F212 Immune System

Define herd immunity

Where a sufficiently large % of population is vaccinated as to almost remove the risk of the disease being transmitted

Define ring immunity

Where people who may have been in contact with an infected person are vaccinated to prevented the local spread

Describe the structure and function of a monocyte

A cell that engulfs pathogens, breaks it up and then displays the antigen on its external membrane

Describe the structure and function of a neutrophil

A cell with lobed nucleus for flexibility of shape which engulfs any type of pathogen and destroys it by phagocytosis using internal enzymes

Define phagocytosis

A phagocyte extends its cells membrane to engulf a pathogen . It encases it in a lysosome where lysozyme enzymes destroy the organism rendering it harmless

Define clonal expansion

As only a few T or B cells will be capable of destroying a pathogen they must divide very quickly by mitosis to from a much larger clone (group)

What are the two types of lymphocyte

B cells and T cells

Describe a B cell and its various forms

B cells are made and matured in the bone marrow . They can be B Plasma cells which secrete antibodies into the bloodstream or B Memory Cells which have antibodies attached to their external membrane giving long term immunity

How do B cells fight infection

B cells produce antibodies that are specific to a particular antigen. The antibody binds to the antigen using complementary receptors. Several bound antigens will clump together and get engulfed by phagocytes. Sometimes if the antigen is from a toxin the binding antibody simply neutralises its toxic effect.

How is an antibody adapted to its function

Constant region able to bind to phagocytes receptors Variable region is different inn each type of antibody to give it specificity to one type of antigen Disulphide bridges give strength Hinged region gives flexibility to bend to allow binding to larger antigens

What is the secondary immune response

If infected by a pathogen for a second time the B memory cells are already active and differentiate into B plasma cells fighting infection immediately - we feel no symptoms as disease is stopped straight away - this is termed immunity

Define natural immunity

Immunity caused by the bodies own response to infection

Define artificial immunity

Immunity caused by the supply of antibodies or inactivated pathogen by another means such as injection

Define active immunity

Immunity developed by the production of own B cells

Define passive immunity

Immunity given by the donation of antibodies

What is a vaccine

Inactivated or dead pathogen injected into a person to protect from disease

How does a vaccine work

It stimulates the primary immune response without causing the disease. This creates B memory cells that are rear to fight off future infections by that antigen

Describe Antigen presentation

Macrophages engulf pathogens by endocytosis, break them up removing the antigen in the process. They then displays the antigen on the macrophages external membrane

Describe the structure of an antibody

Made of 4 polypeptides (2 heavy and constant - 2 light and variable). Shaped like a hinged Y with chains bound by disulphide bridges .

Name the two types of phagocytes

Neutrophil Monocyte (macrophage)

Describe how a government can help protect populations against an epidemic

Notification system where doctors must report incidences Stockpile vaccine Predict the likely affected areas Prioritise the vulnerable for vaccine and treatment Isolation units and decontamination kit for patients and medical staff Monitor evolution of the pathogen

Give 3 differences between passive and active immunity

Passive - no immune response faster immunity can be given after infection e.g snake bite

What is the difference between phagocytes and lymphocytes

Phagocytes are "fast responders" and can destroy/recognise a range of pathogens Lymphocytes are more specific as they have receptors on their surface that can only destroy one type of pathogen

Name the main forms of primary defence to disease

Skin - acts as a barrier Mucus membranes - collect pathogens Gut acids - destroy ingested bacteria

Describe a T cell and its various forms

T cells are made in the bone marrow, mature in the thymus and can either become T Killer cells which can produce molecules that destroy pathogens or T Helper cells which produce molecules that signal to B cells to respond to a pathogen

Define clonal selection

T cells lock onto the antigen displayed on the macrophage membrane using complementary receptors - these T cells are the clones that have been selected by the macrophage

What is the primary immune response

The process of antigen presentation and attack by plasma B cells on a first infection by a particular pathogen. The time delay in this process is why we see symptoms of a disease and then we recover.