Integumentary system histology

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Dr Pankaj Maheria

Learning Objectives: : 

Learning Objectives: Describe its overall structures of skin a nd list the basic functions of the skin State the names of the layers of the epidermis and how to distinguish them histologically Name the non- keratinocytic cells in the epidermis and describe their functions Explain the structures and components in the dermis Describe the segments and components of skin derivatives; hair, sebaceous gland, nail Describe the structures and functions of sweat glands

Skin is actually our first piece of clothing (Our birthday suit).: 

Skin is actually our first piece of clothing (Our birthday suit).

SKIN: 

SKIN Largest organ in the body , both in weight and surface area. Heaviest organ – 16% of body weight Thickest over back( approximately 5mm) and thinnest over eyelid ( approximately 1 mm) . Types of skin: Thick (non-hairy) Thin (hairy)

SKIN: 

SKIN Functions of Skin: Protection barrier against physical, chemical & biological agents Water Sensory function Vitamin D production Lipid soluble drug absorption (topical steroids) Thermoregulation Sexual attractant

Skin: 

Skin - 3 main regions 1. Epidermis : keratinized stratified squamous 2. Dermis : dense, fibrous connective tissue - blood vessel, nerves 3. Hypodermis” or subcutaneous (loose) CNT - connect dermis to underlying tissue and structure - adipose tissue - permit great mobility of skin The integument is composed of - Epidermis , Dermis - specialized derivatives of the skin eg. hair, sweat gland, sebaceous gland, nail Structure of skin Hypodermis Dermis Dermal-epidermal junction Epidermis

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Skin

Skin appendages: 

Skin appendages Hair and its associated structures: Hair follicles Sebaceous glands Arrector pili muscles Apocrine sweat glands Merocrine (Eccrine) sweat glands Nails

Classification of Skin (Based on the thickness of the epidermis): 

Classification of Skin (Based on the thickness of the epidermis) Thick skin Thin skin

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Thick skin Occurs on palms and soles. Stratum lucidum is prominent Has eccrine sweat glands Lacks hair follicles, sebaceous glands, or arrector pili muscles. Thin skin Occurs everywhere on body except palms and soles. Stratum lucidum is not very prominent and thin stratum corneum. Has eccrine sweat glands. Has hair follicles, sebaceous glands, arrector pili muscles .

Epidermis: 

Epidermis

Skin layer : 

Skin layer Epidermis : Stratified squamous keratinized epithelium Cells are known as Keratinocytes.

Skin architecture : 

Skin architecture Epithelial cells. Keratinocytes Non-epithelial cells Protect against sunlight (Melanocytes) Recognize external antigens (Langerhans cells) Mechanoreceptor function (Merkel cells). Rete ridges or epidermal pegs

Layers of the epidermis and keratinization : 

Layers of the epidermis and keratinization The epidermis is a stratified squamous, keratinized epithelium. It is continually renewed every 15–30 days. Rapid cell proliferation occurs in the deepest layer (stratum germinativum or basale) Daughter cells differentiate as they migrate toward the surface. This differentiation involves a process called keratinization. Cells in the epidermis that undergo the keratinization process are called keratinocytes.

Skin layer : 

Skin layer Layers of epidermis: Stratum corneum, in which keratinocyte gradually migrates to the surface and is sloughed off in a process called desquamation Stratum lucidum (prominent in thick skin) Stratum granulosum Stratum spinosum (thickest) Stratum germinativum or basale

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Layers (strata) of the epidermis Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum

Stratum germinativum (basale): 

Stratum germinativum (basale) The cells are arranged as a single layer of cuboidal or low columnar cells which connect to the cells of the prickle cell layer above and the basement membrane below and are mitotically active. The basal aspect of each basal cell is highly irregular and bound to the basement membrane by hemidesmosomes .

Basal layer (stratum basale): 

Basal layer (stratum basale)

Stratum germinativum (basale): 

Stratum germinativum (basale) These cells contain intermediate filaments composed of keratin . Melanocytes & Merkel cells are present in this layer.

Stratum spinosum: 

Stratum spinosum Thickest layer of the epidermis. “Prickle-cell” or spiny cell layer, polyhedral in shape. This layer is so-called because the cells are attached to one another by desmosomes , (node of Bizzozero ) Cellular shrinkage resulting from fixation produces the spine-like structures.

