Any of the smallest blood vessels connecting arterioles with venules.

http://upload.wikimedia.org/wikipedia/commons/2/2f/A_red_blood_cell_in_a_capillary,_pancreatic_tissue_-_TEM.jpg

not all sources agree capillary is a blood vessel - consider adopting EMAPA superclass of vascular element

Any of the tiny blood vessels connecting the arterioles to the venules.[AAO]

blood capillary, capillary vessel

uberon

The appearance of Chordata and subsequently the vertebrates is accompanied by a rapid structural diversification of this primitive linear heart: looping, unidirectional circulation, an enclosed vasculature, and the conduction system.[well established][VHOG]

UBERON:0001982

http://purl.obolibrary.org/obo/uberon.owl, http://purl.obolibrary.org/obo/cl.owl

capillaries lack tunica media and tunica adventitia; only the endothelial wall of the tunica intima belongs

• venule
• arteriole

• transudate

• vein