THE SECOND LINE OF DEFENCE
The second line of defence is enforced when the first line of defence has failed. It involves non-specific responses to pathogens that have invaded the internal environment of the organism. The second line of defence involves specialist cells and white blood cells such as phagotcytes, macrophages, neutrophils, natural killer cells, dendritic cells, complement proteins and mast cells.
Phagocytes are leucocytes (white blood cells) that are made in the bone marrow and circulate through the circulatory and lymphatic systems however can also leave and travel to the site of pathogen entry.
Phagocytes engulf pathogens via a process known as phagocytosis. The phagocyte, containing the engulfed pathogen fuses with the membrane of the lysosome its enzymes digest and destroy the pathogen. In the human body, the macrophage is the most important phagocyte. Macrophages originate in the bone marrow as monocytes and differentiate into macrophages when they leave the bone marrow. Macrophages detect chemical trails of microorganisms and pathogens and engulf them. Upon engulfing the pathogens, the macrophage will present the pathogen’s antigens (proteins) to stimulate recognition on this part of the immune system. They are commonly found in high concentration in the liver and kidney.
Neutrophils can engulf pathogens via endocytosis and are involved in the formation of pus. Neutrophils release chemicals to kill bacteria. Because the neutrophils cannot produce new lysosomes, they will die and form pus.
Natural killer cells attack and kill infected cells of the body and directly kill cancer cells by releasing perforins (chemical), causing perforations in the cell membranes and causing the pathogenic cells to lyse.
Dendritic cells are important in processing antigen material and presenting them on their surface to arouse action from other cells of the immune system. They exist in small numbers in tissue that is in contact with the external environment.
Complement proteins are proteins which assist phagocytes in the recognition of and presence of pathogens, continually circulating the bloodstream. Complement proteins bind to antibodies which have bound to a antigen matter, attracting phagocytes. Complement proteins can lyse the cell membrane of the pathogen to further stimulate phagocytic processes.
Special chemicals such as interferon may also be secreted by cells when pathogens have entered them. interferon is a class of cytokine (messenger protein or glycoprotein molecules secreted for cell communication) secreted to reduce the chance of infection by adjacent uninfected cells by triggering these cells to make particular enzymes which prevent the virus from replicating itself inside the cell.
INFLAMMATION
Mast cells are a type of white blood cell, lining the blood vessels and secreting histamine at the site of inflammation. Inflammation is the reaction to an infection where mast cells secrete histamine to dilate the blood vessels to draw more blood to the area of infection. It is an attempt to exterminate the pathogen and its products and prevent it from spreading to other tissue of the body. The histamine increases the permeability of the capilaries, allowing phagocytes and neutrophils to pass into the bloodstream to the infected tissue. Phagocytes release more histamine to attract more phagocytes which engulf microbes via phagocytosis/endocytosis. Neutrophils releases chemicals which kill bacteria and macrophages can engulf the remnants. Neutrophils are also attracted to and migrate to the site of infection via the detection of cytokines released by the macrophages (phagocytes) (chemotaxes) and then die from age and are engulfed by macrophages to form pus.
Inflammation if characterised by pain, swelling, redness and heat.
FEVER
Fever occurs when a high quantity of pathogens has been detected. Macrophages release a cytokine called interleukin-1 that increases the body’s temperature. This decrease the reproductive and survival rates of pathogen and invading microbes as they do not thrive or reproduce well at higher temperatures, giving the white blood cells an improved chance of overcoming them. Metabolic processes are also increased due to the increase in kinetic energy.
The second line of defence is enforced when the first line of defence has failed. It involves non-specific responses to pathogens that have invaded the internal environment of the organism. The second line of defence involves specialist cells and white blood cells such as phagotcytes, macrophages, neutrophils, natural killer cells, dendritic cells, complement proteins and mast cells.
Phagocytes are leucocytes (white blood cells) that are made in the bone marrow and circulate through the circulatory and lymphatic systems however can also leave and travel to the site of pathogen entry.
Phagocytes engulf pathogens via a process known as phagocytosis. The phagocyte, containing the engulfed pathogen fuses with the membrane of the lysosome its enzymes digest and destroy the pathogen. In the human body, the macrophage is the most important phagocyte. Macrophages originate in the bone marrow as monocytes and differentiate into macrophages when they leave the bone marrow. Macrophages detect chemical trails of microorganisms and pathogens and engulf them. Upon engulfing the pathogens, the macrophage will present the pathogen’s antigens (proteins) to stimulate recognition on this part of the immune system. They are commonly found in high concentration in the liver and kidney.
Neutrophils can engulf pathogens via endocytosis and are involved in the formation of pus. Neutrophils release chemicals to kill bacteria. Because the neutrophils cannot produce new lysosomes, they will die and form pus.
Natural killer cells attack and kill infected cells of the body and directly kill cancer cells by releasing perforins (chemical), causing perforations in the cell membranes and causing the pathogenic cells to lyse.
Dendritic cells are important in processing antigen material and presenting them on their surface to arouse action from other cells of the immune system. They exist in small numbers in tissue that is in contact with the external environment.
Complement proteins are proteins which assist phagocytes in the recognition of and presence of pathogens, continually circulating the bloodstream. Complement proteins bind to antibodies which have bound to a antigen matter, attracting phagocytes. Complement proteins can lyse the cell membrane of the pathogen to further stimulate phagocytic processes.
Special chemicals such as interferon may also be secreted by cells when pathogens have entered them. interferon is a class of cytokine (messenger protein or glycoprotein molecules secreted for cell communication) secreted to reduce the chance of infection by adjacent uninfected cells by triggering these cells to make particular enzymes which prevent the virus from replicating itself inside the cell.
INFLAMMATION
Mast cells are a type of white blood cell, lining the blood vessels and secreting histamine at the site of inflammation. Inflammation is the reaction to an infection where mast cells secrete histamine to dilate the blood vessels to draw more blood to the area of infection. It is an attempt to exterminate the pathogen and its products and prevent it from spreading to other tissue of the body. The histamine increases the permeability of the capilaries, allowing phagocytes and neutrophils to pass into the bloodstream to the infected tissue. Phagocytes release more histamine to attract more phagocytes which engulf microbes via phagocytosis/endocytosis. Neutrophils releases chemicals which kill bacteria and macrophages can engulf the remnants. Neutrophils are also attracted to and migrate to the site of infection via the detection of cytokines released by the macrophages (phagocytes) (chemotaxes) and then die from age and are engulfed by macrophages to form pus.
Inflammation if characterised by pain, swelling, redness and heat.
FEVER
Fever occurs when a high quantity of pathogens has been detected. Macrophages release a cytokine called interleukin-1 that increases the body’s temperature. This decrease the reproductive and survival rates of pathogen and invading microbes as they do not thrive or reproduce well at higher temperatures, giving the white blood cells an improved chance of overcoming them. Metabolic processes are also increased due to the increase in kinetic energy.