Lymphatic system

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Lymphatic system

• Chapter 16

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Miscellaneous

• Network of vessels that assist circulating body
  fluids
• Closely associated with the circulatory system
• Organs of lymphatic system defend against
  infection

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Pathways

• 1. Lymphatic capillaries -microscopic,
  closed-ended tubes
• Extend into interstitial spaces and form complex
  networks that parallel blood capillary networks
• Consist of a single layer of endothelium designed
  to allow tissue fluid from interstitial spaces to
  enter
• Fluid inside the capillary is called lymph

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Pathways continued

• 2. Lymphatic vessels-similar to vein walls but
  thinner
• Consist of an endothelial lining, a middle layer
  of smooth muscle and elastic fibers, and an outer
  layer of connective tissue
• Also have semilunar valves that prevent backup of
  fluids (just like veins)
• Larger lymphatic vessels lead to lymph nodes

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Pathways continued

• 3. Lymphatic trunks and collecting ducts
• Trunks drain lymph from lymphatic vessels and are
  named for the area they serve
• Lumbar trunk drains the lymph from lower limbs,
  lower abdominal wall, and pelvic organs
• Subclavian trunk drains the upper limbs
• Lymphatic trunks joint one of two collecting ducts

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4. Collecting ducts

• Thoracic duct is larger and longer
• Begins at abdomen and passes through diaphragm
• It empties into the left subclavian vein and
  drains lymph from intestinal, lumbar, and
  intercostal trunks, left subclavian trunk, left
  jugular trunk, and left bronchomediastinal trunks
• Right lymphatic duct is smaller and originates in
  right thorax at union of right jugular, right
  subclavian and right bronchomediastinal trunks It
  empties into the right subclavian vein

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Whats next?

• After leaving the two collecting ducts, lymph
  enters blood stream and becomes part of the
  plasma
• Lymph from lower body regions, left upper limb,
  and left side of head and neck enters thoracic
  duct
• Lymph from right side of head and neck, right
  upper limb, and right thorax enters right
  lymphatic duct.

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Tissue fluid formation

• Lymph has the same composition as plasma except
  it doesnt have plasma proteins
• Filtration from plasma exceeds reabsorption
  leading to net formation of tissue fluid
• This increases hydrostatic pressure of tissue
  fluid, and favors the movement of this fluid into
  the lymphatic capillaries, forming lymph.

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Lymph function

• Lymphatic vessels in small intestine play a major
  role in absorption of dietary fats
• Lymph returns to the blood stream most of the
  small proteins that the blood capillaries
  filtered
• Lymphatic capillaries are specially designed to
  receive proteins and foreign particles

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Lymph nodes

• Contain large numbers of macrophages and
  lymphocytes that fight invading pathogens
• Nodes are surrounded by a capsule, which extends
  inside and partially subdivides the node into
  nodules which are the structural units of the
  node
• Function of nodes is to filter potentially
  harmful particles from lymph and to monitor body
  fluids
• Nodes and red bone marrow are the centers for
  lymphocytes production

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Lymphatic tissue

• Aggregations of lymphocytes in the connective
  tissue of mucous membranes and various organs
• Diffuse lymphatic tissue is scattered in body
  passages that open to the exterior and is called
  mucosa-associated lymphatic tissue or MALT
• In respiratory it may be called BALT (brochus
  associated)
• In digestive it may be called GALT (gut
  associated)
• In some places lymphocytes and macrophages
  congregate into masses called lymphatic nodules
  (come and go as you get infections.
• In some places these nodules are always present
  (tonsils, lymph nodes, appendix)
• In distal portion of small intestine they form
  clusters called Peyers patches.

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Lymph organs

• Thymus gland-located above the heart in the
  mediastinum and produces T lymphocytes
• Thymus is largest in childhood and shrinks with
  age
• Spleen is the largest lymphatic organ and filters
  blood to protect against infections
• White pulp in spleen contains many lymphocytes
• Red pulp in spleen contains red blood cells and
  lymphocytes and macrophages
  

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Locations of lymph nodes

• Cervical region
• Axillary region
• Supratrochlear region-medial side of the elbow
• Inguinal region
• Pelvic cavity
• Abdominal cavity
• Thoracic cavity

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Lymphocytes

• Natural killer (NK) cells are lymphocytes that
  attack and kill bacteria, transplanted tissue,
  and host cells that are infected with virus or
  cancer
• T lymphocytes or T cells originate in the thymus
  gland
• They are responsible for Cell Mediated Immunity
• T cells secrete toxins that kill target cells,
  secrete growth-inhibiting factors that prevent
  target cell growth, and secrete interferon that
  protect cells from viruses

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T cells continued

• A lymphocyte must be activated before it can
  respond to antigen
• This is done by antigen presenting cells
  (macrophages and B cells)
• Macrophage phagocytizes a bacterium, and some of
  the bacterial antigens move to the cell surface
  and are displayed.
• Helper T cells become active when their antigen
  receptor combines with this displayed foreign
  antigen (dont carry out the attack themselves)
• Once activated the Helper T cell stimulates a B
  cell to produce antibody that is specific to that
  antigen
• Also known as CD4 cells

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T cells

• Cytotoxic T cells-recognizes cancer cells and
  cells infected by viruses, bacteria, etc and are
  the only ones that directly kill other cells
  (called CD8 cells)
• They bind to cells, clone, and release perforin
  protein to poke holes in the cell
• Memory T cells provide a no-delay response if the
  same antigen comes back
• They differentiate into cytotoxic T cells and
  destroy the pathogen before it has time to
  establish.

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Lymphocytes

• B cells originate in the red bone marrow
• B cells are responsible for humoral immunity
• Some B cells, called plasma cells, produce
  antibody or immunoglobulin (Ig)
• Other B cells become memory cells that respond
  rapidly to additional exposure

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Immunoglobulin (Ig)

• 5 types
• IgG-80 of antibody, activates complement,
  crosses placenta to protect fetus
• IgA-13, found in breast milk, tears, and other
  fluids
• IgM-6 , develops in plasma (anti-A and anti-B
  antibodies), also activates complement
• IgD, found on most B cells, important in
  activating B cells
• IgE, associated with allergic reactions

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Reactions continued

• Type III or immune complex reactions-body doesnt
  clear antigen-antibody complexes.
• Autoimmunity is the loss of the ability to
  tolerate self-antigens (MHC) and is a type III
• Type II or antibody-dependent reactions-example
  is transfusion reaction
• Type IV or delayed reaction allergy-occur after
  repeated exposure (chemical allergies, latex etc)

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Types of Immunity

• Naturally acquired active-exposure to disease
  pathogens
• Artificially acquired active-exposure to vaccine
• Artificially acquired passive-injection of gamma
  globulin containing antibody or antitoxin (often
  made from horse)
• Naturally acquired passive-mom to fetus

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Allergic reactions

• Allergens are antigens that trigger allergic
  reactions
• Type I or immediate reaction allergies occur
  within minutes of expose. People with this have
  super sensitive IgE
• May lead to anaphylactic shock

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Autoimmune disorders

• Includes type I diabetes, graves disease,
  myasthenia gravis, pernicious anemia, ulcerative
  colitis, and more
• Be sure to read Table 16.11 for details
• Immunodeficiency diseases include serve combined
  immunodeficiency disease (SCID) where baby is
  born without an immune system
• Also includes AIDS which has its own clinical
  application to read (HIV targets CD4 cells)

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NOTES

• On the second column of the table containing this
  slide show, youll see a set of written notes for
  this chapter.
• STUDY THAT TOO.