Histomorphologic Studies of the Nasal Cavity of Sheep (<i>Ovis aries</i>) and Its Significance in Temperature Regulation of the Brain

Abstract

10 sheep were used for light microscopic studies to describe the distributions of the blood vessels, epithelium, and glands of the nasal cavity. The animals were killed following intramuscular injection of Rompun solution (xylazine hydrochloride). The heads were sawed and tissues were taken from the alar fold, respiratory, and olfactory regions. More vascularity was noticed in areas of the nasal cavity that were in direct contact with the airstream. Moreover, in the submucosa, the presence of arteriovenous anastomoses, collagen fibers, elastic fibers, thick-walled or cushion veins, and free smooth muscle cells was observed, gradually decreasing from the rostral to caudal regions. The tunica media of the arteries was very thin in the vestibular region and relatively thicker in the respiratory region. On the other hand, luminal diameters of the arteries were very small in the respiratory region and relatively larger in the vestibular region. In addition, a large number of intra-arterial bolsters was present in the respiratory region, but there were fewer in the olfactory region, and they occurred with still less frequency in the vestibular region.

The branches of the descending palatine artery and their relation to the vomeronasal organ inAngoragoats

“…In previous studies, some researchers have studied the arterial supply to the nasal cavity in different species regardless of that of VNO (Dawes and Prichard, 1953;Nawar et al, 1975;Khamas and Ghoshal 1982;Grevers and Heinzmann, 1989), despite the fact that this organ forms part of the nasal cavity. They reported that the blood supply to the nasal cavity was mainly derived from the sphenopalatine and external ethmoidal arteries, and lesser contributions are also made by the major palatine artery.…”

Angularis oculi vein blood flow modulates the magnitude but not the control of selective brain cooling in sheep

“…The AOV in sheep possesses ␣-adrenergic receptors (18), and it is widely held that high sympathetic activity constricts the vessel sphincter, leading to attenuation of SBC (11,26). However, even without AOV blood flow, we saw a rapid rise in brain temperature and abolition of SBC in dehydrated sheep in response to the return of drinking water, an event we believe would be associated with excitement and sympathetic activation.…”

“…Along its course, the AOV receives blood from the dorsal and lateral nasal veins and the maxillary labial vein and, before traversing the supraorbital foramen, tributaries from the forehead and eyelid. Beyond the supraorbital canal, it continues as the dorsal external ophthalmic vein to the ophthalmic plexus, which drains into the cavernous sinus (4,17). Because we sectioned the AOV only near its confluence with the dorsal nasal vein and facial vein, it probably still received some venous blood from other tributaries before the cavernous sinus.…”

“…It seems unlikely, however, that blood flow from these small veins would be controlled by sphincters. In sheep, a significant proportion of venous effluent probably reaches the cavernous sinus via the sphenopalatine veins (17). Blood in the sphenopalatine vein passes to the deep facial vein and then into the cavernous sinus.…”

“…However, these experiments, in which blood flow was occluded briefly by investigators compressing the veins manually, do not exclude the possibility that high levels of sympathetic activity, associated with stress, attenuated SBC through another mechanism. It also is likely, at least in some species, that the AOV is not the only major conduit for venous return to the cavernous sinus; in sheep and pronghorn antelope, blood from deeper veins in the nose and posterior turbinates passes via the sphenopalatine vein to the deep facial vein and then to the cavernous sinus (4,17). The AOV is not present in pigs, yet SBC can be rapidly abolished in these animals (8).…”