University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

414

Pages:

7
Author:

chin5tgu

Gross Anatomy of the Tissues of the Skin Histology of the Skin Epidermis: Cell Types and Layers Cells of the Epidermis • Keratinocytes: Up to 30 layers of keratinocytes continuously move up through the epidermis and ultimately flake off (exfoliate). – Keratinocytes are bound to each other with many desmosomes, especially in the stratum spinosum layer. – Maturing keratinocytes fill with granules of keratin (for strength) and vesicles of glycolipid (for waterproofing). – Exocytosis of the glycolipid forms a barrier around each keratinocyte that cuts off surface cells from diffusion of nutrients from deeper layers of the skin. – Stratum Lucidum is a prominent transition point in thick skin only. – Maturation of keratinocytes from the stratum basale to exfoliation at stratum corneum normally takes about 15-30 days. – In the common skin disease, psoriasis, the rate of cell proliferation (mitosis) in increases so cells move to the surface in about 7 days resulting in a thicker epidermis and greater shedding of dead keratinocytes (scaly skin or dandruff). Thin Skin and Thick Skin Other Cells of the Epidermis • Tactile Cells (Merkel Cells) are touch receptors associated with nerve fibers. • Dendritic Cells (Langerhans Cells) are macrophages (a type of white blood cell) from bone marrow that migrate into the epidermis and help protect against pathogens by engulfing antigens and then “presenting” the antigens to other cells in the immune system. • Melanocytes synthesize melanin pigment and inject it into surrounding keratinocytes. Melainin colors skin, hair and the iris of the eyes. Melanin protects tissues from the damaging effects of UV radiation. Melanocytes are pigment cells in stratum basale layer of the epidermis that do not form desmosomes with keratinocytes. Melanocytes produce and transfer melanin pigment granules (melanosomes) to adjacent keratinocytes by the process of cytocrine injection (melanosome secretion). Rate of melanin production and degradation is primarily controlled by genes. Number of melanocytes among humans is relatively constant, but melanin production varies with skin color. In some individuals, exposure to UV can accelerate melanin production and darken the skin (tanning).