Skin Lecture PDF

Skin(Integumentary system) DR M CHANDRIKA LECTURER DEPARTMENT OF ANATOMY YONG LOO LIN SCHOOL OF MEDICINE  Learning objectives  To understand the structure and function of skin Its two different layers ---- Epidermis and dermis  Epidermal skin appendages ( sweat glands, seba...

Skin(Integumentary system) DR M CHANDRIKA LECTURER DEPARTMENT OF ANATOMY YONG LOO LIN SCHOOL OF MEDICINE  Learning objectives  To understand the structure and function of skin Its two different layers ---- Epidermis and dermis  Epidermal skin appendages ( sweat glands, sebaceous glands ,hair follicle ) and their functions 9/3/20XX Presentation Title 2 Skin (integumentary system ) It is the largest organ that protects our body’s internal environment from the external environment Physical barrier Prevents dessication Immune defense mechanism Largest sensory organ Protection from ultraviolet light Thermoregulation/ Homoestasis of body temperature Vitamin D synthesis and exocrine secretion Epidermis- (superficial layer of the skin ) – Arises from the surface ectoderm Keratinized stratified squamous epithelium - 90% of the epidermal cells are keratinocytes that produce a protein called keratin that is protective and partially water resistant Other cells in the epidermis:  Melanocytes (8%)  Langerhans cells  Merkel cells 9/3/20XX Presentation Title 4 Epidermis – five layers or strata Stratum basale Stratum spinosum (Prickle cell layer) Stratum granulosum Stratum lucidum Stratum corneum 9/3/20XX Presentation Title 5 The epidermis is tightly bound to the underlying layer (dermis) by a specialized basement membrane.  Stratum germinativum (basal layer or stratum basale)  The St germinativum or the basal layer (stratum basale) B is made up of cells that divide to provide new cells for constant regeneration of the other layers of the epidermis.  It consists of a single layer of cuboidal or low columnar cells connected to the basement membrane by hemidesmosomes  These cells contain cytoskeletal intermediate filaments (tonofilaments). Layer Characteristics Stratum corneum Multiple layers of flattened, dead keratinocytes Water resistant Stratum lucidum Present only in thick skin( palms of the hand ,soles of the feet Appears as a homogeneous layer Cells filled with keratin Stratum granulosum Keratinocytes contain keratohyalin granules and keratin Lamellar bodies containing lipids are also present Stratum spinosum Keratinocytes (polyhedral cells) bound together by desmosomes to which tonofibrils of the cytoskeleton are attached Lamellar bodies containing lipids are also present Langerhans cells and some melanocytes present Stratum basale Innermost, basal layer of cuboidal or low columnar cells Attached to basement membrane Cells divide to replenish cells in other layers Melanocytes and Merkel cells are also present  Renewal time : 15 to 30 days Intermediate filaments Different stages in the life cycle of a keratinocyte as it passes from the basal layer to the skin surface ifferent stages in the life cycle of a keratinocyte as it passes from the basal layer to the skin surface  Keratinocytes Cell types in the Epidermis Langerhans’ cell Merkel cell Melanocyte The main features of the epidermis, including its cell layers and different cell types. Melanocytes and Merkel cells are derived from the neural crest and Langerhans cells are derived from bone marrow precursor cells. Melanocytes are present as scattered cells in the basal layer. Their numbers are similar in white and dark-skinned races, but they are considerably more synthetically active in darker-skinned people. The melanocytes can be stimulated to produce more melanin by exposure to UV light. Basal cell /Squamous cell carcinoma Common skin lesions Disorders of melanocytes 'Moles' or naevi are benign accumulations of melanocytes in the dermis, epidermis or both Malignant melanoma is a malignant tumour of melanocytes, particularly affecting pale-skinned people who are exposed to excessive UV light An inherited inability to produce melanin – Albinism Partial or complete loss of melanocytes –irregular white spots - Vitiligo 9/3/20XX Presentation Title 16 Epidermis - Dermis Junction  Disruption of the basement membrane will detach the epidermis from the dermis causing blisters Dermis Made up of connective tissue (collagen and elastic fibres), similar in thick and thin skin-( Derivative of mesoderm) Tightness and firmness of the skin in the young is because of the collagen and elastin which degenerate in old age and as a result of this the skin loses much of its texture and may wrinkle. 9/3/20XX Presentation Title 19  Dermis has two layers Papillary dermis Reticular dermis 9/3/20XX Presentation Title 20 Two layers of dermis Papillary Reticular Outer layer consists of areolar Inner layer consists of irregular dense connective tissue with fine elastic fibers connective tissue, adipocytes, nerves, arterial plexus, ducts of sweat glands, Its surface area is greatly increased by sebaceous glands ,arrector pili muscle finger like projections called dermal and hair follicles papilla Capillaries that nourish the epithelium and the touch receptor ,Meissner’s corpuscle, and other sensory receptors are present in the dermal papilla 9/3/20XX Presentation Title 21   Yellow arrow denotes papillary dermis  Red arrow denotes reticular dermis  Green arrow denotes epidermis Toluidine blue stain used to differentiate papillary and reticular dermis  Meissner’s corpuscle Schwann cells spiraling around a central unmyelinated sensory axon- touch receptors Present in papillary dermis of the pulp of fingers and toes , palms and soles Collagen fiber bundles in the reticular layer lie parallel to one another. In the limbs the predominant direction of bundles is along the long axis of limbs whereas in the trunk and neck the direction is transverse. The lines along which the bundles run are called cleavage lines (Langer's