The Theory of Cell
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• In biology, cell theory is the historic scientific theory, now
universally accepted, that living organisms are made up of cells, that
they are the basic structural/organizational unit of all organisms, and
that all cells come from pre-existing cells. Cells are the basic unit of
structure in all organisms and also the basic unit of reproduction.
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– The microscopes we use today are far more complex than those
used in the 1600s by Antony van Leeuwenhoek, a Dutch
shopkeeper who had great skill in crafting lenses. Despite the
limitations of his now-ancient lenses, van Leeuwenhoek observed
the movements of protista (a type of single-celled organism) and
sperm, which he collectively termed “animalcules. ”
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• In a 1665 publication called Micrographia, experimental scientist
Robert Hooke coined the term “cell” for the box-like structures he
observed when viewing cork tissue through a lens. In the 1670s, van
Leeuwenhoek discovered bacteria and protozoa. Later advances in
lenses, microscope construction, and staining techniques enabled
other scientists to see some components inside cells.
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Structure of an Animal Cell: The cell is the basic unit of life and the
study of the cell led to the development of the cell theory.
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• By the late 1830s, botanist Matthias Schleiden and zoologist
Theodor Schwann were studying tissues and proposed the unified
cell theory. The unified cell theory states that: all living things are
composed of one or more cells; the cell is the basic unit of life; and
new cells arise from existing cells. Rudolf Virchow later made
important contributions to this theory.
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• Schleiden and Schwann proposed spontaneous generation as the
method for cell origination, but spontaneous generation (also called
abiogenesis) was later disproven. Rudolf Virchow famously stated
“Omnis cellula e cellula”… “All cells only arise from pre-existing
cells. “The parts of the theory that did not have to do with the origin
of cells, however, held up to scientific scrutiny and are widely
agreed upon by the scientific community today.
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The generally accepted portions of the modern Cell Theory are as
follows:
1. The cell is the fundamental unit of structure and function in living
things.
2. All organisms are made up of one or more cells.
3. Cells arise from other cells through cellular division.
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The expanded version of the cell theory can also include:
• Cells carry genetic material passed to daughter cells during cellular
division
• All cells are essentially the same in chemical composition
• Energy flow (metabolism and biochemistry) occurs within cells
THE HUMAN CELL
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HISTORY
• Robert Hooke, English scientist first observe plant cells with a crude
microscope in the late 1600’s.
• 1830’s two German scientists, Matthias Schleiden and Theodor Schwann,
proposed that all living things are composed of cells.
• German pathologist Rudolf Virchow extended this idea by contending that
cells arise only from the other cells.
• Since the late 1800’s, cell research has been exceptionally fruitful and
provided us with four concepts collectively known as the cell theory.
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THE CELL
• It is a basic structural and functional unit of living organism. When
you define cell properties, you define the properties of life.
• The activity of an organism depends on both the individual and the
collective activities of its cells.
• According to the principle of complementarity of structure and
function, the biochemical activities of cells are dictated by their
shapes and forms, and by the relative number of their specific
subcellular structures.
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THE CELL
• Continuity of life from one generation to another has a cellular
basis.
• Cells are composed chiefly of carbon, hydrogen, nitrogen, oxygen,
and trace amounts of several other elements.
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TWO TYPES OF CELL
EUKARYOTE
• Organism whose cells contain nuclei
• plants, animals, fungi, slime moulds,
protozoa and algae
• Fifteen times wider than a typical
prokaryote
• Thousand times greater in volume
PROKARYOTE
• Unicellular organism lacking nucleus
• Cells were the first form of life on earth
• Characterized by having vital biological
processes including cell signaling and
being self sustaining
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Two major structures of human cell:
1. Nucleus
- the center of the cell
- Principal molecular components:
• DNA - the genetic material of the cells
- Other Molecular components :
• Some RNA, protein, and water
Nucleolus
- a rounded structure that is attached to the nuclear membrane.
- it contained most of the RNA
Nuclear Membrane
- a double-walled structure that at some location is connected to the endoplasmic
reticulum.
