Defence mechanism 5.1

How does our body prevent microbes getting in ?

Eyes : tears contain the enzyme lysozyme
Nose :contains mucus and hairs to trap microbes
Skin : physical barrier ,if we get cut we bleed .The platelets in the blood form a scab.
Breathing system : makes and is lined with mucus to trap bacteria and cilia to move out bacteria and into the stomach .

Stomach : strong acid that destroys microorganisms

Why are non specific defences useful?

They are always present

What is a pathogen ? And types

Organisms that cause disease

Bacteria virus fungi Protozoa

What is an antigen ?

Foreign protein that stimulates an immune response

What is an antibody

A protein specific to an antigen
Produced by B cells
Created by plasma membranes

What is one type of defence mechanism?

Non specific
The response is immediate and the same for all pathogens

E.g physical barrier
Phagocytosis

What is the second type of defence mechanism?

Specific
Response is slower and specific to each pathogen

Cell mediated response
T lympchytes

Humoral response
B lympchytes

Why is it important lympchytes are able to distinguish between cells ?

Lymphocytes must be able to distinguish the body’s own cells from those that are foreign .

If they can’t the lympchytes would destroy thr organisms own tissues

How does cell recognition work ?

Each cell has specific molecules on its surface of the plasma membrane that identify it
these molecules (antigens ) help thr other cells to identify what type of cell it is .

These antigens are usually proteins

Why is it important that these antigens are proteins ?

Proteins have enormous variety and highly specific Tertiary structure .

It is the variety if specific tertiary structure that distinguishes one cell from another .

What do the protein molecules help the immune system to identify ?

.pathogens
Non self material
Toxins
Abnormal cells such as cancer

How is it that lymphocytes recognize cells belonging to the body?

In the fetus, different lymphocytes are colliding with other cells. Some of these lymphocytes will have receptors that exactly fit those of the body’s own cells
These lymphocytes either die or are suppressed
The only remaining lymphocytes are those that may fit foreign material.

In an adult, lymphocytes produced in the bone marrow initially only encounter self-antigens - these cells undergo apoptosis. Only lymphocytes that might respond to non-self-antigens are left in the blood.

How do doctors minimize the risk of organ rejection?

Tissue type is matched
Immunosuppressants are used

If physical barriers fail, what is the next line of defence in an organism?

Phagocytosis

Why is it important that
lymphocytes are selected?

1)Only a few lymphocytes can mature at a time.

2)Lymphocytes might attack self tissue.

3)It helps when you have a transplant.

4)It keeps the foetus alive.

Differences between a specific and a non-specific defence mechanisms?

Specific mechanism
-Distinguish between different pathogens
-responds slowly
-the lymphocytes that will control the pathogen need to build up their numbers, and this takes time.


Non-specific mechanism
-treats all pathogens in the same way
-responds rapidly
-the body responds immediately by recognizing the pathogen and by phagocytosis.