Skin Anatomy PDF

SKIN Prof. F. Figen Kaymaz MD, PhD Department of Histology & Embryology [email protected] 1 OBJECTIVES: • To learn layers and the cells of the • • • • • epidermis Histological structure of the dermis Histophysiology of the skin Skin appendages Structural components of the sebaceous, eccrine...

SKIN Prof. F. Figen Kaymaz MD, PhD Department of Histology & Embryology [email protected] 1 OBJECTIVES: • To learn layers and the cells of the • • • • • epidermis Histological structure of the dermis Histophysiology of the skin Skin appendages Structural components of the sebaceous, eccrine and apocrine sweat glands, hairs & hair follicles, and nails. the development of the skin 2 •Skin: The largest organ, invests the entire body, continuous with the mucous membranes of the GIS, RS and UGS, with the conjunctiva at the eyelids. It lines the EAM and covers the external surface of the tympanic membrane. •Integument: Skin (epidermis & dermis) and its appendages (sweat glands, sebaseous glands, hair, nail) •Integument : constituting 16% of the body weight, weighs approx. 4 kg, thickness: 1-5 mm, surface area:2,10 m² (BW:70 kg), its color depends on vascularization and pigmentation 4 5 FUNCTIONS: • Protection: against injury, bacterial invasion, desiccation • Thermoregulation: regulation of body temperature by • • • • • blood vessels and glands of the dermis, and the adipose tissue of the hypodermis Reception: touch, temperature, pain Excretion: Na, K and Cl ions excretipn from sweat glands Absorption: of some lipid soluble material and UV radiation from the sun for vit D synthesis. Immune organ: SALT A water proof barrier: prevention of loss of water 6 SKIN: EPIDERMIS & DERMIS • Outer epidermis: composed of ectodermally derived • • • stratified squamous keratinized epithelium. Underlying dermis:derived from mesoderm, composed of irregular dense connective tissue, interdigitating with the epidermis Interface between the epidermis and dermis is formed by dermal ridges (papillae) interdigitating with epidermal invaginations (epidermal ridges). Both form the rete aparatus. Deepest hypodermis (superficial fascia): loose connective tissue containing varying amounts of fat 7 Epidermis: • Thickness: 0.07-0.12 mm. 0.8-1.4 mm on palms and • soles Stratified squamous keratinized epithelium with no neural and vascular elements, composing of: – – – – Keratinocytes Melanocytes Langerhans cells Merkel cells • Keratinocytes are arranged in 5 zones – – – – – Stratum Stratum Stratum Stratum Stratum basale (germinativum) spinosum granulosum lucidum corneum 8 -Stratum corneum -Stratum lucidum - Stratum granulosum - Stratum spinosum - Stratum basale 9 Keratinocytes: • Constitute the largest cell population • They are being continuously sloughed from the surface • and renewed from the basal layers by mitosis (at night) and pushed toward the surface. Along their migration towards the surface (20-30 days), they differentiate in five zones by accumulating keratin filaments in their cytoplasm – Thick skin: covers the palms and soles, lacks hair follicles, arrector pili muscles, sebaceous glands, but possess sweat glands (400-600 µm thick epidermis) – Thin skin: covers most of the body, has a thin str. corneum, lacks str. lucidum, has the hair follicles, arrector pili muscles, sebaceous and sweat glands, (75-150 µm thick epidermis) 11 Thin skin Thick skin 12 Stratum Basale (Germinativum) • Deepest layer adjacent to the • • basement membrane, siting on the dermis and forming an irregular interface Consists of a single layer of mitotically active, cuboidal to low columnar cells containing basophilic cytoplasm and a large nucleus Mitotic figures are common. Stratum Spinosum • Composed of several layers of polyhedral to flattened cells (thickest layer).Basal layers are mitotically active Stratum Granulosum • Consists of 3 to 5 layers of • flattened cells. Most superficial layer in which cells still have nuclei Stratum Lucidum • Present only in thick • • skin Consists of 4-6 rows of flat, clear, homogeneous, lightly stained cells Cells lack organelles and nuclei; 19 Stratum Korneum • Consists of several layers of flat cornified, keratinized dead cells • • with a thickened cell membrane. Cells lack nuclei and organelles, Thickness increase in areas with more friction Cells of Epidermis •Keratinocytes •Langerhans Cell •Merkel cell •Melanocyte Keratinocytes: • Constitute the largest cell population • They are being continuously sloughed from the surface • and renewed from the basal layers by mitosis (at night) and pushed toward the surface. Along their migration towards the surface (20-30 days), they differentiate in five zones by accumulating keratin filaments in their cytoplasm Cytomorphosis – Thick skin: covers the palms and soles, lacks hair follicles, arrector pili muscles, sebaceous glands, but possess sweat glands (400-600 µm thick epidermis) – Thin skin: covers most of the body, has a thin str. corneum, lacks str. lucidum, has the hair follicles, arrector pili muscles, sebaceous and sweat glands, (75-150 µm thick epidermis) Langerhans Cells • Antigen presenting • • dendritic cells located among the the keratinocytes of str spinosum. Originate from precursors in bone marrow Forming 2-4 % of epidermal cell population 24 Merkel Cells • Scattered among str basale • • • • keratinocytes Especially abundant in figertips, oral mucosa and at the base of the hair follicles. They form Merkel cellneurite complexes with unmiyelinated sensory nerves passing the basal lamina Merkel cells may release neurocrine-like substances. Act as Mechanoreceptors 25 Melanocytes • • • • located primarly among the str basale cells. Derived from the neural crest, Synthesizes Melanin This number does not depend on race or sex. 26 Dermis Dermis (Corium) • Irregular dense connective tissue deep to • • epidermis, binding the skin to underlying hypodermis Derived from mesoderm, thickness. 0.3-3mm Composed of a – superficial, papillary layer- Loose con. tissue – a deeper, reticular layer - Dense con. tissue 28 Dermis 29 Dermis 1. Connective tissue 2. Blood vessels 3. Skin apendages Hypodermis • Under the dermis • lipid layer • Connective tissue Skin appendages: 1. Hair follicles 2. Sebaceous glands 3. Sweat glands 4. Arrector pili muscles 5. Nails Sebaceous glands • Found throughout the body except for the palms and soles and sides of the feet inferior to the hairline. • Embedded in dermis and hypodermis, produce sebum (maintenance of skin texture and hair flexibility) Sweat glands • Eccrine sweat glands 34 Apocrine sweat glands • Found only in axilla, areola of the nipple, and anal region • The secretory cells have an odorless viscous • product upon secretion, gaining a distinctive odor after being metabolized by bacteria Secretion is controlled by hormones, starts to function with the puberty Arrector pili muscles • Smooth muscle fibers • attached to the CT sheath surrounding the hair follicles Their contractions errect the hair, when the body is cold 36 Dermatographs/dermatoglyphs • The free surface of the skin is marked by delicate grooves that are • • • deeper on non-hairy areas (knees, elbows, palms, soles). These surface patterns constitute the dermatoglyphs on the finger pads. These fingerprints determined genetically probably by multiple genes (by environmental factors on elbows, knees) They are used for identification of an individual especially for criminal purposes in forensic medicine. 37