Communicable diseases Flashcards
What are non specific responses?
General and more immediate. Physical barriers and some cellular processes eg. phagocytosis.
What are specific responses?
Less rapid but longer lasting. Involve lymphocytes; T cells in cell mediated response and B cells in humoral response.
What is the role of skin as a primary defence?
Made up of cells = keratinocytes. Their cytoplasm is replaced by keratin protein in keratinisation on skin surface. Barrier to pathogens.
Harmless microbes = skin flora live on skin. Prevents pathogenic microbes from colonising by competing with them.
What is the role of blood clotting?
When the blood clot dries, it forms a temporary seal, allowing skin to repair.
Trigger blood clotting - platelets and damaged tissues release clotting factors which activate enzyme cascade. Fibrous collagen deposited under the scab and stem cells divide.
What are mucous membranes?
Exchange surfaces where oxygen and nutrients enter the blood are thinner + more exposed to pathogens. Protected by mucous membranes.
In airways, goblet cells and gland secrete mucous - traps pathogens. Ciliated epithelium.
What are other non specific defence mechanisms?
Explosive reflexes, non specific chemical defences, inflammation.
How do expulsive reflexes work?
Some pathogens can release toxins. When sensitive areas irritated - reflexes. eg. coughing, vomiting.
How do non-specific chemical defences?
eg. saliva and tears. Contain enzyme - lysozyme. Kills bacteria by breaking down bacterial cell wall. Lysis of pathogen stops it entering nose, eyes, mouth.
How does inflammation work?
- pathogen detected in tissues by mast cells
- triggers mast cells to release histamine –> vasodilation, capillary walls in tissues more permeable to WBCs
- more WBCs can move out capillaries into tissue fluid and reach infection
- more tissue fluid produced -> swelling
- excess tissue fluid drained into lymphatic system where more immune cells stored
What is phagocytosis?
A specific type of WBC engulfs and digests pathogens to stop them causing damage. Used to remove dead, damaged and abnormal cells. eg. macrophages and neutrophils.
How do neutrophils work?
Have multi lobed nuclei.
- pathogen has chemical markers on cell surface membrane = antigens. Opsonins help phagocytes to carry out function.
- pathogen engulfed by phagocyte to form a vesicle = phagosome
- lysosomes within phagocyte fuse with phagosome, releasing lysozymes (hydrolyse cell walls)
- products absorbed by phagocytes
What are macrophages?
When neutrophils die, macrophages arrive at infected tissue and engulf pathogenic cells. Not fully digest pathogen. Movies antigen to special protein complex. Macrophage exhibits protein complex on cell surface and becomes antigen presenting cell.
How are phagocytes specialised?
- phagocytes have well developed cytoskeletons - change shape to engulf pathogens and move lysosomes around
- many mitochondria
- many ribosomes to synthesise lysozymes
- neutrophils have lobed nucleus to help them squeeze through narrows gaps
What is an antigen?
A membrane bound molecule used to recognise pathogens, which stimulates an immune response.
What is an antibody?
A specific protein produced by plasma cells that can attach to pathogenic antigens.
Why is there a variety of antibodies?
They have specific binding sites that bind to complementary antigen of a pathogen. Each type of antigen a complementary antibody exists.
What is the structure of antibodies?
Y shaped proteins made of 4 polypeptide chains. 2 long chains = heavy. 2 short chains = light. Disulphide bridges hold polypeptides together.
Variable region binds to antigen. Specific to antigen shape.
Constant region = same in all antibodies and can bind to receptors present on phagocytic immune cells.
Hinge region allows flexibility.
What are opsonins?
Proteins which attach to antigens on surface of pathogen. Non specific antibody and act as binding sites for phagocytes. Enhance their ability to bind and destroy pathogens.
Some made as part of specific immune response. Might be used by pathogen to attach to host cells - stop antigen functioning = neutralisation.
What is agglutination?
Agglutinins help immune cells destroy antigens more effectively.
1 antibody can bind to multiple antigens and cause pathogens to clump together = agglutination
Easier for multiple pathogens to be engulfed by a phagocyte + harder to enter host cells.
What is an anti-toxin?
Subset of antibodies can bind and neutralise toxins released by pathogens to prevent toxin causing damage.
What are the 2 categories of white blood cells?
Cells in non specific responses not distinguish between specific antigens. Respond against any infection for short term protection.
Lymphocytes with specific responses - adaptive response to destroy specific pathogen.
What is the structure and function of lymphocytes?
Large nucleus and specialised receptors on plasma membrane. Specific and LT protection. 2 types: T cells leave bone marrow and mature in thymus gland. B cells stay and mature in bone marrow.
What is clonal selection?
The selection of a specific B or T cell which is specific to the antigen.
What are the different types of T lymphocytes?
T helper cells release chemical messengers = cytokines - involved in stimulating phagocytosis + develop B lymphocytes.
T killer cells attack + kill host body cells displaying foreign antigen.
T memory cells stay in blood for years for LT immunity - fast response if infected again.
T regulator cells stop immune response after pathogen removed. Stop autoimmunity.
