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Integumentary System — skin and body temperature

Skin and Skeletal muscle are the major effectors of body temperature.

Here are the major ways in which the skin helps us maintain a stable internal body temperature.  I’ll list them first and then write a bit about each…

  • adipose tissue in the hypodermis is insulation
  • blood vessels in the skin
    • dilate when we are hot
    • constrict when we are cold
  • eccrine sweat glands
  • arrector pili muscle (don’t do much for most of us)

Adipose tissue in hypodermis

Adipose tissue is a good insulator, it does allow heat to move but not very quickly.  By being a good heat barrier adipose tissue under the skin helps a lot to keep our body temperature stable; this is true especially in cold environments.

  • This is one of the reasons that I say women are tougher than men.  Because women tend to have more fat in their hypodermal layers than men do they have better insulation.  This allows women to survive colder conditions better in at least three ways…  1)  More insulation means that the female body does not get cold as fast.  2)  Because less heat is lost it takes less energy to heat the female body.  3) If food is low women have more adipose tissue to burn in order to stay warm.    (interestingly though, most of the women I have known are more sensitive to cold– as in they don’t like it– than the men that I’ve known…  and I don’t know why).

Blood vessels in the skin

When we get hot the blood vessels in our skin can dilate.  This allows more blood from the hotter core of our bodies to come toward the surface and release that heat which helps cool core of the body.  This is why our skin gets flushed sometimes when we exercise or if we are outside on a hot day.

When we get cold the blood vessels in our skin constrict which reverses the above process (goose bumps usually pop up at at the same time).  Less hot blood from the core of our bodies reaches the surface and this helps prevent heat loss from the core of the body.  By the way, sometimes a person’s skin may turn a bit red in cold weather, that is usually because the skin itself is calling for more blood because it is getting too cold.

One of the things that you can gather from the above two examples is that the temperature of the skin may vary quite a bit, but the temperature in the core of a healthy body will remain pretty stable.  That is why the most accurate way to take a person’s temperature is to take a core temperature.

Eccrine sweat glands

Eccrine sweat glands are stimulated to release sweat when the body’s core temperature starts to head towards the upper normal limit.  These glands release a very watery sweat.  Water requires a lot of heat in order to turn into a gas (high heat of vaporization), so when the sweat dries a lot of heat is lost with that sweat.

When we get cold these glands are inhibited.

Eccrine sweat glands are never completely inactive…  there is a certain level of insensible perspiration that occurs all the time and this is one of the reasons that we need to drink water regularly.

Arrector pili muscles (piloerector muscle)

These small muscles that are attached to hair follicles are the source of goose bumps.  When they contract we see noticeable bumps on our skin and it makes any hair there stand up.  The objective here is to warm us by decreasing air flow across our skin, but most of us do not have enough hair for this to be vary effective (although some guys sure do have enough hair to see a benefit from this reaction to cold).

These muscles are also stimulated to contract during times of emotional excitement such as anger, fear, and sexual arousal.  If you’ve ever seen an angry dog with a line of hair standing up on its back this is a very similar reaction, also caused by arrector pili muscles.  In humans and other primates this “ridge” is across the shoulders including the back of the neck, which explains the tingling on the back of the neck that you might feel during a scary movie or other type of fright (if you are not too scared to notice).

Skeletal muscle

Skeletal muscle is the human body’s major heat producer, this is why we shiver when we are cold.  Shivering:  involuntary rhythmic contraction of skeletal muscle (controlled by the brain) simply for heat production.

Brown adipose tissue (brown fat)

Brown adipose tissue (BAT) is a special form of adipose tissue, found mostly in newborn babies.  It appears brown because its cells contain more mitochondria than white adipose tissue cells and the tissue has more blood vessels than white adipose tissue.  Brown adipose tissue is specialized to produce heat in a very interesting way.  When stimulated the mitochondria in these cells produce more heat than ATP.  The increased vasculature helps distribute the heat produced while also bringing more nutrients and oxygen to these very metabolically active cells.

 

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