HUMAN BIOLOGY AND FUNDAMENTAL PRINCIPLES OF RADIOBIOLOGY Flashcards by Danie Bernal

What is the primary result of X-rays interacting at the atomic level?

Molecular changes in tissue

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The study of the effects of ionizing radiation on biological tissue

Radiobiology

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What are the three stages of early radiation effects on humans?

Hematologic syndrome, gastrointestinal syndrome, central nervous system syndrome

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What are the late effects of radiation on humans?

Leukemia, malignant diseases, local tissue damage, lifespan shortening, genetic damage

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What are the effects of fetal irradiation?

Prenatal death, neonatal death, congenital malformation, childhood malignancy, diminished growth

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What is the principal atomic composition of the human body?

60% hydrogen, 25.7% oxygen, 10.7% carbon, 2.4% nitrogen, and trace elements

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What are the four principal macromolecules in the human body?

Proteins, lipids, carbohydrates, nucleic acids

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What percentage of the human body is water?

80%

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What is the most critical and radiosensitive target molecule in the body?

DNA

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What are the primary functions of proteins in the body?

Provide structure, support, enzymes, hormones, and antibodies

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What is the chemical formula for glucose?

C6H1206

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Provide fuel for cell metabolism

carbohydrates

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What is the main difference between DNA and RNA?

DNA has deoxyribose and thymine; RNA has ribose and uracil

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What are the two principal types of nucleic acids?

DNA and RNA

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What is the double-helix structure of DNA formed by?

Sugar-phosphate backbone and base pair bonding

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What are the two major structures of a human cell?

Nucleus and cytoplasm

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Acts as the “engine” of the cell, producing energy

mitochondria

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Contain enzymes to digest cellular fragments and control intracellular contaminants

lysosomes

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What is a codon in protein synthesis?

A series of three base pairs identifying an amino acid

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What are the two general types of cells in the human body?

Genetic (germ) cells and somatic cells

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What are the four phases of mitosis?

Prophase, metaphase, anaphase, telophase

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Chromosomes align along the equator and are most visible

metaphase

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A process of reduction division in genetic cells

meiosis

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The exchange of chromosomal material between chromatids

crossover

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What percentage of human tissue composition is muscle?

43%

What is the most radiosensitive cell type in humans?

Stem cells

What are the four types of tissues in the human body?

Epithelium, connective and supporting tissue, muscle, nervous tissue

Lines all exposed surfaces of the body

epithelium tissue

What are parenchymal and stromal tissues?

Parenchymal is functional tissue; stromal provides structure

Radiosensitivity depends on metabolic state, proliferation rate, and cell maturity

Law of Bergonie and Tribondeau

What are the physical factors affecting radiosensitivity?

LET, RBE, protraction, and fractionation

Rate at which radiation energy is transferred to soft tissue

linear energy transfer (LET)

What is the typical LET value for diagnostic X-rays?

3 keV/μm

What is the relative biological effectiveness (RBE) of diagnostic X-rays?

1.0

Ratio of radiation dose needed under anoxic vs. aerobic conditions

oxygen enhancement ratio (OER)

What are radiosensitizers?

Agents that enhance radiation effects

What are radioprotectors?

Agents that reduce radiation effects

What is the threshold dose in a dose-response relationship?

The dose below which there is no observed response

Response is directly proportional to dose, with no safe level

inear nonthreshold dose-response relationship

Response increases rapidly after a threshold dose is exceeded

sigmoid dose-response relationship

What is the principal aim of radiobiology?

To understand radiation dose-response relationships

Delivering the total dose in equal portions at regular intervals

fractionation

Delivering the dose continuously but at a lower dose rate

protraction

What is hormesis in radiobiology?

The concept that low levels of radiation may be beneficial

What is a deterministic (nonstochastic) radiation effect?

High-dose exposure causing early radiation response, e.g., skin burn

Low-dose exposure causing late effects, e.g., cancer or genetic effects

stochastic radiation effect

What are two characteristics of dose-response relationships?

They can be linear or nonlinear, and threshold or nonthreshold

What is the most radiosensitive phase of the cell cycle?

