I. Structure.

    A. Lymph: the fluid contained in the lymphatic system.

    B. Lymph capillaries.
        1. Located almost everywhere in the body.
        2. Dead-end, one-way tubes.
        3. Extracellular fluid is under greater pressure than fluid in the lymph capillaries.
        4. Walls of capillaries allow fluid to enter easily, but prevent fluid leaving.

    C. Lymph vessels.
        1. Similar to veins.
        2. Muscle fibers in the walls pump the fluid along.
        3. Movement of skeletal muscles assist the flow of lymph.
        4. Valves prevent back-flow.

    D. Lymph nodes: filter out and destroy foreign matter.

    E. Thoracic duct and right lymph duct: empty into veins near the heart.

II. Purpose.

    A. Drain excess water from the extracellular fluid back into the circulatory system.
    B. Temporary reservoir for fluids taken into the body.
    C. Carry large molecules (e.g. proteins and hormones too large to cross the capillary wall) to the blood.
    D. Transport some food molecules (e.g. fats) from the intestine to the blood.
    E. Fight disease at the lymph nodes.

III. Development of Types of Blood Cells.

    A. All arise from hematopoietic stem cells in the bone marrow.

    B. Erythroids develop into erythrocytes.

    C. Myeloids develop into monocytes and granulocytes.
        1. Monocytes develop into macrophages.
            a. Large phagocytic cells.
            b. Engulf virtually any substance foreign to the body.
            c. Wandering: travel through the blood and lymph.
            d. Fixed: embedded in lymph tissue.
        2. Granulocytes.
            a. The most common leukocytes.
            b. Develop into neutrophils: small phagocytic cells.
    D. Lymphocytes.
        1. Small cells with varying shapes.
        2. The most important leukocytes.
        3. Circulate throughout the body in the blood and lymph.
        4. Perform several immune functions.
            a. Recognize antigens.
            b. Produce antibodies.
            c. Control the immune response.
            d. Remember the immune response somehow.
        5. 2 major types.
            a. T  lymphocytes: undergo further differentiation in the thymus gland.
            b. B  lymphocytes.
                i. Named for the bursa of Fabricius in birds where they undergo further differentiation.
                ii. This differentiation in mammals takes place in the bone marrow.
            c. Look alike, but bear different surface markers and perform different functions.
        6. Both types come in 1000's of different varieties, one for each antigen.

IV. Lymph Nodes.

    A. A network of sinuses lined with lymphocytes and fixed macrophages.
    B. As the lymph passes through, the macrophages engulf bacteria, viruses, etc. and digest them in vacuoles.

V. Immunity.

    A. The ability of the body to destroy a pathogen or render it harmless.

    B. Antigen: any foreign substance against which the body reacts.
        1. Usually a protein.
        2. E.g. part of a viral capsid, or a chemical released by a bacteria.

    C. Antibody: a protein which travels through the body in the blood and lymph to aid in destroying an antigen.

VI. Humoral Immunity.

    A. Destruction of antigens by antibodies in the body humors.

    B. Each person has 1000's of different B lymphocytes, each recognizing a different antigen.

    C. An antigen stimulates a specific B lymphocyte to divide and produce plasma cells and memory B cells.

    D. Plasma cells produce antibodies.
        1. Live 4-5 days.
        2. Produce up to 2,000 antibodies per second.

    E. These antibodies travel throughout the body to find and react with their specific antigen.
        1. Block a receptor site on a viral capsid.
        2. Precipitate the antigen: cause it to clump together.
        3. Cause agglutination: cause infected cells to clump together.
        4. Immobilize flagella.

    F. The neutralized antigen can then be removed by phagocytosis or another means.

    G. Memory B cells may live for several dozen years.
        1. A second infection will trigger them to divide and make antibodies much faster.
        2. The antigen can be eliminated before the person notices any disease symptoms.

VII. Cell-mediated Immunity.

    A. Destruction of cells infected by an antigen.

    B. Certain parts of certain antigens become bonded to the surface of a macrophage attempting to engulf them.

    C. This may stimulate the division and differentiation of a helper T cell.
        1. Helper T cells: provide more cells from which to make the other T cells.
        2. Killer T cells: attack body cells joined to an antigen.
            a. Attach to the affected cell.
            b. Release a membrane lysing enzyme.
            c. The cell membrane ruptures, killing the cell.
        3. Suppressor T cells: stop the activity of the other lymphocytes when the infection has been arrested.
        4. Memory T cells: will circulate in the blood for dozens of years, ready to respond rapidly to another infection.

