All about Skin, Hair, and Nails

Covering the outside of your body is a protective layer that consists of your skin, hair, and nails. Skin is the body’s largest organ and it has several functions. It waterproofs the body and forms a barrier against bacteria, viruses and the harmful effects of sunlight. Skin also contains sensors that detect pressure, pain, heat and cold enabling you to feel your surroundings. Nails and hair are extension of the skin.

Skin

It consists of two layers: Dermis and Epidermis. The epidermis is the thin, but tough outer protective layer of the skin. It has a number of layers. The inner thicker dermis contains sensory nerve endings, blood vessels, hair follicles and sweat glands.

Pigmentation- Cells in the epidermis make a pigment called melanin, which protects the body against damage by strong sunlight. People with darker skin produce more melanin than those with lighter skin.

Temperature control- Skin helps the body maintain an even temperature of about 37c. if your body gets too hot, glands release sweat and blood vessels widen to give off heat. To cool the body, blood vessels get narrower.

Epidermis- The upper layer of epidermis consists of dead cells packed with a tough protein called keratin, which are constantly being worn and replaced. Cells in the lower epidermis divide and push new cells towards the surface to replace the lost ones. As they move upwards, these cells fill with keratin

Nails

Nails are hard coverings that protect the ends of fingers and toes. Cells in the root of the nail divide constantly, pushing the nail forward over the nail bed. Finger nails grow at a rate of about 5 mm (0.2 inches) each month, but toe nails grow more slowly.

Nail Structure- Nails are made of the tough protein, keratin. The nails are colorless but appear pink because they rest on a bed served by blood vessels. They grow from active skin cells under skin folds at their base and sides. An opaque crescent called the lunula at the base of each nail contains many of these active cells.

Fingerprints- The undersides of your fingers are covered with tiny epidermal ridges that, together with a sticky film of sweat and natural oils, help you to grip objects. When you touch an object, some of the film sticks to the object so that you leave behind a fingerprint.

Hair

Millions of hairs cover your body. There are two types of hair. Fine vellus hair grows over most of the body. Thicker terminal hair grows on the scalp, and makes up the eyebrows and eyelashes. Hairs grow out of pits in the skin called follicles. Hair on your head grow about 1 cm (0.4) inches a month.

Hair Structure- The shaft of a hair consists of three layers. The cuticle forms overlapping scales on the surface of the hair. Below the cuticle, the cortex forms the main part of the shaft and the medulla is the tough core. Cells in the follicle divide and push upwards to form the shaft of the hair.

Types of hair- Whether the hairs on your head are straight, wavy, or curly depends on the shape of the hair follicles they grow from. Round follicles produce straight hair, oval follicles produce curly hair; and curved follicles produce wavy hair. 

Animal Behaviour

Everything that an animal does, and the way in which behaviour. All animals respond to their surroundings. A cat, for example, will arch its back when threatening a rival, but lower its body when stalking a mouse. An animal’s behaviour enables it to increase its chances of survival and find a mate so that it can pass on its genes to the next generation. Some behaviours are inbuilt, or instinctive; others are learned during the animal’s lifetime.

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Instinctive Behavior

Instinct is a term used to describe behaviours that an animal performs automatically without having to learn them. Instinctive behavior is programmed by an animal’s genes. It consists of unchanging components called fixed-action patterns. The fixed-action pattern often begins when an animal responds to a feature in its surroundings or on another animal, called a sign stimulus.

Web spinning: Many species of spider, including the black widow spider, spin webs in order to trap their insect food. Web spinning is purely instinctive. A spider would not have time in its limited life to learn how to construct such a complex structure.

Sign Stimulus: In the spring, when these freshwater fish breed, the male’s throat and belly turn. If one male intrudes into the territory of another male, its red color acts as a sign stimulous that produces a fixed-action pattern: the occupying fish drives out the intruder.

Egg rolling: Greylag geese nest on the ground. If an egg rolls out of the nest, the female goose automatically reaches out with her neck and pulls the egg back in. By being in the wrong place, he egg acts as a sign stimulus that causes the female to carry out the fixed action pattern of egg rolling.

 

Learned Behaviour

Learning occurs when an animal adapts to its surroundings by changing its behavior. By responding to experiences and adapting to changing conditions, an animal increases its chances of survival. Learning takes time, and animals that are dependent on learned behavior have long lives and large brains.

Trial and Error learning: An animal will associate an action it carries out with a successful result, such as getting food or defeating a rival. This “reward” motivates the animal to alter its behavior to improve the result of future actions.

Learning tool use: Some animals learn to use simple “tools” in order to feed. Sea otters, found off the coast of California, USA, swim on their backs with a stone on their chests on which they smash the shells of clams and mussels to get at the juicy contents. Young otters learn tool use from their parents.

Insight learning: This involves a form of reasoning. Some animals can solve new problems by drawing on past experiences. Chimpanzees, having learned to extract termites or ants from a nest with a stick, can exploit any shape or size of nest.

Imprinting: This is shown by some young animals that make a strong bond with their parent soon after hatching or birth. Young ducklings, for example, stay close to their mother and improve their chances of survival under her protection.