Mechanisms Responding To Heat And Cold
Responses to Heat
1. Vasodilation
- What Happens? Arterioles widen, increasing blood flow to the skin.
- Why? More blood at the skin's surface allows heat to be lost to the environment.
- Don't confuse vasodilation with blood vessels moving closer to the skin's surface.
- The vessels remain in place, only their diameter changes.
During exercise, your skin may appear flushed as blood vessels dilate to release excess heat.
2. Sweating
- What Happens? Sweat glands release sweat, which evaporates from the skin.
- Why? Evaporation absorbs heat, cooling the body.
Sweating is highly effective because water has a high latent heat of vaporization, meaning it absorbs a lot of heat as it evaporates.
3. Behavioral Adjustments
- Humans also use behavioral strategies to regulate temperature, such as:
- Seeking shade or shelter in hot conditions.
- Wearing layers of clothing in cold weather.
- Drinking cold or warm beverages to adjust internal temperature.
- In what ways do cultural and technological adaptations (e.g., clothing, heating, and cooling systems) complement biological thermoregulation?
- How might this interplay reflect the broader relationship between biology and technology?
Responses to Cold
1. Vasoconstriction
- What Happens? Arterioles (small blood vessels) $narrow$, reducing blood flow to the skin.
- Why? Less blood at the skin's surface means $less heat is lost$ to the environment.
In cold weather, your skin may appear pale because less blood is flowing near the surface.
2. Shivering
- What Happens? Muscles contract and relax rapidly.
- Why? These contractions generate heat as a byproduct of muscle activity.
Shivering can increase heat production by up to five times the normal rate.
3. Uncoupled Respiration in Brown Adipose Tissue
- What Happens? Brown fat cells use $uncoupled respiration$ to generate heat instead of ATP.
- Why? This process is especially important for infants and small mammals, who are more prone to heat loss.
Brown adipose tissue contains many mitochondria, which give it its characteristic color.
4. Hair Erection (Goosebumps)
- What Happens? Tiny muscles at the base of hair follicles contract, causing hairs to stand upright.
- Why? In furry mammals, this traps a layer of insulating air. In humans, it's a vestigial response with little practical effect.
- Imagine wearing a thick sweater.
- The trapped air between the fibers acts as an insulator, just like the air trapped by erect hairs in animals.