VIII. Kinds of Immunity.

    A. Active: the antibodies or T cells are made by the person infected.
        1. Natural: he got the disease.
        2. Artificial: he received a vaccine.

    B. Passive: the antibodies are supplied to the person.
        1. Natural: obtained from his mother, either through the placenta or by nursing.
        2. Artificial: obtained from the blood serum of other humans or animals.
 

I. Organs.

    A. Kidneys.
        1. Filter metabolic wastes from the blood.
        2. Excrete these wastes as urine.

    B. Ureters.
        1. Muscular tubes connecting kidneys to the urinary bladder.
        2. Urine is moved by peristalsis.

    C. Urinary Bladder.
        1. Urine reservoir.
        2. Muscular wall, lining.

    D. Urethra.
        1. Tube leading from the bladder to the outside.
        2. Two sphincters at the exit.
        3. Operation.
            a. Muscles of bladder contract.
            b. Pressure forces one sphincter open.
            c. Other sphincter must be opened voluntarily.

II. Kidneys.

    A. Structure.
        1. Connective tissue: a thin layer surrounds and holds the kidneys in place.
        2. Cortex: contains the outer part of the nephrons.
        3. Medulla.
            a. Pyramids: cone-shaped masses of tissue.
            b. Contains the inner part of the nephrons.
        4. Pelvis: collects urine.

    B. Flow volume.
        1. Out of 5.6 l total of blood, 1.2 l pass through the kidneys each minute.
        2. All the blood passes through the kidneys 280 times per day.

    C. Nephrons.
        1. General.
            a. This is the functional part of the kidney.
            b. 1million per kidney.
        2. Renal corpuscle.
            a. Located in the cortex.
            b. Glomerulus: a capillary bed
            c. Bowman’s capsule: cup-shaped end to the tubule of the nephron.
            d. Blood enters the glomerulus under pressure.
            e. Much of the blood fluid filters into the capsule, including glucose and amino acids.
            f. Large proteins and whole cells are left behind.
        3. Proximal convoluted tubule.
            a. Located in the cortex.
            b. Na⁺ and glucose are returned to the blood by active transport.
            c. Cl^- follows the sodium passively
            d. H₂O follows the Cl^- by osmosis.
            e. 100% of glucose and 75% of salt and H₂O return to the blood.
        4. Loop of Henle.
            a. Extends down into the medulla.
            b. Purpose is to set up a high concentration of NaCl in the medulla.
                i. There is no known carrier that can transport H₂O molecules.
                ii. Cells move water across a membrane by setting up a concentration gradient so H2O will move by osmosis.
            c. Later, H₂O will diffuse out from the collecting duct which also passes through the medulla.
            d. Cl^- is pumped out of the ascending part of the loop, and Na⁺ follows.
            e. H₂O would follow, too, but this part of the loop is impermeable to H₂O.
            f. Since there is more Cl^- in the lower part of the loop, more Cl^- will be pumped out here.
            g. Thus the lower part of the medulla has a higher concentration of NaCl.
            h. As fluid descends the loop, water diffuses out because of this high concentration of NaCl.
            i. (The descending part of the loop is permeable to water.)
            j. Cl^- and Na⁺ also diffuse into the descending part of the loop.
            k. Thus the NaCl are constantly recycled.
            l. The point of all this is to set up a concentration gradient in the medulla so that water will diffuse out of the collecting duct.
            m. This system is called a countercurrent multiplier.
        5. Distal convoluted tubule.
            a. Located in the cortex.
            b. Na⁺ is returned to the blood by active transport.
            c. H₂O follows the Na⁺ by osmosis.
            d. K⁺ and H⁺ enter the tubule by active transport.
            e. NH₃ follows by diffusion.
            f. Secretion of H⁺ helps regulate the pH of the blood.
        6. Collecting duct.
            a. Passes through the medulla and empties into the pelvis.
            b. Urine is concentrated.
            c. H₂O exits the duct by osmosis as it passes through the increasing NaCl gradient.
            d. The Na⁺, Cl^-, and H₂O diffuse back into the capillaries or the lymphatic system.

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