Systems of the Body, Body Systems, Human Anatomy, Anatomy After reading one of the Body Systems - Go take a Quiz! Hair is a "keratinized" threadlike outgrowth from the skin of mammals. A mammal is an animal in the class Mammalia that are distinguished by having hair, a self-regulating body temperature, and in females they have milk-producing mammary glands to feed their young. Back to the word "keratinized;" keratain is an extremely tough protein substance in your hair, fingernails and skin. When a tissue is "keratinized," it becomes hard or horny, therefore it is called horny tissue (hair, skin and nails). Human hair is made of the same stuff (keratin) that is found in human fingernails, animal hooves, feathers, antlers, horns, and claws. The body protein, keratin, grows out of a tiny opening in the skin called a follicle. Human hair is a thin, flexible shaft of horny/hard cells that develops from a cylindrical invagination of the epidermis (top layer of the skin). An invagination means that it is ensheathed in something.

Each hair follicle (tiny sac) consists of a free portion of shaft (scapus pili) and a root (radix pili) embedded within the follicle. While it may seem as though humans are hairless being, this couldn't be further from the truth. All over your body you have hair except of course for your lips and the palms of your hands and soles of your feet. By the time you reach adulthood, you will have at least 5 million hairs growing out of your skin, all over your body. The odd thing is, this is the same as a gorilla, only the gorilla's hair is thick and long. The human hair on the skin is small and thin making it difficult to detect. The shaft of the hair follicle consists of three layers of cells: The cuticle or outermost layer The cortex, forming the main horny portion of the hair The medulla, which is the central axis When it comes to getting goosebumps, even though human hair is small and thin making it difficult, it is easy to detect your hair when you get goosebumps. Then you'll really notice how much hair your have. When your body becomes, frightened or startled, you may develop goosebumps.

They are tiny and temporary bumps on your skin caused by the contraction of the muscles that are attached to the hair follicles. The muscles will tighten on those hairs and WA-LAH, the hairs will stand upright. In animals, the purpose of goosebumps is to fluff up their fur or feathers. This helps them trap air and creates warmth and it also makes them look bigger and scarier. Some hair is curly and some hair is straight. This depends on the actual shape of the follicle (little sac) out of which the hair is growing. Straight hair will lay flat because it is round and grows out of round follicles. Curly hair bends and turns because its cross-section is an oval because it grows out of oval follicles. Some hair is dark, some is white and some hair is completely white or gray. Hair color is dependent on the pigment in the cortex that forms the main horny portion of the hair. Gray or white is simply hair without pigment. This same chemical pigment is what determines our skin color. It is called melanin.

Since hair comes out of skin, if you do not have melanin in your body, this gives you white hair; a little more melanin will create a blonde or strawberry blond appearance; more melanin will make you a red-head; and even more melanin will make brown-hair; and further down the line, even more melanin will make your hair black or even blue-black. JUST THE FACTS: Hair of the eyebrow lasts only 3 - 5 months. Hair of the scalp lasts only 2 - 5 years. About 80 - 100 hairs will fall out of your head every day, and you still have over 100,000 hair follicles left. Even where it "appears" you have no hair on your body, there are about 5 million of them. Hair in each part of your body has a definite period of growth after which it will shed. In the adult human there is a constant and gradual loss and replacement of hair. What are nails made of? | Reference.com What are nails made of? A: Quick Answer Nails are made out of keratin.

Keratin is a tough, fibrous protein that also makes up hair, horns, claws, hooves and feathers. Forms of keratin may also be a component of the silk produced by spiders and caterpillars. Full Answer The cells of the nail begin as epidermal cells below the root of the nail. As more and more cells grow, they are pushed forward and form layers of thin plates that eventually keratinize. These cells are dead, but they are also strong, flexible and permeable. Fingernails grow much more quickly than toenails, and nails generally grow faster during the warm months. Keratin | Define Keratin at Dictionary.com keratin noun 1. a scleroprotein or albuminoid substance, found in the dead outer skin layer, and in horn, hair, feathers, hoofs, nails, claws, bills, etc. Origin of keratin Examples from the Web for keratin Expand The Nuttall Encyclopaedia Edited by Rev. James Wood British Dictionary definitions for keratin Expand noun 1.

a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for keratin Expand n. basic substance of horns, nails, feathers, etc., 1847, from Greek keras (genitive keratos) "horn" (see kerato- ) + chemical suffix -in (2). Online Etymology Dictionary, © 2010 Douglas Harper Scales, Feathers, and Hair - Dictionary definition of Scales, Feathers, and Hair | Encyclopedia.com: FREE online dictionary Scales, Feathers, and Hair COPYRIGHT 2002 The Gale Group Inc. Scales, Feathers, and Hair The term " integument " is applied to any outer covering of an animal.

Basically, it means the skin, although many scientists describe the exoskeleton of arthropods as an integument. An exoskeleton is a coating of hard protein type substances that entierly cover the outside of the animal. It provides a place for muscle attachment. The vertebrate skeleton is internal and muscles attach from the outside. This permits larger growth of the animal. Vertebrate animals have developed some very interesting excrescences, or projections of the skin, some of which are well-known and easily oberved by most people. They are scales, feathers, and hair. Although these characteristics are common among the most vertebrates, they are not all that common in the animal world as a whole. The primary function of the excrescences is protection and insulation. Claws, hooves, and nails are other types of excrescences, but do not provide the animal with the complete body protection it gets from the three main body coverings. All, however, are made from special proteins. The primary protein used by vertebrates is keratin. It occurs as two forms: alpha (more pliable) and beta (more stiff) keratin.

