• Each hemoglobin molecule consists of four polypeptide chains (globin) and four heme groups.

• Each heme group binds one O2 molecule.

Equation:

$\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2$

Production of Erythrocytes (Erythropoiesis)

• Occurs in red bone marrow.

• Regulated by erythropoietin (EPO), a hormone produced by kidneys in response to hypoxia.

• Stages: Hematopoietic stem cell → Myeloid stem cell → Proerythroblast → Erythroblast → Reticulocyte → Mature erythrocyte

Disorders of Erythrocytes

Anemia

• Iron-deficiency anemia: Caused by hemorrhage, low iron intake, or impaired absorption.

• Pernicious anemia: Autoimmune disease affecting vitamin B12 absorption.

• Thalassemia: Genetic disorder affecting globin chain synthesis.

• Sickle-cell anemia: Abnormal hemoglobin causes RBCs to become sickle-shaped.

Polycythemia

• Excess RBCs increase blood viscosity, causing sluggish blood flow.

Leukocytes (White Blood Cells)

Types and Functions

• Granulocytes: Neutrophils, eosinophils, basophils (contain visible cytoplasmic granules).

• Agranulocytes: Lymphocytes, monocytes (lack visible granules).

• Defend against pathogens, remove toxins, and mediate immune responses.

Granulocytes

• Neutrophils: Most numerous, phagocytize bacteria.

• Eosinophils: Combat parasitic infections, modulate allergic responses.

• Basophils: Release histamine, functionally similar to mast cells.

Agranulocytes

• Lymphocytes: T cells (cell-mediated immunity), B cells (produce antibodies).

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

Leukocyte Disorders

• Leukopenia: Abnormally low WBC count.

• Leukemia: Cancerous overproduction of abnormal WBCs.

Platelets and Hemostasis

Platelets

• Fragments of megakaryocytes, essential for clotting.

• Form temporary platelet plugs to seal breaks in blood vessels.

Hemostasis

Hemostasis is the process of stopping bleeding and involves three steps:

1. Vascular spasm: Vasoconstriction reduces blood flow.

2. Platelet plug formation: Platelets adhere to exposed collagen fibers.

3. Coagulation: Fibrin threads reinforce the platelet plug.

Coagulation Pathways:

• Intrinsic pathway: Factors present within blood.

• Extrinsic pathway: Factors needed for clotting are outside blood.

Equation:

$\text{Prothrombin} \xrightarrow{\text{Prothrombinase}} \text{Thrombin}$

$\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

Blood Groups and Transfusion

ABO Blood Groups

Blood Type	Antigens on RBCs	Antibodies in Plasma
A	A	Anti-B
B	B	Anti-A
AB	A and B	None
O	None	Anti-A and Anti-B

Rh Blood Groups

• Rh+ indicates presence of D antigen; Rh- indicates absence.

• Anti-Rh antibodies form only after exposure to Rh+ blood.

Transfusion Reactions

• Occur if mismatched blood is transfused; recipient's antibodies attack donor RBCs, causing agglutination and hemolysis.

Transfusion Compatibility

Donor Type	Universal Donor	Universal Recipient
Type O	Yes	No
Type AB	No	Yes

Restoring Blood Volume

• Volume replacement is critical in cases of severe blood loss.

• Isotonic saline or plasma expanders may be used.

Summary Table: Formed Elements

Element	Structure	Function
RBCs	Biconcave, no nucleus	Oxygen transport
WBCs	Complete cells	Immune defense
Platelets	Cell fragments	Clotting

Additional info: These notes expand upon the original bullet points, providing definitions, context, and examples for key terms and processes relevant to Chapter 17: Blood in Anatomy & Physiology.