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2. Cytoplasm
- the bulk of the cell
- it contains great quantities of all molecular components except
DNA
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Mitochondria
• They are the power plant of a cell, providing most of it’s ATP
supply.
• Mitochondrion is enclosed by two membranes
• The outer membrane is smooth and featureless
• Inner membrane folds inward
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Ribosomes
• are small, dark –staining granules composed of proteins and a variety of RNA’s called ribosomal
RNA’s
• sites of protein synthesis
• Endoplasmic Reticulum (ER) network within the
cytoplasm
• Rough Endoplasmic Reticulum
• External surface of the ER is studded with
ribosomes
• Proteins assembled on these ribosomes thread their way
into the fluid-filled interior of the ER
• It is also the cell’s “membrane factory”
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Ribosomes
• Smooth endoplasmic reticulum play no role in protein synthesis.
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The enzymes catalyze reactions involved with the following task:
Metabolize lipids, synthesized cholesterol
Synthesize steroid- based hormones such as sex hormones
Absorb, synthesize and transport fats. (in intestinal cells)
Detoxify drugs, certain pesticides, and cancer- causing chemicals. (in
liver and kidneys)
• Break down stored glycogen to form free glucose (especially in liver
cells)
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Golgi Apparatus
• The principal “traffic director” for cellular proteins.
• Its major function is to modify, concentrate,
and package the proteins and lipids made at the
rough ER and destined for export from the cell.
• It is also packages digestive enzymes into
membranous lysosomes that remain in the cell
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Peroxisomes
• are spherical membranous sacs containing
a variety of powerful enzymes especially, numerous
in liver and kidneys cells, very active in detoxification
play a role in energy metabolism by breaking down
and synthesizing fatty acids.
• oxidase and catalase
• Oxidase use molecular oxygen
to detoxify harmful substance, including
alcohol and formaldehyde.
• their most important function is to
• neutralize free radicals
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Lysosomes
• “disintegrator bodies”
• spherical membranous organelles
containing activated enzymes
• Lysosomal enzymes can digest almost all
kinds of biological molecules
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Microvilli
• “little shaggy hairs”
• are minute, fingerlike extensions of
the plasma membrane that project
from an exposed cell surface.
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Nuclear Envelope
• the nucleus is bounded by the
nuclear envelope, a double
membrane barrier separated by a
fluid-filled space.
• maintains the shape of the nucleus
and acts as a scaffold to organize
DNA in the nucleus.
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TWO GENERAL TYPES OF CELLS IN THE HUMAN BODY:
• Genetic/ Germ Cells
➢ oogonium (female) and spermatogonium (male)
➢ they undergo meiosis
• Somatic Cells
➢ all cells in the body except oogoniumm and spermatogonium
➢ they undergo mitosis
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Mitosis
• Process of somatic cell division wherein a parent cell divides tform two
daughter cells identical to the parent cell.
• Four subphases: prophase, metaphase, anaphase and telaphase
Two phases of the Cell Cycle (Geneticist)
• Mitotic phase
• Interphase
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Mitosis
➢ Chromosomes: become visible, divided and migrate to daughter cells
➢ DNA: slowly takes the form of the chromosomes as seen microscopically
Prophase
➢ The nucleus sweels
➢ DNA: becomes more prominent; begins to take structural form
Metaphase
➢ Chromosomes: appear and lined up along the equator of the nucleus
➢ mitosis can be stopped
➢ chromosomes can be studies carefully under the microscope
Radiaton induced chromosomes damage is analyzed during metaphase!
