C3.2 defense against disease Flashcards
What are pathogens?
any disease-causing organism. Etc virusses, bacteria, fungi, protists
what is our primary defense against disease?
Skin:
- made of epidermis and dermis
- epidermis (top layer) is constantly replaced as the underlying dermis cells die and are moved upwards
- the layer of dead cells forms a physical barrier against most pathogens
Mucous membrane:
- the entry points in our body not covered by skin are lined with tissue cells that form a mucous membrane
- the mucus traps incoming pathogens
- some mucous membrane tissue is lined with cilia (hair-like extensions) which carry trapped pathogens out of mucous-lined tissues
- e.g. trachea, nasal passages, urethra, vagina
Describe the process of blood clotting
- plasma proteins (prothrombin, fibrinogen) circulate in blood plasma
- When a small blood vessel is damaged from a cut, the damaged cells release chemicals that stimulate PLATELETS to adhere to the damaged area
- the damaged tissue and platelets release CLOTTING FACTORS that convert PROthrombin to thrombin, an active enzyme that catalyses the conversion of soluble FIBRINOGEN to insoluble FIBRIN
- fibrin is a fibrous protein that forms a mesh-like network to stablilize the platelet plug
Differences btwn innate and adaptive immune system
Innate:
- responds to broad categories of pathogen
- does not change during an organisms life
- essentially responds to all things “not-self”, e.g. bacteria, viruses, protists, fungi, dust
- these foreign molecules trigger an immune response called antigens, activating phagocytes which can engulf foreign material by endocytosis
Adaptive:
- develops over time and only after exposure to specific antigens of specific pathogens
- responds in a specific way to particular pathogens
- builds up a memory of pathogens encoutered, more effective with age
- specific long-lived white blood cells that are formed during the first exposure are called memory cells. Upon 2nd activation the memory cells are activated more quickly
Describe infection control by phagocytes
Phagocytes are leucocytes (WBC) that are capable of amoeboid movement.
- amoeboid movement is when cells purposefully extend sections of their plasma membrane, followed by their cytoplasm and organelles.
- amoeboid movement is used to squeeze through capillaries to leave and enter the bloodstream to move through body tissues
- engulfs pathogens by endocytosis, where hydrolytic enzymes of lysosomes in the phagocyte digest the pathogen. (innate immune response)
Where are lymphocytes located
2 major types of leucocytes are B-lymphocytes and T-lymphocytes
- lymphocytes circulate in the bloodstream continuously and are also contained in the lymphatic system, within lymph nodes.
Role of B-lymphocytes
B-lymphocytes:
- there are a large no. of B-cells that each can ONLY make ONE specific type of antibody (y-shaped proteins) that recognizes and binds to a specific antigen at the binding site.
- antibodies have 2 binding sites, and can bind to 2 different pathogens
- multiple antibodies binding to a cluster of pathogens, or binding to the protein coat of a virus = makes it easier for phagocytes to find and engulf
- part of the adaptive immune response
How are antigens recognised by immune system
- Antigens are usually proteins, and many are glycoproteins embedded in the outer membrane of pathogenic organisms.
- The capsid proteins on viruses act as antigens
- antigens on the A, B, Rh protein that determines blood type can be marked as foreign by the immune system if the same blood type is not transfused = agglutination occurs
Role of T-lymphocytes
Helper T-lymphocytes chemically communicate with other leucocytes e.g. B-lymphocytes to signal the presence of a specific antigen
- many types of T-cells, each type can only activate a specific B-cell
- activation of long-lived B-cells requires exposure to antigen of the specfic pathogen AND an activated T-cell that is displaying the antigen on its plasma membrane AND T-cell must be releasing cytokines.
- some helper T-cells are long-lived and are called memory cells
Describe how and why B-cells are cloned to respond to antigens
B and T-cells are antigen specific, but the immune system can only maintain a low no. of each type as there are so many diff antigens.
- when specific B-cells are needed, they are first activated and undergo numerous mitotic cell divisions.
- B-cells are cloned with the genetic instruction to synthesize mass quantities of the antibodies that bind to the antigen of the pathogen
Role of memory cells
Memory cells provide immunity - the ability to eliminate an infectious disease from the body.
- long-term survival of lymphocytes (memory cells) that are capable of making the specific antibodies needed to fight the infection are key
Primary immune response
- the first exposure to a pathogen
- no memory cells = there is time for symptoms of disease to develop
- results in pathogen eventually eliminated
Secondary immune response
- the subsequent exposure causes memory cells produced during the primary infection to respond so quickly that usually symptoms do not show up
- not only occurs faster but produces many more antibodies than the first exposure
how is HIV transmitted
Human Immunodeficiency Virus is transmitted through bodily fluid, e.g blood, semen, rectal/vaginal fluids, breastmilk
- does not survive outside the body
- NOT transmitted by saliva/tears/sweat
- host cell is one of the key lymphocyte cell types for immune response
Results of HIV infection
Host cells are helper T-lymphocytes known as CD4 T-lymphocytes.
- the helper T-cells are killed, but these helper T-ells are used to activate B-cells and other cells involved in an immune response
- CD4 is the name of the glycoprotein found on plasma membrane of helper T-cell and is used by HIV to enter the cell
- low helper T-cell count = weak immune response to pathogens
- this is called Acquired Immune Deficiency Syndrome (AIDS) = susceptible to opportunistic infections
How do antibiotics fight against bacterial infections
Bacteria are prokaryotic whereas humans are eukaryotic:
- antibiotics selectively block some of the biochemical pathways needed by bacteria while having no effect on human/animal cells
- e.g. 1 type blocks protein synthesis in bactera but does not affect eukaryotic cell ability to manufacture proteins
Why do antibiotics fail to control viral infections
Virus have no metabolism as they use their host cells metabolism to create new viruses. So any chemical that inhibits viral metabolic activity would damage our own body.
Why must we be careful in the use of antibiotics?
Bacterial resistance to antibiotics is a serious problem around the world, where pathogenic bacteria evolve and reproduce to become resistant.
This is due to mutations when DNA replicates - as repro count is high, DNA replication rate is high = more likelihood for mutations to be consequential and give the bacteria protection from the biochemical action of a particular antibiotic
What are zoonotic diseases + examples
Infectious diseases that can cross species from animal to human. Can be a virus, bacterium, protist, fungus
etc tuberculosis, rabies, Japanese encephalitis, COVID-19
How do vaccines provide immunity to diseases?
Vaccines act as the first exposure to a pathogen
Modern day:
- vaccine is composed of chemical components such as antigens, nucleic acids (DNA, RNA). The body cells take in the nucleic acids and produce antigens, which are recognised as foreign and stimulate the primary immune response without exposure to the actual pathogen
Traditional:
- The pathogenic virus or bacterium is inactivated so that it cannot cause disease
- when body is exposed, memory cells are produced to provide immunity
What does herd immunity to against epidemics
When a large % of people have immunity to a disease, transmission is greatly impeded.
