Transmission of pathogens
Through contact, transfer of bodily fluids, droplets, ingestion, airborne transmission, vectors
Non-specific defences
Works against all pathogens, and consists of external defences, leucocytes and macrophages, the inflammatory response
Steps of the inflammatory response
- Mast cells release histamine, heparin into extracellular fluid
- Histamine increases blood flow in the area by increasing the permeability of capillaries; causes heat and swelling
- Heparin prevents blood clotting
- Chemicals released by mast cells attract phagocytes
- Abnormal conditions stimulate pain receptors
Function of histomine
increases capillary permeability, hence blood flow in area; causes heat and swelling
Function of heparin
Prevents blood clotting
Fever
High body temperature inhibits the growth of bacteria and viruses, increases the rate of chemical reactions. Can be harmful if exceeds 44 C
External Defences
consists of all external barriers; skin, mucous membranes, sebaceous secretions
Protective Reflexes
Protect the body from injury and infection - sneezing, coughing, vomiting
Lymphatic Systems
collects excess extracellular fluid and returns it to the circulatory system
Lymph node
contains lymphoid tissue that traps large particles such as bacteria
Fever
High body temperature inhibits the growth of bacteria and viruses, increases the rate of chemical reactions. Can be harmful if exceeds 44 C
Specific Immunity
Directed towards a specific pathogen
B cells
Mature in the bones, found in the blood and lymphoid tissue; involves in humoral and cell-mediated immunity
T cells
Matures in the thymus, found in lymph nodesl involved in cell-mediated immunity
Antigens
Any substance capable of causing a specific immune response
Self antigens
recognised by the immune system as belonging to the body - don’t cause an immune response
Non-self antigens
recognised as not belonging to the body - triggers an immune response
Humoral immunity
- Antigen sensitises B cell
- B cell enlarges, clones
Either form plasma cells or memory cells - Memory cells respond to re-exposure of antigen (secondary response), while plasma cells/antibodies attack antigens
Antibodies
Combine with bacterial/ viral toxins/ enzymes and inhibit them
Bind to viruses to prevent cell entry
Coat bacteria – easier phagocytosis
Cause agglutination of foreign particles
Create insoluble substances – easier phagocytosis
Cell mediated immunity
- B cell/macrophage encounters antigen and presents it to nearest lymph node
- T cell becomes sensitised
- T cell enlarges and clones into 3 types of T cells or memory cell
Killer T Cells
migrate and attach to invading cells
Helper T Cells
cause more lymphocytes to become more sensitized, attracts macrophages and intensifies phagocytosis
Suppressor T Cells
Releases substances that inhibit B and T cell activity
Types of Immunity
Natural, artificial, passive, natural