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Anaphase
➢ chromosomes: each splits at the centromere; new chromosome migrate
toward the spindle
➢ centromere and chromatids are connected by a fiber to the poles of a nucleus
➢ the number of chromatid per centromere is reduced by half
Telophase
➢ the final segment of mitosis
➢ characterized by the dissapearance of structural chromosomes into a mass of
DNA
➢ the closing off the nuclear membrane like a dumbell into two nuclei
➢ cytoplasm is divided into two equal parts
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Interphase
➢ the portion of the cell between mitotic events
➢ the period of growth of the cell between divisions
Four phases of the Cell Cycle (Cell Biologist)
• Metaphase
• G1 Phase
• S Phase
• G2 Phase
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G1 Phase
➢ Pre- DNA synthesis phase
➢ the gap in cell growth between M ans S
S Phase
➢ the DNA-synthesis phase
➢ DNA- replicated into two identical daughter DNA molecules
➢ Chromosomes: replicate form a two- chromatid structure to a four- chromatid structure.
G2 Phase
➢ the post- DNA synthesis gap of the celll growth
Interphase
➢ chromosome: not visible
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Meiosis
➢ The process whereby genetic cells undergo reduction division
➢ Second Division: not accompanied by S phase
➢ Result: no replication
➢ ova 46 chromosomes and spermatozoa 46 chromosomes
➢ number of chromosomes reduce to one half
Crossover
➢ process that occurs during meiosis wherein chromatids exchange
chromosomal material
Cell Cycle: Mitosis
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Cell Cycle
Cell proliferation is the act of a single cell or group of cells to reproduce and multiply in number.
The human body consists of two general types of cells, somatic cells and genetic cells.
The genetic cells include the oogonium of the female and the spermatogonium of the male.
All other cells of the body are somatic cells. When somatic cells proliferate or divide, they
undergo mitosis. Genetic cells undergo meiosis.
4 Sequential Phases of Cell Cycle
G1 – Gap 1
S – Synthesis Phase
G2 - Gap 2
M - Mitosis
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Interphase
Interphase is the period of growth of the cell between divisions.
- The genetic material of a cell increases.
- It is also responsible for DNA replication
- The DNA synthesis phase is S. During this period,
each DNA molecule is replicated into two identical
daughter DNA molecules.
The G2 phase is the post-DNA
synthesis gap of cell growth.
During interphase, the
chromosomes are not visible.
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Mitosis
Mitosis
- is the process of cell division that makes possible regeneration of the body parts.
- it is also the separation of nuclei chromosome into 2 identical daughter nuclei.
- when cells undergo mitosis, they split up their duplicated chromosomes in a carefully
organize series of steps.
- it divides into 4 phases
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Prophase
Metaphase
Anaphase
Telophase
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Four Subphases of Mitosis
Prophase
The chromatin become condenses and shorten thick to form a chromosomes.
Each chromosome has 2 sister chromatids joined together at the centromere.
The Nucleolus disappear and nuclear membrane starts to break down.
Centrosome with a pair of centrioles move apart to the opposite poles forming a spindle
between them.
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Four Subphases of Mitosis
Metaphase
Microtubules of the spindle interact with chromosomes causing the chromosomes to move
and align along the middle of the cell.
Sister chromatids are held at the centromere conforming the presence of protein structures
called Kinetochore.
Kinetochore holds the chromosome to the spindle.
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Four Subphases of Mitosis
Anaphase
Sister chromatids separate at the kinetochore and daughter chromosome move toward the
opposite poles as the microtubules shortens.
Poles of the spindle move apart and help to separate the chromosomes into 2 sets.
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Four Subphases of Mitosis
Telophase & Cytokinesis
The daughter chromosomes arrived at the pole and chromatin starts to decoil.
Nucleoli form along the nuclei for reformation of nuclear membrane.
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Cytokinesis
Cytokinesis is the partition of the cytoplasm.
The single cell then pinches in the middle to form 2 separate daughter cells each containing
a full set of chromosomes within a nucleus. This process is known as cytokinesis.
MEIOSIS
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MEIOSIS
• a special type of cell division of germ cells in sexually-reproducing
organisms used to produce the gametes
• Meiosis, meaning "lessening"
• Have 46 chromosomes
• (23) in pair
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• Sex cells divide to produce gametes (sperm and egg cell)
*in males it is called spermatogenesis
*in females it is called oogenesis
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Meiosis: Two Part Cell Division
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Prophase I
Early prophase
Late prophase
• Crossing over occurs
• Homologs pair
• Spindle forms
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Crossing over
• homologous pairs swap pieces of chromosome
• Creates new combinations of traits
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Metaphase I
• Homologous pairs of
chromosomes align
along the equator of
the cell
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Anaphase I
• Homologs separate and move to opposite
poles.