The way in which the keratin is constructed at the molecular level is what determines the structural differences among the various excrescences. Scales Scales occur on fishes and reptiles. Fish scales are made from more than just keratin. They are often derived from bone in the deeper layers of the skin (the middle section of tissues called the mesoderm), which are named the dermal layer. Some have a placoid scale that is formed from bone and covered with enamel, the same covering as the outer portion of a human tooth. Such scales are rough, spiny projections that give the surface of the fish a sandpaper-like feel. A primitive type of scale is the ganoid scale . While this type of scale was common to fishes that lived hundreds of millions of years ago, today it is primarily found in a fish named the gar. Scales of this type are similar to placoid scales, but have an extra coating of a very strong substance called ganoin. It is even stronger than enamel and these gar-type scales are very common in the fossil record. They are believed to have provided a great deal of protection against rocks and abrasive surfaces that fishes may have rubbed against.

It is also possible that they provided some protection against predators, since the scales make it very hard to bite through the skin of fishes. Many scientists believe that the ganoid scale is the precursor or original type scale that led to tooth evolution. The ctenoid scale is found in most modern fishes and is much lighter than the placoid or ganoid scale. Growth rings are an interesting feature of a ctenoid scale. Under a microscope, small circular folds are apparent. There is some debate about the timing of the growth rings. Some researchers once believed they were annual rings, but this has been disproved. The growth rings appear with various timings among varieties of fishes and there are still many questions about what the growth rings may indicate about the life of fishes. In both fishes and reptiles, the scales cover the entire body. The construction of reptile scales, however, is different. Both lizards and snakes have scales over their entire bodies. Many species are identified by the pattern the scales make on the head and body. Reptiles have evolved a unique layer in the skin from their aquatic ancestors.

In order for reptiles to live free from water a waxy layer, the stratum corneum, evolved to keep the animal from drying out on land. These waxy layers lie between the layers that produce the keratin for the scales. The scales are overlapping layers of skin with an inner and outer coating. A unique adaptation is a basal hinge region from which the scales can be somewhat flexible and fold back without falling off. The stratum corneum, or cornified layer, contains beta keratin and in some species both beta and alpha keratin. This provides strength to the scale, which enables reptiles to climb on rocks and slither along various surfaces such as gravel and sand. As the animal grows, every so often epidermis (the outer covering) is sloughed off during a process called shedding. A new epidermis forms and is, in turn, shed as the animal continues to grow. There is a wide variety of scale structures among reptile groups, including turtles and crocodiles who are sometimes excluded by researchers as true reptiles. Colors are achieved by a wide variety of pigments that are incorporated into the scale or that lie in layers of the skin.

Feathers Feathers are interesting excrescences whose origins are not completely understood. It was once believed that only birds had feathers, but later research revealed a striking relationship between dinosaurs and birds. This debate has been recently reduced with the finding of new and important fossils in China . Scientists now see a much closer relationship, if not actual descent, between birds and dinosaurs. Dinosaur fossils discovered in China near the end of the twentieth century revealed a skeleton which is clearly that of a dinosaur but which has impressions of feathers all over the body. The most fascinating discoveries began in the mid 1990s and is ongoing. It is easy to observe the relationship between birds and dinosaurs and their contemporary reptile cousins by looking at a bird. A bird has scales over its legs and have many characters, including skull and skeleton, that are very reptilian. They are highly modified scales composed of beta keratin. A feather is a scale in which a long center shaft, the rachis, is the dominant feature. On either side of the shaft, the keratin is divided into tiny barbs that, under a microscope, look like the close-knit leaves of a fern.

The barbs have tiny hooks, or hamuli, on them, which help the barbs attach to one another and keep them close to each other. These interlocked barbs are called the vane of a feather. There are three basic types of feathers. The contour feathers (tail and flight feathers) are long and used as an aerodynamic device for flight. The plumules (down feathers) are for insulation to keep the bird warm. Their barbs or barbules (smaller versions of barbs) are not closely knit and so the plumules appear fluffy. The feather is built somewhat like a fern frond. There are primary barbs that come of a sturdy shaft. The smaller barbules emerge from the barbs and help hold the feather in shape by interlocking the barbs. This design is crucial for keeping the feather sturdy during flight. The hair feathers (filoplumes) are not as fluffy as the down, but are still used for insulation. Bird feathers are composed of beta keratin. They occur in tracts along the bird's skin called pterylae . These tracts are easily seen on plucked chickens or turkeys used for food.

It surprises many people to learn that the entire bird is not covered with feathers. Hair Hair is one of the most familiar excrescences, since humans are endowed with varying amounts of it. It is a characteristic of mammals. Hair or fur is made from beta keratin and grows from follicles located all over the epidermis. Its primary function is to provide insulation for the animal to keep it warm. However, there are several kinds of hair that provide sensory functions. Whiskers, or vibrissae, are located at places near a mammal's head. The roots of the vibrissae are connected to sensory nerves that are sensitive to movement and so help the animal to detect its environment. The structure of hair is different from that of scales and feathers. A hair is basically a cone of keratin that is derived from keratinized cells in the dermis, or middle layers of skin. The hair is generated and formed in a pit in the skin called the follicle. The hair has an inner and outer sheath. Near the base of each hair attached to the follicle is a small muscle, called an erector pilli. When stimulated, this muscle contracts and pulls the hair straight up. In humans this condition is called goose bumps.

