Possible nervous innervation and characterization of the blood vessels of the counter-current heat exchangers in three species of tuna.

摘要

Tunas can maintain their muscle temperatures above the ambient water temperature by retaining metabolically derived heat through the use of counter-current heat exchangers. I hypothesize that the diameters of the heat exchanger blood vessels are controlled by autonomic nervous connections to the smooth muscle in the walls of the blood vessels. Through the gross dissection of three species of tuna, and via a silver staining method, I have located a major nerve in the dorsal aorta/post-cardinal vein complex. Using transmission electron microscopy I characterized the layers of the blood vessel walls in the central and lateral heat exchangers of the three species and confirmed the presence of smooth muscle in these vessels. All the heat exchanger blood vessels were less than 300 {dollar}mu{dollar}m in luminal diameter and contained the specific ultrastructure which classifies these vessels as arterioles and venules. The endothelial cells of these vessels are connected by desmosomes and interdigitations which are features that are unique to vessels involved in counter-current exchange. Possible autonomic nervous innervation of the arterioles within the heat exchangers has also been identified. Thus, this study provides structural evidence for a proposed mechanism for control of heat loss in tunas.