Integumentary System Includes: Skin (cutaneous membrane) Subcutaneous tissue below the skin Accessory Structures Sweat glands Sebaceous or oil glands Hair Nails
Layers Of The Skin Epidermis – outer composed of stratified squamous epithelium Dermis – inner anchored to a subcutaneous layer Click here to copy and Paste a micrograph of The layers of the skin.
Epidermis Composed of stratified squamous epithelium Avascular as it has no blood supply of its own Oxygen and nutrients diffuse from the underlying dermis The epidermis is a keratinized stratified squamous epithelium. Oxygen and nutrients diffuse from the underlying dermis. Five structurally different layers can be identified:
First Layer of the Epidermis The stratum basale is the deepest layer of the epidermis (closest to the dermis). It is found close to the dermal blood supply. It consists of a single layer of columnar or cuboidal cells which rest on the basement membrane. Basal cells are the stem cells of the epidermis. Their mitotic activity replenishes the cells in more superficial layers as these are eventually shed from the epidermis. The renewal of the epidermis takes about 3 to 4 weeks in humans as millions of cells are produced daily. Cells die as they are pushed away from the source of nourishment. Cells undergo keratinization as a tough protein, keratin, is deposited within the cell. Keratin hardens and flattens the cells as they move outward and it waterproofs the skin.
Optional Epidermal Layers In the stratum spinosum, the cells become irregularly polygonal. The cells are often separated by narrow, translucent clefts. These clefts are spanned by spine-like cytoplasmatic extensions of the cells (hence the name of the layer and of its cells: spinous cells), which interconnect the cells of this layer. The stratum granulosum consists, in thick skin, of a few layers of flattened cells. Only one layer may be visible in thin skin. The stratum lucidum consists of several layers of flattened dead cells. Nuclei already begin to degenerate in the outer part of the stratum granulosum. In the stratum lucidum, faint nuclear outlines are visible in only a few of the cells. The stratum lucidum can usually not be identified in thin skin.
In the stratum corneum, cells are keratinized and form a layer that is about 30 cells thick. Individual cells are difficult to observe because (1) nuclei can no longer be identified, (2) the cells are very flat and (3) the space between the cells has been filled with lipids, which cement the cells together into a continuous membrane. Closest to the surface of the epidermis, the stratum corneum has a somewhat looser appearance. Cells are constantly shed from this part of the stratum corneum. This layer makes up three fourths of the epidermal thickness. The protection of the body by the epidermis is due to the functional features of the stratum corneum. Final Epithelial Layer
Click here to copy the picture skin, thick trichrome And paste it here. Click here to copy the picture skin, thin H&E And paste it here.
Dermis or corium The dermis, or corium, consists of dense fibrous connective tissue with numerous collagenous and elastic fibers. The dermis is much thicker than the epidermis. In thick skin, dermal papillae create a very irregular border between epidermis and dermis. Blood vessels, nervous tissue, some muscle tissue, certain glands, hair and nails are found in the dermis. Nerve endings allow us to sense pain, temperature, pressure, and touch.
Click here to copy and paste the picture skin, thick van Gieson elastin
Melanin Click here to copy and paste a picture of The integument showing melanocytes stained blue
Red and Yellow, Black and White… The red and yellow hues of the skin are due to hemoglobin in the red blood cells, which pass through the capillaries beneath the epidermis, and carotene (yellowish pigment), which accumulates in fat cells found in the dermis and hypodermis (subcutaneous layer beneath dermis). Melanocytes The brown in skin color is due to melanin, which is produced in the skin itself in cells called melanocytes. These cells are located in the epidermis. In the melanocytes, the melanin is located in membrane-bound organelles called melanosomes. Melanocytes can transfer melanin to keratinocytes - mainly to the basal cells. Melanin protects the chromosomes of mitotically active basal cells against light-induced damage. Pigmentation is not just under the control of light. Hormones produced by the pituitary and the adrenal glands also affect pigmentation. Diseases of these two endocrine organs often result in changes of pigmentation of the skin.
Malfunctioning Melanocytes Albinism – melanocytes completely fail to secrete melanin. Hair, skin, and iris are white. Vitiligo – loss of pigment in certain areas of the skin producing white patches. Freckles and moles are formed when melanin becomes concentrated in local areas. Malignant melanoma – a cancerous change in a mole that may metastasize (spread) rapidly and is most difficult to treat. Exposure to sunlight increases risk.
Other Pigments in Skin Carotene – a yellow pigment in skin usually hidden by the effects of melanin. Asians have little melanin which allows the yellow to show more than other nationalities. Pinkish color – seen in fair-skinned persons because the vascular dermis is visible. Cyanosis – blue look to skin due to poorly oxygenated blood Blushing – caused by dilation of blood vessels Pale by fright – caused by restriction of vessels
Response to Disease Jaundice – caused when bilirubin is deposited in skin because a diseased liver is unable to excrete this pigment Skin may appear bronzed due to the deposit of excess melanin when a persons adrenal gland is functioning poorly. A bruise indicates that blood has escaped from the blood vessels and has clotted under the skin. Over eating carotene-rich vegetables such as carrots may cause skin to have a yellow tint.
Accessory Structures of the Skin Hair A characteristic feature of the human skin is the apparent lack of hair on most of the body surface. This is actually not quite true. Most of the skin is haired although the hair in most areas is short, fine and only lightly pigmented. Truly hairless are only the palms of hands and soles of feet, the distal phalanges and sides of fingers and toes and parts of the external genitalia.
