Feeling Hot, Hot, Hot! How does the weather affect the body?

A surprise September heatwave left lots us hot and bothered last week. But how does our body's physiology (functioning) change with the weather?

Homeostasis

Homeostasis describes the maintenance of the body's internal conditions at a steady state, so that as an organism, we can function optimally. Homeostatic mechanisms control things like our blood glucose levels, fluid balance and body temperature. The ideal internal body temperature is 37°C. At this temperature, the cells that make up all the tissues and organs in our body can carry out their regular functions, keeping us healthy and alive.

Hyperthermia

Once our temperature hits 38°C it is beginning to get too high. If the body cannot bring it down, and the body continues to absorb more heat that it can get rid of, we will go into a state known as hyperthermia which is bad news. Hyperthermia can occur when we over exert ourselves in hot and humid conditions, for example if you tried to run a marathon in an ambient (the air around you) temperature of 35°C, without adequate hydration (fluids) and preparation, such as training, wearing a hat or taking regular breaks in the shade. It can lead to heat cramps, heat exhaustion and even heatstroke. Heatstroke occurs when our internal body temperature hits 40°C and it is a medical emergency, as it can lead to organ failure, seizures or even death.

Hypothermia

If our body temperature drops as low as 35°C this is abnormal, and if the body continues to lose heat faster than it can produce it, hypothermia will occur. Hypothermia happens when the body is exposed to cold weather or submerged in cold water. Hypothermia is also a medical emergency and the body cannot function at such low temperatures, leading to organ failure across the nervous, respiratory and cardiovascular systems, ultimately leading to death.

Thermoregulation

Thermoregulation is the process that maintains your internal temperature in the narrow range required for healthy functioning. This process is controlled by the thermoregulatory centre in the hypothalamus, which is a small structure in the brain. The hypothalamus contains temperature receptors, which measure the temperature of the blood flowing through the brain. The hypothalamus also gathers information sent by nerve impulses from thermoreceptors in the skin, which indicate disturbances in the temperature immediately surrounding the skin. As external or internal body temperature changes, the hypothalamus sends electrical nerve impulses to effectors in the skin, signalling them into action.

How the body decreases temperature

Vasodilation

Vasodilation is the term for when the blood vessels in the body dilate (widen). The arterioles (blood vessels that branch off the arteries) widen, allowing heat from the blood to be lost through the skin due to radiation. You may notice the veins on your hands and feet appear bigger and more prominent on a hot day - this is due to vasodilation. You might also notice that you feel and look flushed when you are hot from exercise - this is because the smallest blood vessels, the capillaries, are dilated making your skin pinker and warm to the touch.

Hair muscles relax

There are tiny muscles in the skin, known as hair erector muscles. When they relax, hair lies flat. When this happens, only a very thin insulating layer of air is trapped by the hairs on the skin surface. This enables more heat to be lost to the environment.

Sweating

The sweat glands produce sweat, which sits as beads of moisture on the skin. The heat energy from the skin then heats up and evaporates the beads of sweat. This leaves the skin cooler as heat energy has been used in the evaporation process.

Learn more

Learn more about how the body adapts to hot weather and what can happen if you get too hot here:

Heatwaves and hot temperatures are hard on the body – but a series of in-built adaptations make it easier to cope

How the body increases temperature

Vasoconstriction

Vasoconstriction is the term for when the blood vessels constrict (narrow). As the arterioles at the skin surface constrict, less heat is lost from the blood through the skin.

Hair muscles contract

The hair erector muscles contract, causing the hairs on the skin surface to stand up straight, trapping a thick layer of insulated air against the skin which increases temperature. You may notice goosebumps when you feel cold - this is the hair erector muscles doing their job!

Shivering

Shivering is caused by involuntary (out of your control) muscle contractions. In order to contract, your muscles require energy. As energy is produced, it releases heat, which is then used to warm the body.

Learn more

Learn more about how the body adapts to cold weather and what can happen if you get too cold here:

What happens to your body when you get left in the cold

Watch this

Here is a simple YouTube video that sums everything up.