Download Human Defence System - Mr Murphy`s Science Blog

Mr. E Murphy
Objectives
 Defence Systems
 General Defence System
 Specific Defence System
 Lymphocytes
Human Defence System
The human body defends itself against bacteria, fungi and viruses
that cause disease. Foreign bodies and cells are called pathogens
 Human body can distinguish between its own cells (self) and
foreign cells or structures (non-self)
 General defence system is non specific
 Skin, mucous membranes and their secretions
 White blood cells and chemicals

 Specific defence system (immune system)
 Attacks particular pathogens, by producing antibodies or by
killing infected cells
General Defence System
First line of general defence
 Skin, clotting, lysozyme, sebaceous gland, mucous, cilia,
acid, beneficial bacteria
Second line of general defence
Consists of the destruction of pathogens by white blood cells, production
of a series or proteins that kill or prevent pathogens from reproducing,
and the inflammatory response
Phagocytic White Blood Cells
 When cells are damaged by invading micro-organisms they release




a large number of chemicals, which attract white blood cells into
the bloodstream
White blood cells engulf and destroy any bacteria, viruses or other
micro-organisms that they meet
These white blood cells are called phagocytes (last only a few days)
Some phagocytes are called macrophages, as they are large and live
a long time
Macrophages can be found in the spleen, lymph nodes and other
lymphatic tissue such as the tonsils, adenoids, and appendix
Phagocytic White Blood Cells
Defence proteins
 Complement is a set of about 20 proteins found in the blood
plasma
 Proteins are activated by infection, the end result is the bursting
of viruses and other pathogens
Inflammation
 When cells are infected they release a chemical called




histamine, which results in blood capillaries opening
wider (dilating) and becoming more porous
This leads to localised swelling, redness, heat and pain
It also brings more white blood cells to the area to fight
the infection
Antihistamines
Fever
Specific Defence System
 Specific defence system attacks particular pathogens
 This happens through the production of antibodies or
when white blood cells destroy body cells that are
infected with a particular pathogen
Lymphocytes and monocytes
•Types of white blood cells
•Formed in the bone marrow
•Move from the bone marrow into the blood vessels and into parts of the
lymphatic system such as lymph vessels, lymph nodes, the spleen, the
thymus gland in the chest
•Lymphocytes and monocytes both react to pathogens in different ways
Specific Defence System
Monocytes
 Develop into white blood cells called macrophages
 Macrophages recognise foreign molecules (antigens)
that are present on the surface of pathogens
 When a macrophage digests a pathogen, the antigens
are displayed on the surface of the macrophage
 This results in the antigens stimulating the production
of antibodies
Specific Defence System
Lymphocytes
 Fight infection in two different ways

