Edexcel IGCSE Biology 复习笔记 2.10.10 Temperature Regulation

Edexcel IGCSE Biology 复习笔记 2.10.10 Temperature Regulation

The Role of Skin in Temperature Regulation

The skin is our largest sense organ

It contains many different receptors that enable us to detect various external stimuli, including touch, pressure, pain, heat and cold

Structures within the skin also play an important role in regulating body temperature (an example of homeostasis)

Human skin contains structures involved in processes that can increase or reduce heat loss to the surroundings

Cooling mechanisms in humans

Vasodilation of skin capillaries

Heat exchange (both during warming and cooling) occurs at the body's surface as this is where the blood comes into closest proximity to the environment

One way to increase heat loss is to supply the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation

Arterioles (small vessels that connect arteries to capillaries) have muscles in their walls that can relax or contract to allow more or less blood to flow through them

During vasodilation, these muscles relax, causing the arterioles near the skin to dilate and allowing more blood to flow through capillaries

This is why pale-skinned people go red when they are hot

Sweating

Sweat is secreted by sweat glands

This cools the skin by evaporation which uses heat energy from the body to convert liquid water into water vapour

Flattening of hairs

The hair erector muscles in the skin relax, causing hairs to lie flat

This stops them from forming an insulating layer by trapping air and allows air to circulate over skin and heat to leave by radiation

Responses in the skin when the body temperature is too high and needs to decrease

Warming mechanisms in humans

Vasoconstriction of skin capillaries

One way to decrease heat loss is to supply the capillaries in the skin with a smaller volume of blood, minimising the loss of heat to the environment via radiation

During vasoconstriction, the muscles in the arteriole walls contract, causing the arterioles near the skin to constrict and allowing less blood to flow through capillaries

Vasoconstriction is not, strictly speaking, a 'warming' mechanism as it does not raise the temperature of the blood but instead reduces heat loss from the blood as it flows through the skin

Shivering

This is a reflex action in response to a decrease in core body temperature

Muscles contract in a rapid and regular manner

The metabolic reactions required to power this shivering generate sufficient heat to warm the blood and raise the core body temperature

Erection of hairs

The hair erector muscles in the skin contract, causing hairs to stand on end

This forms an insulating layer over the skin's surface by trapping air between the hairs and stops heat from being lost by radiation

Responses in the skin when body temperature is too low and needs to increase

The core body temperature of humans is kept close to 37°C

This is very tightly controlled as a change in core body temperature of more than 2°C can be fatal

For this reason, the human body must be able to make a coordinated response to any rise or fall in body temperature

Temperature receptors (also known as thermoreceptors) in the skin and hypothalamus (a part of the brain) can detect minute changes in body temperature

The brain then coordinates a cooling or heating response, depending on what is required

Remember - homeostasis involves the maintenance of a constant internal environment; temperature regulation is an example of homeostasis