2nd line of defense
- Sometimes invaders succeed in gaining access through the 1st Line of defense which is where the 2nd line of defense becomes activated.
- Defensive cells:
~Macrophages: Large cells found in body tissues and are able to travel from blood vessels to infected tissues. They are mature versions of monocytes. They are slower to act but are able to ingest larger amounts of foreign matter
~Neutrophils: Most common granulated white blood cells found in blood and tissues which destroy the invading pathogen via phagocytosis. Have a flexible plasma membrane enabling them to squeeze throughcappilaries and into infected tissues
~Eoisinophils: Granulate white blood cell that contain a high concentration of enzymes that can rupture the cell walls of foreign invaders. The chemicals are highly toxic to the tissues of parasites and the host.
~Basophils: White blood cells that circulate the blood that secrete chemicals such as histamine in responding to inflammatory and allergic reactions.
-Natural killer cells: Specialised lymphocytes that target and kill virus infected cells and tumor cells by either secreting chemcials to induce apoptosis or by binding to the glycoproteins of the infected cell to cause apoptosis.
- Examples of chemical defences:
~Interferones: A specific type of cytokine; an anti-viral substance produced by cells that have been infected by viruses to aid non-infected cells by inducing resistance. They act as a warning signal by changing the surfaces of surrounding cells to make it harder for the virus to infect them.
~Complement: A group of proteins produced by macrophages found usually inactive in the blood however when activated by the immune system to usually gather around foreign organism to make it easier for phagocytes to kill the foreign organism
- Physiological responses
~Fever: The rise in body temperature aims to denature pathogens and enzymes in/on the pathogen. However if the temperature exceeds optimum levels it may result in cellular death and therefore organism death. The heat also increases the speed of metabolic reactions
~Inflammatory response: An attempt to get rid of toxins or any other foreign material at the site of injury and to prevent them from spreading. The signs of inflammation (redness, swelling, heat and pain) show that there is a rush of blood carrying red and white blood cells to the specific area that has been infected to quickly heal it.
* The stages of inflammatory response:
1) After tissue injury has occurred mast cells are induced to secret histamine which increases the permeability of blood vessels allowing phagocytes to squeeze through the membrane to the site of infection.
2) Platelets clot the blood around affected area to prevent pathogens from entering
3) Phagocytes engulfs and digests bacteria via phagocytosis to break it down and eliminate it from the tissue.