They come as result of the tightening of the skin which helps prevent heat loss. It serves as a warning gesture in cats and dogs and other mammals. As in most animals with scales and feathers, the loss of hair is cyclic. The heavy winter coats of many animals are shed in spring and replaced by lighter summer ones. Shedding may occur again in fall when a warmer coat is needed. Whatever the excrescence, the variety and color of scales, feathers, and hair make watching animals a pleasant activity. The variety of patterns and structures continually provide a wonderful display of life on earth. see also Keratin. Project Beak: Adaptations: Beaks Feed Me Birds don't have teeth, paw, hands, antlers, horns, or spines, but they do have beaks. The beak – also known as the bill – has two parts: the upper mandible and the lower mandible. Kingfisher (Courtesy NEBRASKAland Magazine/ NGPC) The upper mandible is a fancy name for a bird's upper beak or upper bill. The upper mandible grows out of the skull, just as your upper teeth grow out of your skull. The upper mandible doesn't move independently from the skull.

The lower mandible is the scientific name for a bird's lower beak or bill. The lower mandible can move indepently because it's hinged. It can move up and down, just like your jaw. Unlike your teeth, beaks are covered with skin. This skin produces a substance called keratin – the same material feathers, hair, and fingernails are made of. The keratin produced by a bird's beak will dry and condense to make the bill hard and durable. The dried keratin also gives the beak a glossy appearance. As the keratin wears down, it's replaced so the beak will remain sharp. Does having a beak make up for not having teeth, paws, hands, antlers, horns or spines? It has to. Birds must rely on their beaks to carry out many different tasks. The number one use for the beak is to gather or capture food. However, birds also use beaks to pick up building materials and construct their nests. (Think about building a house with your mouth!) But birds use beaks for even more. When they have to, birds use beaks and feet as weapons to defend themselves, their nests, and their chicks.

Birds use beaks for drinking, feeding their young, and preening. Some birds, like the American White Pelican, even grow special structures on their beaks during breeding season to make themselves more attractive (at least, to each other). Beaks come in a wonderful assortment of shapes and sizes, each perfectly suited for that particular bird's favorite foods and typical feeding behaviors. Some beaks are specialized to be just right for certain diets. Birds with these bills use them the same way you use a spoon to eat ice cream or a fork to eat salad. Skin, Hair, and Nails Skin, Hair, and Nails La piel, el cabello y las uñas Your skin is your largest organ. If the skin of a typical 150-pound (68-kilogram) adult male were stretched out flat, it would cover about 2 square yards (1.7 square meters) and weigh about 9 pounds (4 kilograms). Skin protects the network of muscles, bones , nerves, blood vessels , and everything else inside our bodies. Eyelids have the thinnest skin, the soles of our feet the thickest. Hair is actually a modified type of skin.

Hair grows everywhere on the human body except the palms of the hands, soles of the feet, and lips. Hair grows more quickly in summer than winter, and more slowly at night than during the day. Like hair, nails are a type of modified skin — and they're not just for beauty. Nails protect the sensitive tips of our fingers and toes. Human nails are not necessary for living, but they do provide support for the tips of the fingers and toes, protect them from injury, and aid in picking up small objects. Without them, we'd have a hard time scratching an itch or untying a knot. Nails can be an indicator of a person's general health, and illness often affects their growth. Skin Basics Skin is essential to a person's survival. It forms a barrier that prevents harmful substances and microorganisms from entering the body. It protects body tissues against injury. Our skin also controls the loss of life-sustaining fluids like blood and water, helps us regulate body temperature through perspiration, and protects us from the sun's damaging ultraviolet rays. Without the nerve cells in our skin, we couldn't feel warmth, cold, or other sensations.

Our skin can also respond to situations and emotions: Muscles in the skin called erector pili contract to make the hairs on our skin stand up straight (goosebumps) when we are cold or frightened — for insulation and protection. Every square inch of skin contains thousands of cells and hundreds of sweat glands, oil glands, nerve endings, and blood vessels. Skin is made up of three layers: the epidermis (pronounced: ep-ih-DUR-mis), dermis, and the subcutaneous (pronounced: sub-kyoo-TAY-nee-us) tissue. continue Skin Cells and Layers The upper layer of our skin, the epidermis, is the tough, protective outer layer. It is about as thick as a sheet of paper over most parts of the body. The epidermis has four layers of cells that are constantly flaking off and being renewed. In these four layers are three special types of cells: Melanocytes (pronounced: meh-LAH-nuh-sites) produce melanin, the pigment that gives skin its color. All people have roughly the same number of melanocytes; the more melanin that is produced, the darker the skin.

Exposure to sunlight increases the production of melanin, which is why people get suntanned or freckled. Keratinocytes (pronounced: ker-uh-TIH-no-sites) produce keratin, a type of protein that is a basic component of hair and nails. Keratin is also found in skin cells in the skin's outer layer, where it helps create a protective barrier. Langerhans (pronounced: LAHNG-ur-hanz) cells help protect the body against infection. Because the cells in the epidermis are completely replaced about every 28 days, cuts and scrapes heal quickly. Below the epidermis is the next layer of our skin, the dermis, which is made up of blood vessels, nerve endings, and connective tissue. The dermis nourishes the epidermis. Without certain molecules in the dermis, our skin wouldn't stretch when we bend or reposition itself when we straighten up. These two types of fibers in the dermis, collagen and elastin, help the skin stretch and reposition itself when we move. Collagen is strong and hard to stretch and elastin, as its name suggests, is elastic.

In older people, some of the elastin-containing fibers degenerate, which is one reason why the skin looks wrinkled (most wrinkles are caused by sun exposure, though!). The dermis also contains a person's sebaceous glands. These glands, which surround and empty into our hair follicles and pores, produce an oil called sebum (pronounced: SEE-bum) that lubricates the skin and hair. Sebaceous glands are found mostly in the skin on the face, upper back, shoulders, and chest. Most of the time, the sebaceous glands make the right amount of sebum. As a person's body begins to mature and develop during the teenage years, though, hormones stimulate the sebaceous glands to make more sebum. This can lead to acne when pores become clogged by too much sebum and too many dead skin cells. Later in life, these glands produce less sebum, which contributes to dry skin in older people. The bottom layer of our skin, the subcutaneous tissue, is made up of connective tissue, sweat glands, blood vessels, and cells that store fat. This layer helps protect the body from blows and other injuries and helps it hold in body heat.