Accessory Structures of the Skin In those parts of the skin which we perceive as "hairy" we find terminal hairs. The free part of each hair is called the shaft. The root of each hair is anchored in a tubular invagination of the epidermis, the hair follicle, which extends down into the dermis and, usually, a short distance into the hypodermis. The hair that you groom daily is actually dead keratinized cells. Each hair follicle has an associated bundle of smooth muscle, the arrector pili muscle. This muscle inserts with one end to the papillary layer of the dermis and with the other end to the dermal sheath of the hair follicle. This makes your hair stand up on its end.
Accessory Structures of the Skin Click here and copy and paste the Picture of a hair follicle here.
Hair Color and Texture Hair color is determined by the amount and type of melanin present. Melanocytes become less active with age. Gray hair is a mixture of pigmented and non-pigmented hairs. Red hair results from a a modified type of melanin that contains iron. The shape of the hair shaft determines texture. Round shaft – straight hair Oval shaft – wavy hair Flat shafts – curly or kinky hair Perms use chemicals to flatten shafts and makes hair curly. Alopecia is the term for hair loss.
Accessory Structures of the Skin Nails Plates of stratified squamous epithelial cells with hard keratin Protect distal ends of phalanges Cells are keratinized in the nail root Nail growth occurs in the lunula Cuticle is a fold of stratum corneum on the proximal end of nail
Click here to copy and paste a Picture of the skin and nail here.
Exocrine Glands Sebaceous glands or oil glands are simple branched areolar glands. They secrete the sebum (seb = oil) an oily product. Sebum is usually secreted into a hair follicle. Sebum is a natural skin cream: it helps hair from becoming brittle, prevents excessive evaporation of water from the skin, keeps the skin soft and contains a bactericidal agent that inhibits the growth of certain bacteria. Sebaceous glands are scattered all over the surface of the skin except in the palms, soles and the side of the feet. Vernix caseosa - white covering on fetus. Blackhead Pimple
Exocrine Glands Sweat glands or sudoriferous glands are simple coiled tubular glands. They are divided into two principal types: eccrine and apocrine. Apocrine glands are found mainly in the skin of the armpits, of the anogenital areas and of the areola of the breasts. Their secretory portion can be located in the dermis or in the hypodermis. Their excretory ducts open into hair follicles. Their secretion is more viscous than that of the eccrine glands. They start secreting at puberty and may be analogous to the sexual scent glands of other animals. Eccrine glands are the most common. Their secretory portion can be located in the dermis or in the hypodermis. They produce sweat, a watery mixture of salts, antibodies and metabolic wastes. Sweat prevents overheating of the body and thus helps regulate body temperature. Ceruminous glands (or ear wax glands) and mammary glands are modified apocrine sweat glands.
Click here to copy and paste a picture Of a sweat gland here.
Physiology of the Skin Protection - the epidermis provides a barrier to fluid loss from the body (this protective function is impaired in patients with burns). barrier function - intact skin prevents the entry of micro-organisms into the body. Antimicrobial proteins are produced by the epidermis - they act by piercing holes in the outer membranes of micro- organisms. Resistance to wear and tear - continuous replacement of the outer epidermal cells that wear off - new cells are produced in the deepest layer of the epidermis and gradually migrate towards the surface
Skin can excrete water, salt, and small amounts of waste products such as urea. Vitamin D can be synthesized in skin exposed to sunlight (vitamin D can also be obtained from the diet) The skin provides a barrier to ultraviolet light. The melanocytes contain melanin, which absorbs UV radiation, and also distribute the pigment to neighboring cells. Skin exposed to sunlight becomes wrinkled and creased. Changes seem to be due to disruption of collagen and elastin in dermis, and loss of fibroblasts which make new proteins.
Three types of skin cancer corresponding to three major types of skin cells: basal cells, squamous cells, and melanocytes. Cancer of melanocytes - malignant melanoma - is the most lethal variety, but also the least common. If caught early, most cases of non-melanoma skin cancer are easily treated under local anaesthetic Whites in Australia have the highest rates of skin cancer of all types in the world. The damaging effects of sunlight can occur many years before tumors appear. ultraviolet light causes mutations at points on a DNA strand.
The integumentary system is well-supplied with receptors for touch, pain, temperature, vibration and pressure Sensory information is relayed to the central nervous system via sensory nerves Social interactions are influenced by facial expressions, blushing, touching, etc.
Fun Facts House dust is mainly skin flakes! If you laid out all your skin on a flat surface, it would have an area of about 2 square meters. Skin weighs about 2.5 kilograms - the largest organ in the body. What hurts if you pull it, but doesn't hurt if you cut it? Your hair, of course! Skin is elastic - it springs back into shape when stretched. Some medicines (estrogen, nicotine) can pass through the skin, but others cannot (insulin). Why is that? Because only fat-soluble substances can enter the skin, not water- soluble ones. Your hair stands on end and you develop 'goose bumps' because there are tiny muscles attached to the hair follicles and they contract when you are frightened or cold.
Additional Online Activities Click here to go to McGraw-Hill - Essential Study Partner Click here to go to McGraw-Hill - Essential Study Partner Choose the Unit : Support & Movement Choose Topic : Integumentary System Skin and its Tissues Accessory Organs Temperature Regulation Aging Additional Activities Quiz