The Lymphatic System

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The Lymphatic System

• Chapter 43, Campbell, 6th edition
• Nancy G. Morris
  
• Volunteer State Community College

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The fluid compartment includes

• plasma of the blood
• interstitial fluid of the tissues
• lymph of lymphatic system

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Plasma

• 90 water
• contains electrolytes inorganic salts
  (dissolved ions) that maintain osmotic balance
  buffer blood (electrolyte balance maintained by
  kidneys)
• contains plasma proteins
• immunoglobulins transport lipids through the
  blood
• fibrinogens blood clotting
• serum plasma clotting factors
• transports nutrients, metabolic wastes,
  respiratory gases, hormones

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Cellular elements include

• Erythrocytes RBCs
• Leukocytes -WBCs
• Platelets - thrombocytes

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Erythrocytes RBCs

• biconcave discs that transport oxygen
• mm3 of human blood contains 5-6 million RBCs
• in mammals, RBCs lack nuclei mitochondria
  they generate ATP exclusively by anaerobic
  metabolism (Who knew?)
• contain hemoglobin, an iron containing protein
  that irreversibly binds oxygen about 250 million
  molecules per erythrocyte

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Leukocytes

• white blood cells function in defense and
  immunity
• 5,000-10,000 per mm3 of blood
• 5 types of leukocytes
• lymphocytes (specialized during infection
  produce bodys immune response)
• basophils
• eosinophils
• neutrophils
• monocytes

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SEM specialized lymphocytes attacking a cancer
cell
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Platelets or thrombocytes

• fragments of cells 2-3 µm in diameter
• originate in bone marrow
• lack nuclei
• function in blood clotting

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Replacement of cellular elements

• cells must be replaced as they wear out
• average RBC lives 3-4 months before being
  destroyed by phagocytic cells in the liver
  spleen
• components are usually recycled
• pluripotent stem cells give rise to all three
  blood cells
• stem cells form early in the embryo are renewed
  by mitosis
• found in red bone marrow, especially ribs,
  vertebrae, breastbone, pelvis

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Blood clotting

• a clot forms when platelets clump together to
  form a temporary plug
• platelets release clotting factors that initiate
  a cascade reaction which prothrombin is converted
  to thrombin
• thrombin converts inactive water -soluble
  fibrinogen to active insoluble fibrin
• anticlotting factors prevent spontaneous clotting
  in healthy tissues

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Circulatory Diseases

• Hemophilia an inherited defect in any step
  involved in clot formation
• Thrombus spontaneous clot form
• Cardiovascular disease leading cause of death
  in US (50 of all deaths)
• Heart attack death of the cardiac muscle
• Embolus moving clot
• Atherosclerosis ( Figure 42.16)

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Circulatory Health

• Smoking
• Lack of exercise
• Diet high in animal fat
• All lifestyle choices correlate directly
• with an increased risk of cardiovascular
• disease.

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Lymphatic system

• returns fluid from interstitial spaces to the
  circulatory system
• includes satellite organs important to defense
• filter lymph by removing and phagocytosizing
  pathogens

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Vocabulary

• Lymph
• the fluid part
• (similar in composition to the interstitial
  fluid)
• Lymph vessels
• transport lymph
• have valves to prevent backflow of fluid
• depend on movement of skeletal muscles to squeeze
  lymph along

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Vocabulary

• Lymph nodes
• specialized lymphatic tissue
• filter the lymph attack viruses bacteria
• Lymph capillaries
• penetrate the small intestine villi, absorb
  fats, transport from digestive to circulatory
  system

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The human lymphatic system
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An overview of the bodys defenses
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First line of defense

• Skin
• Unbroken skin is a barrier against bacteria
  viruses
• Secretions from sweat sebaceous glands produce
  a pH of 3 to 5
• Bacterial colonization inhibited by washing
  action of sweat, tears, saliva mucous
• Secretions contain antimicrobial proteins
  lysozyme an enzyme which digests bacterial cell
  walls
• Mucous membranes

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First line of defense

• Mucous membranes
• Secrete mucus a viscous fluid which traps
  microbes and others particles
• Line the digestive, respiratory, and
  genitourinary tracts

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First-line respiratory defenses ciliated
epithelial cells and mucus producing cells of the
respiratory system
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Second line of defense

• Phagocytosis -- the bodys internal mechanism of
  nonspecific defense
• Neutrophils
• Constitute about 60-70 of all leukocytes
• Average life span only a few days
• Upon injury, chemicals released by the invading
  microbes attract neutrophils to the site. This
  is chemotaxis.

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Phagocytic Neutrophil
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Phagocytosis by a macrophage
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Second line of defense

• Monocytes - 5 of all leukocytes
• Migrate into tissues developing into macrophages
  (big eaters)
• Extend long pseudopodia that can attach to
  polysaccharides on the microbes surface, engulf
  microbe, and lysosomes digest
• Some bacteria have capsules to which macrophages
  can not attach
• Other are resistant to lysosomal destruction

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Second line of defense

• Figure 43.4 (p. 842)
• The Human Lymphatic System
• Returns fluids from the interstitial fluid to the
  circulatory system
• Adenoids - Right lymphatic duct
• Tonsils - Thoracic duct
• Lymph nodes - Peyers patches
• Thymus
• Spleen
• Appendix

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The human lymphatic system
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Second Line of Defense

