Editing Porbeagle (section)

===Thermoregulation===
[[File:Lamna nasus with fishmonger.jpg|thumb|alt=A shark lying belly up and sliced transversely through the middle, showing the body cavity and the spinal column beneath it, surrounded by pink muscle with two obviously darker muscle blocks flanking the spine|Cross-section through the trunk of a porbeagle (orientation is belly-up); note the central red muscles.]]
Like other members of its family, the porbeagle is [[endothermy|endothermic]]; [[Metabolism|metabolic]] heat generated by its red muscles is conserved within the body by specialized systems of [[blood vessel]]s called ''retia mirabilia'' ([[Latin]] for "wonderful nets"; singular ''rete mirabile''), that act as highly efficient [[countercurrent exchange|countercurrent]] [[heat exchanger]]s. The porbeagle has several ''rete mirabile'' systems: the orbital ''retia'' accessing its brain and eyes, the lateral cutaneous ''retia'' accessing its swimming muscles, the suprahepatic ''rete'' accessing its [[viscera]], and the [[kidney]] ''rete''.<ref name="carlson et al"/>

Among sharks, the porbeagle's capacity for elevating body temperature is second only to the salmon shark's. Its red muscles are located deep within the body, adjacent to the [[vertebral column|spine]], and its lateral ''rete'' is composed of over 4,000 small [[artery|arteries]] arranged in bands.<ref name="carey et al"/> It has one of the highest core temperatures within its family, {{convert|8|–|10|C-change}} warmer than that of the surrounding water.<ref name="carey and teal"/> Being warm-bodied may allow this shark to maintain higher cruising speeds, hunt in deep water for extended periods of time, and/or enter higher latitudes during winter to exploit food resources not available to other sharks.<ref name="carlson et al"/><ref name="henderson et al"/> The orbital ''retia'' of the porbeagle can raise the temperature of its brain and eyes by {{convert|3|–|6|C-change}}, and likely serve to buffer those sensitive organs against the large temperature shifts that accompany changes in depth; potential benefits of this include increased visual acuity and reduced [[reaction time|response times]].<ref name="block and carey"/>