Structure Function of Skin y1.pptx

Structure & Function of Skin Year 1 Dr Charlotte Illsley [email protected] PSQ C505 Intended learning outcomes By the end of this session, you should be able to: Describe normal human skin and the role it plays in homeostasis Describe the layers of the skin and the functions of each l...

Structure & Function of Skin Year 1 Dr Charlotte Illsley [email protected] PSQ C505 Intended learning outcomes By the end of this session, you should be able to: Describe normal human skin and the role it plays in homeostasis Describe the layers of the skin and the functions of each layer Define the main cell types and their functions Describe the accessory structures of the skin and the functions of each So, what is skin? (aka the integumentary system) The skin is the exterior covering of the body (~15% of your body weight) It weighs more than 3 Kg in the average adult Can cover almost 2 m2 Rapid turnover/repair It is the largest organ of the body It is supplied with blood vessels and nerves Functions of Skin? Structure of the Skin Epidermis – composed primarily of keratinocytes Dermis – composed mainly of connective tissue https://link.springer.com/referenceworkentry/10.1007/978-3-662-47398-6_4 Structure of the human epidermis E D STRATIFICATION – squamous epithelial cells arranged in layers upon a basement membrane only basal layer in contact with the basement membrane the other layers adhere to each other to maintain structural integrity DIFFERENTIATION – process in which cell changes from one cell type to another. Usually more The epidermis Specialised stratified squamous epithelium Keratinocytes make up the majority of cells > 90% Contain cytokeratin proteins 4 morphologically distinct layers - Basal, spinous, granular, corneal Basal layer thought to house the SC population Adhere to one another by desmosomes (a cytoskeleton-liked attachment junction connecting cells to one another in epithelia and some muscle tissues) Adhere to basement membrane via hemidesmosomes a – Stratum Corneum – desquamating keratinocytes; layers of flattened non-nucleated cells provide a barrier vs. trauma & infection b – Granular cell layer – lipids produced by keratinocytes are secreted into the extracellular spaces and forma barrier that retains water in the skin c – Spinous layer – appearance due to a combination of desmosome junctions which join keratinocytes and cell shrinkage during histological processing d– Basal layer – site of stem cells; high rate of cell division; keratinocytes divide here before moving The epidermis Keratin14 Keratin1 Integrinα6 Loricri n The epidermis Keratinocytes round/polygonal morphology Pink cytoplasm filled with keratin bundles Darker staining in the granular layer, kerahanuole granuoles Basal layer contains SC population and responsible for the symmetrical/asymmetrica l cell divisions Stratum basale Basal layer contains SC population and responsible for the symmetrical/ asymmetrical cell divisions Integrin-α6 Stem cells in the epidermis Ki67 Stratum spinosum As cells commit to terminal differentiation they increase steadily in size and switch from the expression of cytokeratin proteins K14/K5 to K1/K10 Keratin1 Spongiotic dermatitis Shows the spines in the spinous layer of the keratinocytes the oedema in the epidermis from this skin condition shows the strong desmosomes between the cells Stratum granulosum & Stratum corneum As spinous cells differentiate into the granular layer they become permeable, stop synthesising keratin, envelope proteins and make their final proteins such as filaggrin and loricrin The final step of terminal differentiation involves the destruction of cellular organelles, including the nucleus, and the secretion of lipids, packed in lamellar granules to form the cornified envelope https://www.mattek.com/products/epiderm/ Basement membrane Laminin Type IV collagen Fibronectin Hemidesmosomes Integrins Epidermis: non-keratinocyte cell types Melanocytes Melanin (gives rise to skin, hair and eye colour) Ubiquitous; seen in all races Same proportion of melanocytes (~8%) regardless of race It is amount and depth of melanin that accounts for differences by race Individuals with albinism don’t make melanin Helps to protect against UV radiation and ROS NO desmosomes https://www.sciencedirect.com/science/article/abs/pii/S0738081X19301245 Healthy epidermis NO desmosomes … Langerhans Cells Dendritic cells found in the mid-layer of the epidermis Assoc. with the presentation of antigens to sensitised T-lymphocytes Significant role on pathogenesis of delayed-type hypersensitivity states Limited capacity to divide https://www.frontiersin.org/articles/10.3389/fimmu.2018.00093/fu Merkel Cells Non-dendritic Basal distribution Often associated with nerve fibres Sensory function Contain small, membrane-bound vesicles which release neurotransmitter Desmosomes attach them to keratinocytes Contain cytokeratins (thus potentially thought to have an epithelial origin) Lymphocytes T- lymphocytes are highly represented in the skin. In healthy individuals, it is estimated there are twice as many in the skin compared to total blood circulation Cells of the adaptive immune system Found in mucosal epithelia, too (oral and gut) https://link.springer.com/referenceworkentry/10.1007/978-3-642-54596-2_925 The Dermis Papillary Dermis – comprised of loose areolar connective tissue Reticular Dermis – comprised of dense irregular connective tissue The Dermis Papillary dermis Reticular dermis Dermis A connective tissue; provides flexible but tough support for the epidermis/epithelium Separated from epidermis by the basement membrane Approx. 