3.1.6 Human Defence Systems

The non-specific defence systems of the human body against pathogens include

The skin
The nose
The trachea and bronchi
The stomach

what is the job of the non specific defence system

to prevent pathogens from entering the human body

The skin

● Acts as a physical barrier

forms a protective layer covering the body

the outer layer of the skin consist of dead cells and this is difficult for pathogens to penetrate

● It produces antimicrobial secretions to kill pathogens

● Good microorganisms known as skin flora compete with the bad microorganisms for space and nutrients

nose

contains hair and mucus which can trap pathogens before they enter the breathing system

The nose

● Has hairs and mucus (sticky substance) which prevent particles from entering your lungs

\

stomach

contains hydrochloric acid kills pathogens before thay can make their way further into the digest system

The trachea and bronchi

● Secrete mucus in order to trap pathogens
● Cilia (hair-like structures on cells) beat to waft mucus upwards so it can be
swallowed

The stomach

● Produces hydrochloric acid that kills any pathogens in your mucus, or food and drink

The specific immune system

destroys pathogens and any toxins they produce

protects us if the same pathogen infects us again

white blood cell functions

ingest and destroy pathogens

\

what are the internal defences

white blood cells, which can act in three different ways
lymphocytes
phagocytes

Phagocytosis

engulf and digest pathogens

uses enzymes to destroy the pathogens

This destroys them, meaning they can no longer make you feel ill.

\

Producing antibodies

Lymphocytes produce antibodies
Each pathogen has an antigen on their surface, which is a
structure which a specific complementary antibody can bind
to. Once antibodies begin to bind to the pathogen, the
pathogens start to clump together, resulting in it being easier
for white blood cells to find them.
If you become infected again with the same pathogen, the
specific complementary antibodies will be produced at a faster
rate. The individual will not feel the symptoms of the illness.
They are said to be immune.

Producing antitoxins

Some pathogens (usually bacteria) can produce substances which act as toxins which make you feel unwell
Lymphocytes can produce antibodies against these substances – in this case, they are called antitoxins
They neutralise the toxins released by the pathogen by binding to them.

stick to toxins and prevent them from damaging cells

how antibodies work

antibodies are protein molecules produces by white blood cells

antibodies stick to pathogens

this triggers the pathogens to be destroyed

antibodies are specific- only protect against specific pathogen

antibodies remain in the blood for a long time- protect us if infected from same pathogen

\

lymphocytes

produce antiobodies

phagocytes

ingest pathogens

White blood cells help to defend against pathogens by:

Phagocytosis
Production of antibodies
Production of antitoxins (these are special types of antibody)

An antigen

is a molecule found on the surface of a cell

An antibody

is a protein made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction

An antitoxin

is a protein that neutralises the toxins produced by bacteria