Skin Anatomy and Functions PDF

Skin HUMAN STRUCTURE AND FUNCTION BMS 1104 A MCCULLA Learning outcomes Describe the histological features of skin and the differences between “thick” and “thin” skin. Describe the relationship between epidermis, dermis and underlying...

Skin HUMAN STRUCTURE AND FUNCTION BMS 1104 A MCCULLA Learning outcomes Describe the histological features of skin and the differences between “thick” and “thin” skin. Describe the relationship between epidermis, dermis and underlying structures. Describe and explain the importance of cutaneous sensory receptors. Describe skin appendages and glands e.g. sebaceous and sweat glands, and hair follicles.  Your skin constantly sheds Did you Know? dead cells, about 30,000 to Your skin is home to more than 1,000 40,000 cells every species of bacteria. Dead skin minute! That’s nearly 9 lbs. comprises about per year! Your skin is its and Skin accounts for a billion tons of Some of thickest thinnest about 15% of dust in the on your the on your your body earth’s eyelids nerves in feet (0.2mm weight. atmosphere. (1.4mm) your skin ). are connecte The skin renews The average person’s skin d to itself every 28 Your skin has covers an area of 2 muscles days. at least five square meters. instead different of the types of brain, Changes in your receptors that sending The average adult’s skin skin can respond to signals weighs approx 9 lbs and sometimes signal pain and (through contains more than 11 miles changes in your touch. the spinal of blood vessels. overall health. cord) to react more quickly to Function Protection Control of Sensati Absorptio Manufact Thermoregulat Storag Excretio evaporati on n ure of ion e and n on Vitamin D synthe sis An The skin Contains Along with Upon Sweat glands and Acts as Sweat anatomical provides a a variety inhalation, exposure to dilated blood a glands barrier from relatively of nerve ingestion UV vessels aid heat storage excrete pathogens dry and endings and radiation, loss, while centre perspirati and semi- that injection, vitamin D3 constricted for on damage impermeab respond dermal is vessels greatly lipids through between le barrier to to heat absorption synthesized reduce cutaneous and skin the internal reduce fluid and cold, is a route of in the skin, blood flow and water pores. and loss. touch, exposure for primarily in conserve heat. Perspirati external pressure, bioactive keratinocyt on is environmen vibration substances es of the made up t; , and including stratum of Langerhans tissue medications basale and nitrogeno cells in the injury.. stratum us wastes skin are spinosum (urea), part of the layers of salts, and adaptive the water. Layers of skin Stratified squamous keratinising epithelium Dense Irregular Connective Tissue Adipose Tissue Stratified squamous keratinising epithelium To change or become changed into a form containing keratin Strata of epidermis Stratum Corneum Surface stratum, cells have no organelles – almost entirely composed of keratin Stratum Lucidum Thick skin only – not always observed Stratum Granulosum 2-3 layers of flattening cells; granules contain a lipid rich secretion, which acts as a water Stratum sealant. Spinosum 2-8 layers; ‘prickle cells’; desmosomes; tonofilaments Stratum Basale (Germinativum) Deepest stratum; single layer of cuboidal cells; hemidesmosomes bond layer to basal lamina and dermis. It is here that new cells are generated for the renewal of the epidermal layers of the skin Cells of epidermis Keratinocytes make up majority Melanocytes synthesise the pigment melanin and are of cells within located in the basal layer. Skin colour is due to production epidermis – they and breakdown; protects against UV - everyone has same produce keratin number. Melanin is transferred from melanocytes to nearby keratinocytes in the basale and spinosum layers Antigen presenting cells called Langerhans cells are usually most clearly seen in the spinous layer – they represent 2-8% of epidermal cells Merkel cells or epithelial tactile cells are sensitive mechanoreceptors essential for light touch sensation Keratinocyte development Cornification Cornified cell envelope, nuclear breakdown Late differentiation Expression of late markers e.g. filaggrin (bundles keratin filaments) Intermediate differentiation Reinforcement of the cytoskeleton Early differentiation Growth arrest, exit from cell cycle Proliferation DNA synthesis and mitosis Dermis Dense Irregular Connective Tissue - Abundant in collagen with less elastin and reticular fibres. Nuclei seen within are fibroblasts – the cells that make collagen. Rich supply of nerve fibres, sensory receptors, blood and lymphatic vessels. Two indistinct layers: Papillary layer - superficial region that interdigitates with epidermal ridges Reticular layer- deeper region that is attached to underlying hypodermis Hypodermis Also known as subcutaneous tissue and is not a part of true skin. A connective tissue layer that is immediately deep to skin. Mostly adipose tissue. Provides padding to the body and helps skin anchor to underlying tissues. Subcutaneous fat allows for thermal insulation and provides an energy reservoir. Target of subcutaneous injections due to it’s vascularity - absorbs drugs quickly. Layers of skin – clinical significance Classificati Layers Sensatio Prognosis on involved n First degree Epidermis Painful Heals well Superficial Superficial papillary Very painful Local infection but second degree dermis typically no scarring Deep second Deep reticular Pressure Scarring, contractures, degree dermis and may require skin discomfort grafting Third degree Extends through Painless Scarring, contractures, entire dermis into amputation subcutaneous fat Fourth degree Through skin and Painless Amputation, significant subcutaneous fat functional impairment into underlying and in some cases muscle or bone death Thick skin v Thin skin N.B. These terms apply only to the relative thickness of the epidermis. Thin skin (epidermis + dermis) is normally thicker than thick skin Thick skin: Thin skin: palms and soles everywhere of feet else Epidermal appendages Merocrine (eccrine) – highest density in palms and soles Sw Apocrine – axillary and anogenital regions eat gla nds Extend from epidermis to dermis Hai Associated sebaceous glands r Arrector pili – smooth muscle folli cles Secrete sebum (oily mixture of lipids) Seb Usually secreted into base of hair follicle ace Sebum softens & lubricates hair and skin, prevents ous brittleness, slows water loss and kills bacteria gla nds Sweat glands Eccrin Apocrin e e Hair follicles Hairs are elongated keratinized structures that form within epidermal invaginations, the hair follicles. The colour, size, shape, and texture of hairs vary according to age, genetic background, and region of the body. Hairs grow discontinuously, with periods of growth followed by periods of rest. Arrector pili muscles are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end (goose bumps). Sebaceous glands Sebaceous glands surrounding a hair Gland’s capsule follicle (C)  Receptors 1 Merkel cells, each associated with expanded nerve endings which function as tonic receptors for sustained light touch and for sensing an object’s texture. Free nerve endings in the papillary dermis and Unencapsula extending into lower epidermal layers, which ted receptors respond primarily to high and low temperatures, pain, and itching, but also function as tactile receptors. Root hair plexuses, a web of sensory fibres surrounding the bases of hair follicles in the dermis that detects movements of the hairs.  Receptors 2 Meissner (tactile) corpuscles are elliptical structures - they initiate impulses when light touch or low-frequency stimuli against skin temporarily deform their shape. They are numerous in the fingertips, palms, and soles. Pacinian (lamellar) corpuscles are large oval structures, found deep in the dermis and hypodermis. They are specialized for sensing coarse touch, Encapsulat pressure (sustained touch), and vibrations, with ed distortion of the capsule amplifying a mechanical receptors stimulus to the axonal core where an impulse is initiated. Krause end bulbs are simple encapsulated, ovoid structures, with extremely thin, collagenous capsules penetrated by a sensory fibre. They are found primarily in the skin of male and female genitalia where they sense low frequency vibrations. Ruffini corpuscles are stimulated by stretch (tension) or twisting (torque) in the skin. Summary