Immune System

Two nonspecific defense systems First line of defense Skin and mucous membranes Second line of defense Nonspecific cellular and chemical protection devices (Third line of defense = specific immune responses to kill particular organisms)

First line of defense Skin and mucous membranes Skin has 4 ways to block entry of disease Structure Dead, dried out keratinized cells – waterproof barrier Continuously replaced – pathogens get sloughed off Acidic pH 5-6 is hostile environment Sweat glands produce antibodies Dermicidin kills a wide range of harmful bacteria

Mucus and other secretions Tears, saliva, earwax Tears & saliva contain lysozyme = bacteria killer Earwax traps particles Mucus secreted in GI tract, respiratory tract mires microorganisms Cilia beat constantly and sweep away pathogens (coughed up or swallowed)

Mucus and other secretions cont’d Digestive and vaginal acids – low pH hostile environment Vomiting, urination, defecation all remove microorganisms Urine is acidic Vomiting cleans the stomach Diarrhea speeds pathogen expulsion

Nonspecific cellular and chemical defense White blood cell army are Generalists – attack everything, clean up & repair crew Phagocystosis – captures and digests Neutrophils – first to respond, digest, destroy Macrophages – engulf and digest large numbers of invaders Eosinophils – cluster around large parasites and bombard with digestive enzymes

Inflammatory Response Warmth, swelling and pain Starts when tissue is damaged Chemical stimulus calls mast cells to release histamine Histamine capillaries  permeable  phagocytes to enter battle along with more blood Extra fluid dilutes pathogens and toxins & brings in clotting proteins to wall off damaged area Extra oxygen & nutrients promote tissue healing & carries away damaged cells, microorganisms & debris Swollen tissue press on nerves causing pain  reduces movement

Adaptive (specific) defense system Works in conjunction with the intrinsic: it identifies the specific invader, participates in the specific invader's destruction by either killing them directly activating the inflammatory response activating complement proteins making antibodies

Lymphocytes role T cells participate in adaptive cellular defense (kill or help with the kill) B cells make antibodies that help with the destruction of the invader

B-cell immune response. Antibody mediated immunity B cells (bone marrow) move to lymphatic tissues and become plasma cells (cells transported by the plasma) that produce antibodies (antibodies are proteins capable of inactivating antigens) B cells must be activated by helper T cells Antibodies are secreted into the blood, lymph and mucus – they combine with the antigen and mark them for destruction

B cell immune response cont’d Once antibody production is enough to cause the antigen to disappear the development of the plasma cells stops Some cells remain (memory B cells) in case of future invasion = active immunity

What is active immunity? How can it be acquired? Occurs when b cells encounter antigens and produce antibodies Artificially acquired – vaccine Naturally acquired – natural contact

What is passive immunity? How do you get it? Antibodies are obtained from the serum of an immune person B cells do not produce new antibodies (there is no antigen challenge) – so no memory cells are made Protection ends when donor antibodies degrade – but search and destroy while present Mother to fetus, breast feeding Snake bite serum, rabies shots