go6 HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



fig. io. Arteriovenous anas- 

 tomosis in the submucous plexus. 

 [From Barlow (8).] 



mose with a tributary of its accompanying vein (fig. 

 io). 



In 1959, Baez (6), using the small intestine of the 

 rat, gave a detailed account of the vasculature at 

 various levels based on observations in the living 

 animal. In discussing the method of observations, 

 Baez points out the advantage of having an intact 

 animal in which the distribution of large supplying 

 arteries and accompanying veins of the wall as well 

 as their relation to the small vasa recta can be deter- 

 mined. The type of a vascular connection at the anti- 

 mesenteric border as well as the vessels of the submu- 

 cosal plexus and the final ramifications of the vessels 

 to the muscular coat can be established. 



The description of the vessels in the submucosal 

 plexus is as follows: Main arteries (60-80 n), which 

 pierce the muscularis in the mesenteric region at 

 intervals, divide into two or three branches in the 

 submucosa. Each branch subdivides into four or six 

 smaller branches (30-40 //) which then proceed to the 

 antimesenteric border where they connect with simi- 

 lar arterial branches from the other side. Other arte- 

 rial anastomoses are formed by interconnections of 

 branches between neighboring recta. Baez uses a 

 general description for main arterial arcades with 

 three characteristics: /) they are located in the outer 

 plane of the submucosa and average 30 to 40 m in 

 diameter; 2) all give rise to secondary arcades, muco- 

 sal arteries, and vessels to nourish the muscular coat; 

 3) the direction of blood flow through them is 

 changing constantly. 



The small vasa recta which arise from the last 



mesenteric arcade terminate quickly by anastomosing 

 with secondary branches of other arcades. The small 

 vasa recta lie between the large vasa recta. They sup- 

 ply the vessels to the submucosa and muscular coats 

 of the gut wall near the mesenteric border (fig. 11). 

 These vessels go in opposite directions, some to the 

 outer smooth muscle coat and others to the inner 

 absorptive surface of the gastrointestinal tract. They 

 seem to have a unique type of blood flow. Unidirec- 

 tional flow in the large and small vasa recta is altered 

 in the meshwork of interconnected arterial vessels in 

 the submucosal plexus. A main arterial arcade may 

 show complete reversal of flow or, as more frequently 

 happens, blood may flow from both sides of an arterial 

 arcade into a mucosal artery. At times, when blood 

 is rushing into an arcade from opposite directions, 

 the converging currents may produce a space of 

 clear plasma at the point where they meet. When this 

 occurs at the origin of a mucosal vessel, plasma is 

 "skimmed" into it. 



The muscular coat of the ileum is supplied by 

 vessels that originate from the proximal end of mu- 

 cosal arteries or from secondary arcades in the sub- 

 mucosa. Baez considers these vessels to be metar- 

 terioles, 18 to 24 n in diameter, which enter the 

 muscularis and run in the plane of cleavage between 

 the circular and longitudinal muscle bundles. In 

 the intermuscular septum the capillaries for the 

 circular muscle bundles stay on the same plane as the 

 parent vessel, while those for the longitudinal muscle 

 bundles turn outward. The capillaries communicate 

 freelv to form a network, both in the same plane and 



