Histology: Integumentary System (Skin) - Short PDF

XY2141. HISTOLOGY. INTEGUMENTARY SYSTEM Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]с.u k  LEARNING OUTCOMES HISTOLOGY.12 - Integument 12.01 - List seven functions of skin 12.02 - Compare the overall structure of the epid...

XY2141. HISTOLOGY. INTEGUMENTARY SYSTEM Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected]с.u k  LEARNING OUTCOMES HISTOLOGY.12 - Integument 12.01 - List seven functions of skin 12.02 - Compare the overall structure of the epidermis, dermis and hypodermis 12.03 - Compare the structure of thick and thin skin and give their location in the body 12.04 - List the layers of the epidermis and describe their main features. 12.05 - Describe the steps involved in keratinization beginning at the basal layer. 12.06 - List those features which contribute to the pigmentation of skin 12.07 - Describe the structure and function of melanocytes. 12.08 - Explain how the rays of the sun cause darkening of the skin (tanning). 12.09 - Describe the structure and function of Langerhans cells. 12.10 - List the components of the dermis 12.11 - Name the sensory nerve endings in skin and give their function 12.12 - State how eccrine and apocrine sweat glands differ 12.13 - Describe the structure of the sebaceous gland 12.14 - List the changes that take place in the skin in response to: age, solar radiation, smoking, alcohol  OVERVIEW Integumentary system comprises of the skin and its derivatives: hair, nails, sweat glands, sebaceous glands, mammary glands. Skin is the largest organ of the body: 15-20% of total body mass, 1,2-2,3 m2 of body surface.  FUNCTIONS OF THE SKIN 1. Protection 2. Immune response 3. Sensation 4. Body temperature regulation 5. Storage and nutrient synthesis 6. Excretion 7. Absorption OVERVIEW OF THE SKIN Epiderm is Dermis Hypoder mis OVERVIEW OF THE SKIN  EPIDERMIS Most superficial layer of the skin Epidermis consists of stratified squamous keratinised epithelium Major functions: Maintenance of fluid and electrolyte balance Protection from ultraviolet light Sensation Immune function  REGIONAL DIFFERENCES OF THE SKIN The terms “thin” and “thick” skin refer to the thickness of the epidermis Thin skin = hairy skin (most of the body) – has no stratum lucidum Thick skin = hairless skin (glabrous skin on palmar/plantar surfaces, i.e. palms/soles) – has all 5 layers Stratum Corneum Stratum Lucidum Stratum Granulosum Stratum Spinosum Stratum Basale Thin Skin Thick Skin Mnemonic to remember the layers of the epidermis. Bottom to Top: Britney Spears Glows Like Candy (If you like her!) Britney Spears Grows Like Cancer (If you don't like her :P ) REGIONAL DIFFERENCES OF THE SKIN Thick skin Thin skin REGIONAL DIFFERENCES OF THE SKIN  Epidermis has 5 layers: 1. Stratum basale (innermost layer) Formed by one row of columnar or cuboidal keratinocytes connected to the basement membrane with hemidesmosomes. Basement membrane is corrugated  increases the strength of the connection with the dermis and the diffusion of nourishment. Layer contains also melanocytes, Merkel's cells and dendritic (Langerhans') cells. Germinal layer for the development of new keratinocytes and skin renewal (mitotically active cells). 2. Stratum spinosum Several layers of polyhedric keratinocytes with sharp protrusions (spines) - prickle cells Protrusions provide for the connection of the cells using desmosomes at their ends Enlarged intercellular spaces between interlocking cells enable for a better diffusion of nourishment to the more superficial layers of the skin Keratinocytes synthesise cytoplasmic intermediate filaments called cytokeratins which accumulate in aggregates called tonofibrils made up of bundles of tonofilaments Germinal layer for the development of new keratinocytes and skin renewal  Attention! Sensitive content will be shown next!  CLINICAL CORRELATION Pemphigus vulgaris is an autoimmune, intraepithelial, blistering disease affecting the skin and mucous membranes. Own antibodies destroy desmosomes of the epidermis. Type II hypersensitivity reaction. IgG antibodies against desmoglein-1 and/or desmoglein-3 (component of desmosomes, which connect keratinocytes in the stratum spinosum).  SKIN PARTICIPATES IN VITAMIN D3 SYNTHESIS First two deepest layers (basale and spinosum) participate in Vitamin D3 synthesis 3. Stratum granulosum (pH 7,1) House membrane-coating granules and non–membrane bound deposits of keratohyalin in which bundles of tonofilaments are embedded Flattened keratinocytes which begin to fill with keratohyalin with filaggrin and trichohyalin Contents of the membrane-coating granules lamellar bodies are exocytosed into the extracellular space superficial to the stratum spinosum  lipid barrier  prevents aqueous fluid from penetrating in either direction. Nucleus and cellular organelles disintegrate, cells gradually die  basis for the following keratinisation and enables the formation and maintenance of the stratum corneum.  