Some lymphocytes attack body cells that contain
antigens on their surface
2) Other lymphocytes produce antibodies
1)
Specific Defence System
Antigen and Antibodies
An antigen is a foreign molecule that stimulates the
production of antibodies
 Antigens include molecules from the coats of viruses
and the cell walls of bacteria, fungi, and other microorganisms
 Antigens can also be found in parts of foreign cells
such as pollen grains , incompatible blood
transfusions, transplanted tissues or organs, and
cancer cells
Specific Defence System
Antigen and Antibodies
An antibody is a protein produced by white blood
cells (called lymphocytes) in response to an antigen
 Antibodies form part of a family of proteins called
immunoglobulins (Igs)
 A large number of antigens are displayed on the
surface of a pathogen
Specific Defence System
Antigen and Antibodies
 Antibodies help to dispose of antigens in the following ways:
Antibodies prevent viruses and bacteria from entering new
host cells. The pathogens are then destroyed by phagocytes
2. Antibodies inactivate pathogens by causing them to clump
together, allowing phagocytes to destroy the pathogens
3. Antibodies trigger the complement system, which results in
the pathogenic cells being burst
 Antigen-antibody reaction is a highly specific reaction
 Each antigen stimulates the production of only one specific
antibody
1.
Specific Defence System
Specific Defence System
Duration of immunity
•After an infection is overcome, some of the antibodyproducing lymphocytes remain in the body for a long
time
•If a second similar antigen enters the body, these
lymphocytes can rapidly produce large amounts of the
specific antibody
•First contact with an antigen, it takes 14 days to produce
the maximum number of antibodies
•The next time, antibodies are produced in large
numbers in about 5 days
Specific Defence System
Problems associated with the antibody-antigen reaction
•Disabled in people suffering from AIDS
•The body can sometimes produce antibodies against its
own tissues, resulting in autoimmune diseases such as
rheumatoid arthritis and multiple sclerosis
•Allergies can occur when the body makes antibodies
against materials which should not be antigenic
Induced Immunity
Induced immunity is the ability to resist disease
caused by specific pathogens by the production of
antibodies
Active immunity
•Active immunity is the production of a person’s own antibodies in
response to antigens that enter the body
•Active immunity develops after a person is infected by a virus or
bacterium or after vaccination
•Long lasting as the lymphocytes remain in the body for a long time
•Natural active immunity
•Artificial active immunity
•A vaccine
•Cowpox and smallpox
Induced Immunity
Passive immunity
•Passive immunity occurs when individuals are given
antibodies that were formed by another organism
•Individual does not have to be infected with the pathogen
•Short-term resistance to infections
•Natural passive immunity
•Antibodies from a mother
•Artificial passive immunity
•Injection of antibodies
Induced Immunity
Advanced Study of Lymphocytes
 Lymphocytes are white blood cells or leucocytes
 Formed in the bone marrow
 Each lymphocyte has a round nucleus with very little
cytoplasm
 B-lymphocytes and T-lymphocytes
 Lymphocytes are distinguished according to the
location in which they mature
B-cells mature in the bone marrow
T-cells mature in the Thymus gland
B-cells
 When they have matured in the bone marrow, B-cells move out into lymphatic
tissue, e.g. spleen and lymph nodes
 There are many millions of different B-cells
 Each B-cell is adapted to recognise only one specific antigen, which is usually
present on the surface of a macrophage
 Each B-cell produces only one type of antibody
 When a B-cell comes into contact with the antigen to which it divides to
produce a group of identical B-cells
 These cells, called plasma cells, produce large amounts of the required
antibody
 Plasma cells only live for a few days but they can produce up to 200 antibody
molecules per second during those few days
 Most of the B-cells die off once the infection has been overcome
 Some remain, allowing for a secondary immune response

 It produces antibodies in response to much smaller amount of antigen
 Produces antibodies much faster
 Produces much greater number so f antibodies than is the case with a first-
time infection
B-Cells
T-cells
 T-cells move from the bone marrow into the thymus
gland where they become activated
 Process is important in the early months and years and
life
 T-cells do not produce antibodies
 They act against viruses and some bacteria
T-cells
 T-cells move from the bone marrow into the thymus
gland where they become activated
 Process is important in the early months and years and
life
 T-cells do not produce antibodies
 They act against viruses and some bacteria
T-cells
Helper T-cells
 Recognise antigens on the surface of other white blood
cells, especially macrophages
 Chemicals produced by helper T-cells, stimulate the
production and activation of antibody-producing Bcells
 Helper T-cells are the main types of cells that are
infected by HIV
 Aswell as stimulating B-cells, helper T-cells also
stimulate killer T-cells to reproduce
T-cells
Killer T-cells
 Killer T-cells attack and destroy abnormal body cells,




including virus-infected cells or cancer cells
Killer T-cells release a protein called perforin, which
forms pores in the membrane of the target cell
Water and ions flow into the target cells through these
pores
Target cell swells and bursts
Cytotoxic
T-cells
Suppressor T-cells
 Stimulated to grow by specific antigens
 Suppressor T-cells inhibit B-cells, other T-cells and
macrophages, controlling the immune response by
stopping different immune responses
Memory T-cells
•Can survive for a long time, often life
•Some stimulate B-cells to start producing antibodies
again later in life
•Some may trigger the production of killer T-cells
•Memory T-cells are responsible for lifelong immunity
from infections
T-cells
Summary
Exam Papers
2010 HL Q 15 c ii)
2009 HL Q 15 c i)
Solutions
P 386
a) Blocks foreign objects entering
b)Prevents pathogens entering the blood
c) Trap pathogens and prevent them from entering the body
d) Protect the respiratory system
e) Kills many pathogens
f) Surround and ingest pathogens
g) Set of proteins which seek and destroy pathogens
h) Prevents the spread of pathogens
i) Kills bacteria
2.
Solutions
P 386
a) Not exposed, passive immunity
b) Nutrients and antibodies from the mother
c) Vaccination contains a small amount of the pathogen
d) Bodies reaction to a foreign pathogen
e) Clean the wound and act as a antibiotic
f) Producing your own antibodies will last longer
g) It allows for immunity to be increased
h) Immune system is not functioning properly
i) Their body sees different things as foreign
7.