There are two types of sweat-producing glands. The eccrine (pronounced: EH-krun) glands are found everywhere in our bodies, although they are mostly in the forehead, palms, and soles of the feet. By producing sweat, these glands help regulate body temperature, and waste products are excreted through them. The other type of sweat-producing gland, the apocrine glands, develop at puberty and are concentrated in the armpits and pubic region. The sweat from the apocrine glands is thicker than that produced by the eccrine glands. Although this sweat doesn't smell, when it mixes with bacteria on the skin's surface, it can cause body odor. A normal, healthy adult secretes about 1 pint (about half a liter) of sweat daily, but this may be increased by physical activity, fever, or a hot environment. previous continue Hair Basics The hair on our heads isn't just there for looks. It keeps us warm by preserving heat. The hair in our nose, ears, and around our eyes protects these sensitive areas of the body from dust and other small particles. Eyebrows and eyelashes protect our eyes by decreasing the amount of light and particles that go into them.

The fine hair that covers our bodies provides warmth and protects our skin. Hair also cushions the body against injury. Human hair consists of the hair shaft, which projects from the skin's surface, and the root, a soft thickened bulb at the base of the hair embedded in the skin. The root ends in the hair bulb. The hair bulb sits in a sac-like pit in the skin called the follicle, from which the hair grows. At the bottom of the follicle is the papilla, where hair growth actually takes place. The papilla contains an artery that nourishes the root of the hair. As cells multiply and produce keratin to harden the structure, they are pushed up the follicle and through the skin's surface as a shaft of hair. Each hair has three layers: the medulla at the center, which is soft; the cortex, which surrounds the medulla and is the main part of the hair; and the cuticle, the hard outer layer that protects the shaft. Hair grows by forming new cells at the base of the root. These cells multiply to form a rod of tissue in the skin. The rods of cells move upward through the skin as new cells form beneath them.

As they move up, they are cut off from their supply of nourishment and start to form a hard protein called keratin in a process called keratinization (pronounced: ker-uh-tuh-nuh-ZAY-shun). As this process occurs, the hair cells die. The dead cells and keratin form the shaft of the hair. Each hair grows about ¼ inch (about 6 millimeters) every month and keeps on growing for up to 6 years. The hair then falls out and another grows in its place. The length of a person's hair depends on the length of the growing phase of the follicle. Follicles are active for 2 to 6 years; they rest for about 3 months after that. A person becomes bald if the scalp follicles become inactive and no longer produce new hair. Thick hair grows out of large follicles; narrow follicles produce thin hair. The color of a person's hair is determined by the amount and distribution of melanin in the cortex of each hair (the same melanin that's found in the epidermis). Hair also contains a yellow-red pigment; people who have blonde or red hair have only a small amount of melanin in their hair.

Hair becomes gray when people age because pigment no longer forms. previous continue All About Nails Nails grow out of deep folds in the skin of the fingers and toes. As epidermal cells below the nail root move up to the surface of the skin, they increase in number, and those closest to the nail root become flattened and pressed tightly together. Each cell is transformed into a thin plate; these plates are piled in layers to form the nail. As with hair, nails are formed by keratinization. When the nail cells accumulate, the nail is pushed forward. The skin below the nail is called the matrix. The larger part of the nail, the nail plate, looks pink because of the network of tiny blood vessels in the underlying dermis. The whitish crescent-shaped area at the base of the nail is called the lunula. Fingernails grow about three or four times as quickly as toenails. Like hair, nails grow more rapidly in summer than in winter. If a nail is torn off, it will regrow if the matrix is not severely injured. White spots on the nail are sometimes due to temporary changes in growth rate. Skin Problems Some of the things that can affect the skin, nails, and hair are described below.

Dermatitis Medical experts use the term dermatitis (pronounced: dur-mah-TY-tus) to refer to any inflammation that might be associated with swelling, itching, and redness of the skin. There are many types of dermatitis, including: Atopic dermatitis is also called eczema . It's a common, hereditary dermatitis that causes an itchy rash primarily on the face, trunk, arms, and legs. It commonly develops in infancy, but can also appear in early childhood. It may be associated with allergic diseases such as asthma or food, seasonal, or environmental allergies. Contact dermatitis occurs when the skin comes into contact with an irritating substance or a substance that a person is allergic to. The best-known cause of contact dermatitis is poison ivy. But lots of other things cause contact dermatitis, including chemicals found in laundry detergent, cosmetics, and perfumes, and metals like jewelry, nickel plating on a belt buckle, or the back of the buttons on your jeans. Seborrheic dermatitis, an oily rash on the scalp, face, chest, and back, is related to an overproduction of sebum from the sebaceous glands. This condition is common in teens.

Bacterial Skin Infections Impetigo . Impetigo (pronounced: im-puh-TY-go) is a bacterial infection that results in a honey-colored, crusty rash, often on the face near the mouth and nose. Cellulitis . Cellulitis (pronounced: sell-yuh-LY-tus) is an infection of the skin and subcutaneous tissue that typically occurs when bacteria are introduced through a puncture, bite, or other break in the skin. The affected area is usually warm and tender and has some redness. Streptococcal and staphylococcal infections. These two kinds of bacteria are the main causes of cellulitis and impetigo. Certain types of these bacteria are also responsible for distinctive rashes on the skin, including the rashes associated with scarlet fever and toxic shock syndrome . Fungal Infections Fungal Infections of the Skin and Nails Candidal dermatitis. A warm, moist environment, such as that found in the folds of the skin in the diaper area of infants, is perfect for growth of the yeast Candida. Yeast infections of the skin in older children, teens, and adults are less common. Tinea infection ( ringworm ).

