Anatomy of the skin; the skin appendages

(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