Defence Against Disease Flashcards
What is the main cause of infectious disease?
Pathogens
5 examples of pathogens
Bacteria
Fungi
Protists (unicellular/multicellular eukaryotic organisms)
Viruses
Prions (infectious proteins)
What are the three layers of the skin?
Epidermis, dermis, hypodermis
On the skin, what layers prevent entry of microorganisms?
Keratin deposits that lay on dead cells on epidermis
Sebaceous Glands in dermis produce oils that keep skin at low pH —> preventing growth of bacteria
What are mucous membranes?
Membranes that line the body cavities (digestive, urogenital, respiratory tract, salivary ducts, lacrimal ducts, mouth, not]se, mammary glands).
Produce mucus which traps potential pathogens entering the cavities.
Mucus contains the enzymes lysozyme—> attacks bacterial cell walls and kills bacteria.
What are mechanical actins that help flush away the mucus along with trapped pathogens?
Respiratory epithilium: cilia that beat in a synchronised manner, coughing, sneezing
Tears
Urine
What are commensal bacteria?
Naturally occurring bacteria on several parts of human body that outcompete pathogens for nutrience/space without harming the body.
Describe the process of blood clotting to seal cuts in the skin
- Activation and accumulation of platelets at site of injury
- Platelets form a plug that seal opening
- Platelets (and injured tissues) release clotting factors including Ca+, thromboplastin (plasma protein)
[clotting factors normally preset in inactive form, once activated they interact in a cascade of reactions]
- Fibrin forms mesh over wound that entraps more platelets and red blood cells—> resulting in blood clotting. Over time clotting dries and forms a scab.
What is the innate immune system?
Immunity present from birth that provides innate immunity.
Responsible for rapid, non-specific defence responses against pathogens encountered daily.
What is the function of the innate immune system?
Prevents entry of pathogens/limits pathogenic spread if entered
Uses chemical and physical barriers provided by skin and mucous membranes&& generalised immune responses like phagocytosis
Not specific to any pathogen
What is the adaptive immune system?
When the innate immune system is unable to control pathogens.
Slower and mediated by lymphocytes (white blood cell type).
What are the main distinguishing features of the adaptive immune system?
- Specificity: directed toward a specific pathogen—> more effective
- Memory: ability to ‘remember’ pathogens—> ensures subsequent infection with same pathogen is faster and efficient
Briefly, what is phagocytosis?
Process by which any foreign materials, including pathogens, and ingested, digested, and eliminated.
What is phagocytosis mediated by?
Specialised leukocytes (white blood cells):
monocytes
neutrophils
macrophages
All cells capable of amoeboid movement and can migrate from blood to site of infection.
Outline the 5 steps of phagocytosis
- Recognition of pathogen by phagocytes. Receptor molecules on plasma membrane of phagocytes recognise and bind to pathogen triggering a chain of reactions that lead to pseudopolia formation
- Pseudopodia encircle target microorganism, both protrusions seal, resulting in formation of phagosome vesicle
- Phagosome undergoes phagosome maturation (series of stages)
- Phagosome fuses with lysosomes forming phagolysosomes. These new structures contain digestive enzymes (originally present in lysosome)
- There enzymes digest microbial components then released from cell
[non-specific secondary line of defence]
What are lymphocytes?
A type of leukocyte (white blood cell)
Produced in bone marrow
Can be divided into T-lymphocytes (T-cells) that mature in thymus (primary lymphoid organ)
and B-lymphocytes (B-cells) mature in bone marrow.
What is the lymphatic system comprised of?
Lymph: watery fluid derived from blood that moves through lymphatic system
lymphoid organs and tissues, and lymphatic vessels.
What is the function of the lymphatic system?
To return fluid back to bloodstream
AND
Immune response of body as bone marrow and thymus (lymphoid organs) are regions where lymphocytes mature .
After reaching maturity, B-cells and T-cells migrate, some remain in circulation some concentrated in secondary lymphoid organs (spleen, tonsils, lymph nodes) where more likely to encounter antigens.
What is an antigen?
Any substance that triggers the immune response resulting in production of antibodies against it. Most antigens are proteins.
Though pathogen is infectious agent, antigen in part of the pathogen that elicits the immune response.
Usually found on surface of pathogen(e.g. cell wall of baterium or coat of virus)
What are self antigens?
Antigens that exist of the cells of our own body that help the immune system to identify and tolerate our cells (e.g. red blood cells, liver cells)
What are B-lymphocytes response to antigens?
Produce antibodies that lead to hormonal immunity
High diversity = can recognise millions of antibodies—>produce highly specific antibodies
What are antibodies?
Protein molecules that:
Identify
Bind to &
Neutralise
Antigens that enter the body
Y-shaped molecule w 2 heavy, 2 light chains
What is the immune repose of T-lymphocytes to antigens?
Cell-mediated immunity
2 types:
- helper T-cells
- cytotoxic T-cells
Helper: helps immune system by activating other components
Cytotoxic: kill infected cells
What determines blood group?
The presence or absence of specific polysaccharide antigens on the surface of erythrocytes (red blood cells):
E.g. A: Antibody in plasma Anti-B and antigen on red blood cell A antigen
O: Antibody A and B but no antigens
What is the Rhesus factor?
RhD can be either -ive or +ive depending on the presence or absence of the RhD antigen.
+ive if present, -ive if absent.
Activation of B & T lymphocytes
For every antigen, there is a B & T cell specific to it.
Until the B and T cells present in secondary lymphoid organs encounter a specific antigen, they are naive.
Once they encounter one, they become effector cells.
What is the activation process of helper T-cells?
Phagocytes that digest a pathogen retain fragments of it.
Antigen-presenting cells present these fragments to specific helper T-cells, activating them:
- increase in number of T-cells that recognise antigen
- activates B-cells specific to the same antigen
- activates cytotoxic T-cells specific to same antigen
What is the activation process of B-cells?
Depends on 2 integrated events:
- When receptor on surface of B-cell recognises and binds to specific antigen
- Stimulation by an activated T-helper cell that recognises same antigen
Multiplication of B-cells
- Activated B-cell undergoes repeated mitotic divisions to create many clones of itself: ** clonal selection theory**
- Once B-cell activated, multiplies and differentiates to form plasma cells and memory cells
- Each plasma cell produces and releases thousands of specific antibodies that circulate in blood
primary immune response is first response
What is clonal selection theory?
That a pre-selected B-cell specific to the antigen divides (mitosis) to form clones which all recognise the same antigen
What are memory cells?
Small percentage of B-cells become memory cells
Long-lived and persist in blood stream and lymph nodes & retain a memory of the antigen
Lie dormant until body in re-infected with same antigen so can quickly differentiate to form plasma cells (that produce antibodies)
secondary immune response
