Blood Components and Immune System

Overview of Blood and Its Functions

Blood is a specialized connective tissue that plays a vital role in transporting nutrients, gases, hormones, and waste products throughout the body. It also contributes to immune defense and homeostasis.

• Connective tissue: Blood is classified as a connective tissue because it consists of cells suspended in a liquid extracellular matrix called plasma.

Main Components of Blood

• Plasma: The liquid portion of blood, making up about 55% of total blood volume. It contains water, proteins, nutrients, hormones, and waste products.

• Formed elements: These include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Key Plasma Proteins

• Albumins: Constitute about 60% of plasma proteins. They help maintain osmotic pressure and transport substances.

• Globulins: Include antibodies (immunoglobulins) and transport proteins.

• Fibrinogen: A key plasma protein essential for blood clotting. It is converted to fibrin during the clotting process.

Formed Elements

• Red blood cells (Erythrocytes): Specialized for oxygen transport. Contain hemoglobin, which binds oxygen via iron ions.

• White blood cells (Leukocytes): Involved in immune defense. Types include basophils, lymphocytes (B and NK cells), and others.

• Platelets (Thrombocytes): Cell fragments derived from megakaryocytes in the bone marrow. Essential for blood clotting by forming temporary plugs at injury sites.

Key Terms and Definitions

• Basophils: White blood cells containing granules filled with histamine, released during allergic reactions and inflammation.

• Type O negative: Blood type lacking A, B, and Rh antigens, making it the universal donor type.

• B lymphocytes (B cells): Differentiate into plasma cells that produce antibodies targeting foreign substances.

• Lymphocytes (NK cells): Natural Killer cells that destroy infected or cancerous cells without prior activation.

• Antigens on red blood cells: Molecules that determine a person's blood type by the presence or absence of specific surface markers.

• Iron ion: Found at the center of heme molecules in hemoglobin, binds oxygen for transport in red blood cells.

• Antibodies (Immunoglobulins): Plasma proteins produced by B cells that defend against foreign antigens.

Blood Clotting and Hemostasis

Blood clotting is a complex process involving platelets and plasma proteins to prevent blood loss after injury.

• Platelets: Aggregate at damaged blood vessels to form a temporary plug.

• Fibrinogen: Converted to fibrin, forming a mesh that stabilizes the platelet plug.

Blood Types and Antigens

• Blood type: Determined by the presence or absence of specific antigens on red blood cell surfaces (e.g., A, B, Rh).

• Type O negative: Universal donor due to lack of A, B, and Rh antigens.

Immune System Organs and Functions

• Liver: Synthesizes and releases more than 90% of all plasma proteins, including albumins, globulins, and fibrinogen.

• Thymus: Site of T cell maturation. Gradually shrinks and becomes less active after puberty, reducing T cell production with age.

• Pancreas: Mixed gland with exocrine (digestive enzyme) and endocrine (insulin and glucagon) functions, located in the abdominopelvic cavity.

• Hypothalamus: Brain region controlling autonomic centers and hormone release from the adrenal medulla during stress responses.

Summary Table: Key Blood Components and Functions

Key Equations

• Percentage of plasma in blood:

• Oxygen binding in hemoglobin:

Examples and Applications

• Universal donor: Type O negative blood can be given to any recipient in emergencies due to lack of A, B, and Rh antigens.

• Allergic reactions: Basophils release histamine, contributing to symptoms such as swelling and redness.

• Immune defense: Antibodies produced by B cells neutralize pathogens and mark them for destruction.