Chapter 22 by uBUFU4r


									 Chapter 22
The lymphatic system
                  The lymphatic system
   Consists of a network of tissues, vessels and organs that help
    maintain body fluid balance.
   Closely tied to the immune system in protecting the body
    against foreign organisms.
   Organs and tissues of the lymphatic system:
       Lymph
       Lymphatic vessels
       Lymphatic cells
       Lymph nodes
       Spleen
       Tonsils
       Peyer’s patches
       Thymus
                The lymphatic system
   Functions:
       (a). fluid recovery: reabsorbs 2-4 l/day; prevents edema.
       (b). Immunity: lymph nodes and lymph organs monitor
                lymph and blood for pathogens and cancer cells.
       (c). lipid absorption through the lacteals in small intestine.
Distribution of lymph
nodes in body.

Lymph flows toward
the heart with the aid
of small valves
                  Lymphatic fluid
   How Formed: produced by filtration of plasma through
    the capillaries and is based on hydrostatic and osmotic
    pressures in capillaries and interstitial space.
   Pathway of Lymph Flow: Flow is always toward
    the heart. Begins in dead ended lymphatic capillaries
    that occur everywhere capillaries exist (except: brain,
    teeth, bones and bone marrow).
Lymphatic capillaries
               Lymphatic capillaries
   lymph capillaries –smallest of lymph vessels; are
    permeable to lymph fluid and proteins. Lymph
    capillaries drain into lymph collecting vessels.

   lacteals: - highly specialized lymphatic capillaries
    located in intestinal mucosa - transport absorbed fat
    from intestines and empty into great thoracic duct
          Lymphatic collecting vessels
   Lymphatic collecting vessels contain valves that act as
    smooth muscle pumps to move lymph toward heart.
   Travel with veins in superficial tissues/arteries in
    deeper tissues.
   Have the same three tunics as blood vessels but walls
    are much thinner and lymph pressure is very low.
   They also have lymph nodes scattered along their
    length to filter the lymph.
                    Lymphatic cells
   Natural killer cells (NK cells) large lymphocytes that attack
    and lyse bacteria, foreign tissue cells and infected host cells.
   T lymphocytes mature in the thymus (4 types Tc, Ts, Th, Tm).
   B lymphocytes mature in red bone marrow and produce
    antibodies when activated.
   Macrophages develop from monocytes and are phagocytic.
   Dendritic cells (branched macrophages) found in skin.
   Reticular cells branched cells in stroma of lymphatic organs.
                   Lymph nodes
   Bean shaped organs that cleanse the lymph of
   ~500 lymph nodes in the body ~ 1mm to 25mm.
   Node is surrounded by a fibrous capsule from which
    trabeculae extend inward to split the node into
    compartments called sinuses.
   Lymph enters node via afferent lymphatic vessel and
    exits through efferent lymphatic vessel back into
    collecting vessels.
   As lymph percolates thru the node macrophages
    cleanse the lymph of all pathogens.
Lymph nodes
                     Lymph Trunk
    Formed by the convergence of several lymph collecting
     vessels that drain large areas of the body.
    Six major trunks in body:
1.   Lumbar trunks- lymph from lower limb, pelvic region and
     anterior abdominal wall.
2.   Intestinal trunk- lymph from stomach, intestines and other
     digestive organs (chyle).
3.   Bronchomediastinal trunk- lymph from thoracic viscera
4.   Subclavian trunks- lymph from upper limbs, inferior neck
     and superior thoracic wall.
5.   Jugular trunks- lymph from head and neck.
6.   Intercostal trunk- lymph from intercostal region
                  Lymphatic ducts
   The lymphatic trunks drain into the largest lymphatic
    vessels: the lymphatic ducts. Most people (80%) have
    2 lymphatic ducts: (1) Thoracic duct (present in all
    people) and (2) the Right lymphatic duct.

   The thoracic duct empties into the venous circulation
    at the junction of the internal jugular and left
    subclavian veins. Lymph is then incorporated into the
    circulating blood, eventually cleansed of foreign and
    dead matter and excreted via the liver.
Thoracic duct and
right lymphatic duct
Thoracic duct drains
right side of face and
most of left thorax and
lower body.

Right lymphatic drains
left side of head and
upper body.
                        Lymphoid tissue
   The most important tissue of the immune system as it is
    responsible for the production and activation of the “B” and
    “T” lymphocytes. Found in two primary sites:
   (1) In the infected mucous membranes of the digestive,
    respiratory, urinary and reproductive tracts. This tissue is
    called MALT (mucosa associated lymphoid tissue).
   (2) In all lymphoid organs except the thymus.
       Lymphoid tissue is a framework of reticular fibers and reticular cells
        in a network of “B” and “T” lymphocytes as well as macrophages.
        This network consists of a network of lymphoid follicles with
        germinal centers of dividing lymphocytes
                    Lymphoid organs
   Primary lymphoid organs are thymus and bone
   Secondary lymphoid organs include the lymph nodes,
    spleen, tonsils, aggregated lymphoid nodules in the
    intestine and appendix.
       The thymus and bone marrow produce “T” and “B”
        lymphocytes and the secondary organs serve to collect and
        destroy the infectious microorganisms where they are
        removed by the liver and spleen.
                   Red bone marrow
   Second largest organ in the body next to skin.
   Two types red and yellow; red actively produces all
    blood cells; yellow is dormant and produces blood
    cells in extreme emergencies.
   Composed of a network of reticular fibers forming
    cave like structures with reticular cells lining the walls.
    Within the caves are blood cells in various stages of
    development and fat cells.
   Capillaries run throughout the network and carry the
    developed blood cells into the circulation.
Red marrow
   Located in the upper left quadrant of abdominal cavity
    with a gastric and renal area.
   Functions to remove blood borne antigens and aged
    or defective blood cells.
   It is a site for hematopoiesis in fetus and storage of
    blood throughout life.
   Consists of red and white pulp. (seen in fresh tissue).
     Red pulp is sinuses engorged with rbc’s.
     White pulp is lymphocytes and macrophages collected like
      sleeves along the splenic artery
Spleen structure
Spleen anatomy & histology
   Located in the oropharynx, they trap bacteria and
    foreign pathogens entering the mouth and nose.
   Palatine tonsils – either side of and posterior end of
    oral cavity
   Lingual tonsils – base of tongue
   Pharyngeal tonsils (adenoids)– posterior wall of
                   Peyer’s patches
   Defined: large isolated clusters of lymphatic nodules
    found intermingled around the ileum of the small
   Function: destroy bacteria and generates memory
    lymphocytes for long term immunity against infection.
   Site where immature lymphocytes develop into “T”
   Secretes thymosin and thymopoietin which stimulate
    “T” cells to become immunocompetent.
   Most prominent in childhood and by age 40 is ~ 5%
Thymus structure & histology

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