Biology 1.6

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Defence mechanisms

non-specific

do not distinguish between pathogens

-barriers like skin

-phagocytosis

specific

unique response to each pathogen

-cell-mediated response

-humoral response

Phagocytosis

Chemical products of pathogen act as attractants

Phagocytes attach to pathogen

Phagocyte engulfs pathogen and forms a phagosome

Lysosomes fuse with phagosome

Lysosomes release lytic enzymes which break down pathogen

soluble products are absorbed into cytoplasm

Insoluble products released out of the cell by endocytosis

https://www.youtube.com/watch?v=7VQU28itVVw (Embed)

T cells and Cell-mediated Immunity

-Phagocytes that have engulfed pathogens show the pathogen's antigens on their surface

-Infected body cells show antigens

-Cancer cells show antigens

1.Receptors on T helper cells fit onto antigens

2.This activates other T cells to divide by mitosis

3.The T cells ...

develop into memory cells

stimulate phagocytosis

stimulate B cells to divide

kill infected cells by making pores in membrane

B cell and Humoral Immunity

1.Surface antigens of pathogen are taken up by B cells.

2.B cells present antigens on their surface.

3.T helper cells attach to B cells and activate them.

4.The B cells are activated to divide by mitosis into plasma cells and memory cells.

Plasma cells

Secrete antibodies

Only survive for a few days

Antibodies attach to antigens and cause agglutination or lysis of pathogens.

Memory cells

Survive for decades

Stay in the blood stream and stimulate a secondary immune response which involves fewer processes so is more rapid.

T cells are lymphocytes that mature in the Thymus gland.

It is called cell-mediated immunity because it is stimulated by the antigens on the surface of body cells not pathogens

Antigenic variability

Antigens are always changing. Therefore Immunity is not possible.

Antibodies

Four polypeptide chains

Two heavy chains (longer)

Two light chains (shorter)

A region which is the same in all antibodies(constant)

A region which is unique(variable)

Monoclonal Antibodies

A single type of antibody that is extracted and cloned.

-Separating a chemical from a mixture

-calculating amount substance in a mixture

-cancer treatment

-transplant surgery

Passive Immunity

Introduction of antibodies into

individuals. Antibodies are not manufactured by that individual. Immunity is temporary.

Active Immunity

Antibodies are produced by the individual so immunity is permanent.

A successful vaccine

Economically available in large quantities

Few side-effects if any

Means of producing,storing and transporting

Means of administering vaccine properly

Possible to vaccinate the vast majority

Why vaccination may not work

Fails to induce immunity in some

Individuals may develop disease immediately after vaccine

Pathogen may mutate frequently

Too many varieties of one pathogen

Certain pathogens 'hide' from body in cells or in small intestine

Individuals may have objections to a vaccine

Problems with cholera

Cholera is an intestinal disease and not easily reached by immune system

Antigenic variability

Mobile populations

Problems with Tuberculosis

HIV lead to many people with defective immune systems

Mobile populations who have poor accommodation

Larger proportion of elderly people

Phagocytosis

Specific defence

Immunity