• Sister chromatids remain attached at their
centromeres
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Telophase I
• Nuclear envelopes reassemble Spindle
• disappears
• Cytokinesis divides cell into two.
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Prophase II
• Nuclear envelope fragments.
• Spindle forms.
• No more crossing will happen
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Metapahase II
• Chromosomes align along equator of
cell.
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Anaphase II
• Sister chromatids separate and move to opposite poles.
Equator
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Telophase II
• Nuclear envelope assembles
• Chromosomes decondense
• Spindle disappears
• Cytokinesis divides cell into two
Result of Meiosis
• Gametes (egg & sperm) form
• Four haploid cells with one copy of each
chromosome
• One allele of each gene
• Different combinations of alleles for different
genes along the chromosome
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• Errors in meiosis resulting in aneuploidy (an abnormal number of
chromosomes) are the leading known cause of miscarriage and the
most frequent genetic cause of developmental disabilities
TYPES OF IONIZING RADIATION
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IONIZING RADIATION
• Ionizing radiation – is a special type of radiation that includes xrays.
– - is any type of radiation that is capable of removing an orbital electron
from the atom with which it interacts
• This type of interaction between radiation and matter is called
ionization.
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• Ionization occurs when an x-ray passes close to an orbital electron
of an atom and transfers sufficient energy to the electron to
remove it from the atom.
• The ionizing radiation may interact with and ionize additional
atoms.
ION PAIR
• The orbital electron and the atom
from which it was separated are
called an ion pair. The electron is a
negative ion, and the remaining
atom is a positive ion.
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TYPES OF IONIZING RADIATION
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PARTICULATE RADIATION
• Many subatomic particles are capable of causing ionization.
Consequently, electrons, protons, and even rare nuclear fragments
all can be classified as particulate ionizing radiation if they are in
motion and possess sufficient kinetic energy. At rest, they cannot
cause ionization.
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ALPHA PARTICLE
BETA PARTICLE
• The alpha particle is equivalent to a
helium nucleus. It contains two protons
and two neutrons. Its mass is
approximately 4 amu, and it carries two
units of positive electric charge.
• the energy of an alpha particle is quickly
lost. It has a very short range in matter.
Whereas in air, alpha particles can travel
approximately 5 cm; in soft tissue.
• Beta particles differ from alpha particles in
terms of mass and charge. They are light
particles with an atomic mass number of 0
and carry one unit of negative or positive
charge. Depending on its energy, a beta
particle may traverse 10 to 100 cm of air and
approximately 1 to 2 cm of soft tissue.
• Positive beta - The same mass with
electrons,
• Negative beta - The same with electrons,
they only differ in origin
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alpha radiation from an external
source is nearly harmless because the
radiation energy is deposited in the
superficial layers of the skin.
Capable of penetrating the skin and
causing radiation damage, such as skin
burns. It can hazardous when it inhaled
or swallowed or absorbed into the
blood stream through wounds.
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Equivalent to a helium nucleus
It contains 2 protons & 2 neutrons
Symbol: α
Mass: 4 amu
Charge: +2
Origin: nucleus of heavy radioactive nuclei
Energy: 4-7 MeV
Range: 1-10 cm (air);
Ionization Rate: 40,000 atoms/cm
Light particles
Symbol: β - or β+
Mass: 0 amu
Charge: -1 or +1
Origin: nucleus of radioactive nuclei
Energy: 0-7 MeV
• Range: 10-100 cm (air); 1-2 cm (soft
tissue)
• Ionization Rate: several hundred of
atoms/cm
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ELECTROMAGNETIC RADIATION
• X-rays and gamma rays are forms of electromagnetic ionizing
radiation.
