Transcript cell-defence-animals

Higher Biology
Cellular Defence Mechanisms
In Animals
By the end of this lesson:
You should be able to:
Know what phagocytosis is
Know what lysosomes are and the job they do
Know how lymphocytes defend our body

2
Introduction

Both plants and animals need to defend
themselves against being:


Eaten by animals
Infected by pathogens
3
Cellular Defence in Animals

The internal environment of an animal
provides the ideal conditions for pathogens
to thrive


I.e. plenty of food
A constant warm temperature
4
Lines of defence

Animals have 3 lines of defence against
attack by pathogens:
1.
First line
Non-specific
2.
Second line
Non-specific
5
Lines of defence
3.
Third line
Specific- acts at the same time as the
second line of defence. The immune system
directly targets the invader.
6
First Line Defence

Consists of:






Skin
Mucous membranes- lining the digestive,
respiratory and genitourinary tracts
Remember- mucus & cilia in the trachea?
Sebaceous & sweat glands give the skin a pH of
3-5, too acidic for most microbes to reproduce.
Tears, saliva and mucous secretions continually
wash away microbes from the surface.
These secretions also contain anti-microbial
proteins (e.g. lysozyme) which can digest the
cell walls of many bacteria.
7
First Line Defence cont.

The highly acidic environment in the stomach
destroy most microbes ingested in food or
drinks.
8
Second Line Defence

Has 3 components:




Phagocytic white blood cells
Antimicrobial proteins
Inflammatory response.
Phagocytosis


Process whereby solid particles are taken up by
a cell.
Carried out by specialised white blood cells
called phagocytes.
9
Phagocytosis

Stages in phagocytosis
1.
2.
3.
4.
Phagocyte detects chemicals released by a
foreign intruder (e.g. bacteria)
Phagocyte moves up the concentration gradient
towards the intruder
The phagocyte adheres to the foreign cell and
engulfs it in a vacuole by an infolding of the cell
membrane.
Lysosomes (organelles which are rich in
digestive enzymes & found in the phagocytes
cytoplasm) fuse with the vacuole & release their
contents into it.
10
Phagocytosis
5.
The bacterium is digested by the enzymes, and
the breakdown products are absorbed by the
phagocyte.

During infection, hundreds of phagocytes
are needed.
Pus is dead bacteria and phagocytes!

link to phagocytosis

11
Third line defence




White blood cells called lymphocytes are
responsible for this.
These cells recognise particles that do not
belong to the individual as foreign and try
to eliminate them
Foreign particles can include transplanted
tissues.
Viruses, bacteria, fungi and parasitic
worms all carry complex molecules on their
surface.
12
Third line defence



These molecules are called
antigens and are recognised by
lymphocytes as foreign.
In response lymphocytes
produce special proteins called
antibodies.
This is a specific response as
each antibody has binding sites
which are specific to one type
of antigen.
13
Third line defence

Immune response- Cells alive site
14
Primary Immune Response



The immune system has the capacity to
respond to millions of different antigenic
molecules.
The first time a lymphocyte is activated to
produce antibodies to a particular antigen
is called the primary immune response.
This is short lived and often unable to
prevent the person from becoming ill.
15
Secondary Immune Response


If the person survives (!) and comes into
contact with this antigen again then the
secondary immune response is activated
This time the disease is usually prevented
because:



Antibody production is much quicker
A higher concentration of antibodies is
produced
Graph from Scholar
16
Secondary Immune Response


The secondary response is possible
because some of the lymphocytes from the
primary response, specific to that antigen,
remain in the blood as memory cells.
This is why people say that if you catch
chickenpox as a child you are unlikely to
catch it as an adult.
17
Organ and Tissue Transplantation

Many types of tissues and organs can be
transplanted




E.g. corneas
Kidneys
Hearts
In addition to the risks associated with
surgery there is also the risk of rejection
18
Organ and Tissue Transplantation
Try to answer the following questions based
on organ and tissue transplants
1. Why do you think is there a growing
demand for tissue and organ transplants?
2. Why are organs and tissues often rejected
following transplantation?
3. Why would it not be a good idea to
transplant tissue into a patient from a
donor whose tissue had been rejected in
the past by that patient?
19
Organ and Tissue Transplantation
4.
5.
6.
7.
Why are the most suitable organ donors
often closely related to the patient?
Who, if they existed, would be the ideal
choice for a donated organ for you?
Usually transplant patients have to take
immunosupressor drugs for the rest of
their lives. Explain the reason for this.
Why can taking immunosupressor drugs
lead to difficulties?
20
Practice Questions
Torrance
 TYK page 73 Q1-3a
 AYK pages 76-77 Q1, 3a and 4.
21