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Stratum Spinosum

The stratum spinosum (spy-NO-sum) consists of several layers of keratinocytes. The deepest cells undergo mitosis and contribute to the replacement of epidermal cells that exfoliate from the surface. As they are pushed farther

2F. S. Merkel (1845-1919), German anatomist

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

6. The Integumentary System

Text

© The McGraw-H Companies, 2003

Epidermis

Dermis

Hypodermis

Sensory nerves Motor nerve

Epidermis

Dermis

Hypodermis

Sensory nerves Motor nerve

Figure 6.1 Structure of the Skin and Its Derivatives.

Sweat pores Hair

Sebaceous gland Hair receptor

Arrector pili muscle Hair bulb

Apocrine sweat gland Merocrine sweat gland

Adipose tissue

Arteriole Venule

Figure 6.1 Structure of the Skin and Its Derivatives.

Dead-

keratinocytes

Living-

keratinocytes

Dendritic cell

Tactile cell

Melanocyte

Sensory nerve ending

Tactile cell

Melanocyte

Dermis

Stratum corneum

Stratum lucidum Stratum granulosum

Stratum spinosum

Stratum basale

Dermis

Friction ridges

Stratum corneum

Stratum lucidum Stratum granulosum

Stratum spinosum

Stratum basale

Dermis

Friction ridges

Stratum corneum

Stratum spinosum

Stratum basale

Dermis

Figure 6.2 Layers and Cell Types of the Epidermis. (a) Drawing of epidermal layers and cell types. (b) Photograph of thick skin from the fingertip. Shows two of the surface friction ridges responsible for the fingerprints. Can you identify a stem cell in figure a?

Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

194 Part Two Support and Movement

194 Part Two Support and Movement

Figure 6.3 Layers of the Dermis. (a) Light micrograph of axillary skin, with the collagen stained blue. (b) The papillary layer, made of loose (areolar) tissue, forms the dermal papillae. (c) The reticular layer, made of dense irregular connective tissue, forms the deeper four-fifths of the dermis. Figures b and cfrom R. G. Kessel and R. H. Kardon, Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy (W. H. Freeman, 1979).

Figure 6.3 Layers of the Dermis. (a) Light micrograph of axillary skin, with the collagen stained blue. (b) The papillary layer, made of loose (areolar) tissue, forms the dermal papillae. (c) The reticular layer, made of dense irregular connective tissue, forms the deeper four-fifths of the dermis. Figures b and cfrom R. G. Kessel and R. H. Kardon, Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy (W. H. Freeman, 1979).

upward, however, they cease dividing. Instead, they produce more and more keratin filaments, which cause the cells to flatten.

When skin is histologically fixed, keratinocytes shrink and pull away from each other but remain attached to their neighbors by several desmosomes. These create bridgelike extensions where one keratinocyte reaches out to another across the gap—a little like two people holding hands while standing farther apart. These bridges give the cells the spiny appearance for which the stratum spi-nosum is named.

The stratum spinosum and stratum granulosum also contain dendritic3 (Langerhans4) cells. These are macrophages that arise in the bone marrow but migrate to the stratified squamous epithelia of the epidermis, oral cavity, esophagus, and vagina. The epidermis has as many as 800 dendritic cells per square millimeter. They help to

3dendr = tree, branch

4Paul Langerhans (1847-88), German anatomist protect the body against pathogens by capturing foreign matter and "presenting" it to the immune system for a response.

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