Human Biology and Radiobiology Flashcards

A comprehensive vocabulary flashcard set covering cellular biology, radiation interaction, radioactive decay, biological effects, radiobiology principles, and dose-response relationships based on the lecture notes.

Deterministic effects

Radiation-induced biological responses that increase in severity with increasing radiation dose and possess a specific threshold dose below which the effect does not occur.

Stochastic effects

Radiation-induced responses where the probability of occurrence, rather than severity, increases with radiation dose without a threshold dose (e.g., leukemia, cancer, and heritable genetic damage).

Cell Theory

The biologic principle demonstrated by Scheider and Schwann in 1838 stating that cells are the basic functional units of all plants and animals.

Deoxyribonucleic acid (DNA)

The command or control nucleic acid located principally in the cell nucleus that carries all hereditary information and is considered the most critical and radiosensitive target molecule.

Enzymes

Molecules required in small quantities to allow biochemical reactions to continue without entering directly into the reaction.

Hormones

Molecules secreted by endocrine glands (such as the pituitary, adrenal, thyroid, parathyroid, pancreas, and gonads) that exercise regulatory control over body functions like growth and development.

Antibodies

Protein molecules that constitute a primary defense mechanism of the body against infection and diseases.

Lipids

Organic macromolecules with the general formula $C_n H_n O_n$ composed of glycerol and fatty acids that serve as cell membrane structural components, thermal insulators, and energy stores.

Carbohydrates

Organic macromolecules composed of carbon, hydrogen, and oxygen whose chief function in the body is to provide fuel for cellular metabolism.

Messenger RNA (mRNA)

A large family of RNA molecules that convey genetic information from DNA in the nucleus to the ribosomes, specifying the amino acid sequence for protein synthesis.

Transfer RNA (tRNA)

A type of RNA molecule that functions at specific sites in the ribosome to decode a messenger RNA sequence into a protein during translation.

Endoplasmic reticulum

A channel or series of membrane channels that allows the cell nucleus to communicate directly with the cytoplasm.

Mitochondria

Large bean-shaped organelles responsible for digesting macromolecules to produce cellular energy, often called the engine of the cell.

Ribosomes

Small dot-like cellular structures that serve as the site of protein synthesis essential for cellular function.

Somatic cells

All non-genetic cells in the human body that undergo cell division and proliferation through the process of mitosis.

Genetic cells

Reproductive cells of the body—including female oogonia and male spermatogonia—that undergo cell division through meiosis.

Mitosis

The process of somatic cell division divided into four subphases (prophase, metaphase, anaphase, telophase) resulting in two identical daughter cells.

Interphase

The growth and development portion of the cell cycle between mitotic divisions during which chromosomes are not visible under a microscope.

Prophase

The initial subphase of mitosis in which the cell nucleus and chromosomes enlarge and DNA begins to take structural form.

Metaphase

The subphase of cell division during which chromosomes align and become distinctly visible under microscopic examination.

Anaphase

The third phase of mitosis during which chromatids repel one another and migrate along the mitotic spindle to opposite sides of the cell.

Telophase

The final subphase of mitosis characterized by structural chromosomes disappearing into a mass of DNA and nuclear membranes closing off to form two distinct nuclei.

Meiosis

The reduction division process occurring in genetic cells that reduces the chromosome complement from 46 to 23 chromosomes.

Stem cells

Immature, undifferentiated, or precursor cells that undergo proliferation and differentiation to become mature, functional tissue cells.

Parenchyma

The functional tissue portion of an organ that carries out its specific organ functions.

Stroma

The structural component of an organ consisting of connective tissue and vasculature that provides support to the organ.

Alpha particle

A heavy nucleus of helium ($^4_2\text{He}$) containing 2 protons and 2 neutrons, with a +2 charge, high energy ($4\text{ to }8\,\text{MeV}$), slow speed ($2 \times 10^7\,\text{m/s}$), and low tissue penetration.

Beta particle

A fast-moving electron originating from an unstable nucleus when a neutron transforms into a proton, carrying a -1 charge and a mass of $0.0055\,\text{amu}$.

Gamma ray

Massless, uncharged electromagnetic radiation of very high frequency and energy emitted when an excited atomic nucleus transitions to its ground state.

