Biological effects of radiations

Benefecial and hazardous effects of radiation

1. Biological Effects
(Molecular and Cellular)
of Radiation
Compiled by:
Prof.Mirza Anwar Baig
Assistant Professor
AI's Kalsekar Technical Campus,Navi
Mumabi
1

2. At the end of topic students
should be able to
•
Describe the biological effects of
radiation mentioned in this section.
•
Enlist the hazardous effects of the
radiations on humans mentioned in
the course.

3. Radiations
•
Radiation is energy that comes from a source and
travels through some material or through space.
•
The different types of radiation differ only in their
respective wavelengths
•
Low wavelength UV has the highest energy and is
potentially the most damaging
•
Sunscreens can protect us from UV damage
3

4. The Electromagnetic Spectrum
The Electromagnetic Spectrum
We

can

see

visible

light
.
We

can

feel

the

heat

from

IR

and

microwave

radiation
.
Our

senses

cannot

detect

most

of

the

other

wavelengths
.

5. The Sun
The Sun
’
’
s Radiation
s Radiation
•

More

than

half

of

the

sun
’
s

radiation

is

in

the

IR


region

of

the

spectrum
•

Nearly
40%
is

in

the

visible

region

of

the

spectrum
•

Only
8%
is

in

the

UV

region
,
but

this

higher

energy


radiation

can

potential

cause

damage

to

living

cells

6. Types of radiations
6

7. 7

8. Types of Radiation
•
Radiation is classified into:
1. Ionizing radiation (nuclear radiation)
Alpha particles
Alpha particles
Beta particles
Beta particles
Gamma rays (or photons)
Gamma rays (or photons)
X-Rays (or photons)
X-Rays (or photons)
8

9. 2.
2.
Non-ionizing Radiation Sources
Non-ionizing Radiation Sources
Visible light
Visible light
Microwaves
Microwaves
Radios
Radios
Video Display Terminals
Video Display Terminals
Power lines
Power lines
Radiofrequency Diathermy (Physical
Radiofrequency Diathermy (Physical
Therapy)
Therapy)
Lasers
Lasers
9

10. Ionizing Versus Non-ionizing
Ionizing Versus Non-ionizing
Radiation
Radiation
Ionizing Radiation
Ionizing Radiation
–
–
Higher energy electromagnetic waves
Higher energy electromagnetic waves
(gamma) or heavy particles (beta and
(gamma) or heavy particles (beta and
alpha).
alpha).
–
–
High enough energy to pull electron
High enough energy to pull electron
from orbit.
from orbit.
Non-ionizing Radiation
Non-ionizing Radiation
–
–
Lower energy electromagnetic waves.
Lower energy electromagnetic waves.
–
–
Not enough energy to pull electron
Not enough energy to pull electron
from orbit, but can excite the electron.
from orbit, but can excite the electron.
10

11. Factors affecting biological activity
of radiations
•
Penetrating power of radiations
•
Tissue sensitivity
•
Dose (energy) of radiations
•
Surface area exposed
11

12. Moderately

r
adiosensitive
•
Skin
•
Vascular
endothelium
•
Lung
•
Kidney
•
Liver
•
Lens (eye)
R
adiosensitivity of
t
issues
High
ly

r
adiosensitive
•
Lymphoid tissue
•
Bone marrow
•
Gastrointestinal
epithelium
•
Gonads
•
Embryonic
tissues
Bone marrow
Bone marrow
Skin
Skin
CNS
CNS
L
east

r
adiosensitive
•
Central nervous
system
(CNS)
•
Muscle
•
Bone and
cartilage
•
Connective tissue

13. Ionizing (nuclear) radiation
A radiation is said to be ionizing when it has enough
energy to eject one or more electrons from the atoms
or molecules in the irradiated medium.
This is the case of alpha and beta radiations, as well
as of electromagnetic radiations such as gamma
radiations, X-rays and some ultra-violet rays. Visible
or infrared light are not, nor are microwaves or radio
waves.
13

14. 14

15. •
Penetration in materials
–
Outside the body, an alpha emitter is not
a hazard unless it is on the skin
–
Inside the body, an alpha emitter is a
bigger hazard if it deposits its energy in
sensitive tissue
Alpha rays
15

16. •
Common alpha-particle emitters
–
adon-222 gas in the environment
–
Uranium-234 and -238) in the
environment
–
Polonium-210 in tobacco
•
Common alpha-particle emitter uses
–
Smoke detectors
–
Cigarettes/cigars
Sources- Alpha radiations
16

17. •
Penetration in materials
–
At low energies, a beta particle is not very
penetrating
–
stopped by the outer layer of
skin or a piece of paper
–
At higher energies, a beta particle may
penetrate to the live layer of skin .
–
Inside the body, a beta particle is not as
hazardous as an alpha particle because it is
not as big
–
Because it is not as big, it travels farther,
interacting with more tissue (but each small
piece of tissue gets less energy deposited)