WATER BARRIER 1) lamellar granules are released into the intercellular space, ensuring water tightness 2) Keratohyaline granules participate in deposition of insoluble proteins on the inner surface of the plasma membrane epidermal water barrier is represented by 2 components: intercellular (exocytosis of lamellar bodies) and intracellular component. 4. Stratum lucidum (in thick skin only) Only 1–2 layers of dead cells Thin layer (due to eleidin significantly eosinophilic) Visible only in strongly keratinised thick skin Flattened dead keratinocytes Keratohyalin begins to change to eleidin Lamellar granules are present 5. Stratum corneum (horny layer) (pH 5,1) various width based on the type of skin keratinisation eosinophilic layer without clear borders between the dead keratinocytes flattened keratinised layers are formed by the residues of dead keratinocytes without nuclei and cellular organelles cells are filed with keratin, which was formed by the transformation from eleidin desmosomes disintegrate by kallikrein-related serine peptidases which become active under low pH; a barrier against physical, chemical and mechanical damage together with the sebum, prevents the loss of water, minerals and proteins prevents skin wettability prevents the entry of foreign microorganisms *6. Stratum disjunctum (sometimes is mentioned) desquamating residues of dead keratinocytes. THICK SKIN. H&E Epidermis Dermis  THICK SKIN (low magnification on left, high magnification on right, H&E stain)  KERATINISATION Desquamatization: Layers of epidermis represent vertical maturation from undifferentiated basal cells to fully differentiated cornified cells Human skin is completely renewed in about 47 days. New keratinocytes are created in the germinative layer. Keratinisation involves breakdown of nucleus and organelles and thickening of plasma membrane Stratum corneum = corneocytes = dead cells with thick plasma membranes, cytoplasmic filaments, and interfilamentous matrix. CLINICAL CORRELATION - PSORIASIS Shorter maturation periods seen in inflammatory conditions such as psoriasis (rapid turnover of keratinocytes ~8–10 days).  CELLS OF THE EPIDERMIS Cells of the epidermis consist of 2 types: keratinocytes nonkeratinocytes. Keratinocyte is the predominant cell type of the epidermis. Originate in the basal epidermal layer. Functions: production of the major structural protein of the epidermis, keratin; formation of the epidermal water barrier.  NONKERATINOCYTES 1. Melanocytes are pigment-producing cells. derived from neural crest and produce melanin, a dark brown pigment. bodies of these cells are situated at the stratum basale, and highly branching processes - at the stratum spinosum.  MELANOCYTES Melanin is produced and stored in sacs called melanosomes Cytocrine secretion transfers melanin granules to the surrounding keratinocytes (melanocytes are often clear cells, pigment is accumulated in keratinocytes) Melanin is accumulated in keratinocytes in the cytoplasm over the nucleus to protect the DNA of multiplying cells. Epidermal melanin unit usually, 10-20 keratinocytes grouped with 1 melanocyte  SKIN COLOR Skin color is influenced by: Melanin: pigment within melanosomes Types: eumelanin (usual type) and pheomelanin (blonde and red hair) Number of melanocytes in normal skin is constant among races – approximately 1 melanocyte per 4-10 basal keratinocytes – but may vary from region to region within an individual Degree of skin pigmentation is dependent on melanosomes in keratinocytes – their number, size, location within the cell (closer to the nucleus in fair-skinned), stability, and degree of melanization Gray hair are due to decreased number and activity of melanocytes in follicular bulbs.  MECHANISM OF TANNING Tanning is due to increased rates of melanin darkening, transfer of melanosomes to keratinocytes, and melanin production Increased pigment shields nucleic acids and proteins from UV radiation.  NONKERATINOCYTES 2. Langerhans' cells are star-shaped cells, found mainly in the stratum spinosum. Primitive yolk sac and fetal liver hematopoiesis contribute to the initial formation of Langerhans’ cells Inflammatory changes in the skin result in their replacement by blood-bone progenitors capable of presenting antigens to T lymphocytes. Bierbeck’s granules (tennis racket vesicles) are structures of tennis racket-like shape in the cytoplasm of Langerhans' cells (visible only under EM).  