Electron capture

A decay mode in proton-rich nuclei where an inner K-shell electron is captured by a nuclear proton to form a neutron, accompanied by characteristic X-ray emission.

Positron

A positively charged antiparticle of an electron ejected at high speed when a nuclear proton transforms into a neutron.

Radioactive activity ($A$)

The rate of nuclear decay measured as the number of nuclear disintegrations occurring per unit time, expressed in curies (Ci) or becquerels (Bq).

Decay constant ($\lambda$)

The fraction of radioactive atoms that undergo decay per unit time, calculated as $\lambda = \frac{0.693}{T_{1/2}}$.

Half-life ($T_{1/2}$)

The duration of time required for half of the radioactive atoms in a sample to undergo decay.

Curie (Ci)

A unit of radioactivity named after Marie Curie, defined as $3.7 \times 10^{10}$ disintegrations per second (Bq).

Becquerel (Bq)

The SI unit of radioactivity named after Henri Becquerel, equal to 1 disintegration per second.

Somatic effects

Radiation-induced biological damage and symptoms that manifest directly in the exposed individual.

Heritable effects

Radiation damage occurring in the germ cells of reproductive organs that results in genetic mutations passed on to future generations.

Physical stage

The initial interaction stage lasting approximately $10^{-16}\,\text{seconds}$ during which radiation energy is deposited in cellular water and causes ionization.

Physiochemical stage

The stage of radiation interaction lasting about $10^{-6}\,\text{seconds}$ where produced ions interact with other water molecules to form new dissociation products and free radicals.

Chemical stage

The stage lasting a few seconds during which free radicals and oxidizing agents (such as $\text{H}_2\text{O}_2$) attack complex intracellular molecules like chromosomes.

Biological stage

The stage ranging from minutes to years where chemical alterations lead to cell death, delayed division, or permanent modifications causing cancer or heritable traits.

Free radical

An uncharged, highly reactive atom or molecule possessing an unpaired electron in its outer shell (e.g., $\text{H}^*$ and $\text{OH}^*$).

Harmful tissue reactions

The modern term for deterministic radiation effects, which arise from cell population depletion above a specific threshold dose.

Erythema

Reddening of the skin caused by radiation exposure, typically produced by approximately $3\,\text{Gy}$ of low-energy X-rays.

Law of Bergonie and Tribondeau

A fundamental radiobiologic principle stating that the radiosensitivity of tissue is directly proportional to its reproductive activity and metabolic rate, and inversely proportional to its degree of differentiation.

Linear Energy Transfer (LET)

The rate at which energy is transferred from ionizing radiation to soft tissue per unit length of travel, expressed in $\text{keV}/\mu\text{m}$.

Relative Biological Effectiveness (RBE)

A mathematical ratio used to express the relative capacity of different types of ionizing radiation to produce a specific biological response compared to a standard radiation (diagnostic X-rays).

Protraction

The continuous administration of a total radiation dose over an extended period at a reduced dose rate, which lowers the overall biological damage.

Fractionation

The delivery of a total radiation dose in smaller equal doses separated by time intervals, allowing cells and tissues time to repair and recover.

Oxygen Enhancement Ratio (OER)

The ratio of radiation dose needed to cause a given biologic effect under anoxic/hypoxic conditions compared to the dose needed under fully oxygenated conditions.

Interphase death

Cell death occurring after irradiation before the cell can enter its next division phase.

Radiosensitizers

Chemical agents (e.g., halogenated pyrimidines and Vitamin K) that enhance the biological effects of radiation when present during exposure.

Radioprotectors

Chemical compounds that decrease the biological effects of radiation exposure, though required in toxic levels for human application.

Radiation hormesis

The hypothesis suggesting that low exposure doses of ionizing radiation produce beneficial or protective biological responses by stimulating immune and hormonal systems.

Linear non-threshold (LNT) model

A dose-response curve model assuming that any radiation exposure, no matter how small, carries a proportional risk of inducing a biological response.

Sigmoid dose-response curve

An S-shaped, non-linear threshold curve characteristic of deterministic effects (harmful tissue reactions) where response severity increases rapidly once the threshold dose is exceeded.

Extrapolation

The mathematical process of estimating radiation response at low doses by projecting trends downward from known high-dose experimental data.