Stratum spinosum: 

Stratum spinosum Cells accumulate bundles of keratin filaments called tonofibrils. Langerhans cells are present in the prickle cell layer . Malphigian layer – Stratum basale + Stratum spinosum

Stratum granulosum: 

Stratum granulosum The cells of the granular layer begin to lose their polyhedral shape and become progressively more flattened nearer the surface.

Stratum granulosum: 

Stratum granulosum Two to four cells thick Cells synthesize basophilic, keratohyalin granules (cysteine & histidine rich), which associate with the tonofibrils. The combination of tonofibrils with keratohyaline produces keratin.

Stratum granulosum: 

Stratum granulosum Cells also accumulate oval lamellated bodies called keratinosomes or Odland bodies Contain A lipid material serves as a sealant and penetration barrier between cells.

Stratum Lucidum: 

Stratum Lucidum More prominent in thick skin (palms & soles only). Flattened non- nucleated cells with desmosomes.

Stratum corneum: 

Stratum corneum Consists of flattened, desiccated cells filled with keratin filaments and coated with a glycolipid that serves a water barrier function. As the keratin accumulates, the cells become enucleated and desiccated and they move through stratum lucidum to the outermost layer, stratum corneum.

Skin is impermeable to water: 

Skin is impermeable to water Because Keratosomes in the granular layer contain a water repellant glycolipid. Keratin is impermeable to water. Hemidesmosomes between basal layer & basement membrane. Desmosomes between other cells holds them together.

Epidermis cell types : 

Epidermis cell types Keratinocytes are the most numerous and are responsible for the production of keratin proteins that provide the barrier function of the epidermis.

Melanocytes: 

Melanocytes Neural crest in origin and located in the basal layer of epidermis. Synthesize melanin From precursors tyrosine and dihydroxyphenylalanine (DOPA) A dark brown pigment that is packaged into melanosomes and transferred to the keratinocytes by cytocrine secretion( phagocytosis of the tip of melanocytes)

Melanocytes: 

Melanocytes The critical enzyme involved in converting tyrosine into melanin is tyrosinase . Melanin caps the nucleus, reducing damage from solar radiation. Increased exposure to UV light, leads to an increase in melanin production , and thus protection from the harmful effects of the radiation.

Melanocytes: 

Melanocytes Pale staining No tonofibrils but contains scanty tiny round or oval dark stain bodies

Melanin: 

Melanin The number of melanocytes is nearly the same for all races, with differences in skin color arising from the amount and location of melanin in the keratinocytes. 3 types of genetically determined melanin: Eumelanin – dark, brown black (prominent in human) Pheomelanin – red color ( lips, glans penis, vagina, nipple) Neuromelanin – Substantia nigra , locus ceruleus

Melanin and disease: 

Melanin and disease Addisons disease – increase in melanin Hyper pigmentation of the skin Lack of cortisol and overproduction of ACTH Albinism – lack of melanin Hereditary No melanin synthesis from melanocyte due to lack of tyrosinase May lead to skin carcinoma Vitiligo – damage to melanocytes Degeneration of entire melanocytes Depigmentation

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Addisons disease, hyperpigmentation

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Vitiligo Well-demarcated zones of pigment loss result from depletion of melanocytes .

Albinism: 

Albinism Congenital defect - Autosomal recessive Lack of pigment in the eyes, hair and skin. Usually associated with Decreased visual acuity Nystagmus (rhythmic side-to-side eye movements) Photophobia (light sensitivity)

Langerhans cells: 

Langerhans cells Langerhans cells lie among the keratinocytes of the stratum spinosum. These cells play a role in cell-mediated immune responses in the skin, with one role being to phagocytose foreign antigens.

Langerhans cells: 

Langerhans cells They extend long processes that radiate out from the cell body to interdigitate between the keratinocytes.

Langerhans cells: 

Langerhans cells Electron micrograph Typical cytoplasmic organelle of Langerhans cells, the Birbeck granule A rod-like structure with regular cross-striations, one end of which frequently distends in a vesicle so that they resemble a tennis racquet shape.

