Study Guide: Blood – Structure, Function, and Components

Blood: An Overview

The Components of the Cardiovascular System

The cardiovascular system is responsible for transporting nutrients, gases, hormones, and waste products throughout the body. Blood is a vital fluid connective tissue that plays a central role in this system.

• Blood consists of plasma (the liquid matrix) and formed elements (cells and cell fragments).

• Functions of blood include transport, regulation, and protection.

Functions of Blood

• Transport: Delivers oxygen and nutrients to tissues, removes waste products, and transports hormones.

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

• Protection: Defends against pathogens and prevents blood loss through clotting.

Physical Characteristics of Blood

• Color: Bright red (oxygen-rich) to dark red (oxygen-poor).

• Volume: 4–6 liters in adults.

• pH: Slightly alkaline, typically 7.35–7.45.

• Viscosity: Thicker than water due to formed elements and plasma proteins.

Composition of Blood

• Plasma: The liquid component, making up about 55% of blood volume.

• Formed Elements: Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Plasma: Components and Functions

Plasma is a straw-colored fluid composed mainly of water, proteins, electrolytes, nutrients, gases, and waste products.

Plasma Protein	% Total Plasma Proteins	Production Site	Functions
Albumin	~60%	Liver	Maintains osmotic pressure, transports substances
Globulins	~36%	Liver, lymphoid tissue	Transport, immune response (antibodies)
Fibrinogen	~4%	Liver	Blood clotting

• Electrolytes: Sodium, potassium, calcium, chloride, bicarbonate, etc.

• Dissolved gases: Oxygen, carbon dioxide, nitrogen.

Formed Elements of Blood

Red Blood Cells (Erythrocytes)

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

• Structure: Biconcave discs, lack nuclei and most organelles, filled with hemoglobin.

• Hemoglobin: Iron-containing protein that binds oxygen; each molecule can carry four oxygen molecules.

• Lifespan: ~120 days; produced in red bone marrow.

White Blood Cells (Leukocytes)

• Function: Defend the body against infection and disease.

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

Type	Function
Neutrophils	Phagocytize bacteria and debris
Eosinophils	Combat parasitic infections, modulate allergic responses
Basophils	Release histamine and heparin during inflammatory responses
Lymphocytes	Produce antibodies, regulate immune response
Monocytes	Differentiate into macrophages, phagocytize pathogens and debris

Platelets (Thrombocytes)

• Function: Essential for blood clotting (hemostasis).

• Origin: Fragments of megakaryocytes in bone marrow.

Production of Blood Cells (Hematopoiesis)

Hematopoiesis

• Occurs primarily in red bone marrow.

• All blood cells arise from pluripotent hematopoietic stem cells.

• Specialized growth factors regulate differentiation into erythrocytes, leukocytes, and platelets.

Blood Typing and Transfusion

Blood Groups

• ABO System: Based on presence or absence of A and B antigens on RBCs.

• Rh System: Presence (+) or absence (−) of Rh antigen (D antigen).

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

• Universal donor: Type O−

• Universal recipient: Type AB+

Blood Transfusion Compatibility

• Transfusions must match both ABO and Rh types to prevent immune reactions.

• Hemolytic disease of the newborn (HDN) can occur if an Rh− mother carries an Rh+ fetus.

Hemostasis

Phases of Hemostasis

• Vascular spasm: Vasoconstriction reduces blood flow.

• Platelet plug formation: Platelets adhere to damaged endothelium and aggregate.

• Coagulation: Fibrinogen is converted to fibrin, forming a stable clot.

Key Terms and Definitions

• Hematocrit: Percentage of blood volume occupied by red blood cells.

• Hemoglobin: Oxygen-carrying protein in red blood cells.

• Leukemia: Cancer of blood-forming tissues, leading to abnormal white blood cell production.

• Lymphoma: Cancer of lymphatic tissue, often involving lymphocytes.

Additional info:

• Blood is a specialized connective tissue with both cellular and liquid components, essential for homeostasis and survival.

• Understanding blood composition and function is foundational for studies in physiology, medicine, and related biological sciences.