The body's largest organ: protector, thermostat, sense organ and waste outlet in one.
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Skin has two main layers over a fat layer. The epidermis is the thin outer layer of flat cells; its outer cells are dead and keep being shed, new ones come from its base, and its cells hold melanin, the pigment that colours skin and absorbs harmful ultraviolet rays. The dermis below is thick and living: it has blood vessels, nerve endings, hair roots, sweat glands, sebaceous (oil) glands and muscles. Beneath lies the subcutaneous fat layer which stores energy and insulates.
Which layer of skin has blood vessels and nerve endings?
The dermis.
What is the function of melanin?
It gives colour to the skin and protects it by absorbing harmful ultraviolet rays from sunlight.
Why is the outer part of the epidermis made of dead cells?
The dead, tough cells form a waterproof, protective barrier and are replaced from below as they wear away.
Skin protects against germs, injury, water loss and ultraviolet rays. It senses touch, pain, heat, cold and pressure through nerve endings. It excretes small amounts of water, salts and urea in sweat. It regulates body temperature: in heat, sweat glands release sweat and the blood vessels in the dermis widen, so more heat is lost; in cold, sweating stops, vessels narrow and hair stands up to trap air. In sunlight the skin also makes vitamin D.
Normal body temperature is 37 °C. Convert it to °F using F = C × 9/5 + 32.
37 × 9/5 + 32 = 98.6 °F.
How does sweating cool the body?
Sweat takes heat from the skin to evaporate, so the body loses heat.
Why do we shiver and get goose pimples in cold weather?
Muscle contractions release heat and the raised hairs trap a layer of warm air next to the skin.
Sebaceous glands make sebum which keeps skin and hair soft and waterproof; if their ducts clog, pimples form. Dirt and sweat can cause skin infections such as boils, scabies and ringworm. Keep skin clean, bathe daily, wear clean clothes, drink water and use sunscreen or covering in strong sun.
What do sebaceous glands secrete? What is its use?
Sebum (oil); it lubricates the skin and hair and makes them water-resistant.
Name two ways to keep the skin healthy.
Any two: daily bathing, clean clothes, enough water, balanced diet, protection from strong sunlight.
Why should we not squeeze pimples?
It can push germs deeper and cause infection and scars.
1. Name the two main layers of skin.
2. Which layer contains sweat glands and hair roots?
3. What is the function of the fat layer under the skin?
4. Name two substances excreted in sweat.
5. Which vitamin does skin make in sunlight?
6. How do blood vessels in the dermis help in cooling?
7. What are sensory receptors in the skin for?
8. Convert 40 °C to °F.
9. Why are people with darker skin better protected from sunburn?
10. Why is skin called the jack of all trades?