An immune system is a system of

biological structures and

processes within an organism

that protects against disease.

In order to function properly, an immune

system must detect a wide variety of

agents, from viruses to parasitic worms,

and distinguish them from the organism's

own healthy tissue.

These agents are referred to as

pathogens – an organism or substance

that could cause a disease.

Pathogens can rapidly evolve and

adapt to avoid detection and

destruction by the immune system.

As a result, multiple defence

mechanisms have also evolved to

recognize and neutralize pathogens.

Physical barriers prevent pathogens

such as bacteria and viruses from

entering the organism.

If a pathogen breaches these barriers,

the innate immune system provides an

immediate, but non-specific response.

Innate immune systems are found in all

plants and animals.

If pathogens successfully evade the innate response, vertebrates possess a second layer of protection, the acquired immune system,

which is activated by the innate response.

Here, the immune system adapts its response during an infection to improve its recognition of the pathogen.

This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory,

and allows the acquired immune system to mount faster and stronger attacks each time this pathogen is encountered.

Innate immune responses are active

immediately upon infection and are the

same whether or not the pathogen has

been encountered previously.

It includes barrier defenses

and internal defenses

Includes:

the skin

Mucus membranes of digestive-, respiratory- urinary and reproductive tract

oBody secretions: mucus, saliva (lysozymes), tears, oil gland secretions, acid in stomach, sweat.

Some cells in mucus membrane produce

mucus.

Mucus is a viscous fluid that enhances

defences – trapping microbes and other

foreign particles

In the trachea, ciliated epithelial cells

sweep mucus and the trapped microbes

upwards, helping to prevent infection of

the lungs.

Body secretions create an environment that in unfavourable for microbes.

Lysozymes in saliva, mucous secretions, and tears destroy susceptible bacteria as they enter the respiratory tract or openings around eyes.

Acid in stomach kill bacteria

Oils and sweat give human skin a pH between 3-5, which is acidic enough to prevent the growth of microorganisms.

If the barrier defences are damaged

and pathogens do enter the body of an

organism, a second line of defence will

be activated.

This defence system is the internal

defence system and is more sensitive

and includes: phagocytosis and

inflammation.

Process by which certain living cells called phagocytes ingest or engulf other cells or particles.

The phagocyte may be a one-celled organism, such as an amoeba, or one of the body cells, such as a leukocyte(white blood cell).

In higher animals phagocytosis is chiefly a defensive reaction against infection and invasion of the body

› Neutrophils engulf and destroy microbes

› Macrophages are part of the lymphatic system and are found throughout the body

› Eosinophils discharge destructive enzymes

› Dendritic cells stimulate development of acquired immunity

When injured or infected by pathogens,

signalling molecules are released,

One example of a signalling molecules is

histamine – stored in mast cells.

These molecules trigger the blood

vessels to dilate and become more

permeable

This increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissues

Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation

Fever is a systemic inflammatory response triggered by pyrogens released by macrophages, and toxins from pathogens

Acquired immunity is a specific immune response system through which the body specifically detects and destroys particular substances.

This immunity protects us against infectious diseases as the body has learnt to recognize foreign substances.

It produces a specific reaction to each infectious agent, eradicating that agent from the body.

This ability to recognize a pathogen that has previously elicited an immune response is the basis for acquiring immunity to specific diseases.

Hence, we suffer from many diseases, such as chicken pox, measles etc. only once.

Thus we can summarize: Acquired immunity involves 2 main activities:

› Destruction of the invaders

› Memory of this response

Special leucocytes, called the

lymphocytes are released from the bone

marrow.

Some reach the Thymus gland and

mature to form T-lymphocytes (T-cells)

Some become B-lymphocytes (B-cells)

and is present in the bone marrow and

lymph no

Active immunity occurs when a person

has already been exposed to antigens

(from pathogens)

And develops a secondary response

against specific pathogens.

People receive vaccinations to develop

a primary response, and then if they get

the pathogens later, active immunity

helps to fight them off.

Antigens are foreign molecules, found on the surface of pathogens, each pathogen has a specific antigen.

The immunity system has countless amounts of B-Lymphocytes.

Each B-lymphocyte is able to recognize a specific antigen.

The B-lymphocytes then produce antibodies that will bond to the antigens.

This will neutralize or destroy the pathogen

Antibiotics are also known as anti-

bacterials.

They are drugs used to treat infections

caused by bacteria.

The first antibiotic was penicillin.

Although there are a number of different types of antibiotic they all work in one of two ways:

› A bactericidal antibiotic kills the bacteria. Penicillin is a bactericidal. A bactericidal usually either interferes with the formation of the bacterium's cell wall or its cell contents.

› A bacteriostatic stops bacteria from multiplying.

A question paper for a preparation test

will be found on your learners’ link…

http://goo.gl/8RoHv

Due date is on 03 May 2013, no late

submissions please, good luck…