EPIDERMISis composed of the outermost layers of cells in the skin
• The epidermis as the bodys major barrier against an inhospitable environment, by preventing pathogens from entering, making the skin a natural barrier to infection.• regulates the amount of water released from the body into the atmosphere through transepidermal water loss
• Keratinocyte is the predominant cell type in the epidermis, the outermost layer of the skin. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells“. The primary function of keratinocytes is the formation of a barrier against environmental damage
• Melanocytes are melanin producing cells located in the bottom layer (the stratum basale) of the skins epidermis, the middle layer of the eye (the uvea),
• Langerhans cells are dendritic cells (antigen- presenting immune cells) of the skin and mucosa, and contain large granules called Birbeck granules• In skin infections, the local Langerhans cells take up and process microbial antigens to become fully functional antigen-presenting cells.
• Merkel cells are oval receptor cells found in the skin of vertebrates that have synaptic contacts with somatosensory afferents. They are associated with the sense of light touch discrimination of shapes and textures.
LAYERS OF THE EPIDERMIS • Stratum Corneum • Stratum Lucidum • Stratum Granulosum • Stratum Spinosum• Stratum Basale/Germinativum
STRATUM GERMINATIVUM• is a continuous layer of cells. It is often described as one cell thick, though it may in fact be two to three cells thick in glabrous (hairless) skin.• is primarily made up of basal keratinocyte cells, which can be considered the stem cells of the epidermis. They divide to form the keratinocytes of the stratum spinosum, which migrate superficially
STRATUM SPINOSUM• This layer is also referred to as the "spinous" or "prickle-cell" layer. This appearance is due to desmosomal connections of adjacent cells.• Keratinization begins.
STRATUM GRANULOSUM• thin layer of cells in the epidermis. Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer. These cells contain keratohyalin granules, protein structures that promote hydration and cross linking of keratin.
STRATUM LUCIDUM• The stratum lucidum is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is found only in areas of thick skin.• The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin.
STRATUM CORNEUM• The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress.• Desquamation, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale.
• During cornification, the process whereby living keratinocytes are transformed into non- living corneocytes, the cell membrane is replaced by a layer of ceramides which become covalently linked to an envelope of structural proteins.• Cells of the stratum corneum contain a dense network of keratin
THICK SKIN AND THIN SKIN A. SHOULDER B. SCALP C. FEET
• Characteristics of the barrier• Physical barrier through keratinocytes attached together via cell– cell junctions and associated to cytoskeletal proteins, which gives the epidermis its mechanical strength.• Chemical barrier through the presence of highly organized lipids, acids, hydrolytic enzymes and antimicrobial peptides.• Immunologically active barrier through humoral and cellular constituents of the immune system.• Water content of the stratum corneum drops towards the surface, creating hostile conditions for pathogenic microorganism growth.• An acidic pH (around 5.0) and low amounts of water make it hostile to many micro organic pathogens.• The presence of non-pathogenic microorganism on the epidermis surface help defend against pathogenic one by limiting food availability and through chemical secretions.
• lies beneath epidermis• the thickest of the three layers of the skin.• home to most of the skin’s structures, including sweat and oil glands (which secrete substances through openings in the skin called pores, or comedos), hair follicles, nerve endings, and blood and lymph ves-sels.• the main components of the dermis are connective tissues (collagenous fibers, elastic fibers, reticular fibers)
Dermal Papillae• Blood vessels in the dermal papillae nourish all hair follicles and bring oxygen and nutrients to the lower layers of epidermal cells.• Responsible for “fingerprints”
Arrector Pili• small muscles attached to hair follicles in mammals . Contraction of these muscles causes the hairs to stand on end - known colloquially as goose bumps.
Nerve Fibers• responsible for the sense of touch, relaying information to the brain for interpretation• Thermoreceptors – trigger shivering
Connective Tissues• Collagen - tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability.• Elas-tin, a similar protein, keeps the skin flexible.
Sweat glands• classified according to two types: the apocrine glands and the eccrine glands.
• The eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and releases heat.• respond to heat, exercise, and fever, and some eccrine glands, such as those on the palms, respond to emo-tional stress as well. It’s these glands that give you clammy hands when you’re nervous.
• Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region.• these glands secrete a milky sweat that encourages the growth of bacteria responsible for body odor. These glands are activated at puberty when stimulated by hormones.
Apocrine vs. Eccrine• Unlike apocrine glands, eccrine glands function from child-hood, though they do increase their activity at puberty.• Though eccrine glands can produce up to two liters of sweat an hour when they’re working at their full potential, they’re not usually to blame for body odor.• Eccrine glands secrete mostly water, which doesn’t encourage the growth of odor-producing bacteria.
Sebaceous glands• attached to hair follicles, cylindrical structures that house the roots of the hair• found everywhere on the body except for the palms of the hands and the soles of the feet.• Usually called into action by hormones during puberty, these glands secrete oil (sebum) that helps keep the skin smooth and supple.• The oil also helps keep skin waterproof and protects against an overgrowth of bacteria and fungi on the skin.• At times, these glands overproduce and cause acne, a condition in which pores become clogged and inflamed.
blood and lymph vessels• blood vessels bring nutrients and oxygen to the skin and remove cell waste and cell products. The blood vessels also carry the vitamin D produced in the skin back to the rest of the body.• Enlarged vessels that can be seen through the skin are known as spider veins or vari-cose veins. Broken blood vessels appear as bruises.• The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains infection-fighting immune system cells. The cells work to destroy any infection or invading organisms as the lymph gradually circulates back through the body’s tissues to the lymph nodes
Hypodermis• Lowermost layer of the integumentary system in vertebrates.• Used mainly for fat storage.• Acts both as an insu-lator, conserving body heat, and as a shock absorber, protecting internal organs from injury.• blood vessels, nerves, adipose tissues, lymph vessels, and hair follicles are found in this layer.
Hair• The hair can be divided into two parts, the root and shaft.• Root - the hair root is contained in a tube- like structure called the hair follicle.• New cells are created in the hair root.• Papilla – Large structure at the base of the hair follicle• Matrix – Surrounds the papilla composed of epithelial cells.• Hair Fiber – composed of keratin.
Hair• Inner root sheath – sheath formed of several layers of cells.• Hair follicle – sac-like anatomical structure from which hair grows.
Hair – Shaft – 3 layers • Cuticle -outer layer, the cuticle is made up of hard, transparent cells. • It is the layer giving elasticity and resiliency to the hair. • Said to be water resistant – Cortex • layer between cuticle and medulla. • This contains the pigment and keratin. • Cortex determines the bulk and strength of hair. – Core/Medulla • Innermost layer composed of large cells. • Supporting structure for a strand of hair.