lines). The cleavage lines are of importance to the surgeon as incisions in the direction of these lines gape much less than those at right angles to them. Wound healing Keloid Scar Skin appendages – Downgrowths from the epidermis into the dermis during second trimester of intrauterine development Hair follicle  Sebaceous glands  Sweat glands Nails  Hair follicle Hair shaft Hair follicle Arrector pili Sebaceous glands Hair root Hair matrix Internal root sheath Hair bulb External root sheath Hair papilla Connective tissue sheath Pacinian corpuscles The germinal matrix is formed of closely packed, mitotically active keratinocytes, among which are interspersed melanocytes. Proliferation of epithelial cells and their downgrowth into the subjacent connective tissue  Sweat glands Merocrine(eccrine) sweat Apocrine sweat glands glands Limited distribution (axillae, areola of Wide spread distribution breast, external genitalia, lower part of Produce thin watery secretion anal canal) Merocrine secretion Produce viscous secretion mechanism Strongly influenced by hormones Controlled by sympathetic Begin to function after puberty nervous system Important in thermoregulation and excretion Some antibacterial action Mammary glands Ceruminous glands in ear – secretes ear Apocrine glands specialized for milk wax secretion merocrine ( eccrine )Sweat glands 1. Coiled tubular glands 2. Secretory portion consists of cuboidal cells resting on a basal lamina 3. Ducts are lined with double layer of cuboidal cells 4. Ducts open on surface of skin 5. Thin secretion 6. Myoepithelial cells present   Eccrine sweat glands are innervated by cholinergic fibres  Apocrine sweat glands are innervated by adrenergic fibres  Sebaceous glands Epidermis Hair shaft 1. Seen typically in relation to hair follicles 2. Each gland consists of alveoli that are connected to a broad duct that opens into the hair follicle 3. Each alveolus is pear shaped, solid mass of cells with hardly any lumen 4. Outer cells rest on a basement membrane 5. Inner cells are filled with lipid which is discharged by disintegration of the cells (holocrine secretion). 6. Proliferation of outer cells replaces the degenerated inner cells.  Sebaceou Hair shaft s gland Acne vulgaris Hair follicle, sebaceous glands and arrector pili muscle form the pilosebaceous unit Goose bumps Innervation of the skin Nerves of the skin include both somatic and autonomic nerves. The somatic sensory system is responsible for pain (nociceptors), temperature, light touch, discriminative touch, vibration, pressure, and proprioception mediated primarily by specialized cutaneous receptors/end organs including Merkel disks, Pacinian corpuscles, Meissner’s corpuscles, and Ruffini corpuscles. The autonomic innervation is responsible for the control of the tone of the vasculature, pilomotor stimulation at the hair root and sweating.  Sensory receptors in the skin Meissner receptors detect light Merkel’s touch ending Pacinian corpuscles perceive deep pressure and vibrational changes Ruffini endings detect deep pressure and stretching of the skin’s collagen fibres Krause’s Pacinian Free nerve endings present in the corpuscle end bulb epidermis respond to pain, light touch and temperature variations Merkel receptors respond to sustained light touch on the skin Meissner’s corpuscle Ruffini’s corpuscle Pacinian corpuscle are encapsulated sensory receptors for pressure and vibration Located in the deep layers of the dermis and hypodermis Pacinian corpuscle  Thermoregulatory function of the skin Two plexuses formed by branching of arteries:  Cutaneous-at the junction of dermis and hypodermis (Hypodermis)  Subpapillary-at the junction of reticular and papillary layers These provide nutrition to the skin and help in thermoregulation  Sweat gland opening Scanning electron micrograph of the skin showing cells in the stratum corneum surrounding opening of a sweat duct  Functions of the skin(METABOLIC) Endocrine :Helps in Vitamin D synthesis which is essential for bone growth 7 dehydrocalciferol converted to cholecalciferol by UV light and then becomes 1,25 dihydroxychlecalciferol ( in liver and kidney) Exocrine: Sweat ( thermoregulation, excretion of waste) and sebaceous glands (lubrication of skin) Burns –depth and area of skin involved Superficial – epidermal Full thickness – All layers of injury with no blisters the skin are involved. Partial thickness – Subcutaneous tissue may epidermis and dermis are be affected partially involved Fourth degree –They  Superficial – Blisters extend beyond the skin into the soft tissue and are  Deep - hair follicles and considered as most glands are damaged severe type of burns  Provides protection against trauma, chemicals and invasion of pathogens Prevents water loss Epidermis Synthesizes vitamin D3 Sensory receptors detect touch, pain, pressure and temperature Co-ordinates immune responses to pathogens and skin cancers Functions of Skin Nourishes and supports the epidermis Papillary layer Sensory receptors for touch present Dermis Stores lipid reserves Attaches skin to deeper tissues Reticular layer Blood vessels assist in thermoregulation Sensory receptors detect pressure, vibrations  Hair follicles Produce hair Assist in thermoregulation Function of Accessory Exocrine glands Excrete wastes structures (sweat and sebaceous glands) Lubricate epidermis Protect and support tips of Nails fingers and toes Functions of skin Regulation of body temperature High temperature /strenuous exercise – sweat gland secretion increases Protection Physical abrasion, bacterial invasion, dehydration and ultraviolet radiation Sensation Abundant sensory nerve endings and sensory receptors Excretion Sweat – excrete water, salts immunity Langerhans cells in the epidermis Synthesis of vitamin D Exposure of the skin to ultraviolet radiation initiates synthesis of Vitamin D 9/3/20XX Presentation Title 43 Thank you