M phase (mitosis)

What is the least radiosensitive phase of the cell cycle?

S phase (DNA synthesis)

What is the lethal dose (LD) for single-cell organisms?

Measured in kilorads

What is the lethal dose for human cells?

Less than 100 rad (1 Gy)

Chromosomes disappear into DNA mass, and the nuclear membrane divides

telophase

What are the two phases of the cell cycle according to geneticists?

M phase (mitosis) and interphase

What occurs during the S phase of interphase?

DNA is replicated into two identical daughter molecules

Chromosomes become visible and start to take structural form

prophase

They connect chromatids to the poles of the nucleus

spindle fibers

They contain enzymes capable of digesting cellular debris

lysosomes

A state of equilibrium among tissues and organs

homeostasis

Binds tissues and organs together and provides elasticity

connective tissue

Site of protein synthesis

ribosomes

What are the two principal types of radiation responses in humans?

Early effects (e.g., acute radiation syndrome) and late effects (e.g., cancer)

What is the effect of radiation on immature (stem) cells compared to mature cells?

Stem cells are more radiosensitive than mature cells

What happens during interphase in the cell cycle?

The cell grows and prepares for division

What are the two types of RNA?

Messenger RNA (mRNA) and transfer RNA (tRNA)

What is the configuration of RNA?

Single-helix

What are the purines in DNA?

Adenine and guanine

What are the pyrimidines in DNA?

Thymine and cytosine

What is the sugar component in DNA?

Deoxyribose

What is the sugar component in RNA?

Ribose

A combination of base, sugar, and phosphate

nucleotide

Control growth, development, and protein synthesis

nucleic acids

What is the principal location of RNA in the cell?

Cytoplasm

What is the oxygen enhancement ratio (OER) for low-LET radiation?

High OER

What is the combined process of intracellular repair and repopulation called?

Recovery

What is the most radioresistant age in humans?

Maturity

What are examples of radiosensitizers?

Halogenated pyrimidines, methotrexate, vitamin K

What are examples of radioprotectors?

Cysteine and cysteamine

Why haven’t radioprotectors been applied in humans?

They require toxic levels to be effective

What is the relationship between LET and RBE?

As LET increases, RBE increases

What is the LET value for diagnostic X-rays?

3 keV/μm

What is the RBE value for diagnostic X-rays?

1.0

What is the function of the radiation weighting factor (WR)?

Adjusts for differences in biological effectiveness of various radiation types

Cell death before replication

Interphase death

What is the function of the mitochondria in radiation response?

Provides energy for cellular repair and survival

What is a deterministic dose-response relationship?

Response increases with dose after a threshold is reached

The response is directly proportional to the dose

linear dose-response relationship

What is the principal use of linear nonthreshold models in radiology?

To establish radiation protection guidelines

What phase of mitosis is best for analyzing chromosome damage?

Metaphase

What tissues are classified as having high radiosensitivity?

Lymphoid tissue, bone marrow, gonads

What are the primary effects of radiation on the central nervous system?

Edema, convulsions, and death at very high doses

What is the typical dose range for intermediate radiosensitivity tissues?

1,000–5,000 rad (10–50 Gy)

What organs have low radiosensitivity?

Muscle, brain, and spinal cord

What is the purpose of dose-response curves in radiation therapy?

To design therapeutic treatments and set radiation safety guidelines

What is the structure of a chromatid during the S phase?

Replicates from a two-chromatid to a four-chromatid structure

Produces collagen and other fibers for structural support

fibroblasts

What is the impact of radiation on intestinal crypt cells?

Highly radiosensitive, leading to gastrointestinal syndrome

Chromosomes split at the centromere and migrate to opposite poles

anaphase

Chromosomes become visible and take structural form

prophase

What is the impact of low LET radiation on tissue damage?

Causes less biological damage than high LET radiation

What is the difference between deterministic and stochastic effects?

Deterministic effects have a threshold; stochastic effects do not

Modifies, sorts, and packages proteins

Golgi apparatus

What are stem cells classified as?

Undifferentiated cells with high radiosensitivity