Ringworm, which isn't a worm at all, is a fungus infection that can affect the skin, nails, or scalp. Tinea (pronounced: TIH-nee-uh) fungi can infect the skin and related tissues of the body. The medical name for ringworm of the scalp is tinea capitis; ringworm of the body is called tinea corporis; and ringworm of the nails is called tinea unguium. With tinea corporis, the fungi can cause scaly, ring-like lesions anywhere on the body. Tinea pedis ( athlete's foot ). This infection of the feet is caused by the same types of fungi (called dermatophytes) that cause ringworm. Athlete's foot is commonly found in adolescents and is more likely to happen during warm weather. Other Skin Problems Parasitic infestations. Parasites (usually tiny insects or worms) can feed on or burrow into the skin, often resulting in an itchy rash. Scabies and lice are examples of parasitic infestations. Both are contagious — meaning they can be easily caught from other people. Viral infections.

Many viruses cause characteristic rashes on the skin, including varicella (pronounced: var-ih-SEL-uh), the virus that causes chicken pox and shingles; herpes simplex, which causes cold sores; human papillomavirus (HPV), the virus that causes warts ; and a host of others. Acne (acne vulgaris). Acne is the single most common skin condition in teens. Some degree of acne is seen in 85% of adolescents, and nearly all teens have the occasional pimple, blackhead, or whitehead. Skin cancer. Skin cancer is rare in children and teens, but good sun protection habits established during these years can help prevent skin cancers like melanoma (pronounced: mel-uh-NO-ma, a serious form of skin cancer that can spread to other parts of the body) later in life, especially among fair-skinned people who sunburn easily. In addition to these diseases and conditions, the skin can be injured in a number of ways. Minor scrapes, cuts, and bruises heal quickly on their own, but other injuries — severe cuts and burns, for example — require medical treatment.

Disorders of the Scalp and Hair Tinea capitis, a type of ringworm, is a fungal infection that forms a scaly, ring-like lesion in the scalp. It's contagious and common among school-age children. Alopecia (pronounced: ah-luh-PEE-sha) is an area of hair loss. Ringworm is a common cause of temporary alopecia in children. Alopecia can also be caused by tight braiding that pulls on the hair roots (this condition is called traction alopecia). Alopecia areata (where a person's hair falls out in round or oval patches on the scalp) is a less common condition that can sometimes affect teens. Anatomy and Physiology of Animals/The Skin - Wikibooks, open books for an open world Anatomy and Physiology of Animals/The Skin From Wikibooks, open books for an open world Jump to: navigation , search original image by Fran-cis-ca cc by The skin is the first of the eleven body systems to be described. Each chapter from now on will cover one body system. The skin, sometimes known as the Integumentary System is, in fact, the largest organ of the body. It has a complex structure, being composed of many different tissues.

It performs many functions that are important in maintaining homeostasis in the body. Probably the most important of these functions is the control of body temperature. The skin also protects the body from physical damage and bacterial invasion. The skin has an array of sense organs which sense the external environment, and also cells which can make vitamin D in sunlight. The skin is one of the first systems affected when an animal becomes sick so it is important for anyone working with animals to have a sound knowledge of the structure and functioning of the skin so they can quickly recognise signs of disease. Contents After completing this section, you should know: the general structure of the skin the function of the keratin deposited in the epidermis the structure and function of keratin skin structures including calluses, scales, nails, claws, hoofs and horns that antlers are not made either of keratin or in the epidermis the structure of hairs the structure of the different types of feathers and the function of preening the general structure and function of sweat, scent, preen and mammary glands the basic functions of the skin in sensing stimuli, temperature control and production of vitamin D the mechanisms by which the skin regulates body temperature The Skin[ edit ] Skin comes in all kinds of textures and forms.

There is the dry warty skin of toads and crocodiles, the wet slimy skin of fish and frogs, the hard shell of tortoises and the soft supple skin of snakes and humans. Mammalian skin is covered with hair, that of birds with feathers, and fish and reptiles have scales. Pigment in the skin, hairs or feathers can make the outer surface almost any colour of the rainbow. Skin is one of the largest organs of the body, making up 6-8% of the total body weight. It consists of two distinct layers. The top layer is called the epidermis and under that is the dermis' The epidermis is the layer that bubbles up when we have a blister and as we know from this experience, it has no blood or nerves in it. The cells at the base of the epidermis continually divide and push the cells above them upwards. As these cells move up they die and become the dry flaky scales that fall off the skin surface. The cells in the epidermis die because a special protein called keratin is deposited in them. Keratin is an extremely important substance for it makes the skin waterproof.

Without it land vertebrates like reptiles, birds and mammals would, like frogs, be able to survive only in damp places. Skin Structures Made Of Keratin[ edit ] Claws, Nails and Hoofs[ edit ] Reptiles, birds and mammals all have nails or claws on the ends of their toes. They protect the end of the toe and may be used for grasping, grooming, digging or in defense. They are continually worn away and grow continuously from a growth layer at their base (see diagram 5.2). Diagram 5.2 - A carnivore’s claw Hoofs are found in sheep, cows, horses etc. otherwise known as ungulate mammals. These are animals that have lost toes in the process of evolution and walk on the “nails” of the remaining toes. The hoof is a cylinder of horny material that surrounds and protects the tip of the toe (see diagram 5.3). Diagram 5.3 - A horse’s hoof Horns And Antlers[ edit ] True horns are made of keratin and are found in sheep, goats and cattle. They are never branched and, once grown, are never shed.

