2nd defense line

• Immunity


  The body's ability to resist infection or toxicity
• Natural Immunity


  The body's innate ability to resist infection or toxicity
• 2ND LINE OF DEFENSE


  • Acts if pathogens succeeded in penetrating the first line of defense and invaded body tissues
  • Uses successive nonspecific mechanisms that surround the invading microbes to prevent the microbes from spreading throughout the body
  • Starts by a severe inflammation
• External immunity


  Defenses external to the blood that kill pathogens or bacteria that try to enter the body
• Internal immunity


  Immunity that occurs in the blood and lymph when immune cells recognise pathogens as foreign and carry out defense responses
• Inflammatory response


  Nonspecific defense mechanism around the area of injury as a response to the damage of tissues caused by the injury or by the infection
• Natural Immunity


  Mechanism of action of second line of defence
• Mechanism of action of second line of defence

  1. Microbes or foreign bodies invade the body

  2. Inflammation leads to changes at site of injury

  3. Specialized cells like mast cells and basophils secrete inflammation-generating substances like histamine

  4. Histamine causes dilation of blood vessels

  5. Increases permeability of arterioles and capillaries to blood fluids

  6. Fluids leak from blood circulation

  7. Swelling of tissues at site of inflammation

  8. Allows passage of chemicals that kill and dissolve bacteria

  9. Enables white blood cells like neutrophils, monocytes and macrophages to fight and kill foreign bodies and microbes
• Immunity


  When microbes or foreign bodies invade the body, Inflammation leads to some changes that happen in the site of injury
• Inflammation generating substances like histamine cause dilation of blood vessels to the maximum limit
• Changes that happen in the site of injury

  1. Specialized cells like mast cells and basophils secrete large quantities of inflammation-generating substances

  2. The most important one is histamine
• Inflammation generating substances like histamine increase the permeability of arterioles and capillaries to blood fluids which then leak from the blood circulation
• Inflammation generating substances (e.g. histamine)

  • Dilate blood vessels to the maximum limit
  • Increase the permeability of arterioles and capillaries to blood fluids which then leak from the blood circulation
• Swelling of tissues occurs at the site of inflammation (injury)
• Inflammation generating substances (e.g. histamine)

  Lead to swelling of tissues in the site of inflammation (injury)
• Increased permeability of blood vessels allows the passage of chemicals that kill and dissolve bacteria to the site of injury
• Increased permeability of blood vessels

  • Allows the passage of chemicals that kill and dissolve bacteria to the site of injury
  • Enables white blood cells as neutrophils, Monocytes and Macrophages to fight and kill foreign bodies and microbes
• Increased permeability of blood vessels enables white blood cells like neutrophils, monocytes and macrophages to fight and kill foreign bodies and microbes
• Level of Protection over Time

  • Physical barrier
  • Innate Immunity
  • Acquired Immunity
• Mast Cells


  A type of white blood cells found in the loose connective tissues, especially under the skin and around blood and lymphatic vessels, similar in function to basophils, they store inflammatory mediators such as histamine, which are produced in response to local penetrative injury or allergies
• Mast cell response to damaged cells

  1. Damaged cells send signals

  2. Mast cells release histamine
• Histamine


  Causes the capillaries and blood vessels in the skin to increase in diameter, allowing more blood to flow to the area around the wound
• Phagocytes


  Macrophages and neutrophils that engulf pathogens like bacteria to eliminate them in a process called phagocytosis
• Components of the second line of defense

  • Interferons
  • Natural killer cells (NK)
• Natural killer cells (NK)

  A type of lymphocyte that can recognize stressed, infected, or abnormal cells and eliminate them, unlike B and T lymphocytes they do not need to be activated by other immune cells
• Wound healing


  1. Formation of a blood clot that contains immune cells

  2. Eventually, a scab is formed to prevent the entry of pathogens into the body