Integumentary system

• Organization– Skin

• Epidermis• Dermis

– Accessory Structures• Hair & Hair follicles• Exocrine glands• Arrector pili• Sensory Receptors

• Layers beneath the skin – Subcutaneous layer – Deep fascia

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• Functions of the Skin– Protection– Water-resistance– Temperature regulation– Vitamin D synthesis– Sensations– Immunity – Social signaling

– Stratum Germinativum• Stem cells • Melanocytes• Merkel cells

The Epidermis

– S. Spinosum• “Pre-keratinocytes”• Melanocytes• Langerhans cells

The Epidermis

– S. Granulosum – S. Lucida

• Keratinocytes in both layers

The Epidermis

– S. Corneum• Dead keratinocytes

The Epidermis

Skin cell-eating mite

The Dermis

The Dermis

• Reticular layer– Dense irregular CT– Provides strength

and elasticity

The Dermis

• Papillary layer– Areolar CT– Contains cap’s and

sensory neurons for epidermis

– Arranged as dermal papillae

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• Perform secretory functions

• Perform transport functions

• Maintain physical integrity

• Ciliated epithelia move materials across their surface

Specializations of epithelium

The Polarity of Epithelial Cells

• Cells attach via cell adhesion molecules (CAM)

• Cells attach at specialized cell junctions– Tight junctions– Desmosomes– Gap junctions

Maintaining the integrity of epithelium

Intercellular connections

Animation: check tutorials

• Basal lamina attaches to underlying surface– Lamina lucida– Lamina densa

• Germinative cells replace short-lived epithelial cells

Structure of typical epithelium

• Number of cell layers– Simple– Stratified

• Shape of apical surface cells– Squamous– Cuboidal– Columnar

Classification of epithelia

Squamous Epithelia

Cuboidal Epithelia

Cuboidal Epithelia

Transitional Epithelium

Columnar Epithelia

Columnar Epithelia

Columnar Epithelia

Pigmentation

• Melanin

• Carotene

• Hemoglobin

Epidermal Derivatives

• Hair Follicles and Hair

• Skin Glands

Hair

• Function– Protection– Touch Sensation

• Structure– Root– Shaft– Bulb

Hair

• Hair Follicle– Sheath of epithelial

cells– Surrounds root– Merges with bulb

Hair

• Associated structures– Dermal papilla– Sebaceous glands– Arrector pili

Hair

• Growth Cycle– 2-5 yrs: growth

stage– 2 yrs: resting stage

Skin Glands

• Sebaceous glands– secrete sebum– help to protect hair

and skin

Skin Glands

• Merocrine (eccrine) sweat glands– BT control– excretion– protection

Skin Glands

• Apocrine sweat glands– Secrete pheromones?

Skin Glands

• Mammary glands

• Ceruminous glands

Skin Sensory Receptors

• Free nerve endings

• Pacinian corpuscles

• Meissner’s corpuslces

Lines of Cleavage

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