![EPIDERMIS
CELLS
• Keratinocytes (90%)Keratin (/ˈkɛrətɪn/[1][2]
) is a family of fibrous structural proteins.
Keratin is the key structural material making up the outer layer of human skin. It is also the key
structural component of hair and nails. are polymers of type III and type IV intermediate
filaments, They are composed of a family of related proteins sharing common structural and
sequence features (muscle)
• Melanocytes (produce melanin)
• Langerhans ‘cells (MACROPHAGES)
• Merkel cells (touch sensation: sensory receptors)
LAYERS
• Stratum basale (8% melamcoyte)
• Stratum Spinosum
• Stratum Granulosum
• Stratum Lucidum
• Stratum Corneum (outermost layer of the epidermis, consisting of 25
to 30 layers of dead, keratin-filled squamous cells).](https://image.slidesharecdn.com/lecture7theintegumentarysystem-210211193731/85/Lecture-7-the-integumentary-system-4-320.jpg)
Lecture 7 the integumentary system
- 1. Anatomy and Physiology THE INTEGUMENTARY SYSTEM The skin and its associated structures (hair, nails, sweat glands, and oil glands) make up a complex set of organs called the INTEGUMENTARY SYSTEM. The skin is one of the largest and heaviest organ of the body. The skin performs many functions, most of which are PROTECTIVE: 1. Skin cushions and insulates the deeper organs. 2. It protects the body from mechanical damage, harmful chemicals and invading bacteria (staphylocouss auras –normal flora) . 3. The skin is waterproof, preventing dehydration. 4. The skin's capillaries and sweat glands regulate heat loss, helping to control body temperature. 5. The skin excretes water, urea and salts in sweat. 6. Skin screens out damaging ultraviolet (UV) radiation from the sun. 7. Skin also uses the UV rays that penetrate the skin to synthesize (make) vitamin D. 8. The skin contains sense organs called sensory receptors that detect touch, pressure, pain, and temperature.
- 2. The skin consists of 2 layers, - 1 - the outer epidermis, derived from the embryonic ectoderm - 2 - the inner dermis which develops from the mesoderm. The appendages of the skin such as hair, nails, sebaceous glands and sweat glands develop from the embryonic epidermis. Beneath the dermis is the hypodermis (=subcutaneous tissue = superficial fascia) which anchors the skin loosely to underlying tissues (mainly muscles). The hypodermis is NOT part of the skin. Because of its adipose tissue, the subcutaneous layer also acts as a shock absorber and insulates the deeper body tissues from heat loss.
- 4. EPIDERMIS CELLS • Keratinocytes (90%)Keratin (/ˈkɛrətɪn/[1][2] ) is a family of fibrous structural proteins. Keratin is the key structural material making up the outer layer of human skin. It is also the key structural component of hair and nails. are polymers of type III and type IV intermediate filaments, They are composed of a family of related proteins sharing common structural and sequence features (muscle) • Melanocytes (produce melanin) • Langerhans ‘cells (MACROPHAGES) • Merkel cells (touch sensation: sensory receptors) LAYERS • Stratum basale (8% melamcoyte) • Stratum Spinosum • Stratum Granulosum • Stratum Lucidum • Stratum Corneum (outermost layer of the epidermis, consisting of 25 to 30 layers of dead, keratin-filled squamous cells).
- 5. Millions of dead cells from the stratum corneum are worn off by abrasion every day, and we have a totally new epidermis every 4 weeks. In healthy epidermis, the production of new cells balances the cell loss at the skin surface.
- 6. The epidermis consists of several layers of cells. From the deepest to the most superficial we have: - 1 - the stratum basale (or stratum germinativum): is the deepest epidermal layer. Melanocytes that synthesize the pigment melanin. Melanin passes on from the melanocytes into the keratinocytes and will protect them from the destructive effect of ultraviolet radiation.. Merkel cells
- 7. - 2 - the stratum spinosum: Langerhans'cells that are most abundant in this layer. - 3 - the stratum granulosum: here the keratinization process begins and the cells begin to die. - 4 - the stratum lucidum is only found in thickened areas of the epidermis such as the sole of the feet. - 5 - the stratum corneum: is the outermost layer composed of dead, flat, keratinized cells which are being sloughed off. Corneum means horn: hard dead cells. DERMIS
- 8. The DERMIS lies deep to the epidermis and consists of connective tissue. The average thickness of the dermis is about 1 to 2 mm and varies from 0.6 mm on the eyelids to 3 mm or more on the soles and palms. It contains lots of nerve fibers, sensory receptors, blood and lymphatic vessels as well as the hair follicles, and the sebaceous and sweat glands. The dermis is HIGHLY VASCULAR, while the epidermis is AVASCULAR. Epithelial cells in the epidermis receive their oxygen and nutrients from the blood vessels in the dermis. The dermis consists of two layers: 1 - Papillary layer
- 9. Is the outer layer closest to the epidermis. Its superior region contains fingerlike projections called dermal papillae. Dermal papillae contain: - capillaries - bare nerve endings (pain receptors) - Meisner corpuscles (touch receptors: make us feel light touching) - disclike sensory nerve endings of the Merkel disks.
