Anatomy of the skin; the skin appendages

Skin anatomy

Skin layers

(A) Epidermis

1. Cell types

• Corneocytes (dead, anucleated keratinocytes)
• Keratinocytes
• Basal cells (stem cells for continuous production of keratinocytes)
• Melanocytes (production of melanin pigment)
• Langerhans cells (a type of dendritic cell characterized as antigen presenting cells - APCs)
• Merkel cells (mechanoreceptor nerve endings)

2. Layers

• Stratum corneum: the outermost layer of epidermis which consists of keratin filaments and corneocytes (dead, anucleated keratinocytes)
• Stratum lucidum: this layer is present only in thick skin such as palms and soles
• Stratum granulosum: this layer consists of keratinocytes that become flat and lose their nuclei
• Stratum spinosum: this layer consists of a bulk of keratinocytes and Langerhans cells and also contains the processes of melanocytes that extends from the stratum basale
• Stratum basale: this layer consist of basal cells, melanocytes and Merkel cells

(B) Dermis

1. Cell types

• fibroblasts
• macrophages
• mast cells

2. Layers

• Papillary dermis: this layer is composed of loose connective tissue and it is the junction between dermis and epidermis
• Reticular dermis: this layer is composed of dense connective tissue and contains all skin appendages along with blood and lymphatic vessels

Skin adnexal anatomy

(A) Pilosebaceous unit

• hair follicle
• sebaceous glands
• arrector pili muscles
• apocrine sweat glands (present only in axillae and groins)

(B) Eccrine sweat glands

(C) Nails