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Related Concept Videos

Diffusion01:21

Diffusion

Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
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Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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The cardiovascular system's chief role is to disseminate gases, nutrients, waste, and other substances to the body's cells. Small molecules like gases, lipids, and lipid-soluble substances directly diffuse through capillary wall endothelial cell membranes. Glucose, amino acids, and ions, including sodium, potassium, calcium, and chloride, use transporters for facilitated diffusion via membrane-specific channels. Glucose, ions, and bigger molecules may also pass through intercellular clefts.
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Vasogenic edema is a major form of cerebral edema characterized by abnormal accumulation of fluid in the brain’s extracellular space due to disruption of the blood–brain barrier (BBB). The BBB is a specialized structure composed of endothelial cells connected by tight junctions, supported by astrocytic endfeet and a basement membrane. Under normal conditions, it tightly regulates the movement of ions, proteins, and solutes between the bloodstream and brain parenchyma. When this barrier loses...

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Real-time Iontophoresis with Tetramethylammonium to Quantify Volume Fraction and Tortuosity of Brain Extracellular Space
10:45

Real-time Iontophoresis with Tetramethylammonium to Quantify Volume Fraction and Tortuosity of Brain Extracellular Space

Published on: July 24, 2017

Diffusion in brain extracellular space.

Eva Syková1, Charles Nicholson

  • 1Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic.

Physiological Reviews
|October 17, 2008
PubMed
Summary
This summary is machine-generated.

Brain extracellular space (ECS) diffusion is governed by volume fraction and tortuosity. Studies reveal how these properties change with age, disease, and interventions, impacting molecular transport and drug delivery.

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Area of Science:

  • Neuroscience
  • Biophysics
  • Physiology

Background:

  • Diffusion in the brain's extracellular space (ECS) is crucial for molecular transport.
  • The ECS diffusion is characterized by volume fraction and tortuosity, influencing molecular movement.
  • Deviations from standard diffusion models indicate molecular loss mechanisms like blood-brain barrier crossing or cellular uptake.

Purpose of the Study:

  • To review and synthesize current understanding of diffusion properties within the brain's ECS.
  • To highlight the methods used for measuring diffusion and the factors influencing it.
  • To underscore the importance of ECS diffusion knowledge for understanding brain function and therapeutic strategies.

Main Methods:

  • Real-time iontophoresis (RTI) for small ions.
  • Integrative optical imaging (IOI) for macromolecules.
  • Theoretical models and simulations of ECS geometry and molecular interactions.

Main Results:

  • In normal brain tissue, ECS volume fraction is ~20% and tortuosity is ~1.6 for tetramethylammonium (TMA).
  • ECS diffusion parameters vary with development, aging, and in disease states like Alzheimer's, Parkinson's, and gliomas.
  • Interventions such as brain stimulation and ECM component knockout alter diffusion properties.

Conclusions:

  • ECS diffusion properties are dynamic and influenced by various physiological and pathological factors.
  • Understanding ECS diffusion is vital for comprehending extrasynaptic transmission and developing targeted brain drug delivery.
  • Glia and extracellular matrix play significant roles in modulating the ECS microenvironment and molecular diffusion.