List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite

Dr. med.
H. Jastrow

of use
Overview capillaries (Vasa capillaria):
Pages with explanations are linked to the text below the images if available! (Labelling is in German)
cross section of a
capillary 1 (monkey)
cross section of a
capillary 2 (monkey)
erythrocyte in a
heart capillary(monkey)
venole in neuro-
hypophysis (monkey)
capillary of the heart
capillary in the nasal sub-
mucosa (monkey)
erythrocyte in a capillary of a
human pharyngeal tonsil
lymphocyte penetrating
the wall of a human capillary
fenestrated capillary: Bruch's
membrane (monkey)
venoles and capillaries
capillary of the trachea
capillary in brain, blood-
brain barrier (rat)
sinusoid of the liver, open
fenestrations in endothel (rat)
sinusoid overview x-section
capillary + fenestrated endo-
thelium, suprarenal gland (rat)
basement membrane of a
glomerular capillary (monkey)
longitudinal section of a
monkey pancreas capillary
capillary in cerebral

Capillary vessels or simply capillaries (Terminoligia histologica: Vasa capillaria) are the smallest blood vessels. Their diameters vary about that of an erythrocyte (red blood cell; diameter ~ 7.5 µm) whereby the smallest capillaries even require an adaptive deformation of the erythrocyte since their lumen is only 6 µm in width. The largest capillaries, however, have diameters of up to 15 µm. Usually a capillary forms a capillary arch (Terminoligia histologica: Ansa capillaris) as described here: they receive blood from the metarteriols  which drain into arterial capillaries (Terminoligia histologica: Vasa capillaria arterialia, Vasa precapillaria; ~ 8 µm in diameter) which begin when the smooth muscle cells and the tiny internal elastic membrane are no longer detectable. The following midcapillaries (Terminoligia histologica: Vasa capillaria intermedia) are only 6-7 µm in width. Here the blood flows with a speed of about 0.5 mm per second and the intravascular pressure is between 2-4 kPa (15 - 30 mm Hg). The next portion of the arch are the venous capillaries (Terminoligia histologica: Vasa capillaria venosa, vasa postcapillaria) with a width of 8-9 µm which drain into smallest venules whose diameters are above 15 µm sind. In the area of the venous capillaries and of the venules the intercellular space between the lining flat endothelial cells partly is widened to a few hundred nanometres which is termed (Terminoligia histologica: Apertura intercellularis, Apertura transcellularis). This is why this is the typical location for white blood cells to leave the vascular system to become free connective tissue cells. A very intense exchange of metabolites is performed in the capillary region since the blood gases and nutrients can easily reach the surrounding tissue due to the very thin in some places additionally fenestrated wall of the capillaries (fenestrated endothelial cells).
When looking from iside to outside a capillary begins with an intima (missing in Terminoligia histologica; proposal: Tunica intima, Tunica interna) consisting of only one very flat fenestrated endothelial cell followed by a basal membrane. Few reticular fibres (collagen type 3) anchor the capillary to the surrounding connective tissue. A media is missingThe directly following adventitia (missing in Terminoligia histologica; proposal: Tunica adventitia, Tunica externa) is variabel often incontinuous adventitial cells (Terminoligia histologica: Cellulae adventitiales) are present. These immotile connective tissue cells are called pericytes (Terminoligia histologica: Pericyti). From point of view of function and morphology they are in between fibroblasts and smooth muscle cells. By contraction of the microfilaments of their cytoskeleton (actin filaments) they can moderately influence the width of the capillary. Depending on organ and function the chemical composition of the basal lamina of capillaries may vary. In general we can differentiate
1. capillaries of the muscle type with continuous endothelium (non fenestrated endothelium; Terminoligia histologica: Endothelium non fenestratum, Endothelium continuum) on a non-interrupted basal lamina,
2. capillaries of the visceral type on a continuous basal lamina with endothelial cells showing pores covered by tiny diaphragms forming a fenestrated endothelium (Terminoligia histologica: Endothelium fenestratum).

--> endothelial cells, blood barriers, blood cells, blood vessels, arteriole, venole
--> Electron microscopic atlas Overview
--> Homepage of the workshop

Some images were kindly provided by Prof. H. Wartenberg; other images, page & copyright H. Jastrow.