The document describes the human immune system and how it protects the body from pathogens like viruses and bacteria. It discusses both the innate immune response, which provides immediate protection through physical barriers and internal defenses like phagocytes, and the acquired immune response, which adapts over time to improve recognition and response. The acquired response results in immunological memory that allows faster responses upon reexposure to a pathogen. Key components of the immune system include white blood cells, antibodies, antigens, and the development of active immunity through vaccination or prior exposure.

2.  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.

3.  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.

4.  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.

5.  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.

7.  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

8.  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.

9.  Some cells in mucus membrane produce
mucus.
 Mucus is a viscous fluid that enhances
defences – trapping microbes and other
foreign particles

10.  In the trachea, ciliated epithelial cells
sweep mucus and the trapped microbes
upwards, helping to prevent infection of
the lungs.

11.  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.

12.  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.

13.  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

14. › 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

16.  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

17.  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

18.  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.

19.  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

20.  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

21.  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.

22.  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

23.  Antibiotics are also known as anti-
bacterials.
 They are drugs used to treat infections
caused by bacteria.
 The first antibiotic was penicillin.

24.  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.

26.  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…