Skin-Structure & function ................
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The integumentary system, consisting of skin and its accessory structures, plays crucial roles in protection, temperature regulation, and sensation. The skin is the largest organ, made up of two main layers: the epidermis and the dermis, with various sublayers and accompanying structures such as hair, nails, and glands. Each component contributes to overall homeostasis and physical protection, while the skin's intricate structure facilitates vital functions.
Skin-Structure & function ................
- 1. Dr.Vishnu Neharkar, M.Pharm, Ph.D Prof & Head RMDIPER, Chinchwad, Pune.
- 2. The integumentary system consists of the skin and its accessory structures, including the hair, nails, sebaceous glands, and sweat glands. The integumentary system contributes to homeostasis by protecting the body and helping regulate body temperature. It also allows you to sense pleasurable, painful, and other stimuli in your external environment
- 3. The skin is the exterior covering of the body. It weighs around 16% of average adult body weight, and covers more than 3,000 square inches. It is the largest organ of the body. It is supplied with blood vessels and nerves
- 4. Protection….. The skin provides protection. It protects against invasion by bacteria and other harmful agents. It protects delicate cells beneath the surface from injury. It inhibits excessive loss of water and electrolytes. It produces a protective pigmentation to protect the body against excessive exposure from the sun. It helps to produce Vitamin D.
- 5. Temp regulation…. The skin regulates body temperature. When the body is too cold, the skin’s blood vessels constrict. This allows more heat-carrying blood to circulate to the muscles and organs. When the body is too hot, the blood vessels in the skin dilate. That brings more blood to the surface for cooling by radiation. At the same time, sweat glands secrete more sweat that cools the body when it evaporates.
- 6. Sensations.…. It contains millions of nerve endings that act as sensory receptors for pain, heat, cold, and pressure. When stimulation occurs, nerve impulses are sent to the cerebral cortex of the brain… and the brain triggers any necessary response
- 7. Structurally, the skin consists of two main parts. The superficial, thinner portion, which is composed of epithelial tissue is the epidermis. The deeper, thicker connective tissue portion is the dermis. Deep to the dermis, but not part of the skin, is the subcutaneous layer. Also called the hypodermis this layer consists of areolar and adipose tissues.
- 8. Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface which also serves as a barrier to infection. The epidermis contains no blood vessels, and cells in the deepest layers are nourished almost exclusively by diffused oxygen from the surrounding air. The main type of cells which make up the epidermis are keratinocytes, melanocytes, Langerhans cells and Markel's cells. The epidermis helps the skin to regulate body temperature.
- 10. Epidermis is divided into the following 5 sub layers Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale
- 11. The stratum corneum is the outermost layer of the epidermis. It consisting of dead cells (corneocytes). The stratum corneum is the rate limiting barrier that restricts the inward & outward movement of chemical substances. These corneocytes are embedded in a lipid matrix composed of ceramides, cholesterol, and fatty acids. Ceramides made up of long-chain fatty acids help create a barrier to prevent permeability. 1. Stratum corneum
- 12. The stratum corneum functions to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress. stratum corneum contain a dense network of keratin, a protein that helps keep the skin hydrated by preventing water evaporation. These cells can also absorb water, further aiding in hydration. This layer is responsible for the "spring back" or stretchy properties of skin. 1. Stratum corneum
- 13. 2. Stratum lucidum The stratum lucidum is present only in the thick skin of areas such as the fingertips, palms, and soles. It consists of three to five layers of flattened clear, dead keratinocytes that contain large amounts of keratin and thickened plasma membranes.
- 14. At the middle of the epidermis, the stratum granulosum consists of three to five layers of flattened keratinocytes that are undergoing apoptosis. A distinctive feature of cells in this layer is the presence of darkly staining granules of a protein called keratohyalin, which converts the tonofilaments into keratin. Tonofilaments are keratin intermediate filaments that makes up tonofibrils in the epithelial tissue 3. Stratum granulosum
- 15. Superficial to the stratum basale is the stratum spinosum, arranged in 8 to 10 layers of many-sided keratinocytes fitting closely together. These keratinocytes have the same organelles as cells of the stratum basale. When cells of the stratum spinosum are prepared for microscopic examination they appear rounded and larger in living tissue. Langerhans cells and projections of melanocytes are also present in this layer. 4. Stratum spinosum
- 16. Deepest layer, composed of a single row of cuboidal or columnar keratinocytes that contain scattered tonofilaments (intermediate filaments); stem cells undergo cell division to produce new keratinocytes. Keratinocytes play an important role in providing skin structure and in functioning of the immune system Melanin is a pigment produced by melanocytes, and is responsible for providing the skin color 5. Stratum basale
- 17. The dermis is the layer of skin beneath the epidermis that consists of epithelial tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many nerve endings that provide the sense of touch and heat. It contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels.
- 18. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as from the Stratum basale of the epidermis. The dermis is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary region, and a deep thicker area known as the reticular region.
- 19. Papillary Layer: superficial layer The Lies directly beneath epidermis Houses nerve endings that provide body with sense of touch pain, heat, cold, pressure, touch Contains papillae, small, cone shaped projections of elastic tissue that point upwards Papillae contain looped capillaries or nerve fiber endings Reticular Layer: deeper layer Reticular region are the roots of the hair, sebaceous glands, sweat glands, receptors, nails and blood vessels.
- 20. Fatty layer… attaches dermis to underlying structures. Composed of adipose and connective tissue. Serve as shock absorbers for vital organs, stores energy. Varies in thickness according to age, sex, general health of individual. Gives smoothness, contour to body, contains fats for use as energy, as a heat insulator. Circulation is maintained by network of arteries and lymphatics. (removes bacteria and foreign, materials, produces antibodies to fight infection) Subcutaneous layer
- 21. The hair is a threadlike structure formed by a group of cells that develop within a hair follicle or socket. Each hair has a shaft that is visible and a root that is embedded in the follicle. A pilomotor muscle is attached to the side of each follicle. It is stimulated by skin irritants, emotion, or cold temperatures, and reacts by contracting. This causes goose flesh or goose pimples.
- 22. At the base of each hair follicle is a bulb enclosing a loop of capillaries. It is called the hair papilla - provides nourishment to the hair & It is one of the few living parts of the hair, and is responsible for hair growth.
- 23. The transparent cuticle covers the hair shaft like shingles on a roof, protecting it from the elements and chemicals and from losing moisture. The cortex provides most of the hair’s weight. It contains melanin which provides color to the hair, stores oils, provides flexibility and elasticity, and adds shape to the hair. When the cuticle is damaged and exposes the cortex, hair looks dull and dry. The medulla is a inner hollow core that runs the length of the shaft.
- 24. Sebaceous glands are oil glands. They have tiny ducts that open into each hair follicle. Each sebaceous gland secretes sebum, which lubricates the hair and skin. The amount of secretion varies with age, puberty, and pregnancy.
- 25. … Fingernails and toenails are hard keratin structures that protect the ends of the fingers and toes. The nail root, also called the germinal matrix or nailbed, begins several millimeters into the finger and extends to the edge of the white, crescent-shaped lunula. This is where the growth occurs approximately 1 mm. per week. The under-surface of the nail plate or body of the nail has grooves that help anchor it.