Body Defence

11.1 Body Defence
 
Introduction
  • The body defence system reacts when pathogen infects the body.
  • A pathogen is a microorganism that causes diseases.
  • Examples of pathogens include bacteria (singular:bacterium), viruses and parasites.
  • Pathogens can only cause diseases if they successfully infect body cells.
  • The body defence system recognises pathogens as foreign particles that enter the body and subsequently stimulate the immune response.
  • Antigen stimulate the lymphocytes to produce antibodies into the blood flow to destroy antigens.
  • Antibodies are proteins found in the lymphocytes surface or proteins released by lymphocytes into the blood plasma.
  • The interaction berween antibodies and antigens that cause antigens to be destroyed is called the immune response.
  • Immunity is the body's ability to fight infections caused by pathogens or other foreign objects, through specific attacks on the pathogens.
  • When our body can fight a disease, we are said to be immune to that disease.
  • There are three lines of defence to fight against diseases in our body.
    • The first line of defence.
    • The second line of defence.
    • The third line of defence.
 
The First Line of Defence
  • Consists of the physical and chemical line-up that prevent pathogens from entering the body.
  • The first line defence is the defence line that is not specific and acts to prevent pathogens from entering the body.
Lysozyme
  • Lysozyme found in the secretion of tears, nasal mucus and saliva, is an antimicrobial protein that can dissolve and destroy some types of bacteria.
Mucous Membrane
  • The mucous membrane that lines the respiratory tract secretes a sticky fluid called mucus.
  • Mucus contains lysozyme that destroys bacteria found in the air that enters the respiratory system.
Mechanism of Blood Clotting
  • The blood clotting mechanism prevents bacteria from entering through wounds
Hydrochloric Acid
  • Hydrochloric acid in the stomach destroys bacteria present in food and drinks.
Skin
  • It is the physical defence that prevents the entry of pathogens because it is tough and is difficult for microorganisms to penetrate.
  • The continuous shedding of dead cell layers on the skin surface makes it difficult for various types of microorganism to grow.
  • Acts as a chemical shield through the secretion of sebum.
  • Oil and acid in the sebum prevent the growth of various types of microorganisms.
  • Sweat secreted by the skin contains lysozyme, a type of enzyme that breaks down the cell wall of some bacteria.
 
 
 
The Second Line of Defence
  • The second line of defence is fever, phagocytosis and inflammation.
  • The mechanism of the second line of defence is also not specific.
Fever
  • Fever is the second line of defence mechanism that fights infections.
  • Fever increases phagocytic activity and fights against microorganisms that infect the body.
Phagocytosis
  • The phagocyte is a leucocyte that can carry out phagocytosis.
  • Neutrophils and monocytes are phagocytes.
  • Phagocytosis is the process by which microorganisms or other particles such as dead cells are trapped and digested by phagocytes.
  • When an infection occurs, the phagocytes move to the infected area and enter the tissue fluid through the pores of the capillary wall.
  • When a phagocyte encounters a pathogen, the phagocyte will engulf the pathogen and the lysozyme in the phagocyte will digest the pathogen.
Inflammation
  • Inflammation is the immediate response that destroys and neutralises harmful actions of microorganisms and toxins at the early stages of infection.
  • The inflamed area will swell, turn red and feel painful.
  • The response to inflammation is as follows:
    • The damaged tissue releases histamine.
    • Histamine will stimulate an immediate inflammatory response.
    • Histamine will cause the blood capillaries to expand for more blood to flow to the infected area.
    • Histamine also increases the permeability of blood capillaries to phagocytes.
    • The phagocytes and clotting factors will accumulate in the infected area.
    • The phagocytes carry out phagocytosis.
 
 
 
The Third Line of Defence
  • If pathogens overcome the second line defence, the third line of defence will be activated.
  • The third line of defence is the immune response of the lymphocytes.
  • The lymphocytes formed in the lymph nodes produce antibodies.
  • The actions of antibodies are specific.
  • Each type of antibody can only combine with a certain type of antigen.
  • When a person is infected with pathogens, a large number of lymphocytes will accumulate in the lymph nodes to destroy the antigens and foreign particles.
  • This will cause the lymph nodes to swell.
  • The lymph nodes also contain macrophages that destroy bacteria, dead tissues and foreign particles through phagocytosis.
  • Lymphocytes are divided into two types, T lymphocytes and B lymphocytes.
  • The T lymphocyte attacks cells infected by pathogens.
  • T lymphocytes stimulate B lymphocytes to produce memory cells.
  • If the same pathogen attacks, the memory cells will be stimulated to produce antibodies immediately.

