The body’s defense against

  • disease causing organisms or infectious agents 
  • malfunctioning cells or abnormal body cells as cancer
  • foreign cells or particles 

Basic Immunity 

  • Depends on the ability of the immune system to distinguish between self and non-self molecules
  • Self molecules are those components of an organism’s body that can be distinguished from foreign substances by the immune system
    • Autoimmunity is an immune reaction against self molecules (causes various diseases)
  • Non-self molecules are those recognized as foreign molecules
    • One class of non-self molecules are called antigens (short for antibody generators) and are defined as substances that bind to specific immune receptors and elicit an immune response 

Immune System Components

  • specific cells – lymphocytes, macrophages, etc.,    originate from precursor cells  in the bone marrow and patrol tissues by circulating in either the blood or lymphatics, migrating into connective tissue or collecting in immune organs
  • lymphatic organs– thymus, spleen, tonsils, lymph nodes
  • diffuse lymphatic tissue -collections of lymphocytes and other immune cells dispersed in the lining of the digestive and respiratory tracts and in the skin
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Organs of the Lymphatic System Aid Immunity 

immune system

Lymph Nodes

  • Small (1- 25 mm) round structures found at points along lymphatic vessels that have fibrous connective tissue capsule with incoming and outgoing lymphatic vessels
  • Each nodule contains a sinus filled with lymphocytes and macrophages
  • They occur in regions: auxiliary nodes in armpits and inguinal nodes in the groin
  • Occur singly or in groups of nodules:
    • Tonsils are located in back of the mouth on either side
    • Adenoids on the posterior wall above the border of the soft palate
    • Peyer’s patches found within the intestinal wall


  • Located in upper left abdominal cavity just beneath diaphragm.
  • Structure similar to lymph node; outer connective tissue divides organ into lobules with sinuses filled with blood
  • Blood vessels of spleen can expand so spleen functions as blood reservoir  making blood available in times of low pressure or oxygen need
  • Red pulp containing RBCs, lymphocytes, and macrophages; functions to remove bacteria and worn-out red blood cells
  • White pulp contains mostly lymphocytes 
  • Both help to purify the blood


  • Located along trachea behind sternum in upper thorax
  • Larger in children; disappears in old age
  • Divided into lobules where T lymphocytes mature
  • Interior (medulla) of lobule secretes thymosin thought to aid T cells to mature

Red Bone Marrow

  • Site of origin of all types of blood cells
  • Five types of white blood cells (WBCs) function in immunity
  • Stem cells continuously divide to produce cells that differentiate into various blood cells
  • Most bones of children have red blood marrow
  • In adult, red marrow is found in the skull, sternum, ribs, clavicle, spinal column, femur, and humerus
  • Red blood marrow has a network of connective tissue where reticular cells produce reticular fibers; these plus stem cells fill sinuses; differentiated blood cells enter bloodstream at these sinuses

Immune tissue associated with various organs

GALTgut-associated lymphatic tissue; comprised of lymphoid tissue (lymph nodules) in the intestinal wall containing lymphocytes, plasma cells, and macrophages.

  • The digestive tract is a very important part of the immune system and the intestine possesses the largest mass of lymphoid tissue in the body.           

Lymphoid tissue in the gut comprises the following:

  • Tonsils (Waldeyer’s ring)
  • Adenoids (Pharyngeal tonsils)
  • Peyer’s patches – lymphoid follicles in wall of small intestine  
  • Lymphoid aggregates in the appendix and large intestine
  • Lymphoid tissue accumulating with age in the stomach
  • Small lymphoid aggregates in the esophagus
  • Diffusely distributed lymphoid cells and plasma cells in lining of the gut

MALTmucosa-associated lymphatic tissue; lymphoid tissue associated with the mucosa of the female reproductive tract, respiratory tract, etc.

SALTskin-associated lymphatic tissue; lymphatic tissue associated with the dermis of the skin.

Plan of ProtectionImmunity is the ability to defend against infectious agents, foreign cells and abnormal cells eg. cancerous cells  

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