 Thermoregulation

Thermoregulation is the ability of an organism to keep its body temperature within certain
boundaries, even when the surrounding temperature is very different. A thermoconforming organism,
by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding
the need for internal thermoregulation

Humans and other mammals are homeothermic, able to maintain a relatively constant
body temperature despite widely ranging environmental temperatures. Although the
average human body temperature is 36.7 degrees Celsius (98.2 degrees Fahrenheit),
this temperature varies depending on individual differences, time of day, the stage of
sleep, and the ovulatory cycle in women.
“ Temperature regulation, or thermoregulation, is the balance between heat production
mechanisms and heat loss mechanisms that occur to maintain a constant body
temperature.”

 Types of Thermoregulation (Ectothermy vs. Endothermy)

Thermoregulation in organisms runs along a spectrum from endothermy to ectothermy.

 Mammals Are Endothermic

All mammals are endothermic—that is, they maintain and regulate their own body
temperature, no matter the external conditions. (Cold-blooded vertebrates, like snakes
and turtles, are ectothermic.) Living in widespread environments around the world,
mammals face daily and seasonal fluctuations in temperatures and some—for example,
those indigenous to harsh arctic or tropical habitats—have to deal with extreme cold or
heat. To maintain their correct internal body temperature, mammals must have a way to
produce and conserve body heat in colder temperatures, as well as dissipate excess body
heat in warmer temperatures.

 Heat Conservation and Dissipation

Animals conserve or dissipate heat in a variety of ways.

 Insulation :

In certain climates, endothermic animals have some form of insulation, such as fur, fat,
feathers, or some combination thereof. Animals with thick fur or feathers create an
insulating layer of air between their skin and internal organs.
Examples:Polar bears and seals live and swim in a subfreezing environment, yet they
maintain a constant, warm, body temperature.

The arctic fox uses its fluffy tail as extra insulation when it curls up to sleep in cold
weather.

Arrector

Mammals have a residual effect from shivering and increased muscle activity: arrector
pili muscles create “goose bumps,” causing small hairs to stand up when the individual
is cold; this has the intended effect of increasing body temperature

Mammals use layers of fat to achieve the same end; the loss of significant amounts of
body fat will compromise an individual’s ability to conserve heat.

circulatory systems

Endotherms use their circulatory systems to help maintain body temperature. For
example, vasodilation brings more blood and heat to the body surface, facilitating
radiation and evaporative heat loss, which helps to cool the body.

However, vasoconstriction reduces blood flow in peripheral blood vessels, forcing blood
toward the core and the vital organs found there, conserving heat.

Some animals have adaptions to their circulatory system that enable them to transfer
heat from arteries to veins, thus, warming blood that returns to the heart. This is called a
countercurrent heat exchange; it prevents the cold venous blood from cooling the heart
and other internal organs. This adaption, which can be shut down in some animals to
prevent overheating the internal organs, is found in many animals, including dolphins,
sharks, bony fish, bees, and hummingbirds. In contrast, similar adaptations (as in
dolphin flukes and elephant ears) can help cool endotherms when needed.

 Thermoregulation components:
Thermoregulatory components include:
In cold environments,
mammals employ the following adaptations and strategies to minimize heat loss:

1. Using small smooth muscles (arrector pili in mammals), which are attached to feather or hair
shafts; this distorts the surface of the skin making feather/hair shaft stand erect
(called goose bumps or pimples) which slows the movement of air across the skin and
minimizes heat loss.
2. Increasing body size to more easily maintain core body temperature (warm-blooded animals
in cold climates tend to be larger than similar species in warmer climates (see Bergmann's
Rule))
3. Having the ability to store energy as fat for metabolism
4. Have shortened extremities
5. Have countercurrent blood flow in extremities – this is where the warm arterial blood
travelling to the limb passes the cooler venous blood from the limb and heat is exchanged
warming the venous blood and cooling the arterial (e.g., Arctic wolf[9] or penguins[10][11])
In warm environments
, birds and mammals employ the following adaptations and strategies to maximize heat loss:

1. Behavioural adaptations like living in burrows during the day and being nocturnal
2. Evaporative cooling by perspiration and panting
3. Storing fat reserves in one place (e.g., camel's hump) to avoid its insulating effect
 4. Elongated, often vascularized extremities to conduct body heat to the air

In humans

body temperature is controlled by the thermoregulatory centre in the hypothalamus. It receives input
from two sets of thermoreceptors: receptors in the hypothalamus itself monitor the temperature of the
blood as it passes through the brain (the core temperature), and receptors in the skin (especially on the
trunk) monitor the external temperature. Both sets of information are needed so that the body can
make appropriate adjustments. The thermoregulatory centre sends impulses to several different
effectors to adjust body temperature: Our first response to encountering hotter or colder condition is
voluntary - if too hot, we may decide to take some clothes off, or to move into the shade; if too cold, we
put extra clothes on - or turn the heating up! It is only when these responses are not enough that the
thermoregulatory centre is stimulated. This is part of the autonomic nervous system, so the various
responses are all involuntary. When we get too hot, the heat loss centre in the hypothalamus is
stimulated; when we get too cold, it is the heat conservation centre of the hypothalamus which is
stimulated. Note that some of the responses to low temperature actually generate heat
(thermogenesis), whilst others just conserve heat. Similarly some of the responses to cold actively cool
the body down, while others just reduce heat production or transfer heat to the surface. The body thus
has a range of responses available, depending on the internal and external temperatures.

The thermoregulatory centre normally maintains a set point of 37.5 ± 0.5 °C in most mammals. However
the set point can be altered in special circumstances:

• Fever. Chemicals called pyrogens released by white blood cells raise the set point of the
thermoregulatory centre causing the whole body temperature to increase by 2-3 °C. This helps to kill
bacteria, inhibits viruses, and explains why you shiver even though you are hot

• Hibernation. Some mammals release hormones that reduce their set point to around 5°C while they
hibernate. This drastically reduces their metabolic rate and so conserves their food reserves e.g.
hedgehogs.

• Torpor. Bats and hummingbirds reduce their set point every day while they are inactive. They have a
high surface area/volume ratio, so this reduces heat loss.