Microvasculature of the Guttural Pouch Mucosa and Relationship With the Internal Carotid Artery in Horses

The objectives of this study were to describe the microvasculature of the guttural pouch and consider its provable function. We suggest a working hypothesis that the guttural pouch is an additional organ of thermoregulation. Vascular corrosion casts were prepared for scanning electron microscopy by injecting acrylic resin via the common carotid artery, and tissue sections were prepared for histologic examination in 10 equine cadavers. The arteries supplying the guttural pouch originated from the external carotid artery and its branches, and the arteries formed a capillary network in the pouch mucosa. Some of the superficial arterioles and capillaries extended toward the internal carotid artery (ICA) after supplying the pouch mucosa and formed a fine, compact network in the tunica adventitia of the ICA. The capillaries formed two types of vascular plexuses surrounding the ICA: one with capillary bundles parallel to the ICA in the outer layer of the tunica adventitia (outer periarterial plexus) and the other with vein-artery-vein triads in the inner layer of the tunica adventitia (inner periarterial plexus). The microvascular arrangement and the ICA in the guttural pouch were closely related and consisted of a countercurrent heat exchanger. Such an arrangement supports the hypothesis that the guttural pouch participates in selective brain cooling. Results of the present study help provide a better understanding of the function of the guttural pouch in horses. (C) 2018 Elsevier Inc. All rights reserved.