Category Human Body

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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Humans could not survive without all 12 of the body systems – groups of body parts that carry out different tasks. The systems communicate continually by passing instructions to each other, so the body works as one.

The 12 systems are the skin, hair and nails, muscular, skeletal (bones), nervous (brain and nerves), cardiovascular (heart and blood), lymphatic (drainage), immune (defence), respiratory (lungs and breathing), digestive (processing food), urinary (kidneys and bladder), reproductive (sex), and endocrine (hormones) systems.

Working together

Body systems are interdependent, which means they rely on each other to function. Some organs belong to more than one system – the pancreas plays a role in digestion but also releases hormones, so it belongs to both the digestive and endocrine systems.

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From babyhood to old age, the body changes as it grows and ages. At the age of around 20-30, humans reach maximum height, and are physically at their strongest. After that, the body very gradually decreases in power with age. However, the brain actually continues to improve over several more years. As it gains more experience, it gets better at analyzing situations and making decisions.

Making a man

Here are the stages of life for a human man. Size and height are the most obvious changes, but there are many other changes on the way to adulthood and old age.

Baby

Learning to stand and walk is a gradual process for growing babies. Babies have a large head and short arms and legs. By around 18 months, they have gained enough strength and muscle control to stand and start to walk.

Toddler

At about age 2, the arms and legs grow so the head no longer looks as large. The brain develops rapidly, and children learn to talk and use their hands with more precision.

Child

From the ages of 5-10, children continue to grow and learn complex physical skills such as riding a bike and swimming. Milk teeth are replaced by adult teeth by the age of about 11.

Teenager

During puberty, hormones trigger major change: height increases, the body takes on more adult features, and emotional swings are common. A surge in hormones produces a big growth spurt.

Young adult

The body reaches its adult height, and bones stop growing. People are physically capable of reproducing – having children.

Adult

Humans are physically strongest between 20 and 35 years of age. Muscle development is complete and body systems continue to function well.

Middle-aged adult

Between the ages of 50 and 70, the skin becomes less stretchy and wrinkles appear. Muscles weaken. Vision and hearing begin to deteriorate.

Elderly adult

A person gets shorter as they age because their spine shortens. Their muscles also get weaker, and together with stiff joints this can make movement slower.

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