• Eosinophils
• 1.5 of all leukocytes
• Defense against larger parasitic invaders such as
  blood flukes, Schistosoma mansoni
• These cells position themselves against the
  parasite wall discharge destructive enzymes

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Natural Killer (NK) cells

• Nonspecific defense
• Do not attack the microorganism directly but
  destroy virus-infected body cells abnormal
  cells that could form tumors
• Not phagocytic
• Attach the cell membrane causing lysis

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The Inflammatory Response

• Figure 43.5
• Upon injury, blood flow to the injury increases
• This is responsible for the characteristic
  redness heat of inflammation
• The filled capillaries leak fluid into
  neighboring tissues causing edema (swelling)

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Inflammatory Response

• Initiated by chemical signals
• Some arise from the invading organism itself
• Others, such as histamine (produced by
  basophils), are released by cells of the body in
  response to tissue injury

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• Release of histamine or prostaglandins
• Increased permeability leaking attraction of
  phagocytes and lymphocytes
• Clot formation
• Phagocytes consume pathogens debris

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Nonspecific Defense

• Figure 43.1
• 1st line skin, mucous membranes, their
  secretions
• 2nd line phagocytic leukocytes, antimicrobial
  proteins, inflammatory response
• These are nonspecific because they do not
  distinguish among specific pathogens.

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Antimicrobial Proteins

• Lysozyme enzyme in tears, saliva
• Complement system a set of 20 serum proteins
  which carry out a cascade of steps leading to the
  lysis of microbes
• Interferon secreted by virus infected cells,
  spread to adjacent non-infected cells and prevent
  their infection

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How specific immunity arises

• Lymphocytes
• Provide specificity
• Provide diversity
• Because lymphocytes recognize respond to
  specific microbes and foreign molecules, they are
  said to display specificity.
• A foreign molecule that elicits a specific
  response by a lymphocyte is an antigen.

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How specific immunity arises

• Vertebrates have two cells specialized in
  different types of antigens and they carry out
  different defensive actions.
• B lymphocytes (mature in bone marrow)
• T lymphocytes (mature in thymus)

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How specific immunity arises

• Antigens can elicit a response by activating B
  lymphocytes to secrete proteins called
  antibodies.
• Antigens have a quaternary structure for which a
  specific complimentary antibody is synthesized.
• Antigen is a contraction of antibody-generator.

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How specific immunity arises

• B cells have specific antigen receptors on the
  plasma membrane (membrane antibodies or
  immunoglobulins). Antigens can be agglutinated by
  the receptors on the surface or by free
  antibodies that have synthesized secreted by B
  cells.
• T cell receptors are just as specific but are
  never secreted.
• A single B or T lymphocyte bears about 100,000
  antigen receptors, all with exactly the same
  specificity.

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Specific receptors of lymphocytes
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Antigens elicit 2 responses

• Immune response
• Immunological memory

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• Each antigen, by binding to specific receptors,
  selectively activates a tiny fraction of cells
  from the bodys diverse pool of lymphocytes this
  relatively small number of selected cells gives
  rise to clones of thousands of cells, all
  specific for and dedicated to eliminating that
  antigen.
• This is clonal selection.

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Primary Immune Response

• proliferation and differentiation of lymphocytes
  that occurs the first time the body is exposed to
  an antigen
• requires 10 17 days from initial exposure to
  antigen for lymphocytes to response with maximum
  force
• During this period, plasma cells are cloned which
  produce antibodies against the invading antigens.

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Clonal Selection Figure 43.6
Antigens
Cell proliferation
clone of plasma cells
Clone of memory cells
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Clonal Selection
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Secondary Immune Response

• occurs if and when an individual is exposed a
  second time to the same antigen
• the response is faster (only 2 7 days),
  stronger, prolonged.
• Figure 43.7
• Memory cells are poised to proliferate
  differentiate rapidly.

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Immunological Memory
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Immune Response

• Humoral Immunity
• Involves B cell activation and results from the
  production of antibodies that circulate in the
  blood plasma lymph. (Fluids were long ago
  called humors.)
• Defend against free bacteria, toxins, and viruses
  in body fluid.
• DEFEND AGAINST EXTRACELLULAR PATHOGENS

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B Lymphocyte
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Humoral Immunity
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Immune Response

• Cell-mediated immunity
• Active against bacteria viruses within infected
  body cells and against fungi, protozoa,
  parasitic worms
• Crucial in transplanted tissue cancer cells
  both of which are identified as nonself.
• DEFEND AGAINST INTRACELLULAR PATHOGENS

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Overview of Immune Responses

• Figure 43.10
• Figure 43.16

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Immunity

• Can be achieved either naturally or artificially
• Active immunity occurs when the immune system
  responds to a foreign antigen acquired either by
  natural infection or artificially by
  immunization.
• Passive immunity occurs when antibodies are
  transferred from one individual to another
  (mother to fetus mother to breastfeeding child
  artificially when antibodies produced by one
  organism transferred to another organism

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• Immune systems capacity to distinguish self from
  nonself limits blood transfusion and tissue
  transplant
• Abnormal immune function can lead to disease
  (allergy, rheumatoid arthritis, insulin-dependent
  diabetes)
• AIDS immunodeficiency disease caused by a
  virus. Figure 43.19

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Budding HIV
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HIV on Lymphocyte
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HIV Infections Stages
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Cytotaxic Cell
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Cytotaxic Cell