mechanisms of defence Flashcards
in general, give two passive host defences and two active host defences
passive
-physical and chemical barriers
-normal flora
active
-innate immunity
-adaptive immunity
how does epithelium of specialised cell surfaces act as a physical barrier?
-forms continuous cell layers
-forms tight junctions
-allows for cell turnover
name some secretions and how they act as a
-physical barrier
-chemical barrier
tear film, stomach fluid, saliva, mucus
-physical by forming a slimy surface to repel and incapacitate infection agents
-chemical as bactericidal enzymes destroy the bacteria
give some reflexes that protect the body against pathogens
-eyelid blinking
-sneezing/ coughing
-vomiting
where in the body are resident microbes located?
-skin
-oral cavity and respiratory tract
-gut/ intestinal tract
-genitourinary tract
what is the purpose of the innate immune system?
to detect pathogens by recognition of general molecular mechanisms and hence does not lead to long term immunity
what is the purpose of the adaptive immune system?
to focus on a specific target and provides long term immunity against that specific pathogen
Where are most immune cells derived from and what is the exception?
stem cells in the bone marrow where they are most mature. Exception is T cells which mature in the thymus where they emerge tolerant to self proteins
What are the two types of leukocytes?
-polymorphonuclear granulocytes
-mononuclear agranulocytes
give the three Polymorphonuclear granulocytes and what they do
-neutrophils: mobile phagocytic specialists, first in bacterial infection, scavenge to clean up debris
-eosinophils: increase in allergic conditions e.g. parasitic infection
-basophils: synthesise, store and release histamine and heparin
give the two mononuclear agranulocytes and what they each do
-phagocytes, last 1-2 days in blood and months - years in tissue as large mature macrophages
- lymphocytes which consist of B cells that make plasma cells and antibodies and then T cells which are part of cell mediated immunity
give two types of innate defence mechanisms
- physical barriers like skin, ciliated epithelium, tears, mucus, saliva and conc. HCl in the stomach.
- phagocytosis
Describe the steps of humoral immunity (antibody - mediated immunity)
- The surface antigens of an invading pathogen are taken up by a specific B
- The B cell processes the antigen and presents them on its surface
- Helper T cells from the cell mediated immunity attach to the processed antigens on the B cell hence activating the B cell by releasing cytokines cell causing it to divide by mitosis to give a clone of plasma cells
- The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
- The antibody attaches to antigens on the pathogens and destroys them through agglutination, opsonisation, neutralisation and inactivation via antigen antibody complexes
- Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies (this is the secondary immune response).
give the steps of cell mediated immunity
- Pathogens invade body cells or are taken up by phagocytes
- The phagocyte places antigens from the pathogen on its cell-surface membrane (antigen presentation)
- Receptors on a specific helper T cell fit exactly onto these antigens
- This attachment activates T cells to rapidly divide by mitosis and form a clone of genetically identical cells
- The cloned T cells then:
- develop into memory cells that enable a rapid response to future infections by the same pathogen
- stimulate phagocytes to engulf pathogens by phagocytosis
- stimulate B cells to divide and secrete their antibody
- activate cytotoxic T cells
whats the lifespan of b and t lymphocytes?
100-300 days
