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Biology for Secondary Schools

The dermis has numerous blood capillaries, nerve endings, fat deposits, hair follicles
(roots) and the inner ends of the sweat glands. The structures found in the dermis have
different functions. For example, sweat glands produce a waste fluid called sweat. The
evaporation of sweat cools the body. Erector muscles raise the hairs in the skin. Raised
hair and fat help to conserve heat in the body. Sebaceous glands secrete sebum, an oily
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fluid which prevents cracking of the epidermis. The dermis also contains touch, pain,
pressure and temperature receptors as seen in Table 2.2. The blood vessels assist in
maintaining body temperature and nourishing the skin by supplying food and oxygen
to the skin and remove excretory products.

Table 2.2: Skin receptors
Receptor Location Function
Thermoreceptors In the dermis Sensitive to temperature changes
Low temperature (cold) In the dermis, at the base Sensitive to low temperature
receptors of the dermis
High temperature In the epidermis Sensitive to high temperatures,
receptors (malpighian layer) above 30°C
Touch receptors In the lower part of the Sensitive to touch. They enable
dermis a person to distinguish between
different textures. They are more
concentrated on fingers
Pressure receptors In the lower part of the Sensitive to pressure
dermis, evenly distributed
throughout the skin
Pain receptors Free nerve endings below Sensitive to pain. Protects the
the dermis body against harmful stimulus
by initiating reflex actions

Functions of the skin (b) Excretion: sweat glands produce a
The skin has many functions. These fluid called sweat. Sweat consists
functions include: of water and small quantities of
nitrogenous waste. Salts are also
(a) Protection: the skin protects the excreted through sweat.
body against desiccation, wear due
to friction with external bodies and (c) Temperature regulation: heat
entrance of germs that cause disease. produced by respiration is distributed
The skin also produces melanin which by the blood and is largely lost to
protects the body from ultraviolet the air as blood flows through the
radiation which can cause skin cancer. capillaries in the skin. Heat is lost
from the skin by radiation, convection,
conduction and evaporation.

41 Student’s Book - Form Three

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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 41
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 41 KAMISHNA 23/10/2025 11:52:35 KAMISHNA