Blood vessels and the occurrence of arteriovenous anastomoses in cephalic heat loss areas of mallards, Anas platyrhynchos (Aves)

Midtgård, Uffe

doi:10.1007/bf00312014

Cited by 37 publications

(42 citation statements)

References 46 publications

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“…Cooling is effected through a well-developed rete ophthalmicum which is situated in the temporal region and receives its venous supply from the nasal cavity and the palate. Recent observations (Midtgard 1984a) suggest that the cooling of the eye produced by this vascular apparatus can be important in restriction of ophthalmic heat loss in cold environments, a conclusion consistent with the results of other studies (Frost et al 1975;Midtgard 1983Midtgard , 1984b. Birds sleeping in the cold may obtain some further thermal benefits from closing their eyes (Midtgard 1984 b).…”

Section: Heat Loss From the Headsupporting

confidence: 65%

Avian Adjustments to Cold

Marsh

Dawson

1989

Advances in Comparative and Environmental Physiology

112

104

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Section: Heat Loss From the Headsupporting

confidence: 65%

Avian Adjustments to Cold

Marsh

Dawson

1989

Advances in Comparative and Environmental Physiology

112

104

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“…As such, warm-raised animals have greater capacity for losing heat from their thermolytic organs [41]. Heat dumping from the bill may also result from vascular morphology, which unlike the counter-current system found in avian limbs, is not conducive to simultaneously exhibiting nutritive blood supply to tissues while conserving body heat [10,42]. Our results suggest that blood vessel density and/or the control over bill blood flow retains a memory of the thermal environment experienced during development.…”

Section: Discussionmentioning

confidence: 84%

Post-hatch heat warms adult beaks: irreversible physiological plasticity in Japanese quail

et al. 2013

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Across taxa, the early rearing environment contributes to adult morphological and physiological variation. For example, in birds, environmental temperature plays a key role in shaping bill size and clinal trends across latitudinal/thermal gradients. Such patterns support the role of the bill as a thermal window and in thermal balance. It remains unknown whether bill size and thermal function are reversibly plastic. We raised Japanese quail in warm (308C) or cold (158C) environments and then at a common intermediate temperature. We predicted that birds raised in cold temperatures would develop smaller bills than warm-reared individuals, and that regulation of blood flow to the bill in response to changing temperatures would parallel the bill's role in thermal balance. Cold-reared birds developed shorter bills, although bill size exhibited 'catch-up' growth once adults were placed at a common temperature. Despite having lived in a common thermal environment as adults, individuals that were initially reared in the warmth had higher bill surface temperatures than coldreared individuals, particularly under cold conditions. This suggests that blood vessel density and/or the control over blood flow in the bill retained a memory of early thermal ontogeny. We conclude that post-hatch temperature reversibly affects adult bill morphology but irreversibly influences the thermal physiological role of bills and may play an underappreciated role in avian energetics.

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“…The oral region has been shown to influence head temperatures (Spotila et al 1977;Smith, 1979), so there is a mechanism for cooled blood to be shunted around the head and not just drained into pathways that bypass neurosensory tissues. If venous drainage could be regulated by smooth muscles in the maxillary or palatomaxillary vein, as has been demonstrated in birds (Midtg ard, 1984), blood flow could be shunted through the nasal region, where there would be a clear potential to influence the temperature of neurosensory tissues (Fig. 14).…”

Section: Discussionmentioning

confidence: 96%

Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange

2016

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Extant crocodilians are a highly apomorphic archosaur clade that is ectothermic, yet often achieve large body sizes that can be subject to higher heat loads. Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. The cephalic vascular anatomy of extant crocodilians, particularly American alligator (Alligator mississippiensis) was investigated using a differential-contrast, dual-vascular injection technique and high resolution X-ray micro-computed tomography (μCT). Blood vessels were digitally isolated to create representations of vascular pathways. The specimens were then dissected to confirm CT results. Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The evolutionary history of crocodilians is complex, with large-bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building-blocks for such an extensive vascularization of sites of thermal exchange. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids.

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Blood vessels and the occurrence of arteriovenous anastomoses in cephalic heat loss areas of mallards, Anas platyrhynchos (Aves)

Cited by 37 publications

References 46 publications

Avian Adjustments to Cold

Avian Adjustments to Cold

Post-hatch heat warms adult beaks: irreversible physiological plasticity in Japanese quail

Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange

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