Merkel cell: 

Merkel cell Merkel cells are sensitive mechanoreceptors located in the basal layer of epidermis , especially in sensitive areas such as the fingertips. They contain neurosecretory vesicles and form a synaptic junction with the sensory nerve ending contacting the cell. Merkel’s corpuscle - combination of the neuron and epidermal cell.

DERMIS : 

DERMIS The dermis is a connective tissue layer of mesodermal origin below the epidermis and its basement membrane. The dermis-epidermal junction is characterized by numerous papillary interdigitations of the dermal connective tissue and epidermal epithelium. Dermal papillae - Upward, finger-like protrusion of connective tissue from the dermis.

Dermis :: 

Dermis : Function Thermoregulation and vascular supply to the avascular epidermis with nutrients. The dermis is composed of collagen and elastic fibres, and is responsible for the tone and texture of the skin.

Dermis : 

Dermis Two zones: A papillary dermis A reticular dermis.

Dermis: 

Dermis

Papillary dermis: 

Papillary dermis The papillary layer lies immediately beneath the epidermis. Composed of loose (areolar) collagenous connective tissue, mixed with thick elastic fibers. It contains the capillary loops that support, but do not penetrate the epidermis. It also contains Meissner's corpuscles , which are very sensitive mechanoreceptors. The intimate interdigitation of the dermal papillae with epidermal ridges strengthens the attachment of epidermis to dermis.

Reticular layer: 

Reticular layer The reticular layer lies below the papillary layer and is composed of dense, irregular collagenous connective tissue , with the collagen fibers lying mostly parallel to the surface. This layer contains sweat glands, sebaceous glands, hair follicles and arrector pili muscles.

Dermis: 

Dermis Cells in the dermis: Fibroblasts – produce ground substance, collagen & elastin Lymphocytes & mast cells Network of elastic fibers & collagen fibers . Many blood & lymph vessels Papillary layer vessels supply epidermis Hair follicles, sweat & sebaceous glands penetrate into the dermis Many sensory nerves located in the dermis

Dermal ridges & Epidermal pegs: 

Dermal ridges & Epidermal pegs Epidermal Pegs: Downward projections of the epidermis. Dermal Ridges: Corresponding upward projections of the dermis. Increased in areas of high friction.

Hypodermis : 

Hypodermis The hypodermis is a layer of loose vascular connective tissue infiltrated with adipocytes, and it corresponds to the superficial fascia of gross anatomy. Not a part of the integument. Panniculus adiposus (store house for energy) May contain the bases of sweat glands and hair follicles.

Skin appendages: 

Skin appendages Hair and its associated structures: Hair follicles Sebaceous glands Arrector pili muscles Apocrine sweat glands Merocrine (Eccrine) sweat glands Nails

Skin appendages: 

Skin appendages

Hair: 

Hair Long keratinized structures formed by germinal matrix cells , which are immediately adjacent to the dermal papilla. Continued mitosis of new cells in the germinal matrix pushes the hair upwards. Hair formation occurs in the bulb, the expanded base of the hair follicle. Consists of : Shaft – projecting out Root & Follicle – embedded in skin

Hair follicle: 

Hair follicle

Hair Root: 

Hair Root Medulla - forms axis of hair, formed by vacuolated cells of moderate keratinization Cortex – form bulk of hair; several layers of cells with high keratinization. Contains pigment that gives color Cuticle – formed by overlapping squamous cells that are heavily keratinized.

Hair Follicle: 

Hair Follicle Hair follicle ends in an enlargement called “hair bulb” which is lodged in a follicular involution of the epidermis. It contains mitotic cells. (str.Basale…melanocytes There is an invigilation of the dermis called “dermal papilla” which contains nerves & vessels.

Root sheath: 

Root sheath Inner root sheath: Multi-layered covering, resembles Str lucidum . Contains Cuticle of internal root sheath Huxley’s layer of 1-3 layers of cells & Henle’s layer of single layer of cubical cells.

Root sheath: 

Root sheath Outer root sheath: Similar to Malphigian layer. Separated from outer connective tissue sheath by “glassy membrane”.

Hair follicle: 

Hair follicle

Arrector Pili muscle: 

Arrector Pili muscle Bundle of smooth muscle fibers attached to the hair follicle just below the sebaceous gland. Extends & attached to dermal papilla. Contraction causes secretion of sebum into the hair follicle movement of sebum to the skin surface. Under sympathetic control Piloerection also caused by cold & fear.

