IMMUNITY: How does the human immune system respond to exposure to a…
How does the human immune system respond to exposure to a pathogen?
Innate immune system (non-specific)
2. Second line of defence
damaged cells release chemical called "histamine"
capillaries dilate (widen) increasing blood flow, bringing phagocytes and clotting factors,
capillary walls become more porous, creating more space for phagocytes to move in to attack pathogens, also creates higher pressure to push fluid into the lymph system and move pathogens out of the area
heat restricts the growth of pathogens and speeds up chemical reactions to repair the damage faster
inflammation: heat, swelling, redness, pain
The complement response
series of proteins activate each other in a chain reaction.
other immune cells are attracted to the area
pathogens are clumped together.
Cell lysis (dissolving cell walls of bacteria)
Pathogens are marked so that phagocytes can recognise them
The action of phagocytes
detects foreign antigens
Phagocytes engulf and destroy anything displaying "not self" antigens by digesting them with enzymes (phagocytosis)
destroy pathogens then display their antigens on their own surfaces
spread themselves to pathogens, then engulf them and destroy them by releasing enzyme that digest them, from granules in their cytoplasm
capable of squeezing through capillary walls into tissues, changing into "macrophages". Release cytokines to communicate with other immune cells
1. First line of defence
mucous is a sticky fluid and helps trap pathogens
hair-like projections, beat rhythmically and sweep mucous upwards out of the lung
tough layer of tightly packed cells, too dry, continually flake away
automatic responses to clear materials that contain pathogens out of the lungs and nasal
The digestive tract
create acidic/alkaline conditions that kill of pathogens
Surface of the eyes, Saliva and breast milk
lysozyme (antibacterial enzyme)
Urinary and reproductive passages
skin is mildly acidic, promoting growth of protective microflora (friendly microbes)
Sweat glands and hair follicles
oily secretions have antimicrobial chemicals . which create favourable environment for microflora.
The adaptive immune system (specific)
3. Third line of defence
Helper T cell communicates with Cytotoxic T and Plasma B cells, teaching them to recognise the pathogens antigens
activated Cytotoxic T and Plasma B cells immediately begin to clone themselves
triggered by phagocyte that has digested pathogen which then travels via lymph to a lymph node and activates the Helper T cell
Cytotoxic T cells are released into lymph and migrate to infection site, where they bind to infected cells displaying pathogen antigens and release toxic chemicals to destroy them. (cell-mediated)
Meanwhile Plasma B cells remain at the lymph node and begin producing millions of antibodies. Antibodies at released into lymph, then travel around the body via the bloodstream until they meet a pathogen antigen and lock onto them, effectively inactivating the pathogen. (antibody-mediated)
once the infection has been defeated, Suppressor T cells release chemicals to switch off the production of Cytotoxic T and Plasma B cells, turning off the immune response.
Memory T and Memory B cells provide immunity by remaining in the circulatory system.
If ever the same pathogen reinvades, the immune response will be much faster than that from primary exposure to the pathogen.
leucocyte: any white blood cell
lymphocyte: a white blood cell that is part of the adaptive immune response (i.e B cells and T cells)
lymph nodes filter debris out of the lymph and contain extra phagocytes and lymphocytes
system of one way tubes running parallel to vein
The lymphatic system is an arrangement of interconnected tissues and organs that
aid in the removal of toxins, cellular wastes, excess fuids and pathogens.
Its primary role is to carry white blood cells around the body
lymph nodes become swollen during a serious infection
returns fluids that seep out blood vessels into tissues back into the circulatory system