- 10. 2 - Reticular layer is the deeper layer and the thickest consists of DENSE IRREGULAR CONNECTIVE TISSUE, which contains collagen and elastic fibers that give skin its strength and elasticity. The reticular layer is richly supplied with blood vessels and nerves, and contains sensory endings for touch (Pacinian corpuscle for sensing deep pressure such as bumps), pain, heat, cold, etc. The epidermis projects down into the dermis to form sweat glands, sebaceous glands and hair follicles. THE SKIN APPENDAGES Hair, nails, oil glands, and sweat glands are called epidermal derivatives. This means that they are structures that developed from the embryonic epidermis during prenatal development. Although they are considered to be epidermal structures, some of them are located deep in the dermal layer. HAIR and HAIR FOLLICLE- Hair is a flexible structure that consists of two regions: 1- Shaft: 2 - Root: Associated with each hair follicle is a tiny band of smooth muscle: the arrector pili. The arrector pili muscles are attached to the hair follicle in such a way that their contraction pulls the hair follicle into an upright position, producing "goosebumps". The arrector pili muscles are regulated by the nervous system and are activated by cold external temperatures or fright. Hair pigment is made by MELANOCYTES in the MATRIX of the hair bulb of the hair follicle. The melanin is transferred to the cells in the hair shaft. Different proportions of brown-black, yellow and reddish melanin combine to produce all varieties of hair color from blond to black. Gray or white hair results from a decrease in melanin production. The melanin is replaced by air bubbles in the hair shaft.
- 11. NAILS A NAIL consists of a plate of hard, keratinized epidermal cells that form a clear protective covering on the dorsal surface of the distal part of a finger or toe. Nails protect the ends of the digits from trauma, allow us to scratch various parts of our body and help us grasping and manipulating small objects. The nail body appears pink because of the rich bed of capillaries in the underlying dermis. As the nail cells are produced by the matrix, they become heavily keratinized, and the nail body slides distally over the nail bed. The average growth rate of fingernails is 1 mm per week, but the growth rate is slower in toenails. Longer digits have faster nail growth. SKIN GLANDS: SEBACEOUS GLANDS : SEBACEOUS (OIL) GLANDS secrete an oily secretion called SEBUM. The sebum contains fats, cholesterol, proteins, salts, and dead cell fragments. Sebum is usually secreted into a hair follicle but in a few regions of the body (lips and mammary papilla for example) they are directly secreted onto the skin surface. Sebum is a natural skin cream: - it helps hair from becoming brittle - prevents excessive evaporation of water from the skin - keeps the skin soft - 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. They are small on the body trunk and limbs, but quite large on the face, neck and upper chest. The SECRETORY PORTION of the gland lies deep in the dermis. The DUCT of the sebaceous gland usually empties into a hair follicle, or to a pore on the skin surface if no hair is present (like the skin of the lips).
- 12. SUDORIFEROUS (SWEAT) GLANDS Sweat glands or sudoriferous glands are simple coiled tubular glands. They are divided into two principal types: eccrine and apocrine: 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 (99%) of salts, antibodies and metabolic wastes (urea, uric acid, ammonia, lactic acid) and vitamin C. - Sweat prevents overheating of the body and thus helps regulate body temperature. They are particularly abundant on the palms of the hands, soles of the feet and in the forehead. APOCRINE SWEAT GLANDS are largely confined to the AXILLARY (armpit) and INGUINAL (groin or pubic area) regions, as well as the areola (colored area around the nipple) and the bearded area of a man’s face. Their excretory ducts open into hair follicles. Apocrine secretion contains the same basic components as eccrine sweat, but it also contains fatty acids and proteins, giving the sweat a milky or yellowish color. The
- 13. secretion is odorless, but bacteria on the skin decompose the fatty acids and proteins, giving it its characteristic musky odor. They are responsive to emotional stress. CERUMINOUS GLANDS Ceruminous glands (or ear wax glands) are modified sweat glands found in the lining of the external ear canal. The combined secretion of ceruminous and sebaceous glands in the ear canal is called CERUMEN, or ear wax, a sticky substance that apparently repels insects and blocks the entrance of foreign material. MAMMARY GLANDS are also modified apocrine sweat glands.