Hair growth: 

Hair growth Growth Phase ( Anagen ): Proliferation of germinal matrix Length of this phase depends on location For eyebrows 4 mths, for scalp 3-7 years. Transition / Resting phase (Catagen): Follicles stop growing and hair detaches & retreats towards the surface. Quiescent phase (Telogen): Final resting phase Shedding phase Hair rudiment attached to follicle

Types of hair: 

Types of hair Terminal hair: Long & coarse found in scalp & beard in male Long and straight follicle Long anagen & short telogen phase. Vellus hair: Short & fine, short follicle Forehead & anterior surface of forearm.

NAILS : 

NAILS Nails, like hair, are a modified stratum corneum of the epidermis. They contain hard keratin that forms in a manner similar to the formation of hair. Nail matrix - germinative zone beneath the root. Cells divide & move distally.

NAILS : 

NAILS Nail plate that corresponds to the stratum corneum of the epidermis. Nail bed – nail plate rest on nail bed consist of cells corresponding to the stratum spinosum and stratum basale (germinativum).

NAILS : 

NAILS Nail root - The skin overlying the root of the nail its highly keratinized free edges is known as the eponychium . The skin beneath the free end of the nail is known as the hyponychium .

Nail: 

Nail Root – into the groove of the skin. Body – exposed portion. Free edge – that projects out. Nail color due to blood vessels in underlying dermis. Can indicate oxygen content. Nail grows 0.1mm/day. Finger nails grow faster than toe nails.

Nail: 

Nail Lunula – crescent shaped white area near root; cells are partially keratinized. (visible part of nail matrix) Eponychium – formed by str. corneum, keratinized edge of nail fold over lunula. Hyponychium – thickened epidermis below free edge of nail.

Sweat gland: 

Sweat gland Merocrine or eccrine : These are simple coiled tubular glands located in the deep dermis or superficial hypodermis. They have role in thermoregulation. Located in all regions of the body except the axillary , areola of the breast and anal regions ; produce a watery secretion that empties onto the surface of the epidermis by myoepithelial cells , that contract to aid in the expulsion of the sweat.

Sweat gland : 

Sweat gland Has 2 parts: secretory portion & duct Secretory portion has simple cuboidal epithelium that has mainly 3 types of cells Clear cells – pale cells resting on BM. Secrete watery sweat Dark (mucoid) cells – few, pyramidal cells contain granules of glycoproteins Myoepithelial cell – contractile cells located at BM.

Sweat gland : 

Sweat gland Duct – stratified cuboidal, cells smaller & darker. Absorb NaCl & glycoproteins. Secretion includes NaCl, ammonia, urea & uric acid . Secretion is HYPOTONIC .

Types of sweat glands : 

Types of sweat glands Merocrine or eccrine: These are simple coiled tubular glands located in the deep dermis or superficial hypodermis. They have role in thermoregulation. Located in all regions of the body except the axillary, areola of the breast and anal regions ; produce a watery secretion that empties onto the surface of the epidermis by myoepithelial cells , that contract to aid in the expulsion of the sweat.

Merocrine (eccrine) sweat gland: 

Merocrine (eccrine) sweat gland

Apocrine sweat gland: 

Apocrine sweat gland Restricted to the axillary , areola of the breast and anal regions; much larger diameter than eccrine gland. These glands become functional only at puberty. They are innervated by the sympathetic nervous system. Apocrine secretion occurs in response to emotional stimuli but not to heat. Viscous secretion containing proteins, carbohydrates and lipids. Bacteria act on lipids and produce odoriferous compounds. (Pheromones) Secrete sweat into the hair follicle.

Sebaceous glands: 

Sebaceous glands Sebaceous glands are simple, branched holocrine acinar glands and secrete sebum, an waxy oily substance that coats the hair follicle and skin surface. Sebaceous glands are common on the face, scalp and forehead, develop as an outgrowth of the external root sheath of the hair follicle.

Sebaceous glands: 

Sebaceous glands During maturation, the entire sebaceous gland cell becomes filled with sebum, which consists of a mixture of cholesterol and triglycerides .

Sebaceous glands: 

Sebaceous glands

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