for class 9 cbse chapter of the same name

1. Why Do We Fall Ill?
-Apoorva Doshi-Apoorva Doshi

2. • Health is a state of physical, mental and social well-
being.

3. • Disease – Any disturbance in the structure and /or
function of any organ or part of body.

4. Factors on which health depends
• Physical and Social environment
• Public facilities /Public cleanliness
• Good economic conditions/ good jobs
• Social equality and Harmony
• Most important :- personal Hygeine

5. Distinction between healthy and
disease-free
Healthy
1. It is a state of physical,
mental and social well-
being.
2. It refers not only to the
individual but also its
social and community
environment
3. A ‘healthy’ person is
able to perform normal
under given situation.
4. For e.g. being able to
do graceful positions
while dancing.(for a
dancer)
Disease-free
1. It is a state of absence of
any kind discomfort or
derangement of
functioning of body.
2. It refers to individual.
3. A disease free person
may or may not be
healthy.
4. For e.g. free of disease
but not able to stretch
body properly while
dancing.(for a dancer)

6. What does a disease look like ?
• When there is a disease, the functioning of 1 or more
body systems will change for worse.
• These changes give rise to symptoms.
• Symptoms of a disease are things that we feel are
wrong. They don’t tell what us which disease we are
suffering from but just indicate that we may be
“diseased”.
• For example :- a headache may mean just
examination stress and in very rare case a disease.
• Whereas Signs are what physicians/doctors look for
on the basis of symptoms. They will give a more
definite indication of presence of a disease.
• Physicians may get laboratory tests to pinpoint the
disease further.

7. TYPES OF DISEASES
• Acute disease – Some diseases last for only very
short periods of time, and these are called acute
diseases.
E.g. common cold

8. • Chronic diseases :- The diseases which last for a
long time , sometimes for even a lifetime , are
known as chronic diseases.
• For e.g. Tuberculosis, elephantiasis ,etc.

9. • Congenital disease – The diseases that are
present since birth. They are caused due to genetic
abnormalities / due to metabolic disorder /
malfunctioning of organ. They are permanent,
generally not easily curable & may be inherited to
children.
• For example :- Congenital blindness, congenital
deafness, etc.

10. • Acquired diseases –The diseases which are
developed after birth.
• For example :- Myopia, Hypermetropia ,etc.

11. Acquired diseases – Which
develop after birth
• Infectious disease –The diseases that are
communicated from diseased person to healthy
person. Caused by some biological agents /
pathogens like – Viruses, bacteria, protozoan,
nematodes, fungi
• Non-infectious disease – the diseases that
are restricted only to those persons who are
suffering. Diseases that are not caused by
infectious agents. Otherwise, diseases that
ARE CAUSED FROM “INTERIOR“ OF THE
BODY. For example :- High blood pressure,
“genetic” cancer ,etc.

12. Comparison of damages to health
by acute & chronic diseases
• Common cold
• Tuberculosis

13. Damages done by acute
diseases
• Little bit tiredness
• Small headache
All this are very short term damages done and don’t
have any effect on long term life.

14. Damages done by chronic diseases
• Long term weakness .
• Feeling tired 24x7.
• Becoming short of breadth.
• Losing excessive weight.
• Prolonged general poor health.
• Breathing problems.(rare)
These all happen because of being “long-term” sick.

15. Causes of a disease
• Each disease has immediate as well as contributory
causes. They are known as levels of causes.
• For example:-If a baby is suffering from loose motions
it is clear that he has been infected with a virus. This
is the first level cause/immediate cause. But where
does the virus came from?
• If it came from water then why only he is infected not
other babies? May be his not healthy because he
doesn't enough nutrition OR he may have any genetic
impairment that makes him more prone to the disease
than other babies of his age. So this becomes the
second level of cause/ contributory cause.

16. Infectious and Non-infectious causes
• Immediate causes belong to two types:-
– Infectious Causes (microbes)
– Non-Infectious causes(genetic abnormalities, etc.)

17. Infectious Causes

18. Non-Infectious causes

19. Infectious agents - Organisms that
can cause disease are found in a wide
range of such categories of
classification.

20. • Some of them are viruses, some are bacteria, some
are fungi, some are single-celled animals or
protozoans. Some diseases are also caused by
multicellular organisms, such as worms of different
kinds.