They consist of a core of bone arising in the dermis of the skin and are fused with the skull. The horn itself forms as a hollow cone-shaped sheath around the bone (see diagram 5.4). Diagram 5.4 - A horn The antlers of male deer have quite a different structure. They are not formed in the epidermis and do not consist of keratin but are entirely of bone. They are shed each year and are often branched, especially in older animals. When growing they are covered in skin called velvet that forms the bone. Later the velvet is shed to leave the bony antler. The velvet is often removed artificially to be sold in Asia as a traditional medicine (see diagram 5.5). Diagram 5.5 - A deer antler Other animals have projections on their heads that are not true horns either. The horns on the head of giraffes are made of bone covered with skin and hair, and the ‘horn’ of a rhinoceros is made of modified and fused hair-like structures. Hair[ edit ] Hair is also made of keratin and develops in the epidermis.

It covers the body of most mammals where it acts as an insulator and helps to regulate the temperature of the body (see below). The colour in hairs is formed from the same pigment, melanin that colours the skin. Coat colour may help camouflage animals and sometimes acts to attract the opposite sex. Diagram 5.6 - A hair Hairs lie in a follicle and grow from a root that is well supplied with blood vessels. The hair itself consists of layers of dead keratin - containing cells and usually lies at a slant in the skin. A small bundle of smooth muscle fibres (the hair erector muscle) is attached to the side of each hair and when this contracts the hair stands on end. This increases the insulating power of the coat and is also used by some animals to make them seem larger when confronted by a foe or a competitor(see diagram 5.6). The whiskers of cats and the spines of hedgehogs are examples of special types of hairs. Feathers[ edit ] The lightness and stiffness of keratin is also a key to bird flight. In the form of feathers it provides the large airfoils necessary for flapping and gliding flight.

In another form, the light fluffy down feathers,also made of keratin, are some of the best natural insulators known. This superior insulation is necessary to help maintain the high body temperatures of birds. Diagram 5.7 - A Contour Feather Countour feathers are large feathers that cover the body, wings and tail. They have an expanded vane that provides the smooth, continuous surface that is required for effective flight. This surface is formed by barbs that extend out from the central shaft. If you look carefully at a feather you can see that on either side of each barb are thousands of barbules that lock together by a complex system of hooks and notches. if this arrangement becomes disrupted, the bird uses its beak to draw the barbs and barbules together again in an action known as preening (see diagram 5.7). Diagram 5.8 - A Down Feather Diagram 5.9 - A Pin Feather Down feathers are the only feathers covering a chick and form the main insulation layer under the contour feathers of the adult. They have no shaft but consist of a spray of simple, slender branches (see diagram 5.8).

Pin feathers have a slender hair-like shaft often with a tiny tuft of barbs on the end. They are found between the other feathers and help tell a bird how its feathers are lying (see diagram 5.9). Skin Glands[ edit ] Glands are organs that produce and secrete fluids. They are usually divided into two groups depending upon whether or not they have channels or ducts to carry their products away. Glands with ducts are called exocrine glands and include the glands found in the skin as well as the glands that produce digestive enzymes in the gut. Endocrine glands have no ducts and release their products (hormones) directly into the blood stream. The pituitary and adrenal glands are examples of endocrine glands. Most vertebrates have exocrine glands in the skin that produce a variety of secretions. The slime on the skin of fish and frogs is mucus produced by skin glands and some fish and frogs also produce poison from modified glands. In fact the skin glands of some frogs produce the most poisonous chemicals known. Reptiles and birds have a dry skin with few glands. The preen gland, situated near the base of the bird’s tail, produces oil to help keep the feathers in good condition.

Mammals have an array of different skin glands. These include the wax producing, sweat, sebaceous and mammary glands. Wax producing glands are found in the ears. Sebaceous glands secrete an oily secretion into the hair follicle. This secretion, known as sebum, keeps the hair supple and helps prevent the growth of bacteria (see diagram 5.6). Sweat glands consist of a coiled tube and a duct leading onto the skin surface. Their appearance when examined under the microscope inspired one of the first scientists to observe them to call them “fairies’ intestines” (see diagram 5.1). Sweat contains salt and waste products like urea and the evaporation of sweat on the skin surface is one of the major mechanisms for cooling the body of many mammals. Horses can sweat up to 30 litres of fluid a day during active exercise, but cats and dogs have few sweat glands and must cool themselves by panting. Scent in the sweat of many animals is used to mark territory or attract the opposite sex. Mammary glands are only present in mammals.

They are thought to be modified sebaceous glands and are present in both sexes but are rarely active in males (see diagram 5.10). The number of glands varies from species to species. They open to the surface in well-developed nipples. Milk contains proteins, sugars, fats and salts, although the exact composition varies from one species to another. Diagram 5.10 - A Mammary Gland The Skin And Sun[ edit ] A moderate amount of UV in sunlight is necessary for the skin to form vitamin D. This vitamin prevents bone disorders like rickets to which animals reared indoors are susceptible. Excessive exposure to the UV in sunlight can be damaging and the pigment melanin, deposited in cells at the base of the epidermis, helps to protect the underlying layers of the skin from this damage. Melanin also colours the skin and variations in the amount of melanin produces colours from pale yellow to black. Sunburn And Skin Cancer[ edit ] Excess exposure to the sun can cause sunburn. This is common in humans, but light skinned animals like cats and pigs can also be sunburned, especially on the ears. Skin cancer can also result from excessive exposure to the sun.