• X-rays and gamma rays are often called photons.
• Photons have no mass and no charge.
• They travel at the speed of light (c = 3 × 108 m/s)
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GAMMA
Gamma rays are emitted from the nucleus
of a radioisotope and are usually associated
with alpha or beta emission.
Uses of gamma
• Sterilize medical equipment
• Used as tracers in medicine
• Radio Therapy in oncology, to kill
cancerous cells.
X-RAY
It is emitted from the electron cloud
Uses of x-ray
• It is produced in diagnostic imaging
systems
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Symbol: γ
Mass: 0
Charge: 0
Origin: nucleus/radioactive
nuclei Energy: 0-5 MeV
• Range: 0-100 m (air); 0-30 cm
(soft tissue)
• Ionization Rate: 100 ip/cm
(equal to beta particles)
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Symbol: X
Mass: 0
Charge: 0
Origin: electron cloud
Energy: 0-25 MeV
Range: 0-100 m (air); 0-30 cm
(soft tissue)
• Ionization Rate: 100 ip/cm
(equal to beta particles)
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ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum includes the entire range of electromagnetic energy.
- The known electromagnetic spectrum has three regions most important to radiologic
science:
• visible light
• x-ray radiation and gamma radiation
• Radiofrequency
- Other portions of the spectrum include
• ultraviolet light
• infrared light
• microwave radiation.
• Radiofrequency
• Three Regions Important to Radiologic Science
– Visible light Region: viewing condition of a radiographic &
fluoroscopic images are critical to diagnosis
– X-ray Region: fundamental to producing a high quality
radiograph
– Radiofrequency Region: with the introduction of MRI, become
more important in medical imaging
– Others: UV light, infrared light, & microwave radiation
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• Visible Light
–It occupies the smallest
segment of
electromagnetic
spectrum
–It is described in terms of
wavelength
–Range: 400 nm (violet) to
700 nm (red)
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• Refraction
–The deviation of course that occurs when photos of
visible light traveling in straight lines pass from one
transparent medium to another
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• Sunlight
– 2 Invisible Light: infrared & UV
light
• Infrared
– Longer λ than visible light
– Shorter λ than microwaves
– It heats any substance on which
it shines (radiant heat)
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• UV Light
–It causes sunburn
–Lies between visible light
& ionizing radiation
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• Radiofrequency
– Range: 0.3 kHz-300 GHz
– Range in MRI: 1-100 mHz
– Low energy & long
wavelength
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• Microwave
–Very-short wavelength
RF
–Higher than broadcast
RF
–Lower than infrared
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SOURCES OF IONIZING RADIATION
I. Natural Environmental Radiation
Sources:
• 1. Cosmic rays- radiation coming from outer space
•
Aircraft crews and passenger flying at an altitude of 10, 000 meters
receive an extra
cosmic radiation for every 5,000 km jet flight
(0.03mSv)
• 2. External terrestrial radionuclide principally from 226, 228 Ra, 220, 222
Rn and 14 C
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3. Internal radionuclide principally from 40 K.
Our own body is radioactive. It contains radioactive radium and
polonium in our skeleton, radioactive carbon and potassium in our
muscles and radioactive noble gases and tritium in our lungs.
The largest component of natural environmental radiation is radon. Radon
is a radioactive gas produced by the natural decay of uranium. All earth
based materials, such as concrete, bricks and wood ( gypsum wallboard
contain radon and therefore radioactive it emits alpha particles and
contributes dose to the lungs.
It is the largest source of human exposure to radiation ( radon )
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• II. MAN – MADE RADIATION OR ARTIFICIAL DIATION
Sources:
1. Medically employed x-rays, both diagnostic and therapeutic
( largest source of man-made radiation)
2. Nuclear weapons testing which results from radioactive fallout
3. Radiopharmaceuticals
4. Nuclear power generation: research institutes, several sections of
metal industry and coal-fired power plant
5. Consumer items such as watch dials, exit signs, smoke detectors,
television receiver airport surveillance system, camping lantern
mantles and fluorescent numbers.
