Skin and it’s Appendages

Hsiao, Hsiao-Sheng 5-4-2012

Skin

- The largest organ

- Divided into two distinct layers

• dermis (mesoderm)

dermis

• epidermis (ectoderm) epidermis

Epidermis

Contains four main cell types

- Keratinocytes : most abundant cell type in epidermis

- Melanocytes (neural crest cell)

- Merkel cells

- Langerhans cells

• produce keratin ( a tough fibrous protein)

• melanin

Layers of Epidermis

Stratum basale (Stratum geminativum)

Stratum spinosum

Stratum granulosum

Stratum lucidum

Stratum corneum

Stratum basale (Stratum geminativum)

Stratum spinosum

Stratum granulosum

Stratum corneum

Stratum basale (Stratum geminativum)

Stratum spinosum

Melanocytes

Stratum basale (Stratum geminativum)

Stratum spinosum

Stratum spinosum

- Exhibit numerous cytoplasmic processes or spines

Keratohyaline granules Only in thick skin

e.g. palms and soles

Stratum granulosum

Stratum lucidum

Stratum granulosum

Keratohyaline granules

Stratum corneum

- The flattened, desiccated, anucleate cells

- Filled with keratin filaments

Stratum corneum

- The flattened, desiccated, anucleate cells

- Filled with keratin filaments

Junction of the epidermis and dermis

Dermal papillae

Epidermal ridges

General sensory receptors are

- Divided into two groups

• Free nerve ending

• Encapsulated nerve ending

＊ Meissner’s corpuscle

＊ Pacinian corpuscle

Meissner’s corpuscles

-Spiraling nerve ending surrounded by modified Schwann cells

-Occur in the dermal papillae

-Rapidly adapting receptors for light touch

-Occur in sensitive, hairless areas of the skin

Pacinian corpuscles

-Single nerve ending surrounded by layers of flattened Schwann cells

-Occur in the deep portion of dermis

-Sensitive to deep pressure rapidly adapting receptors

Inner core

Inner core

A single large

unbranched

non-myelinated

nerve fiber

Appendages of Skin

• Hair follicle

• Nail

• Sweat gland

Sweat glands

-widely distributed on body

-Secretory units and excretory units

Myoepithelial cells Excretory unit

Secretory unit

Secretory unit

Excretory unit

Myoepithelial cells

Shalf

Root

Hair

- Flexible strand of dead, keratinized cells

- Hard keratin- tough and durable

Hair follicle

- External root sheath from epidermis

- Internal root sheath from matrix cells

Hair follicle

- Glassy membrane

- External root sheath

- Internal root sheath

Hair follicle

- Glassy membrane

- External root sheath

- Internal root sheath

Hair bulb

- Deep, expanded end of the hair follicle

Dermal papilla

Dermal papilla

Hair matrix

Sebaceous glands

- Occur over entire body- except palms and soles

- Secrete sebum; holocrine secretion

-Develop as outgrowths of the external root sheath

of the hair follicle

Sebaceous glands

- Simple alveolar glands

- Acinar form

Arrector pili muscle

- Boundle of smooth muscle

- Hair strands erect when arrector pili contracts

Nail root

Nail fold

Nail matrix

Nail plate

Nail bed

Hyponychium

Lunula

Eponychium

Nail

- Scalelike modification of epidermis

- Made of hard keratin

- Parts of the nail

Nail plate

Hyponychium

Nail fold

Nail root Nail matrix

Nail bed

Nail

Eponychium

Nail plate

Nail bed