The Immune System

• Organs and cells dedicated to defend against microbial invasions and injuries
• The defence mechanisms include physical barriers and cellular defences
• Response can be either specific or non-specific

Antigens

• Any substance that stimulates an immune reaction
• Substances that are "foreign" to the host's body
  • The immune system produces WBCs, antibodies, and other proteins to tackle it
• Types:
  1. Pathogens (bacteria, viruses, fungi, parasites, protozoa)
  2. Mutant Cells (those that are abnormal to the body)
  3. Cellular debris
  4. Worn out cells (that are likely to dysfunction or result in cancerous cells and tumours)

Blood and the Lymphatic System

• A network of tissues, organs and cells that work to remove waste, toxins, other antigenic threats

• Primary function: to transport lymph, a fluid containing WBCs

• Consists of:

  • Lymph
  • Lymphatic vessels
  • Lymphoid tissues and organs
  • Lymphocytes

1. Primary lymphoid tissues

   • Where lymphocytes are formed and mature (red bone marrow → bone marrow + thymus)

   ⇒ Thymus - behind the sternum; only active till puberty, releases thymosin which promotes the maturing of T cells → after puberty the gland shrinks and turns into fat; protects the body against autoimmunity;

2. Secondary lymphoid tissues

   • Spleen, tonsils, appendix, lymph nodes, adenoids, Peyers patches on the intestine (they act as filters monitoring the contents of Extracellular fluids)

Lymphocytes

1. T cells (mature in the thymus)
2. B cells (mature in bone marrow)
3. NK cells

Phagocytes