Beta rays
17

18. Gamma radiations
•
Ionizing power is poor
•
High penetrating power
•
Form free radicals
•
Injurious to health
X rays
Penetration power is sufficient to penetrate
tissues and can be detected outside.
Ionizing power is low
18

19. Properties of nuclear radiations
•
High ionizing power- 1. alpha radiations
Moderate ionizing power- beta rad.
Low ionizing power- gamma & X rays
High penetrating power- gamma & X rays
Moderate penetrating power- Beta rays
Low penetrating power- alpha rays
19

20. 20

21. The time scales for the short and long term effects
The time scales for the short and long term effects
of radiation are symbolized in the figure and listed
of radiation are symbolized in the figure and listed
in the table
in the table
21

22. •
Radiation Causes Ionizations of:
ATOMS
which may affect
MOLECULES
which may affect
CELLS
which may affect
TISSUES
which may affect
ORGANS
which may affect
THE WHOLE BODY
22

23. 23

24. Types of UV Radiation
Types of UV Radiation

25. 25

26. Biological Effects of UV Radiation
Biological Effects of UV Radiation
The

consequences

depend

primarily

on
:
1.
The

energy

associated

with

the

radiation
2.
The

length

of

time

of

the

exposure
3.
The

sensitivity

of

the

organism

to

that

radiation
The

most

deadly

form

of

skin

cancer
,
melanoma
,
is

linked

with

the

intensity

of

UV

radiation

and

the

latitude

at

which

you

live
.

27. Protection from UV Radiation
Protection from UV Radiation

28. Effect of radiation on body
(1) Hair
The
losing
of hair quickly and in
clumps
occurs with
radiation exposure at 200 rems or higher.
(2) Brain
Since brain cells do not reproduce, they won't be
damaged directly unless the exposure is 5,000 rems
or greater. can cause
seizures
and
immediate

death
.
(3) Thyroid
The thyroid gland is susceptible to radioactive
iodine. In sufficient amounts, radioactive iodine can
destroy all or part of the thyroid.
(4) Reproductive Tract
Because reproductive tract cells divide rapidly, these areas of
the body can be damaged at rem levels as low as 200. Long-
term, some radiation sickness victims will become
sterile
.• 
28

29. (5) Blood System
When a person is exposed to around 100 rems,
the blood's
lymphocyte cell count will be reduced,
victim more susceptible to
infection. This refered to as mild radiation sickness. Early symptoms
of radiation sickness mimic those of flu.
According to data from Hiroshima and Nagaski, show that
symptoms may persist for up to 10 years and may also have an
increased long-term risk for leukemia and lymphoma.
(6) Heart
Intense exposure to radioactive material at 1,000 to 5,000 rems
would do immediate damage to small blood vessels and probably
cause heart failure and death directly.
(7) Gastrointestinal Tract
Radiation damage to the intestinal tract lining will cause
nausea,
bloody vomiting and diarrhea.
This is occurs when the victim's
exposure is 200 rems or more.
29

30. The Effects of Radiation on the
Cell at the Molecular Level
•
When radiation interacts with target atoms,
energy is deposited, resulting in
ionization

or
excitation.

•
The absorption of energy from ionizing
radiation produces damage to molecules by
direct and indirect actions.
•
For
direct action
, damage occurs as a result
of
ionization
of atoms on key molecules in
the biologic system. This causes inactivation
or functional alteration of the molecule.
•
Indirect action
involves the production of
reactive
free radiacals
whose toxic damage
on the key molecule results in a biologic
effect.
30

31. Damage by ionising
radiation
•
Indirect effect:
–
Ionising event can break molecular
bonds but effect may manifest
elsewhere
–
e.g. ionisation of water molecules can
produce free radicals (molecule with
unpaired electron in outer shell).
•
Highly reactive
•
Capable of diffusing a few micrometres to
reach and damage molecular bonds in
DNA
31

32. Indirect Action
•
These are effects mediated by free
radicals.
•
A free radical
is an electrically
neutral atom with an unshared
electron in the orbital position. The
radical is electrophilic and highly
reactive. Since the predominant
molecule in biological systems is
water, it is usually the
intermediary of the radical
formation and propagation.
32

33. Indirect Action- Radiolysis of
Water
Free radicals readily recombine to electronic and orbital
neutrality. However, when many exist, as in high radiation
fluence, orbital neutrality can be achieved by:
1.Hydrogen radical dimerization (H
2
)
2.The formation of toxic hydrogen peroxide (H
2
O
2
).
3.The radical can also be transferred to an organic
molecule in the cell.
H-O-H
®
H
+
+ OH
-
(ionization)
H-O-H
®
H
0
+OH
0
(free radicals)
33

34. Indirect Action
•
H
0
+ OH
0
®
HOH (recombination)
•
H
0 +
H
0
®
H
2
(dimer)
•
OH
0
+

OH
0
®
H
2
O
2
(peroxide dimer)
•
OH
0
+ RH
®
R
0
+ HOH (Radical transfer)
•
The presence of dissolved oxygen can modify
the reaction by enabling the creation of other
free radical species with greater stability and
lifetimes
•
H
0
+O
2

