Histology Of The Integumentary System

Histology of the Integumentary System

Body Membranes  EPITHELIAL 

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Cutaneous- Skin = Epidermis (stratified squamous epithelium) + Dermis (dense irregular connective tissue) Mucous- Mucosae- mucin-secreting ‘moist’ lining of body cavities that open to the outside (respiratory; digestive; genito-urinary; reproductive) = lining epithelium + lamina propria Serous- Serosae- line closed body cavities

Body Membranes  CONNECTIVE

TISSUE Membranes derived from the mesoderm

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Synovial membrane - no epithelium; lines the fibrous capsule surrounding joints, providing a smooth surface & secreting a lubricating synovial fluid; & also lines the small sacs, the ‘bursae’ of connective tissues, & tendon sheaths

Embryology Primary Ectoderm Neuroectoderm Neural tube

gland

Neural Eccrine crest

Extracutaneous Sympathetic NS

2° Ectoderm

Epidermis Melanocytes

Melanoblasts

Pilar complex

Skin  Epidermis -

stratified squamous epithelium; its thickness determines thickness of the skin  Dermis - also ‘Corium’ or ‘Cutis’- dense irregular (fibroelastic) connective tissue - contains glands & follicles that are derived from

The Epidermis 

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Stratum corneum - 20 to 30 cell layers, it constitutes 75% of epidermal thickness; renews every 35-45 days - consists of cornified horny cells ‘corneocytes ’- in a loose basketweave pattern - keratin - on the surface - very tough protein; mechanical barrier; impervious to water Stratum lucidum - clear zone - rich in elastic fibers- usually seen in acral portions of the body; cells appear homogenous Stratum granulosum - 3 to 5 cell layers, its thickness is usually proportional to

The Epidermis 

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Stratum spinosum/malpighii - 2 to 6 cell layers - gives mechanical stability to the skin; cells are closely attached to one another - consists of polygonal cells with abundant desmosomes- ‘prickle’ or ‘spinous’ cells; the upper cells contain lamellar bodies also known as ‘keratinosomes’ ‘cementosomes’ or ‘Odland bodies’ Stratum germinativum/basale - single layer of flat, cuboidal, or columnar cells attached to the underlying basement membrane by hemidesmosomes, & to the upper cells by

Other Cells of the Epidermis 

Langerhans cells - comprise 3 to 8% of epidermal cells - indented nucleus; cytoplasmic racquetshaped Birbeck granules - immunologic function - help present Ag to helper T lymphocytes

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Merkel cells - found only in the basal layer, cells have irregular lobulated nuclei & cytoplasm with membrane bound granules - abundant in areas with high tactile sensitivity; innervated by myelinated nerve fibers Melanocytes - about every 10th cell in the basal

Other Elements in the Epidermis  Herxheimer

spirals - thick bundles of intracellular tonofibrils that form the attachment of desmosomes

 Colloid

bodies - also ‘hyaline’ ‘civatte’ ‘eosinophilic’ bodies - deeply eosinophilic, degenerated epithelial cells

 Keratin -

very stable protein- can be dissolved only by strong acid; impervious to water

 Melanin -

yellow to brown to black pigment produced by melanocytes; acts like a

Keratin & Melanocytes/Melanin

The Dermis 

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Papillary (superficial) layer - irregular mesh of collagen fibers; - uneven, undulating contour due to dermal papillae – folds of dermis that increase the contact area between the epidermis & dermis; (rete ridges- epidermal folds) - stains pale pink with H & E - contains capillary loops, cutaneous receptors, sweat pores Reticular (deep) layer - coarser, criss-crossed collagen bundles; - deeply eosinophilic with H&E - with blood vessels, sweat & oil glands,

Dermal papillae & Rete ridges

The Dermis Blood Supply  

Rete cutaneum - deep network of branches of the main arteries that supply the skin Rete subpapillare - network at the junction between papillary & reticular layers; small arterioles branch into the papillae

Extracellular Matrix & Fibers  

Glycosaminoglycans: Hyaluronic acid, Chondroitin sulfate, Dermatan sulfate mostly Type I Collagen fibers + some type III; Elastic fibers

Cells of the Dermis  Fibroblasts

produce cells

- fusiform or stellate cells that collagen - main parenchymal

 Mast

cells - analogues of basophils found around blood vessels - contain metachromatic cytoplasmic granules

 Macrophages

Histiocytes

 Wandering

- phagocytic cells –

cells - transients - erythrocytes,

Dermal Appendages: Glands 

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Sebaceous (oil) - found all over the skin EXCEPT in palms & soles - ducts empty into hair follicles or skin surface - holocrine type of secretion - Sebum - mixture of oils & fragmented cells; abundant triglycerides & FFA; keeps hair supple & skin soft; - also has antibacterial properties Sudoriferous (sweat) : >2.5 million/person Eccrine - distributed all over the body EXCEPT in the Lips, Clitoris, Penis, & Labia majora; - coiled glands in the deep dermis, pores open to skin surface 

Sebaceous glands

Dermal Appendages: Glands 

Apocrine - limited to the axillary & genital areas, nipples, face, scalp, & anterior trunk; larger, complex glands; cells are large plump eosinophilic - ducts open into hair follicles or onto skin surface - secretion is a milky to yellowish fluid, rich in fatty acids, proteins, H2O & salts; odorless, but bacterial action can produce an unpleasant odor (‘body odor’) Ceruminous glands - in the ear; secrete Cerumen

Eccrine & Apocrine Glands

Dermal Appendages Hair - present on body surfaces EXCEPT in

the hands, feet, lips - flexible, tubular; minor protective function in humans, more of an aesthetic role Hair follicle – tubular invaginations of the epidermis;  Bulb - inferior end- basaloid cells & melanocytes  Matrix - growth zone; dark mass of cells 

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Papilla - dermal papilla invaginating into the bulb Root - enclosed by dermal & epidermal sheaths Shaft : consists of the medulla (core); cortex; & cuticle; its shape determines

Dermal Appendages 

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Arrector muscle/Arrectores pilorum muscle - smooth muscle connected to hair - contraction pulls the hair upright Haarscheibe - round dermoepidermal disc in close vicinity to hairs - is a slow-adapting touch receptor Sensory Receptors - Pacinian corpuscles (pressure); Krause end-bulbs (warmth); Ruffini’s (cold); Meissner’s (touch);

Dermal Appendages

Dermal Appendages Nail - scale-like 

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modification of the epidermis Nail bed - stratum germinativum Nail matrix Root Body with free edge Cuticle Nail fold Eponychium Hyponychium Lunula

Skin: Other Considerations  

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Skin thickness Skin color - results from a combination of factors: - amount & kind of Melanin - amount of Carotene - level of Oxyhemoglobin in blood/ skin circulation General functions:  Protective vs chemical, biological, ultraviolet, mechanical, thermal damage/invasion & dessication  Excretory - sweat, sebum, cerumen (urea, uric acid, water, salts)

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