Body Defence

11.1 Body Defence
 
Introduction
  • The body defence system reacts when pathogen infects the body.
  • A pathogen is a microorganism that causes diseases.
  • Examples of pathogens include bacteria (singular:bacterium), viruses and parasites.
  • Pathogens can only cause diseases if they successfully infect body cells.
  • The body defence system recognises pathogens as foreign particles that enter the body and subsequently stimulate the immune response.
  • Antigen stimulate the lymphocytes to produce antibodies into the blood flow to destroy antigens.
  • Antibodies are proteins found in the lymphocytes surface or proteins released by lymphocytes into the blood plasma.
  • The interaction berween antibodies and antigens that cause antigens to be destroyed is called the immune response.
  • Immunity is the body's ability to fight infections caused by pathogens or other foreign objects, through specific attacks on the pathogens.
  • When our body can fight a disease, we are said to be immune to that disease.
  • There are three lines of defence to fight against diseases in our body.
    • The first line of defence.
    • The second line of defence.
    • The third line of defence.
 
The First Line of Defence
  • Consists of the physical and chemical line-up that prevent pathogens from entering the body.
  • The first line defence is the defence line that is not specific and acts to prevent pathogens from entering the body.
Lysozyme
  • Lysozyme found in the secretion of tears, nasal mucus and saliva, is an antimicrobial protein that can dissolve and destroy some types of bacteria.
Mucous Membrane
  • The mucous membrane that lines the respiratory tract secretes a sticky fluid called mucus.
  • Mucus contains lysozyme that destroys bacteria found in the air that enters the respiratory system.
Mechanism of Blood Clotting
  • The blood clotting mechanism prevents bacteria from entering through wounds
Hydrochloric Acid
  • Hydrochloric acid in the stomach destroys bacteria present in food and drinks.
Skin
  • It is the physical defence that prevents the entry of pathogens because it is tough and is difficult for microorganisms to penetrate.
  • The continuous shedding of dead cell layers on the skin surface makes it difficult for various types of microorganism to grow.
  • Acts as a chemical shield through the secretion of sebum.
  • Oil and acid in the sebum prevent the growth of various types of microorganisms.
  • Sweat secreted by the skin contains lysozyme, a type of enzyme that breaks down the cell wall of some bacteria.
 
 
 
The Second Line of Defence
  • The second line of defence is fever, phagocytosis and inflammation.
  • The mechanism of the second line of defence is also not specific.
Fever
  • Fever is the second line of defence mechanism that fights infections.
  • Fever increases phagocytic activity and fights against microorganisms that infect the body.
Phagocytosis
  • The phagocyte is a leucocyte that can carry out phagocytosis.
  • Neutrophils and monocytes are phagocytes.
  • Phagocytosis is the process by which microorganisms or other particles such as dead cells are trapped and digested by phagocytes.
  • When an infection occurs, the phagocytes move to the infected area and enter the tissue fluid through the pores of the capillary wall.
  • When a phagocyte encounters a pathogen, the phagocyte will engulf the pathogen and the lysozyme in the phagocyte will digest the pathogen.
Inflammation
  • Inflammation is the immediate response that destroys and neutralises harmful actions of microorganisms and toxins at the early stages of infection.
  • The inflamed area will swell, turn red and feel painful.
  • The response to inflammation is as follows:
    • The damaged tissue releases histamine.
    • Histamine will stimulate an immediate inflammatory response.
    • Histamine will cause the blood capillaries to expand for more blood to flow to the infected area.
    • Histamine also increases the permeability of blood capillaries to phagocytes.
    • The phagocytes and clotting factors will accumulate in the infected area.
    • The phagocytes carry out phagocytosis.
 
 
 
The Third Line of Defence
  • If pathogens overcome the second line defence, the third line of defence will be activated.
  • The third line of defence is the immune response of the lymphocytes.
  • The lymphocytes formed in the lymph nodes produce antibodies.
  • The actions of antibodies are specific.
  • Each type of antibody can only combine with a certain type of antigen.
  • When a person is infected with pathogens, a large number of lymphocytes will accumulate in the lymph nodes to destroy the antigens and foreign particles.
  • This will cause the lymph nodes to swell.
  • The lymph nodes also contain macrophages that destroy bacteria, dead tissues and foreign particles through phagocytosis.
  • Lymphocytes are divided into two types, T lymphocytes and B lymphocytes.
  • The T lymphocyte attacks cells infected by pathogens.
  • T lymphocytes stimulate B lymphocytes to produce memory cells.
  • If the same pathogen attacks, the memory cells will be stimulated to produce antibodies immediately.