Possible thermoregulatory functions of the internal vertebral venous plexus in man and various other mammals: Evidence from comparative anatomical studies

Abstract

Comparative anatomy was used to collect more evidence for a thermoregulatory function of the internal vertebral venous plexus (IVVP). The venous connections of the IVVP were studied and compared in various mammals in order to find evidence for the existence of climate related anatomical adaptations. Humans and vervet monkeys were chosen as representatives of mammals living in moderate climates, the IVVP of the dolphin was studied because this animal is always surrounded by cold water. The springbok was chosen as a representative of mammalian species living under very hot conditions. The present study was exclusively performed on post mortem material. After filling the venous system with latex the IVVP and its venous connections were dissected. It appeared that in the dolphin, veins from the trunk muscles were directly and exclusively connected to the IVVP in the absence of an azygos vein. In the vervet monkey and human specimens, veins originating in the muscles drained both into the caval veins and into the IVVP. In these mammals veins draining from brown fat areas were also connected to the IVVP. In the springbok, drainage of blood from the muscles was prevented to enter the IVVP by the presence of valves. In humans and vervet monkeys we found that the lumbar parts of the IVVP were connected to subcutaneous veins of the back. It was concluded that the anatomy of the IVVP and its connecting veins may serve to thermoregulate the spinal cord and that climate related anatomical adaptations were present in the species studied.

The extracranial venous system in the heads of beaked whales, with implications on diving physiology and pathogenesis

“…This vein represents an enlarged right intercostal vein and is the result of numerous (at least three) right intercostal veins coalescing after they exit the neural canal via their respective intervertebral foramina. As described in other odontocete species, these intervertebral veins coalesce to form a large single vein which drains directly into the cranial vena cava (Fraser, ; Harrison and Tomlinson, ; Barnett et al, ; Hoogland et al, ). After receiving the enlarged right intercostal vein, the cranial vena cava extends rostromediad a short distance and then simultaneously gives off two large branches which project in opposite directions.…”

Vertebral Hemangiomas and Their Correlation With Other Pathologies

“…18 Interestingly, the intricacy of the diploic system has been hypothesized to assist in thermoregulation of the brain in modern humans; 19 -21 as has the venous vertebral system for spinal thermoregulation. 17,22 Due to their geometrical differences, heat regulation will differ between a complex of blood channels (normal vessels) and a pool of blood (i.e., a VH). The first will conduct heat in an efficient manner, as a channel has a larger surface of contact with the environment, allowing for fast temperature exchange.…”

The posterior intercostal vein: A thermoregulatory gateway to the internal vertebral venous plexus

“…Previous studies on the internal vertebral venous plexus (IVVP) have shown that this venous system may play a role in thermoregulation of the spinal cord. Venous blood from muscles and brown fat areas can supply the IVVP with heat, whereas blood from subcutaneous veins may provide the plexus with cooled blood from the skin (Zenker and Kubik, ; Hoogland et al, ). This pattern of blood supply to the IVVP, suggests a blood flow regulating system for veins connecting with the IVVP.…”

“…A study in the springbok ( Antidorcas marsupialis ) showed that a certain degree of overfilling will result in incompetency of otherwise competent valves in the azygos and posterior intercostal veins (Hoogland et al, ). This is in line with the findings of Yeh et al () who reported that retrograde filling of the azygos vein was more often seen after high rates (3.5–5.0 ml/sec) of contrast medium injections, which may have resulted in a certain degree of venous overfilling.…”

“…In the springbok, sphincter‐like structures were shown in the wall of the posterior intercostal veins, which connected the azygos vein with the IVVP. These sphincters may additionally influence the direction and quantity of blood flow in the posterior intercostal veins (Hoogland et al, ).…”