phase 1 week 2 Flashcards
Describe the structure of bacteria
Single-celled prokaryotes with characteristic cellular organisation
Describe gram-positive bacteria
has peptidoglycan ;ayers on the outside of the cell wall
stains purple
Describe gram-negative bacteria
has one layer of peptidoglycan between the two membranes
stains pink
Describe natural flora in the gut
normal flora is acquired soon after birth and changes with age. Benefits - competition and bi-products inhibit establishment of infection
vitamins (K&B) in the gut are produced by bacteria
the rate at which bacteria grow and divide depends on the nutritional state of the environment.
How does bacteria replicate?
The genomic DNA replicates from the origin of replication and must be accurate
formation of a septum in the middle of a cell
division of the cell to give separate daughter cell
How do bacteria cause virulence in the body?
they colonise, invade and release toxins
describe some examples of other microbial defences of bacteria
antigenic mimicry, antigenic masking, encapsulation, invasion of the host’s immune response
How does bacteria enter the body?
coughs, sneezes, vomit, bites from infected animals, exposure to infected body fluids through sexual intercourse or from sharing hypodermic needles
What are viruses?
obligate intercellular parasites
why do some viruses have an envelope?
they acquire a lipid bilayer as they bud from the surface of the cell
What is the genetic material of a virus contained in?
A coat or capsid, made up from a number of protein molecules.
How do viruses invade?
via inhaled water droplets
food or water
direct transfer from other infected host
from bites of vector arthropod
Describe the life cycle of a virus
virus attaches to cell
virus penetrates the cell membrane and injects nucleic acid (RNA or DNA) into the cell
viral nucleic acid replicates itself using host cell machinery
new viral nucleic acids are packaged into viral particles and released from the cell. The host cell may be destroyed in the process
what is the most common type of WBC?
phagocytes
how do phagocytes kill pathogens in extravascular tissue?
enter the extravascular tissue, ingest microbes then die within hours
where are macrophages found?
healthy macrophages are found in all tissues and organs
what are macrophages?
differentiated monocytes found in tissue that can survive for long periods of time
What do macrophages do?
they initiate and regulate inflammation, ingest microbes, clear dead tissue and initiate tissue repair
What are dendritic cells?
Link between the innate and adaptive immunity
antigen presenting cells
they also produce cytokines for inflammation and stimulate adaptive immune responses
What are mast cells?
found in the skin in the mucosal epithelium
both innate and adaptive
cytoplasmic granules - vasoactive amines e.g. histamines cause vasodilation and increased capillary permeability
proteolytic enzymes kill bacteria or inactivate toxins
synthesise lipid mediators and cytokines
What are natural killer cells?
secrete cytokines that activate macrophages
contain granules which are released into the extracellular space at the point of contact with the infected cell and bring about apoptosis
usually kills viral cell
What do eosinophils do?
many functions - inflammatory processes, trapping substances, killing cells, mainly anti-parasitic functions
allergy
Describe the function of lymphocytes
each lymphocyte binds to a specific antigen
once activated, lymphocytes multiply to produce clones
some B lymphocytes differentiate to plasma cells which produce antibodies
helper t cells produce cytokines which stimulate antibody production
cytoxic t cells bind to and kill infected cells and cancer cells
memory b cells
B cells also display antigens and secrete cytokines
What are lymph nodes for?
the site of immune response activation
What is the function of the spleen?
blood-borne antigens are captured by antigen-presenting cells in the spleen
What are the three outcomes from the complement cascade?
recruitment of inflammatory cells
opsonisation of pathogens
killing of pathogens
what are the three complement cascade pathways?
classical pathway
MB-lectin pathway
alternate pathway
What activates the classical pathway?
antigen:antibody complexes
what activates the MB-lectin pathway?
lectin binding to pathogen surfaces
What activates the alternate pathway
pathogen surfaces
What are the primary lymphoid organs?
bone marrow
thymus
what are the secondary lymphoid organs?
lymph nodes, spleen
What is the role of the thymus?
maturation of T lymphocytes - CD4+ “helper” and CD8+ “killer”
selection of auto reactive cells for removal to prevent autoimmunity
Export a repertoire of T cells for life
What are the 5 types of antibody?
IgM (5), IgA (2), IgD (1) ,IgG (1) , IgE (1)
From the afferent lymph vessels to the efferent vessels, in what order does the lymph pass immune cells?
B cells
T cells
Plasma cells and macrophages
