SKIN

EPIDERMIS

Composition: stratified squamous keratinizing epithelium

• Stratum basale (germinativum) - single layer of cells that rests on the basal lamina. It contains the stem cells and keratinocytes
• Stratum spinosum - keratinocytes exhibit numerous cytoplasmic processes or spines.
• Stratum granulosum - keratinocytes contain numerous keratohyalin granules
• Stratum lucidum - only in thick hairless skin. The cytoplasmic organelles of disappear and the cell gradually fills with the protein keratin
• Stratum corneum consists of anucleate squamous cells filled with keratin

CELLS OF EPIDERMIS

• Keratinocytes

Origin: ectoderm

Function: production of keratin and creation of an extracellular water barrier.

• Melanocytes

Origin: neural crest

Location: dendritic cells found scattered among the cells of stratum basale in ratio to keratinocytes from 1:4 to 1:10 in different parts of body

Function: production of melanin within the melanosomes that are transferred to the keratinocytes by phagocytosis

• Langerhans cells

Origin: mesenhyme, monocytes

Location: dendritic cells found scattered in the stratum spinosum

Function: plays a role in the immune response by presenting antigens to T lymphocytes

• Merkel cells

Origin: ectoderm

Location: strarum basale

Function: cutaneous sensation

DERMIS

Composition:

• Papillary layer - superficial layer, consists of loose connective tissue with blood vessels, nerve processes and sensory nerve free and encapsulated (Pacinian corpuscles, Meissner's corpuscles, Ruffini endings) endings
• Reticular layer - consists of irregular dense connective tissue
• Hypodermis (subcutaneous layer) - consists of adipose tissue, loose connective tissue and small bundles of smooth muscle cells