Functional morphology of the vascular plexuses associated with the cetacean uterus

Abstract

The cetacean reproductive system is surrounded by thermogenic locomotory muscle and insulating blubber. This arrangement suggests elevated temperatures at the uterus that could induce detrimental effects on fetal development. We present anatomical evidence for a complex countercurrent heat exchange system that could function to regulate the thermal environment of the uterus and a developing fetus. Cooled venous blood from the surfaces of the dorsal fin and flukes enters the abdominal cavity via the lumbo-caudal venous plexus. This plexus is juxtaposed to the arterial and venous plexuses associated with the uterus. The morphology of the lumbo-caudal venous plexus suggests that it acts as a "heat sink" for the adjacent tissues. Heat may be transferred to the cool, lumbo-caudal venous plexus from the warm blood in the arterial and venous plexuses supplying the uterus. Heat may also be transferred from adjacent locomotory muscles to the cool lumbo-caudal venous plexus. The countercurrent heat exchanger created by the juxtaposition of the lumbo-caudal venous plexus with the uterovarian arterial plexus is similar in design to that of the countercurrent heat exchanger described for male cetaceans. The functional implications of introducing cool superficial blood into the abdominal cavity of a diving, and locomoting female cetacean are discussed.

Anatomical adaptations of aquatic mammals

“…Heat dissipation is also necessary during exertion or during pregnancy. Vascular adaptations channel excess heat from locomotor muscles or the reproductive organs to large flat surfaces (flukes, flippers, fin) which act as radiators (Rommel et al, 1992(Rommel et al, , 1993(Rommel et al, , 1995(Rommel et al, , 2001. Oral rete allow cetaceans to regulate heat loss from the oral cavity (Werth, 2007, this issue).…”

Functional morphology of venous structures associated with the male and female reproductive systems in Florida manatees (Trichechus manatus latirostris)†

“…Veins from the vertex of this plexus penetrate the abdominal wall and feed cooled blood to an internal plexus before joining the vena cava. Additionally, superficial veins from the peduncle and flukes also feed cooled blood to the internal plexus (after Rommel et al, 1992Rommel et al, , 1993. D: In phocid seals, the superficial veins from the hind flipper, which dive deep within the body near the tail rather than follow the hind limb, feed cooled venous blood to internal plexuses before joining the vena cava (after Rommel et al, 1995).…”

“…Arteries were injected via the aorta. Veins and arteries were identified by dissection, photographed, and drawn to record size, shape, and position (Rommel et al, 1992(Rommel et al, , 1993.…”

“…We have previously shown that cetaceans and phocid seals possess vascular structures to regulate the temperatures of their reproductive organs despite their positions deep within the body (Rommel et al, 1992(Rommel et al, , 1993. Our goal in this study was to investigate the anatomy of Florida manatees (Trichechus manatus latirostris) to determine whether these marine mammals possess vascular structures similar to those found in cetaceans and phocid seals.…”

“…In terrestrial mammals, about 85% of the fetal metabolic heat is transferred by convection via the maternal circulatory system. The remaining 15% of the fetal metabolic heat is transferred by conduction across the uterine wall and through the abdominal wall (the abdominal wall thermal window) to the environment (reviewed in Rommel et al (1993)). Additionally, because the primary locomotory muscles of terrestrial mammals are appendicular, much of the muscle heat of locomotion is transferred to the environment rather than directed into the body cavities.…”