1-4mm thick (depending on age/body location) Contains blood & lymph vessels and nerves; these supply the skin as well as the adnexal structures Principal cell type is the fibroblast (synthesis ECM and collagen) providing the structural framework for tissues; plays a critical role in wound healing Numerous other cells incl. inflammatory cells Hypodermis (subcutaneous layer) Fat layer which separates the dermis from the deeper underlying tissues e.g. muscle and fascia Insulates the body; serves as an energy supply; cushions/protects the skin; allows for it’s mobility over 4 Appendages Adnexal Structures (hair, erector pili muscles, sebaceous glands, sweat glands) Hairs – shaft and follicle Erector pili muscles – smooth muscles stimulated by the sympathetic branch of the autonomic system; when they contract, the skin appears a ‘goosebumps’ Sebaceous glands – found in skin all over body (predominantly face & scalp; seen intraorally as Fordyce Spots) Sweat Glands Apocrine – associated with hair follicles; secret a ‘fatty’ mixture into the gland tubule Eccrine – major sweat glands; do not involve Sebaceous glands Simple Branched Compound Compound tubular Lipid-filled cells Holocrine secretion of sebum onto hair Cells replaced by mitosis Sebaceous gland secretions are stimulated by androgens & inhibited by estrogen. In puberty, acinar cells are more sensitive = Apocrine sweat glands Typically found in areolae of breast, axillae and genital regions Produce oily and protein-rich secretion Malodorous when in contact with commensal bacteria on the skin Secrete into adjacent hair follicle Pheromones Apocrine glands are not functional until puberty. In women secretions undergo cyclical changes under the influence of the menstrual cycle hormones. Collection of sensory information Specialized receptors for different modalities Fine touch Pressure Light touch Pain Temperature Primary cutaneous nerve branch in hypodermis with branching in dermis (and some free nerve endings in epidermis) Vasculature Nutrition Immune response Wound healing Stimulated by changes in body temp Activation of cutaneous (skin) receptors in response to environmental temp and hypothalamic receptors in response to core temp. Info processed by hypothalamus Age changes in skin Dry epidermis Thin epidermis Reduction in sebaceous gland activity Fewer melanocytes Slower repair Decreased Vit D production Reduced number of Langerhans cells Paler skin Reduced tolerance to sun exposure Thin dermis Fewer active follicles Sagging and wrinkling due to collagen and elastin fibre loss Thinner, sparse hair Reduced sweat gland activity Changes in distribution of fat and hair Due to reduction in sex hormone levels Tendency to overheat Reduced blood supply Slower healing Reduced ability to lose heat Hypodermis – aged skin Overall the volume of subcutaneous fat typically decreases Although overall proportion of subcutaneous fat throughout body typically increases until age 70. Fat distribution changes Face, hands and feet decrease Thighs, waist and abdomen increase Physiological significance may be thermoregulatory Figure 2. Differences in skin structure between young and aged skin https://link.springer.com/referenceworkentry/10.1007/978-3-662-47398-6_4 Ultra-violet (UV) radiation UVB (290-320 nm) acts preferentially on the epidermis Damaging melanocytes, keratinocytes and causes the production of proteolytic enzymes UVA (320-400 nm) penetrates deeper than UVB Exerts direct effect on both dermis and epidermis Figure 1. Wavelength-dependent penetration of UV radiation into hum Skin cancer Nonmelanoma skin cancers (most common) Epidermal tumours can be divided into two groups: melanoma and non-melanoma skin cancer (NMSC). Non-melanoma skin cancers are one of the most common forms of cancer in humans, accounting for 20% of malignancies in white populations and originates most frequently in sun exposed areas of the skin. In situ (Bowen’s disease) Invasive SCC 3 Skin cancer Healthy human skin Epidermi s Dermis Squamous cell carcinoma Epidemiology Incidence rates are known to be under-estimated Policies for the recording of NMSC are varied Excluded from figures for all cancers in many publications Unreliability in estimates that arises from variation in policies and practices in the diagnosis and treatment. Rich number of subtypes Registration of NMSC is not mandatory In some countries the first case in a patient is registered any subsequent cases are not recorded Systematic review of NMSC cases reveal a notably higher incidence in the south west in England, associated with the highest risk of UV radiation. SCC has been thought to have a higher incidence in males, but SCC originating on the legs has been found to be more common in females / s i s o n g a Di t …Observation is key! n e m t a Tre How long has it been there? The 5 S’s to describe a skin lesion 1. Site 2. Size 3. Shape 4. Surface, edge 5. Surroundings Why is this important for you to know? Dental management of patients with skin conditions Early referral For identification and quick treatment Sensitive treatment by understanding and knowledgeable practitioners e.g. Immunosuppressants Tetracycline (acne) Corticosteroids (asthma, IBS, RA) Skin conditions are very emotive for the sufferer Understanding of the effect of typical dermatological drugs on oral health/treatment Skin structure summary The Epidermis Intended learning outcomes By the end of this session, you should be able to: Describe normal human skin and the role it plays in homeostasis Describe the layers of the skin and the functions of each layer Define the main cell types and their functions Describe the accessory structures of the skin and the functions of each