Vascular permeability, often in the form of capillary permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules (ions, water, nutrients) or even whole cells (lymphocyte

Lymphocyte

A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

s on their way to the site of inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

) in and out of the vessel. Blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

 walls are lined by a single layer of endothelial cells. The gaps between endothelial cells (cell junction

Cell junction

A cell junction is a type of structure that exists within the tissue of a some multicellular organism . Cell junctions consist of protein complexes and provide contact between neighbouring cells or between a cell and the extracellular matrix...

s) are strictly regulated depending on the type and physiological state of the tissue.

An example of increased vascular permeability is in the initial lesion of periodontal disease, in which the gingival plexus becomes engorged and dilated

Vasodilation

Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...

, allowing large numbers of neutrophils to extravasate

Leukocyte extravasation

Leukocyte extravasation is the movement of leukocytes out of the circulatory system, towards the site of tissue damage or infection. This process forms part of the innate immune response, involving the recruitment of non-specific leukocytes...

 and appear within the junctional epithelium

Junctional epithelium

The junctional epithelium is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. It attaches to the surface of the tooth with hemidesmosomes and is, on average, roughly 1 mm in width, constituting about one half of the biologic width.The junctional...

 and underlying connective tissue

Connective tissue

"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

.