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Topic: Third Line of Defense Biology Buzz I. BLOOD… a fluid tissue that serves three important functions: 1. Responsible for transport of materials throughout the body. “Materials” include enzymes, lipids, hormones, CO2, O2, urea, nutrients such as simple sugars and amino acids. 2. Regulates pH, body temperature, and water content of cells. 3. Protects against disease causing microorganisms known as pathogens. Blood is made up of four components: a) Plasma- liquid part of blood mostly made up of water with dissolved materials. b) Red Blood Cells (RBC’s)Carries O2 and CO2 to and away from cells of the body. Contains hemoglobin (a protein on the surface of RBC’s) c) PlateletsResponsible for clotting blood. d) White Blood Cells (WBC)- Leukocytes Protects body against infection. Made in bone marrow and lymph nodes. Carried in blood but can also move out of blood vessels to tissues of body. There are two main types of WBC’s: 1. Phagocytic WBC Fight microorganisms by phagocytosis (to engulf) 2. Lymphocytes (B and T cells) Produces antibodies that recognize foreign substances (B cells) Kill foreign/infected cells directly (T cells) Third Line of Defense- Activation of the Immune System (Immune Response) Lymphocytes (WBCs) recognize, attack, and then destroy pathogens. This is done in two ways: 1. B cells produce antibodies which recognize specific antigens to inactivate them (Antibody/antigen relationship is very specific. 2. T cells known as cytolytic T cells physically bind with a pathogen and destroy the pathogen or infected cell. Antigen vs. Antibody ANTIGEN- proteins found on the surface of pathogens that cause an immune response activation of B and T cells (WBCs) ANTIBODY- a Y shaped protein made by B cells and helps to destroy pathogens in a couple of ways: 1. Marks pathogens for identification. 2. Binds to antigens and covers surface of pathogen to inactivate it. *An antibody recognizes a specific antigen! Now answer Questions 2 and 3!