®
HO
2
0
(hydroperoxy free radical)
•
R
0
+O
2

®
RO
2
0
(organic peroxy free radical)
34

35. Indirect Action - The Lifetimes of Free
Radicals
•
The lifetimes of simple free radicals (H
0
or
OH
0
) are very short, on the order of 10
-10

sec. While generally highly reactive they
do not exist long enough to migrate from
the site of formation to the cell nucleus.
However, the oxygen derived species
such as
hydroperoxy free radical
does not
readily recombine into neutral forms.
These more stable forms have a lifetime
long enough to migrate to the nucleus
where serious damage can occur.
35

36. Indirect Action- Free
Radicals
•
The transfer of the free radical to a
biologic molecule can be sufficiently
damaging to cause
bond breakage
or
inactivation of key functions
•
The
organic peroxy free radical
can
transfer the radical form molecule to
molecule causing damage at each
encounter. Thus a cumulative effect can
occur, greater than a single ionization
or broken bond.
36

37. BIOCHEMICAL REACTIONS WITH
IONIZING RADIATION
•
DNA
is the most important material
making up the chromosomes and
serves as the master blueprint for
the cell
.
It determines what types of
RNA are produced which, in turn,
determine the types of protein that
are produced.
I I
S
-
AT
-
S
I I
P

P
I I
S
-
CG
-
S
I I
P

P
I I
S
-
GC
-
S
I I
P

P
I I
S
-
TA
-
S
I I
37

38. •
There is considerable evidence
suggesting that
DNA is the primary
target for cell damage
from
ionizing radiation
.
•
Toxic effects at low to moderate
doses (cell killing, mutagenesis,
and malignant transformation)
appear to result from damage to
cellular DNA. Thus, ionizing
radiation is a classical
genotoxic
agent
.
38

39. •
The lethal and mutagenic effects of
moderate doses of radiation result
primarily from damage to cellular DNA.
•
Although radiation can induce a variety
of DNA lesions including specific base
damage, it has long been assumed that
unrejoined DNA double strand breaks

are of primary importance in its
cytotoxic effects
in mammalian cells.
39

40. •
Active enzymatic repair processes
exist
for the repair of both DNA base damage
and strand breaks. In many cases
breaks in the double-strand DNA can be
repaired by the enzymes,
DNA
polymerase
, and
DNA ligase
.
•
The repair of double strand breaks is a
complex process involving
recombinational events, depending
upon the nature of the initial break.
40

41. •
Residual unrejoined double strand
breaks are lethal to the cell, whereas
incorrectly recoined breaks may
produce important mutagenic lesions. In
many cases, this DNA misrepair
apparently leads to DNA deletions and
rearrangements. Such large-scale
changes in DNA structure are
characteristic of most radiation induced
mutations.
41

42. Radiation Induced Chromosome
Damage
•
Chromosomes are composed of
deoxyribonucleic acid (DNA), a
macromolecule containing genetic
information. This large, tightly coiled,
double stranded molecule is sensitive to
radiation damage. Radiation effects
range from complete breaks of the
nucleotide chains of DNA, to point
mutations which are essentially radiation-
induced chemical changes in the
nucleotides which may not affect the
integrity of the basic structure.
42

43. Radiation Induced Chromosome
Damage
•
After irradiation, chromosomes may appear to
be "
sticky
" with formation of temporary or
permanent interchromosomal bridges
preventing
normal chromosome
separation

during mitosis and transcription of genetic
information. In addition, radiation can cause
structural

aberrations
with pieces of the
chromosomes break and form aberrant shapes.
Unequal division of nuclear chromatin material
between daughter cells may result in production
of nonviable, abnormal nuclei.
43

44. Radiation Induced Membrane
Damage
•
Biological membranes serve as highly specific
mediators between the cell (or its organelles)
and the environment. Alterations in the
proteins that form part of a membrane
’
s
structure can cause changes in its
permeability to various molecules, i.e.,
electrolytes. In the case of nerve cells, this
would affect their ability to conduct electrical
impulses. In the case of lysosomes, the
unregulated release of its catabolic enzymes
into the cell could be disastrous. Ionizing
radiation has been suggested as playing a role
in plasma membrane damage, which may be
an important factor in cell death (
interphase
death
)
44

45. Cell Cycle
•
Irradiation of the cell causes cell
death at mitosis as a result of the
inability to divide
.(Mitotic death)
•
RNA and protein synthesis do not
halt in the sterilized cell. The result
is the production of the giant cell,
whose unbalanced growth
eventually proves lethal to the cell.
45

46. applications
•
Contrast media and diagnosis
•
Therapeutic applications
teletherapy: removal of lesions not possible by
surgery (gamma)
surface source: dermatologic and ophthalmic use
(beta)
extracorporeal (on blood vessels): change in
immune response (x ray)
infusions: to treat peritoneal and pleural diffusion
in malignant tumours (gamma and beta ray)
•
Diagnostic applications
46