As holes in the ozone layer increase exposure to the sun’s UV rays, so too does the rate of skin cancer in humans and animals. The Dermis[ edit ] The underlying layer of the skin, known as the dermis, is much thicker but much more uniform in structure than the epidermis (see diagram 5.1). It is composed of loose connective tissue with a felted mass of collagen and elastic fibres. It is this part of the skin of cattle and pigs etc. that becomes commercial leather when treated,. The dermis is well supplied with blood vessels, so cuts and burns that penetrate down into the dermis will bleed or cause serious fluid loss. There are also numerous nerve endings and touch receptors in the dermis because, of course, the skin is sensitive to touch, pain and temperature. When looking at a section of the skin under the microscope you can see hair follicles, sweat and sebaceous glands dipping down into the dermis. However, these structures do not originate in the dermis but are derived from the epidermis. In the lower levels of the dermis is a layer of fat or adipose tissue (see diagram 5.1).

This acts as an energy store and is an excellent insulator especially in mammals like whales with little hair. The Skin And Temperature Regulation[ edit ] Vertebrates can be divided into two groups depending on whether or not they control their internal temperature. Amphibia (frogs) and reptiles are said to be”cold blooded” (poikilothermic) because their body temperature approximately follows that of the environment. Birds and mammals are said to be warm blooded (homoiothermic) because they can maintain a roughly constant body temperature despite changes in the temperature of the environment. Heat is produced by the biochemical reactions of the body (especially in the liver) and by muscle contraction. Most of the heat loss from the body occurs via the skin. It is therefore not surprising that many of the mechanisms for controlling the temperature of the body operate here. Reduction Of Heat Loss[ edit ] When an animal is in a cold environment and needs to reduce heat loss the erector muscles contract causing the hair or feathers to rise up and increase the layer of insulating air trapped by them (see diagram 5.11a).

Diagram 5.11a) Hair muscle relaxed...............Diagram 5.11b) Hair muscle contracted Heat loss from the skin surface can also be reduced by the contraction of the abundant blood vessels that lie in the dermis. This takes blood flow to deeper levels, so reducing heat loss and causing pale skin (see diagram 5.12a). Diagram 5.12a) Reduction of heat loss by skin Shivering caused by twitching muscles produces heat that also helps raise the body temperature. Increase Of Heat Loss[ edit ] There are two main mechanisms used by animals to increase the amount of heat lost from the skin when they are in a hot environment or high levels of activity are increasing internal heat production. The first is the expansion of the blood vessels in the dermis so blood flows near the skin surface and heat loss to the environment can take place. The second is by the production of sweat from the sweat glands (see diagram 5.12b). The evaporation of this liquid on the skin surface produces a cooling effect. The mechanisms for regulating body temperature are under the control of a small region of the brain called the hypothalamus. This acts like a thermostat.

Diagram 5.12b) - Increase of heat loss by skin Heat Loss And Body Size[ edit ] The amount of heat that can be lost from the surface of the body is related to the area of skin an animal has in relation to the total volume of its body. Small animals like mice have a very large skin area compared to their total volume. This means they tend to loose large amounts of heat and have difficulty keeping warm in cold weather. They may need to keep active just to maintain their body temperature or may hibernate to avoid the problem. Large animals like elephants have the opposite problem. They have only a relatively small skin area in relation to their total volume and may have trouble keeping cool. This is one reason that these large animals tend to have sparse coverings of hair. Summary[ edit ] Skin consists of two layers: the thin epidermis and under it the thicker dermis. The Epidermis is formed by the division of base cells that push those above them towards the surface where they die and are shed. Keratin, a protein, is deposited in the epidermal cells. It makes skin waterproof. Various skin structures formed in the epidermis are made of keratin.

These include: claws, nails, hoofs, horn, hair and feathers. Various Exocrine Glands (with ducts) formed in the epidermis include sweat, sebaceous, and mammary glands. Melanin deposited in cells at the base of the epidermis protects deeper cells from the harmful effects of the sun. The Dermis is composed of loose connective tissue and is well supplied with blood. Beneath the dermis is insulating adipose tissue. Body Temperature is controlled by: sweat, hair erection, dilation and contraction of dermal capillaries and shivering. Are porcupine quills like hairs or like feathers? | NCPR News Are porcupine quills like hairs or like feathers? Porcupine quills are hollow, like feathers, and are made from the same material, but... Jan 08, 2015 — by Natural Selections , in Canton, NY North American porcupine.

Photo: Mary Harrsch , Creative Commons, some rights reserved Listen to this story Jan 08, 2015 — Porcupine quills are hollow, like feathers, and are made from the same material, but then so are hairs, and fingernails, and claws and scales. The quill is a unique adaptation of one of nature's commonest substances and it varies even among porcupines. African porcupines can weigh as much as 60 pounds and have quills as thick as soda straws. Martha Foley and Dr. Curt Stager talk about "prickly" matters. Martha Foley: We had a listener question about porcupine quills, and his starting point was his dog—who has the most intimate relationship with porcupines—but he was thinking about the quills and noted how much they are like feathers. Curt Stager: That is a neat observation, and I’ve never thought of it, but that definitely makes sense. Actually feathers and porcupine quills are made of the same material. Same thing as hair, actually, porcupine quills are modified hairs. MF: They’re considered hair?

CS: Yeah, it’s a protein outgrowth from the skin, same as feathers, it’s keratin. MF: So would feathers be considered hair, too? CS: You could almost say it would be like a modified hair, if you go back in the evolutionary time scale, and you go back to the Mesozoic era, when the reptile-type things were giving rise to bird-like things and to mammals, reptiles actually have protein outgrowths on their skin too, the scales, and it’s speculated that hair and feathers would have both arisen from some sort of scale, which is made of the same keratin material. Our fingernails and animal claws are made of the same stuff. MF: Okay, but back to quills. That’s our starting point. But they are. . . the base definitely looks feather-like. African brush tailed porcupine. Photo: Glamhag , Creative Commons, some rights reserved CS: Yeah, and it’s this hollow shaft with this pulpy interior.

