Question

The question can be answered in a variety of ways. You are encouraged (and in some case required) to use graphs and diagrams as part of your answer, to illustrate your argument or particular concept.

Neobatrachus, Varanus and Camelus walk out of the desert and into a pub in the Australian outback. There, over cold pints of Toohey’s and Cooper’s, they regale other pub patrons with stories how they survived an extremely hot and dry summer season. Fill in their narrative, using your understanding of terrestrial these animals’ thermo- and osmoregulation.

Answer 1

The ability to maintain core temperature as well as volume and composition of body fluids within narrow ranges is a major characteristic of mammals. Yet, the ability to maintain a stable core temperature often relies on physiological responses that perturb the stability of body fluids. A common thermoregulatory mechanism that affects body fluid homeostasis is evaporative cooling, by sweating and/or panting, to dissipate heat from the body when core temperature is elevated. However, these responses result in a reduction of total body water, thereby reducing blood volume and increasing the osmotic pressure of body fluids. While both panting and sweating are highly effective means of preventing core body temperature from increasing, unless the resultant body fluid losses are replaced (by intake of water), hypertonicity, hypovolemia, and circulatory collapse can ensue. Thus, physiological control mechanisms have evolved to limit thermoregulatory body fluid losses once they have become a liability and panting and sweating are inhibited. Thus, mammals will tolerate a higher core temperature to minimize further loss of body water. Osmoreceptors located within the lamina terminalis of the brain suppress panting and sweating when the effective osmotic pressure (tonicity) increases. Selective brain cooling (SBC) has been observed in several domesticated mammals when blood flowing to the brain in the carotid rete is cooled. Such SBC promotes reduced panting and sweating, thereby preserving body water. It is also notable that the behavioural response of drinking water can rapidly invoke panting and sweating that override osmoregulatory inhibitory influences on these responses. The preoptic region of the brain has an important role in osmoregulatory and thermoregulatory mechanisms.