Jejunal microvasculature of the llama and alpaca

The vasculature of the jejunum was studied in 6 llamas and 1 alpaca, using a combination of microangiography, standard light microscopy, and vascular cast imaging. The casts were examined by use of scanning electron microscopy and low-power dissecting microscopy. After administration of 40,000 IU of heparin, all animals were euthanatized by administration of an overdose of sodium pentobarbital. Three sections of jejunum and their respective arcuate vessels were isolated from each animal. One section was immediately placed in formalin for later H&E staining. The second and third sections were placed in warm saline solution, and the vasculature was flushed free of all blood by repeated infusions of the solution. Once flushed of all blood, one section was infused with a radio-opaque medium and subsequently evaluated by microangiography, and the remaining section was perfused with a methylmethacrylate polymer for creation of vascular casts. The arcuate vessels branched into extensive primary and secondary arcades prior to giving rise to the marginal rete. Muscular arteries and small veins left the marginal rete and penetrated the tunica serosa and tunica muscularis to provide nutrients or drain the mesenteric angle, respectively, or entered into the circumferential submucosal network. The primary penetrating vessels in the submucosa formed an extensive submucosal plexus that supplied the tunica serosa, tunica muscularis, and tunica mucosa. The primary penetrating vessels anastomosed with vessels from oral and aboral sections and with their counterparts from the opposite side at the antimesenteric border. Vessels supplied the tunica serosa and tunia muscularis by branching centrifugally from the submucosal plexus supplying the inner circular and outer longitudinal muscle layers parallel to their respective muscle layers. The arterioles supplying the tunica mucosa branched at right angles, penetrated the muscularis mucosa, and gave rise to clusters of arterioles supplying either the villi or the intervening crypts; anastomosis occurred between these 2 systems toward the base of the villus. The arterioles gradually developed a discontinuous smooth muscle layer as they approached the base of the villus. Each villus was supplied by a single centrally placed metarteriole that spiraled to the tip of the villus, divided, and descended in a fountaining capillary network. The individual capillaries in the cascade coalesced to drain via 2 to 4 venules at the base of the villus. Branches from the venules entered into an anastomosing network in the lamina propria to drain the crypts. Venules drained in the submucosal plexus and continued paralleling the arterial supply toward the mesenteric border and the arcuate veins. The jejunal vasculature of South American camelids contains an extensive set of anastomotic connections at all levels after formation of the arcuate vessels. Within the scope of this examination into the microvasculature of llamas and alpacas, differences were not detected between the individual species.