Physics Gemini Study Guide

Chapter 31 Penguins

At nearly every stage in the sequence, it is possible to repair ________ and to _______

radiation damage; recover

Radiobiology is the study of the

effects of ionizing radiation on biologic tissue

Macromolecules are very large

molecules that sometimes consist of hundreds of thousands of atoms.

The chief function of carbohydrates in the human body is to

provide fuel for cell metabolism.

What is the radiation-sensitive target molecule?

DNA

What type of base bonding is possible in DNA?

adenine–thymine and cytosine–guanine

Cellular membranes provide

structure and form for the human cell and its components.

A series of 3 base pairs, called a ________, identifies

codon; 1 of the 22 human amino acids available for protein synthesis

Cell proliferation is the act of a single cell or group of cells

reproducing and multiplying in number

Radiation-induced chromosome damage is analyzed during

metaphase

Meiosis is the process whereby

genetic cells undergo reduction division.

Organ Systems =

Nervous, Reproductive, Digestive, Respiratory, and Endocrine.

Stem cells are more sensitive to radiation

than mature cells.

Ch. 31 Outline

What are the two main structures of a human cell?

Nucleus and cytoplasm

What is the function of the nucleus?

Control center of the cell; contains DNA

What is the most radiation-sensitive target in the cell?

DNA in the nucleus

What structure inside the nucleus contains most of the cell’s RNA?

Nucleolus

What does the cytoplasm contain?

All molecular components except DNA

What is the function of the endoplasmic reticulum?

Allows communication between nucleus and cytoplasm, manufactures protein/lipids

What are mitochondria responsible for?

Producing energy by digesting macromolecules

What is the function of ribosomes?

Protein synthesis

What do lysosomes do?

Digest cellular debris and contaminants

What is the role of the cell membrane?

Provides structure and allows selective diffusion

What determines a cell’s radiosensitivity?

Its maturity and function

Which is more sensitive to radiation: nucleus or cytoplasm?

Nucleus

Are immature or mature cells more radiosensitive?

Immature (stem) cells

Name four highly radiosensitive cells.

Lymphocytes, spermatogonia, erythroblasts, intestinal crypt cells

What tissues are highly radiosensitive?

Lymphoid tissue, bone marrow, gonads

What dose range affects highly radiosensitive tissues?

2–10 Gy

Name two effects of radiation on highly sensitive tissues.

Atrophy (shrinkage of cell), hypoplasia (underdevelopment)

Name four cells with intermediate radiosensitivity.

Endothelial cells, osteoblasts, spermatids, fibroblasts

What are seven tissues have intermediate radiosensitivity?

Skin, GI tract, cornea, bone, kidney, liver, thyroid

What dose range affects intermediate tissues?

10–50 Gy

Name three effects on intermediate tissues.

Erythema, ulcers, cataracts

Which cells have low radiosensitivity?

Muscle and nerve cells

What tissues are least radiosensitive?

Muscle, brain, spinal cord

What dose is required to damage low-sensitivity tissues?

Greater than 50 Gy

Name two severe effects on low-sensitivity tissues.

Fibrosis, necrosis

Chapter 32 Penguins

The LET of diagnostic x-rays is approximately

3 keV/um

RBE is the ratio of a standard radiation dose to produce the

same response as that following a test radiation dose

The RBE of diagnostic x-rays is

1

Dose protracted and fractionated cause less effect because the longer irradiation time

allows for intracellular repair and tissue recovery.

OER is the ratio of radiation doses under anoxic conditions to produce

the same response as that following irradiation under oxygenated condtions

Diagnostic digital imaging is performed under

conditions of full oxygenation.

INterphase death occurs when the cell

dies before replicating

The combined processes of intracellular repair and repopulation contribute to

recovery from radiation damage.

Human responses to radiation exposure fall into two types:

deterministic or stochastic.

Radiation-induced cancer, leukemia and genetic effects follow a

linear, nonthreshold dose-response relationship

Skin effects resulting from high-dose fluoroscopy follow a

sigmoid-type dose-response relationship

No human radiation responses have been observed after radiation doses less than

100 mGyt

Ch 32 Questions

What is Linear Energy Transfer (LET)?

Measure of energy transferred from ionizing radiation to tissue per distance (keV/μm).

What happens as LET increases?

Biologic damage increases.

Why does higher LET cause more damage?

More frequent ionizations → higher chance of hitting target molecules.

What is Relative Biologic Effectiveness (RBE)?

Ratio of dose of standard radiation to test radiation needed to produce the same effect.

What is the RBE of diagnostic x-rays?

1

What happens to RBE when LET is lower than x-rays?

RBE < 1, RBE has a direct relationship to LET

What happens to RBE when LET is higher?

RBE increases.

What happens to RBE at very high LET (overkill)?

RBE decreases

What law governs cellular radiosensitivity?

Law of Bergonie and Tribondeau.

According to this law, what determines radiosensitivity?

Maturation and metabolism.

Which cells are most radiosensitive: stem or mature?

Stem Cells

What type of cells are radioresistant?

Mature Cells

How does proliferation rate affect radiosensitivity?

Higher proliferation → more radiosensitive

How does metabolic activity affect radiosensitivity?

Higher metabolism → more radiosensitive

When are humans most radiosensitive in life?

In utero (before birth)

When are humans most radiioresistant?

At maturity

What happens to radiosensitivity in old age?

Increases slightly

What is the oxygen effect?

Oxygenated tissues are more sensitive to radiation.

How does hypoxic/anoxic conditions affect sensitivity?

Decrease radiosensitivity

What is a dose-response relationship?

Relationship between radiation dose and biological effect.

What is a linear dose-response

Response directly proportional to dose

Give examples of linaer responses

Cancer, leukemia, genetic effects

What is a nonlinear dose-response?

Responses not proportional to dose

What shape can nonlinear curves have?

Sigmoid (S-shaped)

What is a threshold-dose response?

No effect until a certain dose is reached.

Example of threshold response?

Skin burns

What is a nonthreshold dose-response?

Any dose can cause an effect.

What does nonthreshold imply about safety?

No commpletely safe dose

What can occur even at zero dose?

Natural incidence of effects (e.g, cancer)

Ch. 33 Penguiins

In vitro is irradiation that occurs

outside the cell or body

In vivo is irridation that occurs

within the cell

Point lesions can result in the ____________ radiation effects observed at the __________ level

stochastic; whole-body

Metabolism consists of

catabolism and anabolism

DNA is the most

radiosensitive molecule in the human body

Half as much DNA is present in

G1 as in G2

What happens during a Main-chain scission (single strand)

A break in one DNA strand (backbone is cut on one side)

What happens during a Main-chain scission (double strand)

A break in both DNA strands (complete DNA break)

What happens during a Main-chain scission + cross-linking

Broken DNA strands become stuck together abnormally, preventing normal separation

What happens during a Rung breakage

Base pairs are disrupted and separate from each other

What happens during a Base damage (change or loss)

A DNA base is altered, damaged, or completely removed (can cause mutation)

What are results from irradiation of DNA?

Cell death, malignant disease, and genetic effects

A free radical is an uncharged molecule that contains

a single unpaired electron in the outer shell

The effect of radiation is direct when

the ionizing event occurs on the target molecule

The principal effect of radiation on humans is

indirect

Ch.33 Questions