Immunity Flashcards
What is a pathogen?
a disease causing micro-organism
e.g. bacteria, virus, fungi
bacteria cause disease by producing toxins
virus cause disease by dividing in cells causing them to burst
Body’s defence against pathogens?
I, Barriers (prevents pathogens entering the body)
II, Phagocytes (perform phagocytosis and stimulate specific response)
III, Specific Response (uses lymphocytes to produce memory cells and antibodies)
What are the Barriers (I)?
Skin, an impermeable barrier made of keratin
Cilia & Mucus in Lungs
Stomach Acid (denatures/breaksdown pathogens)
Describe the process of Phagocytosis (II)?
pathogen releases chemicals
this attracts the phagocyte
the phagocyte binds to the pathogen
the phagocyte engulfs the pathogen
forms a phagosome around the pathogen
lysosomes inside the phagocyte release digestive enzymes into the phagosome
breaking down the pathogen by hydrolysis
Describe the Specific Response (III)?
phagocytes perform phagocytosis (engulf and destroy pathogen) without destroying the antigen, they place antigens on their surface, they present antigens
t lymphocytes (t cells) bind to the antigen and become stimulated
they divide by mitosis to form 3 types of cells: t helper, t killer, t memory
t helper cells stimulate b lymphocytes (b cells)
t killer cells kill infected cells (infected by virus)
t memory cells provide long term immunity
b lymphocytes (b cells) engulf and present antigens on their surface, the t helper cells bind to this
the b cells become stimulated and divide by mitosis to make 2 types of cells: Plasma Cells & B Memory Cells
Plasma cells make antibodies
B memory cells provide long term immunity
What is a antigen?
a protein on the surface of a pathogen that stimulates an immune response
How does the immune response lead to production of antibodies?
the phagocytes stimulate the t cells, the t cells form t helper cells, the t helper cells stimulate the b cells, the b cells form plasma cells, the plasma cells make antibodies
What is an antibody?
a globular protein
made by plasma cells
has 3 regions: variable region, hinge region, constant region
variable region has a different shape in each antibody, contains the antigen binding sites, these bind to complementary antigens (on a pathogen) to form an antigen-antibody complex, destroying the pathogen
hinge region gives the antibody flexibility
constant region the same shape in all antibodies, binds to phagocytes to help with phagocytosis
How do Memory cells (B/T) work?
made during the specific immune response after a new infection by a pathogen (called a primary infection)
B and T memory cells remain in the blood
if person is reinfected by the same pathogen (called a secondary infection) the memory cells will recognise the pathogen and produce antibodies RAPIDLY and to a LARGE amount
therefore the pathogen is killed before it can cause harm = immunity
How does a vaccine produce immunity?
involves giving an injection that contains dead/weakened pathogens that carry antigens which stimulates the immune response leading to production of antibodies & memory cells
Active vs Passive immunity?
Active = individual has memory cells – can make their own antibodies & provides long term immunity
Passive = person given antibodies, these work then die, no long term immunity, no memory cells.
How does activity immunity occur?
naturally = by primary infection, artificially = by vaccination
How does passive immunity occur?
naturally = from mother to baby (placenta or breast milk),
artificially = by injection
What is herd immunity?
when a large proportion of the population is vaccinated, therefore most people will be immune, only a few will not be a immune, increases chance of non-immune person coming into contact with immune person, so the pathogen has no where to go, so it dies out
What is antigenic variability?
the pathogen mutates, the antigen changes shape, so the memory cells no longer complementary – do not recognise the pathogen, therefore the pathogen can reharm
