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Related Concept Videos

Bystander Effect02:09

Bystander Effect

The discussion of bullying highlights the problem of witnesses not intervening to help a victim. This is a common occurrence, as the following well-publicized event demonstrates. In 1964, in Queens, New York, a 19-year-old woman named Kitty Genovese was attacked by a person with a knife near the back entrance to her apartment building and again in the hallway inside her apartment building. When the attack occurred, she screamed for help numerous times and eventually died from her stab wounds.
Dose-Response Relationship: Overview01:03

Dose-Response Relationship: Overview

Agonists can bind with and activate receptors, resulting in the formation of drug-receptor complexes. Once formed, these complexes catalyze many biochemical processes at the cellular level and subsequently induce a pharmacologic response. The degree of response is directly proportional to the fraction of activated receptors, which in turn, depends on the concentration of the drug at the receptor site as well as the sensitivity of the receptor. An increase in the administered dose contributes to...
Dose Response Curve: Conventional Versus Nonmonotonic01:21

Dose Response Curve: Conventional Versus Nonmonotonic

The correlation between a drug's dosage and its impact on a biological system is a cornerstone of pharmacology and toxicology. Conventional dose–response curves, which include graded and quantal relationships, are key to this understanding. Graded dose–response curves depict the spectrum of a biological reaction to different doses within an individual, indicating that as the drug dosage increases, so does the intensity of the response. On the other hand, quantal dose–response relationships...
Desensitization and Tachyphylaxis01:20

Desensitization and Tachyphylaxis

Tachyphylaxis is described as a rapid decrease in response to a drug after repeated or continuous administration of the same drug dose. It is a phenomenon where the body becomes less responsive to a particular substance or intervention over time, requiring higher doses or stronger interventions to achieve the same effect. It results from adaptive changes in the body's receptors, signaling pathways, or physiological processes that occur in response to prolonged exposure to a stimulus.
Several...
Dose-Response Relationship: Potency and Efficacy01:22

Dose-Response Relationship: Potency and Efficacy

The potency of a drug is the measure of its ability to produce a biological response and can be compared by looking at the half-maximum effective concentration or EC50 values of different drugs. A lower EC50 value indicates higher potency of the drug. In the dose–response curve of two antihypertensive drugs, candesartan and irbesartan, a significant difference is observed in their EC50 values. A lower EC50 value for candesartan indicates that it is more potent than irbesartan, as it produces...
Drug Toxicity: Dose-Dependent Reactions01:24

Drug Toxicity: Dose-Dependent Reactions

Drug toxicities can be stratified into pharmacological, pathological, or genotoxic based on their mechanisms. The incidence and severity of these toxicities generally increase with the drug's concentration in the body and exposure time.Pharmacological toxicity is evident when the therapeutic effects of drugs overshoot into adverse reactions in a predictable, dose-dependent manner. Central nervous system (CNS) depression from barbiturates is a classic example, with effects escalating from...

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Related Experiment Video

Updated: Jun 24, 2026

Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
06:20

Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition

Published on: March 11, 2021

The bystander effect: recent developments and implications for understanding the dose response.

R E J Mitchel1

  • 1Radiation Biology and Health Physics Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario, K0J 1J0 Canada.

Nonlinearity in Biology, Toxicology, Medicine
|March 31, 2009
PubMed
Summary
This summary is machine-generated.

Cellular bystander effects, triggered by radiation, can cause damage or adaptive responses. Below 100 mGy, protective effects dominate; above this, detrimental effects prevail, impacting radiation risk assessment.

Keywords:
Trp53bystander effectscancerionizing radiationmice

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A Mimic of the Tumor Microenvironment: A Simple Method for Generating Enriched Cell Populations and Investigating Intercellular Communication
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A Mimic of the Tumor Microenvironment: A Simple Method for Generating Enriched Cell Populations and Investigating Intercellular Communication

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Last Updated: Jun 24, 2026

Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
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Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition

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A Co-culture Method to Investigate the Crosstalk Between X-ray Irradiated Caco-2 Cells and PBMC
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A Mimic of the Tumor Microenvironment: A Simple Method for Generating Enriched Cell Populations and Investigating Intercellular Communication
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A Mimic of the Tumor Microenvironment: A Simple Method for Generating Enriched Cell Populations and Investigating Intercellular Communication

Published on: September 20, 2016

Area of Science:

  • Radiobiology
  • Cellular Biology
  • Radiation Protection

Background:

  • The bystander effect describes cellular responses to events in adjacent cells, mediated by intercellular communication.
  • These effects are crucial for understanding ionizing radiation risk, especially at low doses where not all cells are directly hit.
  • Current radiation protection models assume linear risk increase with dose, which may not account for bystander effect amplification.

Purpose of the Study:

  • To review data on radiation-induced bystander effects in mammalian cells.
  • To correlate in vitro bystander effect data with in vitro and in vivo low-dose radiation risk observations.
  • To evaluate the balance between detrimental and protective bystander effects in relation to radiation dose.

Main Methods:

  • Review of existing in vitro data on radiation-induced bystander effects.
  • Correlation of in vitro findings with in vitro and in vivo low-dose radiation risk data.
  • Analysis of dose-response relationships for bystander effects.

Main Results:

  • Two types of radiation-induced bystander effects observed: detrimental (damage, mutation, lethality) and adaptive (increased resistance).
  • Detrimental effects include damage and mutagenic events in unhit cells.
  • Adaptive effects involve enhanced resistance to spontaneous or radiation-induced events in bystander cells.

Conclusions:

  • Radiation-induced bystander effects challenge linear no-threshold models for radiation risk assessment.
  • Below approximately 100 mGy, protective bystander effects appear to outweigh detrimental ones.
  • Above 100 mGy, detrimental bystander effects are suggested to dominate, altering the overall risk profile.