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Deterministic effect of Radiation
• Early Effects of Radiation
• A radiation response in human within a few days to months
• It is described as deterministic
• Deterministic Radiation Response
• Biologic response whose severity varies with radiation dose
• A dose threshold usually exists
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ACUTE RADIATION LETHALITY
• doses of 200 to 1000 rad delivered in a few hours will cause
serious illness with poor outlook at the end of the range. The
whole body doses of more than 1000 rad are almost invariably
fatal or lethal.
• The most devastating human response to radiation exposure
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Stochastic effect
• The result of low doses delivered over a long period
• It is also known as stochastic effects
• Stochastic effects of radiation exposure exhibit an increasing incidence
of response—not severity—with increasing dose
• No dose threshold has been established for a stochastic response.
• Followed linear dose-response relationship
• Principal Late Effects: radiation-induced malignancy & genetic effects
– Others: shortening of life span & local tissue effect
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Stochastic Radiation Response
• Probability of frequency of the biologic response to radiation as a function
of radiation dose
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•
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Principal early effects of radiation exposure on humans
and the approximate threshold dose
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Threshold
Anatomic site
effect
200 rad
Whole body
Death
25 rad
Whole body
Hematologic depression
200 rad
Small field/small region
Skin erythema
300 rad
Small field/ small region
Epilation
5 rad
Whole body
Chromosome aberration
10 rad
Local tissue
Gonadal dysfunction
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• Diagnostic x-ray beams always result in
partial-body exposure, which is less
harmful than whole-body exposure!
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Acute Radiation Syndrome
• Radiation sickness that occurs in human after the whole-body dose s of 1
Gy (100 rad) or more of ionizing radiation delivered over a short time
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Three Syndromes
• Hematologic Death,
• Gastrointestinal (GI) Death
• Central Nervous System (CNS) Death
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Prodomal Period
This immediate response of radiation sickness is the prodromal period.
Prodomal Period
• The immediate response of radiation sickness
• Approximate Dose: > 100 rad
• Mean Survival Time:
• Clinical S&S: nausea, vomiting & diarrhea
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Latent Period
• The latent period is the time after exposure during which there is no sign of
radiation sickness.
Latent Period
• The time after exposure during which there is no sign of radiation sickness
• extends from hours or less (at doses in excess of 50 Gyt) to weeks (at doses from 1
to 5 Gyt).
• Approximate Dose: 100-10, 000 rad
• Mean Survival Time:
• Clinical S&S: none
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Manifest Illness
• Manifest Illness
– The dose necessary to produce a given syndrome and the mean
survival time are the principal quantitative measures of human
radiation lethality
– At very high radiation doses, the latent period disappears
altogether. At very low radiation doses, there may be no
prodromal period at all.
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Hematologic Syndrome
• The hematologic syndrome is characterized by a reduction in white blood
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cells, red blood cells, and platelets
appear in a matter of a few hours and may persist for several days.
Approximate Dose: 2 to 10 Gyt (200–1000 rad)
Mean Survival Time: 10-60 days
Clinical S&S: nausea, vomiting, diarrhea, anemia, leukopenia, hemorrhage,
fever & infection
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• Prodomal Period: mild symptoms (matter of a few hours)
• Latent Period: general feeling of wellness
• Period of Manifest Illness: vomiting, mild diarrhea, malaise,
lethargy & fever
• Recovery: 2-4 weeks or 6 months (full)
• Cause of Death: generalized infection, electrolyte imbalance &
dehydration
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Gastrointestinal Syndrome
– It occurs principally because of severe damage to the cells lining the
intestines
– Approximate Dose: 10 to 50 Gyt (1000–5000 rad)
– Mean Survival Time: 4-10 days
– Clinical S&S: same as hematologic plus electrolyte imbalance, lethargy,
fatigue & shock
– GI death occurs principally because of severe damage to the cells lining
the intestines.
