Integumentary System The 3 layers of skin Epidermis

Integumentary System The 3 layers of skin • Epidermis – Stratified squamous keratinized epithelium – Grows continuously • Dermis – Connective tissue – Mechanical support • Hypodermis (Subcutaneous fascia) – Contains adipose tissue – A. k. a. superficial fascia from anatomy

Epidermis and dermis Epidermis (purple) Dermal papillae Dermis • Superficial papillary layer contains loose connective tissue, blood vessels, nerves, and lymphatics • Deeper reticular layer has dense fibrous irregularly arranged connective tissue

Layers of epidermis • Stratum basale (germinativum) – Single layer of cells on basal lamina – Stems cells which give rise to keratinocytes – Contain melanin transferred from melanocytes – May see mitotic figures – Desmosomes and hemidesmomes

Layers of epidermis • Stratum spinosum – Several cells thick – Cytoplasmic processes (spines) – Desmosomes

Layers of epidermis • Stratum granulosum – Boundary between non -keratinized and keratinized layers of epidermis – 1 to 3 cells thick – Keratohyalin granules contain cystine-rich and histidine-rich proteins that associate with keratin filaments

Layers of epidermis • Stratum lucidum – Present only in thick skin – Cells in which keratinization is advanced

Layers of epidermis • Stratum corneum – Superifical keratinized layer – Cells • • Almost filled with keratin Flattened, anucleate Most differentiated Coated with extracellular lipids that form water barrier of skin • Layer that varies most in thickness

Structures of skin: nerve Meissner’s corpuscle • Touch receptor • Within dermal papillae, just beneath epidermal basal lamina • Perpendicular to skin surface • Contains Schwann cells and unmyelinated endings of nerve fibers

Structures of skin: nerve Pacinian corpuscle • Larve ovoid structures in deep dermis and hypodermis • Myelinated nerve ending surrounded by capsule • Concentric lamellae, looks like an onion cut in half • Responds to pressure and vibration

Structures of skin: hair follicle • • • Invagination of epidermis Hair contains keratin and melanin Dermal papilla – Connective tissue invagination into bulb, has capillary network • Matrix – Germinative layer adjacent to dermal papilla – Also contains melanocytes • Sebaceous gland – Secretion empties into hair follicle • Arrector pili muscle – Smooth muscle, inserts on hair follicle and base of epidermis (dermal papilla) bulb

Structures of skin: sweat glands Two types of sweat glands – Eccrine • Not associated with hair follicle • Duct segment – less coiled, leads to epidermis – Stratified cuboidal epithelium • Secretory segment – in deep dermis or hypodermis – Secretory cells – Myoepithelial cells lie between secretory cells, contraction expels sweat – Pseudostratified epithelium – Apocrine • Found in limited areas • Empty into hair follicle