21. Infectious agent Disease
Virus Common cold, influenza,
dengue fever, AIDS
Bacteria Typhoid fever, cholera,
tuberculosis, anthrax
Fungi Many common
infectious disease
Protozoan Malaria, kala azar
Worms worm infections,
elephantiasis

22. Why is it important that we think
of these categories of infectious
agents?
• These categories are important factors in deciding
what kind of treatment to use. Members of each one
of these groups
– viruses, bacteria, and so on
– have many biological characteristics in common.
• All viruses, for example, live inside host cells,
whereas bacteria very rarely do.
• Viruses ,bacteria and fungi multiply very quickly,
while worms multiply very slowly in comparison.
• Taxonomically, all bacteria are closely related to
each other than to viruses and vice versa.

23. Why is it important that we think
of these categories of infectious
agents?
• This means that many important life processes
are similar in the bacteria group but are not
shared with the virus group. As a result, drugs
that block one of these life processes in one
member of the group is likely to be effective
against many other members of the group. But
the same drug will not work against a microbe
belonging to a different group.

24. As an example, let us take
antibiotics.
• They commonly block biochemical pathways
important for bacteria. Many bacteria, For
example, make a cell-wall to protect themselves.
The antibiotic penicillin blocks the bacterial
processes that build the cell wall. As a result, the
growing bacteria become unable to make cell-
walls, and die easily.

25. • Human cells don’t make a
cell-wall any way, so
penicillin cannot have such
an effect on us. Penicillin
will have this effect on any
bacteria that use such
processes for making cell-
walls. Similarly, many
antibiotics work against
many species of bacteria
rather than simply working
against one.

26. • But viruses do not use these pathways at all,
and that is the reason why antibiotics do not
work against viral infections. If we have a
common cold, taking antibiotics does not reduce
the severity or the duration of the disease.
However, if we also get a bacterial infection
along with the viral cold, taking antibiotics will
help. Even then, the antibiotic will work only
against the bacterial part of the infection, not the
viral infection.

27. Means of spread of infectious disease
1. Air borne diseases Common cold,
pneumonia, tuberculosis
2. Water borne
diseases
Cholera, amoeboisis
3. Sexually
transmitted
diseases
Syphilis, AIDS
4. Through vectors Anopheles mosquitoes –
vector of malaria

28. Organ specific & tissue specific
Manifestations
(After entry of microbes in our body
where do they go?)

29. Answer depends on Point of entry
• e.g. tuberculosis - caused by bacteria - entry
point through Nose to lungs

30. • e.g. typhoid – caused by bacteria through - Mouth to
Guts

31. • e.g. jaundice – caused by viruses – through
mouth to liver

32. • Sex organs – lymph nodes – e.g. virus – AIDS

33. • e.g. Japanese encephalitis (brain fever) – virus-
enter through a mosquito bite infect the brain.

34. Principles of treatment :-
• The treatment of infectious diseases consists of
two steps. They are to reduce the effects of the
disease (symptoms) and to kill the microbes
which caused the disease.
1. To reduce the effects of the disease :- This can
be done by taking medicines to bring down the
effects of the disease like fever, pain or loose
motions etc. and by taking bed rest to conserve
our energy.
2. To kill the microbes :- This can be done by
taking suitable antibiotics and drugs which kills
the microbes and the disease is cured.

35. Principles of prevention :-
• There are two ways of prevention of infectious
diseases. They are general ways and specific ways.
• i) General ways of prevention :-
• Public hygiene is most important for prevention of
infectious diseases. Proper and sufficient food for
every one will make people healthy to resist
infection.
• Air borne diseases can be prevented by living in
conditions that are not crowded. Water borne
diseases can be prevented by providing safe
drinking water. Vector borne diseases can be
prevented by providing clean environment.

36. ii)Specific ways of Prevention
• The specific ways to prevent infectious disease
is immunization by taking vaccines. Vaccines
provide immunity from infectious diseases like
tetanus, diphtheria, whooping cough, measles,
polio etc.
• Our body has an immune system which fights
microbial infection. When this system first sees
an infectious microbe, it kills the microbe and
remembers it. So if the microbe enters the body
the next time, it responds more vigorously.
Vaccines mimic the infectious microbe and
strengthens our immune system and protects
the body from infectious diseases.

37. Vaccination