Circle of Villus in the Small Intestine
The "circle of villus" refers to the microvascular architecture within intestinal villi, specifically describing the arrangement of arteries, capillaries, and veins that form a circulatory loop to supply blood to these finger-like projections of the small intestinal mucosa 1.
Anatomical Structure
In humans and primates, each villus contains a single centrally located vein that drains a subepithelial capillary plexus converging at the apex of the villus, alongside a single eccentrically positioned artery that rises to the midlevel of the villus before branching into subepithelial capillaries 1. This creates a functional circulatory pattern where:
- The arterial supply enters the villus base and ascends eccentrically (off-center) to approximately the midpoint of the villus 1
- At the mid-villus level, the artery branches extensively into a subepithelial capillary network that spreads beneath the epithelial layer 1
- These capillaries converge at the villus apex and drain into a single central vein that descends through the core of the villus 1
- The capillary beds in the middle and lower intestine typically comprise a hairpin loop configuration with cross-connections 2
Functional Significance
The microvascular arrangement creates a countercurrent exchange system that is critical for nutrient absorption and maintaining the osmotic gradient necessary for digestive function 2. Key functional aspects include:
- Blood vessels pass through progressively hypertonic zones as they approach the villus apex, with red cell packing density (hematocrit) increasing from base to apex 2
- The vascular architecture supports the dynamic movements of villi during intestinal contractions, which generate laminar eddies that augment radial mass transfer between the inter-villous space and intestinal lumen 3
- This circulatory pattern enhances nutrient absorption and mixing at the periphery of the lumen, particularly for highly diffusible nutrients 3
Clinical Relevance
Understanding villus microvascular anatomy is essential when interpreting duodenal biopsies, as proper villus architecture with intact vasculature indicates normal absorptive capacity 4. The British Society of Gastroenterology emphasizes that:
- Normal villous architecture requires a villous height to crypt depth ratio >3:1 4
- Proper biopsy orientation by experienced laboratory technicians is necessary to accurately assess villous height and the underlying vascular support structures 4
- The lamina propria core of villi contains the microvasculature and lacteals (lymphatic vessels) that work in concert with the blood supply 5
Structural Support and Maintenance
Subepithelial myofibroblasts form a contractile network around the villus vasculature and play a crucial role in villus motility, which propels absorbed nutrients through the lacteal and maintains blood flow through the capillary plexus 5, 6. These myofibroblasts:
- Originate from local fibroblast progenitors that differentiate into mature smooth muscle fibers via an intermediate contractile phenotype 6
- Continuously renew throughout adult life to maintain villus function 6
- Contract to propel absorbed dietary fats through the adjacent lymphatic lacteal into blood circulation 6