NONKERATINOCYTES 3. Merkel's cells spheric cells in the stratum basale of the epidermis Merkel’s tactile menisci – functional connection with nerve fibers mechanoreceptors for fine touch, higher concentration in the finger pads contain neurosecretory granules in the cytoplasm origin is not completely clear; phylogenetically, they are probably specialized keratinocytes or neuroectoderm cells. CELLS OF THE EPIDERMIS  CLINICAL CORRELATION CUTANEOUS ROOT FOR DRUG DELIVERY: Lipid-soluble drugs can be absorbed by skin when applied as ointment, spray, or patches.  DERMIS OR CORIUM Strong layer of connective tissue (CT) of mesodermal origin, important mainly for the nourishment of the skin and its mechanical strength. Dermis contains two layers: papillary reticular.  PAPILLARY DERMIS (STRATUM PAPILLARE) Papillary dermis – superficial layer of vascular loose collagenous CT Dermal papillae (papillae dermidis) – protrusions located against the epidermal ridges Increase the contact area with the epidermis, reinforce the dermoepidermal connection and improve the nourishment of the dermis *Also results in an undulating pattern which vary by anatomic location and individual resulting in grooves in the epidermis = dermatoglyphics (fingerprints).  RETICULAR LAYER (STRATUM RETICULARE) Reticular layer - deeper, thicker, composed of irregular dense CT. Contains thick, irregular bundles of mostly type I collagen and elastic fibers. This elastic network is responsible for the elasticity of the skin. RETICULAR LAYER (STRATUM RETICULARE) Sebaceous Glands Reticular Dermis Erector Pili Hair Follicle muscle LANGER’S LINES Collagen and elastic fibers form regular lines of tension in the skin, called Langer’s lines. Skin incisions are usually made parallel to Langer’s lines.  HYPODERMIS (SUBCUTANEOUS TISSUE) Mixture of LCT + adipose tissue The thickness is variable. Hypodermis  DERMAL APPENDAGES Sebaceous Glands Hair Follicle Eccrine Sweat Glands Pilar Muscle  SWEAT GLANDS Produce sweat for perspiration. Besides excretion of products of metabolism these glands help in temperature regulation by sweating. Sweat gland consists of 2 parts: – secretory portion lies deep in the dermis, lined by a simple cuboidal epithelium. – ducts (excretory portions) are lined by 2 layers of dark cuboidal cells.  TYPES OF THE SWEAT GLANDS There are 2 types of sweat glands - merocrine and apocrine.  ECCRINE GLANDS Merocrine sweat glands Release to adjust body temperature Cholinergic regulation Secretory portion: 3 cell types: – Dark cells: pyramid shaped with secretory granules line lumen of tubule; contain more ER, produce proteins, ions, metabolites – Clear cells: located toward basement membrane; produce water proximal section of the duct – Myoepithelial (basket) cells: spindle participates in the reuptake of ions shaped contractile cells, facilitate sweat and processing the primary sweat to the secondary sweat (only ions secretion without water are absorbed, thus Duct is lined by double layer cuboidal epithelium. creating hypotonic sweat)  APOCRINE GLANDS Apocrine glands – also merocrine – Larger lumens and ducts empty onto superficial regions of hair follicle – Release product by shedding of part of cytoplasm = apocrine snouting – Influenced by hormones (sexual scent glands) – Only found on axilla, areola, perianal and genital area – Secrete pheromones – Adrenergic regulation APOCRINE GLANDS  SEBACEOUS GLANDS Usually associated with hair follicles Simple branched acinar glands – Several acini (rounded secretory portions) that empty into single duct Holocrine secretion Empty “sebum” into hair follicle Secretory portions (the acini) covered by stratified epithelium Consists of 2 types of epithelial cells: – small outmost basal cells rest on the basal lamina. – inner cells are larger, more rounded and filled with lipid. – cells gradually, from the perimeter to the duct, undergo lipid degeneration – filed with lipid vacuoles, nucleus shrinks (pyknosis).  Sebaceous glands, that opens into a hair follicle together, they form a pilosebaceous unit * free sebaceous glands present only in the eyelid, in the external acoustic meatus, nasal wing, red part of lip, nipple, labia minora, internal surface of the preputium and around the anus. SEBACEOUS GLANDS Changes that take place in the skin in response to: age, solar radiation, smoking, alcohol  BOTOX Botox (Botulinum toxin) injections relax the muscles in your face to smooth out lines and wrinkles, such as crow's feet and frown lines. It's not permanent – it usually lasts for around 3 or 4 months. MCQ test for self-control https://forms.gle/KrNxLLLTxVNHVhUy6 References