ME2 - regulation of body temperature

What is the body's thermoregulatory centre, and how does it work?

The hypothalamus; it compares body temperature to a set-point and triggers heat-conserving or heat-losing responses

What are endotherms, and how do they maintain body temperature?

Animals (mammals, birds) whose high metabolic rate produces enough heat to maintain a relatively constant body temperature above ambient

Where are the thermoreceptors that inform the hypothalamus about body temperature?

In the hypothalamus itself (blood temperature) and in the skin and deeper tissues

Name four responses the hypothalamus can activate to correct body temperature.

Changes in skin blood flow, sweating or panting, shivering, and behaviour

What is heat?

The transfer of thermal energy from a region of higher temperature to a region of lower temperature

What is radiation, as a mode of heat transfer?

Transfer of heat by electromagnetic (mainly infrared) waves between the body and surrounding objects/surfaces

What is conduction, as a mode of heat transfer?

Transfer of heat between objects in direct contact, from the warmer to the cooler object

What is convection, as a mode of heat transfer?

Transfer of heat between a surface and a moving fluid (air or water)

What is evaporation, as a mode of heat transfer?

Heat is removed when water changes from liquid to vapour, taking energy from the body

How does the body transfer heat produced in tissues to the skin surface?

By conduction to nearby tissue and blood, then convection as blood circulates and distributes heat throughout the body

What two general strategies do animals use in cold conditions to maintain body temperature?

Reduce heat loss (insulation, vasoconstriction) and, if needed, increase heat production (shivering, non-shivering thermogenesis)

How does vasoconstriction help reduce heat loss in cold conditions?

It reduces blood flow to the skin, limiting heat transfer to the body surface and environment

What is shivering, and how does it generate heat?

Rapid, involuntary skeletal muscle contractions that increase metabolic activity and generate heat

What is non-shivering thermogenesis?

Heat production without muscle contraction, driven by thyroid hormones and sympathetic nervous system stimulation, mainly via brown adipose tissue

How does brown adipose tissue generate heat?

Its mitochondria dissipate a greater proportion of metabolic energy as heat rather than capturing it as ATP

Which animals have brown adipose tissue, and which lack it?

Present in many newborn mammals (ruminants, rodents, humans); absent in pigs and birds

Why is non-shivering thermogenesis especially important for newborn animals?

Newborns move from the warm uterus to a much colder environment, and evaporation of birth fluids further increases heat loss, so brown adipose tissue helps maintain body temperature

Why is heat loss harder to achieve in hot conditions?

The increased ambient temperature minimises or reverses the temperature gradient between body and environment, reducing the effectiveness of radiation, conduction, and convection

What is sweating, and how does it cool the body?

Sweat glands secrete fluid onto the skin; as it evaporates, heat is removed from the skin and underlying blood

Which domestic species relies most heavily on sweating for cooling?

Horses (cattle use it to a lesser extent; dogs, cats, and pigs rely on it only minimally)

What is panting, and how does it cool the body?

Rapid, shallow breaths that increase airflow over moist respiratory surfaces, promoting evaporative cooling with little effect on blood gases

How does increased blood flow to the tongue and oral/nasal mucosa aid panting?

It brings warm core blood closer to the surface, and tongue enlargement increases surface area for heat exchange

What provides the water for evaporative cooling during panting?

Salivary secretion and moisture on the respiratory mucosa

Why do dogs rely heavily on panting rather than sweating for cooling?

They have relatively few functional sweat glands, so they depend on evaporative cooling from the respiratory tract

In which two ways can the body's temperature set-point change, and what is a household analogy for the hypothalamus's role?

The set-point can shift, e.g. during fever; the hypothalamus works like a thermostat, comparing body temperature to a set-point and triggering corrective responses