Category Zoology

Unlike most warm-blooded land animals, humans have no fur to keep them warm – most of the hair that covers our bodies is very fine. Bare skin is good for keeping the body cool, but in colder climates, humans need to wear clothes to maintain their body temperature.

Hair growth

Each hair grows out of a deep, narrow shaft called a follicle. At the base of the hair, living cells divide and push the hair upwards. Hair does not grow constantly. Instead it grows in spurts and has periods of rest in between.

• Active follicle: The active follicle creates new cells inside the hair root. As these die, they are pushed out to form the shaft, which gets longer and longer.
• Resting stage: The follicle becomes narrower, and the hair stops growing. The hair gets pulled away from the root, losing its blood supply.
• New growth: The follicle begins a new cycle. As people age, their hair becomes thinner because fewer follicles reactivate and grow new hairs.

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One of the skin’s many functions is to make vitamin D, by harnessing the Sun’s rays. However, ultra-violet light from the Sun can damage the skin, so the body produces a substance called melanin to protect it. Melanin is what makes skin look darker or lighter.

Skin colour

Human skin has adapted to suit the conditions on Earth. Near the Equator, the Sun’s rays are most intense. The body produces lots of melanin for maximum protection, so skin is darker. Far from the Equator, less melanin is needed, so skin is lighter.

Dark skin

Lots of melanin is produced by cells called melanocytes.

Pale skin

The skin produces smaller amounts of melanin pigment.

Freckles

Some people have a gene for freckles. These small dots show where s=many melanocyte cells have grouped together. They can become more visible when exposed to sunlight.

Freckled face

Freckles are most common on the face, but they appear on arms and shoulders too.

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The main skin types are hairy or hairless (also called glabrous skin). Most of the body is covered in hairy skin, even though the hair is sometimes too fine for us to see it easily.

Hairy skin

Most of the skin that covers the body is hairy. This type of skin has hair follicles and oily sebaceous glands. The hair on a child’s skin is less visible than on an adult’s.

Glabrous skin

Glabrous skin has no hair. Without any hair follicles, glabrous skin is much smoother than hairy skin. It provides padding for the lips, palms of the hands and soles of the feet.

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When it’s too hot or cold, skin and hair play important roles in keeping the temperature at a safe and comfortable level. A thermostat in the brain’s hypothalamus monitors signals from the body’s sensors. It then sends signals for the body to act to cool itself down or stay warm.

Sweating

Sweat cools the skin as it evaporates.

Keeping cool

If the temperature rises above 38ºC (100.4ºF), sweat glands produce watery sweat to cool the skin. Blood vessels at the skin’s surface widen, so heat can escape easily. Hair relaxes, so heat is released into the air.

Keeping warm

When the temperature drops, skin goes into heat-retention made. Blood vessels become narrower to prevent heat loss from the warm body. Muscles contract to make the skin’s hairs stand upright to trap warm air. These muscles pull on the skin above, making lumps known as goosebumps.

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The human body is almost entirely covered in a layer of skin and hair for protection and warmth. Together, the skin and hair form the body’s largest sensory organ, with an array of sensors that give the brain detailed data about the body’s surroundings. The body has different skin and hair types, depending on where they are and their role.

Basically, the skin is comprised of two layers that cover a third fatty layer. These three layers differ in function, thickness, and strength. The outer layer is called the epidermis; it is a tough protective layer that contains the melanin-producing melanocytes. The second layer (located under the epidermis) is called the dermis; it contains nerve endings, sweat glands, oil glands, and hair follicles. Under these two skin layers is a fatty layer of subcutaneous tissue, known as the subcutis or hypodermis. 

Head hair helps protect the scalp from sun exposure. It also helps insulate the body. It traps air so heat can’t escape from the head. Hair in eyelashes and eyebrows helps keep water and dust out of the eyes. Hairs inside the nostrils of the nose trap dust and germs in the air so they can’t reach the lungs.

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There is one system that extends over the entire surface of your body. Known as the integumentary system, it consists of the skin, hair and nails, which together cover and protect the other body systems against the outside world.

The skin is the largest organ of the body, wrapping it in a waterproof and germproof barrier. It is also essential in helping you to touch and feel things around you, to control the body’s temperature, and to filter out harmful rays from the Sun. Hair and nails provide extra protection for some parts of the body. They grow from the skin and are made from dead cells of a tough substance called keratin.

Skin and hair

The skin has two main layers. The epidermis is the thin, protective outer covering, made up mostly of dead, scaly cells. Beneath it lies the thicker dermis, which is rich in blood vessels and nerve endings to sense pressure, temperature, and pain. Strands of bendy hair cover almost all the body’s surface. Hair grows from follicles, which are deep pits in the skin.

Epidermis

This is the thin, protective outer layer of skin.

Dermis

The dermis is a thick layer packed with glands, nerves, and touch sensors.

Fat layer

This inner lining of fat stores energy and keeps in body heat.

Skin removal

The skin is removed by new cells pushing to the surface where they flatten and die, turning into tough keratin.

Hair

Millions of short hairs grow out of the skin’s surface.

Hair follicles

Hair grows out of pockets called follicles.

Erector muscle

This tiny muscle pulls hairs upright when the body is feeling cold.

Pacinian corpuscles

These receptors at the base of the dermis detect vibrations and pressure.

Sweet gland

These coiled glands ooze moisture on to the skin’s surface where it evaporates to keep the body cool.

Sensory receptors

Different types of receptor react to heat, cold, or touch.

Oil gland

These glands produce a substance called sebum to soften hair and skin.

Cornified layer

The skin’s outer layer is mostly dead and dying keratin-filled cells.

Base layer

New skin cells are formed in the base of the epidermis, ready to move up to the surface.

Finger layer

Fingerlike bulges hold the epidermis in place – and create the ridges that make fingerprints.

Nerves

These networks carry signals between touch receptors and the brain.

Artery

This supplies oxygen and nutrients to the skin.

Protective shield

Skin protects the body, while being flexible enough to let you move around easily. The hair on your head keeps you warm and gives the scalp an extra layer of defence. Fine hairs on the rest of your body make you more sensitive to touch.

Nail structure

Nails are hard plates of dead cells that protect the ends of your fingers and toes. They also help you to grip and pick things up. New cells grow in the root of the nail, and as these cells move forward, they harden and die, it takes about six months for cells to move from the base of a nail to the tip.

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