Actually, come to think of it, this comparison between porcupine quills and feathers is interesting, because there actually is a type of porcupine in Africa, they’re called a brush tailed porcupine, where if you look closely at the quills, they have little saw-tooth feathery barbs coming out the side of them. MF: You mean, more than one. Ours sort of have one barb at the end. CS: Right, ours are barbed, but the barbs are kind of flat; they’re kind of hard to see, and they point down the shaft so it sort of anchors the quill into you. MF: Very nicely, yeah. CS: These, if you look at the quill, running down either side of the shaft, it would look a little bit fuzzy; it’s not really soft, and these are kind of like saw-teeth, so it hurts more I guess when it goes in. But they’re not pointing downwards and you could say, “boy that looks a little featherlike, too.” MF: Are there lots of different porcupine quills? You depend on NCPR to stay informed and we depend on you to help pay for that connection.

Click to donate today. The crested porcupine (shown here living in captivity) can grow as large as 60 pounds. Photo: C-8 , Creative Commons, some rights reserved CS: Yes, there are lots of kinds of porcupines. They live pretty much all over the world, all different species. One of the biggest ones in Africa is like 60-something pounds. MF: Wow, like a big beaver, or something. CS: Yeah, I actually saw one driving down the road at night in East Africa, it was really scary. It was like seeing I don’t know what—a bush walking across the road with these long quills. MF: Long quills? Keratin - definition of keratin by The Free Dictionary Keratin - definition of keratin by The Free Dictionary (kĕr′ə-tĭn) n. 1. Any of a class of filamentous proteins that are abundant in the cytoskeleton of vertebrate epithelial cells and are the main constituents of the outer layer of skin and tough epidermal structures such as hair, nails, hooves, feathers, and claws. 2. Material composed principally of keratin proteins.

[Greek keras, kerāt-, horn; see ker-1 in the Appendix of Indo-European roots + -in .] ke·rat′i·nous (kə-răt′n-əs) adj. keratin ceratin n (Zoology) a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc ker•a•tin (ˈkɛr ə tɪn) n. a tough, insoluble protein that is the main constituent of hair, nails, horn, hoofs, etc., and of the outermost layer of skin. [1840–50; < Greek kerat-, s. of kéras horn + -in 1] ker`a•tin•i•za′tion, n. ker′a•tin•ize`, vb ke•rat•i•nous (kəˈræt n əs) adj. ker·a·tin (kĕr′ə-tĭn) A tough, fibrous protein that is the main structural component of hair, nails, horns, feathers, and hooves. Did You Know?

Nature ingeniously uses the same chemicals to perform a wide variety of functions in living things. An example is the group of closely related proteins known as the keratins. When nature wants something hard and tough for an animal, it turns to keratins. Your nails and hair are made mostly of a kind of keratin, and so are a dog's claws, a bird's beak, and a goat's horns. Even the hard material called baleen that some whales have in their mouths to help them eat is made of a variety of keratin. All proteins are strings of amino acids, and the keratins' secret is the amino acid known as cysteine. This amino acid tends to form strong bonds with other cysteines in the protein. The different keratins vary in hardness, depending on how many cysteine bonds are present. The bonds are what make the keratins tough as, well, nails. keratin A hard, waterproof protein found in the epidermis, hair, and nails.

ThesaurusAntonymsRelated WordsSynonymsLegend: Keratin layer - definition of keratin layer by The Free Dictionary Keratin layer - definition of keratin layer by The Free Dictionary (kĕr′ə-tĭn) n. 1. Any of a class of filamentous proteins that are abundant in the cytoskeleton of vertebrate epithelial cells and are the main constituents of the outer layer of skin and tough epidermal structures such as hair, nails, hooves, feathers, and claws. 2. Material composed principally of keratin proteins. [Greek keras, kerāt-, horn; see ker-1 in the Appendix of Indo-European roots + -in .] ke·rat′i·nous (kə-răt′n-əs) adj. keratin ceratin n (Zoology) a fibrous protein that occurs in the outer layer of the skin and in hair, nails, feathers, hooves, etc ker•a•tin (ˈkɛr ə tɪn) n. a tough, insoluble protein that is the main constituent of hair, nails, horn, hoofs, etc., and of the outermost layer of skin.

[1840–50; < Greek kerat-, s. of kéras horn + -in 1] ker`a•tin•i•za′tion, n. ker′a•tin•ize`, vb ke•rat•i•nous (kəˈræt n əs) adj. ker·a·tin (kĕr′ə-tĭn) A tough, fibrous protein that is the main structural component of hair, nails, horns, feathers, and hooves. Did You Know? Nature ingeniously uses the same chemicals to perform a wide variety of functions in living things. An example is the group of closely related proteins known as the keratins. When nature wants something hard and tough for an animal, it turns to keratins. Your nails and hair are made mostly of a kind of keratin, and so are a dog's claws, a bird's beak, and a goat's horns. Even the hard material called baleen that some whales have in their mouths to help them eat is made of a variety of keratin. All proteins are strings of amino acids, and the keratins' secret is the amino acid known as cysteine.

This amino acid tends to form strong bonds with other cysteines in the protein. The different keratins vary in hardness, depending on how many cysteine bonds are present. The bonds are what make the keratins tough as, well, nails. keratin A hard, waterproof protein found in the epidermis, hair, and nails. ThesaurusAntonymsRelated WordsSynonymsLegend:

Question: What substance are feathers, fingernails and hair made of?
Answer: KERATIN