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• Prodomal Period: vomiting & diarrhea occur within hours of
exposure or w/n a day
• Latent Period: 3 to 5 days follows (no symptoms present)
• Period of Manifest Illness: second wave of nausea & vomiting,
followed by diarrhea, anorexia
• Cause of Death: unprevented rapid progression of symptoms (4 to
10 days of exposure)
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Central Nervous System Syndrome
•
Central Nervous System Syndrome
– Its ultimate cause is elevated fluid content of the brain
– Characterized By: increased intracranial pressure, vasculitis & meningitis
– Approximate Dose: > 50 Gyt (5000 rad) (death within a matter of hours to
days)
– Mean Survival Time: 0-3 days
– Initial onset : extremely nervous and confused, burning sensation in the
skin, lose vision, lose consciousness within the first hour
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•
•
•
•
Clinical S&S: same as GI plus ataxia, edema, system vasculitis & meningitis
Prodomal Period: severe nausea & vomiting
Latent Period: earlier symptoms disappear
Period of Manifest Illness: more severe prodomal symptoms, disoriented,
loss muscle coordination, dyspnea, convulsive seizures, loss of equilibrium,
ataxia & lethargy
• Outcome : always death within a few days of exposure
•
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• Regardless of the medical attention given the patient, the
symptoms of manifest illness appear rather suddenly and always
with extreme severity
• CNS syndrome is characterized byIncreased intracranial pressure,
inflammatory changes in the blood vessels of the brain (vasculitis),
and inflammation of the meninges (meningitis).
The ultimate cause of death in CNS syndrome is elevated fluid content of the
brain.
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Local tissue damage
• When only part of the body is irradiated, in contrast to wholebody irradiation, a higher dose is required to produce a response.
• Every organ and tissue of the body can be affected by partial-body
irradiation. The effect is cell death, which results in shrinkage of
the organ or tissue. This effect can lead to total lack of function for
that organ or tissue, or it can be followed by recovery.
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Effect on skin
•
Erythema
– 1st wave
– A sunburn-like reddening of the skin
– The first observed biologic response to radiation exposure
– dose of 3 to 10 Gyt (300–1000 rad) first or second day
•
Moist Desquamation
– 2nd wave
– The clinical tolerance for radiation therapy
•
Desquamation
– 3rd wave
– Ulceration & denudation of the skin
– required interruption of treatment.
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• Small doses of x-radiation do not cause
erythema. Extremely high doses of x-radiation
cause erythema in all persons so irradiated.
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POTENTIAL RADIATION RESPONSES OF SKIN FROM HIGH-DOSE
FLUOROSCOPY
Approximate Time of
• Potential Radiation
Threshold Dose
Response
Onset
Early transient erythema
200 rad/ 2Gy
Hours
Main erythema
600 rad/ 6Gy
10 days
Temporary epilation
300 rad/ 3Gy
3 weeks
Permanent epilation
700 rad/ 7Gy
3 weeks
Moist desquamation
1500 rad/ 15Gy
4 weeks
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Effects on gonald (ovaries)
• The most radiosensitive cell during female germ cell development is the oocyte in the
mature follicle!
• 100 mGyt (10 rad) - suppress menstruation in a mature female.
• 2 Gyt (200 rad) - produces temporary infertility
• 5 Gyt (500 rad) - results in permanent sterility.
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Effects on gonald (testes)
– 10 rad/ 100mGy - reduce the number of spermatozoa
– 200 rad - temporary sterility (approximately 2 months after irradiation
and persists for up to 12 months.)
– 500 rad - sterility (male patient normally retains his ability to engage in
sexual intercourse)
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Cytogenetic damage
• cytogenetic damage - damage to the DNA. This are the
abnormalities arising from nondisjunction event . It may lead to
additions or deletions of entire chromosomes.
• Some of the disorders are down syndrome and genetic mutation
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Radiation Exposure Experience By Personnel
Low dose & low LET
Chronic in nature Delivered intermittently over long periods
• Radiodermatitis
– Developed on early radiologists who performed fluoroscopic
examination
– Skin Appearance: callused, discolored & weathered (hands &
forearms)
– Skin Characteristics: very tight, brittle & severely crack or flake
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• At worst, humans can expect a reduced life span of
approximately 10 days for every rad!
