Immune System B Defense against invasion by foreign organisms.

Non-Specific Defenses B Mechanical and Chemical

    1.  Epithelial Membrane barriers
    2.  Acidic secretions (sweat, oils, stomach acid, vaginal acids, etc.)
    3.  Lysozyme B general bactericidal enzyme found in saliva, tears
    4.  Inflammatory response (in response to chemicals released from damaged cells/infected areas)
              Important for diluting infectious agents, sealing off area, bringing white blood cells and
             antibodies to the area, etc.
    5.   Non-specific phagocytic cells B macrophages, for instance.

Specific Defenses B Lymphocytes
    B-cells (matured in bone marrow) B make antibodies (Ab=s); in huge number when activated by antigen
            Antibody structure B two light/two heavy polypeptide chains stuck together, with constant and
                   variable regions; variable regions slightly different from B-cell type to B-cell type
            Variable regions are what bind to antigens (foreign molecules); all Ab=s made by one B-cell bind to   
                   one and only one antigen; Ab=s only attach, they do not kill anything by themselves

    T-cells (matured in thymus) B different classes: cytotoxic (direct cell attack) and helper (co-stimulatory)
            Cytotoxic T-cells are involved in direct cell attack; drop chemical bombs (enzyme containing 
                   vesicles), particularly on virus-infected and tumor cells

Both require presence of specific antigen, which binds to specific receptors in the B-cell and/or T-cell membranes, to activate them. When activated, produce tremendous numbers of plasma cells (involved in attack with the current infection -- primary response) and memory cells (stored for later use B immunity with the secondary response).

Naturally and Artificially acquired (vaccinations) immunity B passive (Ab=s only)/ active (produce memory cells)

Macrophages B Although macrophages are not specific to particular antigens themselves, they can travel through the tissue spaces (and so encounter foreign pathogens with frequency) and also through the lymphatic and circulatory systems. Since lymph nodes house large numbers of lymphocytes, particularly B-cells, macro-phages can present pieces of the bacteria, etc. to lymphocytes in lymph nodes (and elsewhere) in order to activate them. As such, macrophages play a role in specific immunity by being Antigen-Presenting Cells (APC=s).

Helper T Cells B Co-stimulators; release chemicals that, along with antigen exposure, activate both the B-cells and T-cells (a few other cells can release specific co-stimulatory chemicals as well). Without this co-stimulation, neither group of cells can begin producing plasma cells which means that there would be no immune response without co-stimulation. The HIV (human immuno-deficiency virus; cause of AIDS) attacks precisely these helper T cells, which explains why it is so devastating.

Function of Antibodies B Ab=s only attach; but this can:

1. neutralize and inhibit function
2. clump
3. activate other aspects of both specific and non-specific defenses
4. make it possible for phagocytes to latch onto antigens/pathogens and eliminate them
   

GAS EXCHANGE B more than 90% of energy in glucose available only with O₂; CO₂ produced
              gases must be exchanged across moist membranes B gases must dissolve to be absorbed
        small aquatic organisms use diffusion only
        diffusion not enough for large, 3-d organisms
        terrestrial organisms B additional problem of dessication

Organs must have:

1. sufficient surface area
2. transport mechanisms for O₂/CO₂
3. protection (from damage)
4. preventive mechanisms for eliminating water loss

Plants B Stomates; Roots

Animals
     Aquatic B simple animals use diffusion
        complex use gills (KNOW STRUCTURE of fish gill) with rich supply of blood vessels (for transport)
                many variations on gills (external, internal, plastron)
        fish use countercurrent exchange mechanism; you will need to know how it works

     Terrestrial
        mammals B use diaphragm to create negative pressure
                Know structure of the human system (nostrils, nasal cavities, pharynx, trachea, bronchi,         
                bronchioles, alveoli) and importance of each
        birds B one way flow through air sac system, with some countercurrent exchange
        frogs B use positive pressure (mouth pouch), and also skin

Insect tracheal systems B
      Tubes branch profusely so that air-filled passageways come in contact with virtually every single stationary cell in the body. Allows rapid diffusion through air tubes; and independent of the circulatory system

Breathing B Inhalation/Exhalation; diffusion of gases at exchange surfaces.
        Remember, both respiratory gases are small, non-polar molecules that can pass through membranes easily; this is a good thing as the gases simply follow concentration gradients at both the lungs and the tissues; no extra ATP required for exchange.

O₂/CO₂ transport B the oxygen-Hemoglobin dissociation curve
        O₂ B attached to hemoglobin
        CO₂ B directly or as bicarbonate ions in plasma; some attached to amino acid portion of Hb

                        CO₂ + H₂O ----> H₂CO₃ ----> H⁺ + HCO₃^-

    The Bohr effect: curve shifts to right in acidic conditions (at tissues); to left in alkaline conditions (at lungs)
    Temperature effects: high shifts curve to right, low shifts curve to left.

        The important aspect of both of these is to increase oxygen unloading at tissues under conditions where this would be needed (increased acid due to CO₂/lactic acid and higher temps, both occur with exercise).