[Intramural blood vessels of the large intestine of the horse (Equus przewalskii f. caballus)].

The research article investigates the vascular system of the large intestine in horses, using various techniques such as vascular corrosion casts, histology and transmission electron microscopy.

Study Overview

• Twelve horses were included in the study. The aim was to obtain a detailed understanding of the vascular system in the horses’ large intestines. This was done through detailed anatomical analysis and the use of various techniques like vascular corrosion casts, histology, and transmission electron microscopy.
• The study precisely examined the paths and interconnections of different types of vessels (arteries and veins, long and short) in the large intestine – how they traverse through the different layers of the intestinal wall, and how they contribute to the vascular network in the submucosa of the intestine.

Observations

• Short arteries and veins directly enter the deeper layers of the wall, whereas long arteries and veins reach the submucosa by first following a variable subserous course.
• The submucosa – the area between the serous membrane and the muscular layer – houses an arterial and a venous vascular network. Wider areas have a more complex, three-dimensional network which is split into a deep and superficial vascular plexus that are interconnected.
• The blood supply to the deep arterial plexus is maintained by the short and long arteries and veins. This plexus is integral to supplying parts of the circular muscle layer.
• The blood supply for the mucosa, or the functional layer of the intestine, originates from the superficial submucosal plexus.

Mucosal Vascularisation

• The so-called ‘ascending arteries’ form a transversal network that branches out into capillaries surrounding each crypt of Lieberkühn, small tubular glands in the intestine.
• Close to the lumen, or inside the space within the tubular structures, capillaries form a subepithelial capillary system with a polygonal shape. These capillaries then become postcapillary venules that lie immediately below the epithelium surface of the mucosa.

Vanous Structure and Endothelial Lining

• Veins move through the submucosa vertically and enter back into the submucosal plexus with few inflowing branches.
• Connections between the subserous and submucosal regions form an intermuscular plexus between the circular and longitudinal muscle layer, supplying the blood vessels in the muscular layer (tunica muscularis).
• The capillaries inside the subepithelium predominantly have a fenestrated endothelium, whereas capillaries around the mucosa have a continuous endothelial lining. The latter may also contain multiple vesicles known to form transcytoplasmic channels.

Hemodynamic Regulatory Structures

• Sphincter-like muscle bundles at points where the capillaries transition into venules could provide a means to regulate blood flow in the horse’s submucosa.
• Veins with cushions of smooth muscle fibres, known as ‘throttle veins’, were also identified in the study.

A detailed understanding of the vascular system of the horse’s large intestine is important for veterinary medicine, especially for targeted treatments and surgical procedures.