Physiological Thermoregulation

Physiological Regulation

1 Panting

2 Sweating

3 Piloerection (GOOSEBUMPS)

4 Brown Adipose Tissue (BAT)

5 Carotid Rete

6 Counter Current Heat Exchange

PANTING

Air moves across the dead space of the respiratory tree - only the large airways (not alveoli)

High humidity = panting is less efficient

PILOERECTION

SWEATING

BROWN ADIPOSE TISSUE

CAROTID RETE

COUNTERCURRENT HEAT EXCHANGE

Humans and horses are rare in that they sweat profusely. Horses lose an estimated 4 gallons of water during hard exercise!

This is an insensible heat transfer, so cannot be detected with a thermometer. Respiration has a similar effect, but loses only water. Sweat contains both water and electrolytes.

Low Humidity = More Efficient Sweating

= Heat loss

Goose Bumps

Cooler environments cause muscle cells to contract, making the hairs stand erect. This reduces air movement across the surface so that heat is not lost as quickly.

In warm weather, muscle cells surrounding hair follicles are relaxed and allow airflow to remove heat.

BAT is thermogenic = generates heat. Mostly found in neonates, it is activated by the sympathetic nervous system to provide extra heat to the core.

Why only in babies? They have a higher surface area to volume ratio, so lose heat at a faster rate in proportion to their bodies than full grown animals.

It's HOT outside

- Cooled blood from the nasal cavity

- Hot blood from the heart is on its way up to the brain in the carotid artery

- Cavernous sinus at base of brain provide space for vessels to branch into an intersecting network = carotid rete

- blood does not mix, but heat from the artery is transferred to the cool vein because of the temperature differential

- cool, arterial blood then travels to the brain

= heat gain

= Brain protection

Hares & Camels have good carotid retes!

Heat is exchanged across blood vessels traveling in opposite directions in the body.

SHUNTING

Muscular sphincters (depicted by A and B) may contract or relax around the blood vessels to control blood flow in that region.

In hot weather, the bands expand and increase flow to the surface, maximizing heat loss.

When cold, the bands constrict to shunt blood away from the surface & extremities. This keeps large volumes of blood from cooling at the surface and then decreasing the core temperature as it re-enters the core.