Biology 30S Unit #5 Protection & Control

“Immunity”

Non-Specific Defence Mechanisms

Skin and Mucous

Membranes (the 1st line of

defence)

• Skin is a physical barrier that when intact

cannot normally be penetrated by bacteria and

viruses

• secretions from oil and sweat glands give the skin

a pH ranging from 3 to 5 which is acidic enough

to prevent the growth of most microorganisms

• BUT, skin can be damaged (cuts and scrapes)

which can allow foreign material into body tissues

• Mucous Membranes are physical barriers that

line and protect organ systems in the body

• These membranes secrete Mucous and other

fluids (saliva, tears, lysozymes) that trap, wash

away and/or destroy potential invaders.

The Inflammatory

Response (The 2nd Line of

Defence)

• Should the physical protective barriers of

the body be breached by foreign material

the body, this slightly more vicious line of

defence is called to action and triggers an

Inflammatory Response

• The cells involved in this line of defence are

primarily White Blood Cells and use

Phagocytosis to eliminate foreign material

(they basically “eat” it)

• There are 6 types of cells involved in the

Inflammatory Response

1. Mast Cells (The Thin Blue Line)

• “local law enforcement”

• These cells are found in skin tissue, joints,

connective tissue, muscle and blood vessels

• Mast Cells are NOT blood cells. They

don’t circulate in the blood stream

• These cells will trigger an inflammatory

response when a physical protective barrier

has been breached, damaged, infected or

encounters a toxin

• These cells also coordinate the bodies

allergic responses and wound healing

2. Basophils

• the early warning cells

• these White Blood Cells patrol the blood

• during an “injury” blood vessels dilate

(widen) carrying more blood to the injured

area

• Basophils detect foreign material and

release Histamine and other chemical

signals which begins the inflammatory

response

3. Neutrophils

• The “Soldiers”

• 60 – 70% of all white blood cells

• attracted to chemical signals

produced by the Basophils

• enter infected tissue and “self

destruct” destroying foreign invaders

• average life span is a few days

4. Monocytes

• 5% of all white blood cells

• the “heavy artillery”

• when these cells detect foreign

material they develop and enlarge

into Macrophages (“big eaters”)

• as Macrophages, they attach to and

ingest (“eat”) foreign material and

destroy them with digestive enzymes

5. Eosinophils

• the “big game” hunters

• these white blood cells attack larger

parasites and worms using an arsenal

of destructive enzymes

6. Natural Killer Cells

• the “executioners”

• these cells destroy infected cells, cells

harbouring viruses and abnormal

cells that could develop into tumours

“The Immune System”

Specific Defence Mechanisms

(The Last Line of Defence)

• There are a number of parasites,

viruses and diseases that the body

cannot deal with using non specific

methods

• The Immune System defends the

body against specific invaders

• The Immune System uses 2 Specific

Defence Mechanisms:

1. Cell Mediated Immunity (CMI)

• Bone Marrow (Labelled A1) produces

Immature T – Lymphocytes (Labelled B)

which mature in the Thymus (labelled C)

• They emerge from the Thymus as Mature T

–Lymphocytes (labelled D1) or Helper T –

Lymphocytes (labelled D2) and are stored in

the lymph nodes

• Each T-Lymphocyte has a receptor (labelled

D3)

• T- Lymphocytes are stimulated by Antigens

(labelled E) from foreign chemical substances

(such as viruses, bacteria, cancer cells, fungi

etc.)

• When a foreign substance enters the body,

the antigen is eventually detected by a T-

Lymphocyte with a specific receptor that

matches the antigen

• when this happens the T- Lymphocyte is

activated (with the help of a Helper T –

Lymphocyte) into a Cytotoxic T –

Lymphocyte (Labelled F)

• The Cytotoxic T – Lymphocytes then

circulate through the blood seeking and

destroying cells that contain the antigen

2. Antibody Mediated Immunity (AMI)

• Bone marrow produces Mature B –

Lymphocytes (labelled H) which are stored

and replicate in the Lymph Nodes

• Like T – Lymphocytes, B- Lymphocytes

have receptors (Labelled H1, H2, and H3)

that bind to specific Antigens

• Antigens (Bacteria, Fungi, Viruses)

stimulate that production of B –

Lymphocytes

• Eventually the antigen is detected by a B –

Lymphocyte with a specific receptor that

matches the antigen

• when this happens the B – Lymphocyte

activates and turns into a Plasma Cell

(labelled J)

• the Plasma Cell releases a large number

of Antibodies (labelled K) which attach

to the antigens

• the antibodies attract phagocytes which

engulf and destroy the foreign material

• the antibodies stay in circulation for

years which results in long-term

immunity