Human Skin Structure and Types

Study Notes

Skin is the heaviest and largest organ in the human body, making up 15-20% of total body weight.
There are two types of skin: thick skin (found on palms and soles) and thin skin (found on the rest of the body).

The skin consists of two distinct regions: epidermis (outer) and dermis (inner).
Epidermis:
- Thin
- Derived from ectoderm
- Non-vascular but rich in sensory nerve endings
Dermis:
- Thick
- Derived from mesoderm
- Characterized by connective tissue, vascular, and nerves

Beneath the dermis lies the hypodermis, a loose connective tissue that may contain pads of adipocytes.
Hypodermis binds skin loosely to the underlying tissues.

Keratinocytes: most abundant cells in the epidermis
Non-keratinocytes:
- Melanocytes: pigment-producing cells
- Langerhans cells: antigen-presenting cells
- Merkel cells: tactile epithelial cells

Composed of 5 layers of keratinocytes
Keratinocytes in the stratum basale contain intermediate filaments composed of keratins
Function: renewal of keratinocytes

Stratum Spinosum (prickle cell layer):
- Cells have short cellular extensions around the tonofibrils
- Appearances of many short spines or prickles at the cell surfaces
Stratum Granulosum (granular layer):
- Cells have keratohyaline granules and lamellar granules
- Contains lipids that produce sheets that envelop the cells
Stratum Lucidum (clear zone):
- Only seen in thick skin
- Cells have flattened nuclei and are degenerating
- Cytoplasm consists almost only of densely packed keratin filaments

Depend on the interaction of three factors:
- Melanin: yellow to brown to black pigment produced by melanocytes
- Carotene: orange-yellow pigment found in some vegetables
- Hemoglobin: red coloring from blood cells in dermis capillaries
Melanocytes:
- Specialized cells of the epidermis found among the cells of stratum basale and in the hair follicles
- Synthesize melanin from tyrosine and store it in vesicles called melanosomes