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Related Concept Videos

Capillary Exchange01:28

Capillary Exchange

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.
Capillary Beds01:20

Capillary Beds

Capillary beds are networks of tiny blood vessels that play a crucial role in the circulatory system. These beds are where the exchange of gases, nutrients, and waste products occurs between the blood and surrounding tissues. Each capillary bed consists of numerous capillaries, which are the smallest blood vessels in the body, typically only one cell-thick. This thinness allows for the efficient diffusion of substances.
Capillaries connect arterioles, small branches of arteries, to venules,...
Capillaries and Their Types01:20

Capillaries and Their Types

Capillaries, a crucial constituent of the circulatory system, are diminutive vessels with a diameter between 5–10 micrometers, accommodating perfusion to the tissues through the phenomenon known as microcirculation. Through their permeable walls, consisting of an endothelial layer ensconced by a basement membrane and sporadically dispersed smooth muscle fibers, the exchange of substances between the blood and the interstitial fluid becomes plausible. Variance in wall composition exists, with...
Transcellular Transport of Solutes01:23

Transcellular Transport of Solutes

Transcellular transport of solutes is the movement of substances like monosaccharides and amino acids through polarized cells. This transport mechanism is primarily seen in epithelial and endothelial cells aided by membrane transport proteins such as channels and transporters. The tight junctions between these cells confine the membrane proteins to the two sides of the cell. The epithelial cells have distinct apical and basolateral domains. In contrast, the endothelial cells show the luminal...
Fluid Movement Between Compartments01:18

Fluid Movement Between Compartments

The force applied by fluids against a surface, known as hydrostatic pressure, initiates the transfer of fluid among different compartments. Within our blood vessels, the blood's hydrostatic pressure is a result of the heart's pumping action. At the arteriolar end of capillaries, hydrostatic pressure (capillary blood pressure) exceeds the opposing colloid osmotic pressure created primarily by plasma proteins like albumin. This discrepancy in pressure propels plasma and nutrients from the...
Tight Junctions01:29

Tight Junctions

Tight junctions are molecular seals between cells that prevent the leaking of fluids, ions, and other small solutes across cavities and compartments in multicellular organisms. They are mainly composed of claudin and occludin transmembrane proteins, and other proteins such as tricellulin and JAM (junctional adhesion molecule). All these proteins are 4-pass transmembrane proteins, except JAM, which is a single-pass transmembrane protein belonging to the immunoglobulin superfamily. The...

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Updated: Jun 19, 2026

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability
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Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability

Published on: June 7, 2022

The ultrastructural basis of transcapillary exchanges.

M J Karnovsky1

  • 1Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115.

The Journal of General Physiology
|October 30, 2009
PubMed
Summary
This summary is machine-generated.

Capillary ultrastructure correlates with permeability. Continuous endothelium junctions act as small pores, vesicles as large pores, while fenestrated capillaries allow molecule passage via fenestrae.

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Microperfusion Technique to Investigate Regulation of Microvessel Permeability in Rat Mesentery
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High-resolution Confocal Imaging of the Blood-brain Barrier: Imaging, 3D Reconstruction, and Quantification of Transcytosis
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High-resolution Confocal Imaging of the Blood-brain Barrier: Imaging, 3D Reconstruction, and Quantification of Transcytosis

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Last Updated: Jun 19, 2026

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability
10:56

Endothelial Cell Transcytosis Assay as an In Vitro Model to Evaluate Inner Blood-Retinal Barrier Permeability

Published on: June 7, 2022

Microperfusion Technique to Investigate Regulation of Microvessel Permeability in Rat Mesentery
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Microperfusion Technique to Investigate Regulation of Microvessel Permeability in Rat Mesentery

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High-resolution Confocal Imaging of the Blood-brain Barrier: Imaging, 3D Reconstruction, and Quantification of Transcytosis
10:30

High-resolution Confocal Imaging of the Blood-brain Barrier: Imaging, 3D Reconstruction, and Quantification of Transcytosis

Published on: November 16, 2017

Area of Science:

  • Cell Biology
  • Physiology
  • Microcirculation

Background:

  • Capillary permeability is crucial for substance exchange.
  • Understanding capillary ultrastructure aids in explaining physiological permeability.

Purpose of the Study:

  • To correlate capillary ultrastructure with permeability characteristics.
  • To investigate the role of endothelial junctions and vesicles in capillary transport.

Main Methods:

  • Utilized peroxidase (in vivo) and colloidal lanthanum (in vitro) as ultrastructural tracers.
  • Examined continuous, fenestrated, and discontinuous endothelium capillaries.
  • Assessed transport across brain capillaries.

Main Results:

  • Continuous endothelium junctions (maculae occludentes) represent a small-pore system (~40 A gap).
  • Vesicles in continuous endothelium function as a large-pore system.
  • Fenestrated capillaries exhibit high permeability due to fenestrae.
  • Brain capillaries possess tight junctions (zonulae occludentes), forming a blood-brain barrier for larger molecules.
  • Discontinuous endothelium capillaries allow easy tracer passage through intercellular gaps.

Conclusions:

  • Capillary morphology correlates well with observed physiological permeability.
  • Endothelial junctions, vesicles, fenestrae, and basement membranes play distinct roles in regulating molecular passage.
  • The blood-brain barrier in brain capillaries is attributed to tight endothelial junctions and lack of vesicular transport for large molecules.