• Our radiation protection guides are based on the
stochastic effects of radiation and on linear,
nonthreshold dose-response relationships.
Tissues organs and
Radiosensitivity
College of Radiologic Technology
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Terminology
• Tissue - a collection of cells with
similar structure and function
Examples of tissue
epithelial, connective, muscle,
nervous
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Tissue composition of the body
TISSUE COMPOSITION OF THE BODY
TISSUE
ABUNDANCE
Muscle
43%
Fat
14 %
Organs
12 %
Skeleton
10 %
Blood
8%
Subcutaneous tissue
6%
Bone marrow
4%
Skin
3%
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Terminology
organ – a collection of different
tissues precisely arrange to
accomplish a specific function
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radiosensitivity
• It is the relative susceptibility of
cells, tissues, organs, organism to
the harmful effect of ionizing
radiation
• Irradiation – exposure to radiation
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Radiosensitivity of Tissues & Organs
• Determined by the function of the organ in the body
• The rate at which cells mature within the organ
• The inherent radiosensitivity of the cell type
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Radiosensitivity of cell type
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Cellular composition of tissues
Cells within a tissue may be divided into cellular compartments
1. Stem cells
2. Differentiating cells
3. Functional ( Mature )cells
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Stem cell compartment
• Also known as “precursor cells”
• Contains immature (poorly
differentiated) cells
• Purpose is reproduction and
replenishment of cell line
• Cells do not perform the function
of the tissue
• Highly radiosensitive
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Differentiating Cell Compartment
• Also called transit cells
• Population originates from the
stem cells
• Differentiation process has begun
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Differentiating Cell Compartment
• Classified as:
1. Simple transit – stop dividing and
start to be more complex
2. Dividing transit – they are still
changing but not as rapidly as the
stem cell
• More highly differentiated and more
slowly dividing than Stem Cells
• Cells do not perform of the tissue
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Functional cell compartment
• Also known as “Static Population”
• Mature, fully differentiated cells
• No mitotic activity
• Cells do perform the functions of
the tissue
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Functional Cell Compartment
• Classified as:
1. Decaying population – dying
group of cells through maturation
2. Closed static population – no cell
production but functioning
properly
• Replaced by cells from the
differentiating cells compartment
when life span is over
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Response to radiation
• Tissue and organ response depend on:
1. Inherent cell sensitivity
2. Kinetics of cell population
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Law of T&B
Louis Tribondeau
Jean Bergonie
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Inherent cell sensitivity
• Cell population who are rapidly divided and poorly differentiated
has high radiation sensitivity
These are the cells who are in the stem cell compartment
• Cell population who are not dividing and highly differentiated has
low radiation sensitivity
These are the cells who are in the functional cell compartment
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Kinetics of cell population
• Rate of cell renewal also known as proliferation rate
• The various stages or phases of the cell cycle.
• Dynamic characteristics of cell populations, includes rate of cell
deviation, cell migration, and death of the cell
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Response to irradiation
ACUTE
• Inflammation – redness or swelling
• Edema – swelling cause of excess fluid in
the tissue
• Hemorrhage – excessive bleeding
• Denudation of mucosal surfaces - loss of
the surface tissue
CHRONIC
• Atrophy – decrease in size of a body part
• Stricture – abnormal narrowing of the
passage in the body
• Stenosis – narrowing of the blood vessels
• Necrosis – death of the cells
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Consequences of tissue irradiation
• As the functional cells are lost, they are not replaced due to
damage to stem cells
• Functional cell is only affected at extremely high doses
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Consequences of tissue irradiation
• Tissues response depends on the
life span of the functional cell
- short lifespan means rapid
severe response
- long lifespan means slower
and less severe response
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Summary
• Damage to tissues is due to the loss of reproductive capacity of
stem cells.
• Rapidity and severity of the response is related to the normal
lifespan of the functional cells.