Anatomy and Physiology of Skin Layers, Cells, and Color Changes

List the layers of the skin and briefly describe subcutaneous tissue.

The skin has two layers: the epidermis and dermis. Beneath the dermis is the subcutaneous tissue, or hypodermis. It is not part of the skin. It loosely anchors the skin to deeper structures, absorbs shock, insulates, and is made mostly of adipose tissue with some areolar connective tissue.

Name the tissue types composing the epidermis and dermis.

The epidermis is made of keratinized stratified squamous epithelium. The papillary dermis is made of areolar connective tissue, and the reticular dermis is made of dense irregular connective tissue.

List the cell types of the epidermis and describe the functions of each type.

Keratinocytes produce keratin and make up most of the epidermis. Melanocytes produce melanin, which protects keratinocyte nuclei from UV damage. Dendritic cells, also called Langerhans cells, ingest foreign substances and help activate the immune system. Tactile epithelial cells, also called Merkel cells, are sensory receptors for touch.

List the major layers of the epidermis and describe the functions of each layer.

Stratum basale: deepest layer and contains mitotically active stem cells. Stratum spinosum: contains keratinocytes joined by desmosomes and helps resist tension. Stratum granulosum: last living layer where keratinization begins and water-resistant glycolipids help reduce water loss. Stratum lucidum: found only in thick skin and contains clear, dead keratinocytes. Stratum corneum: outer protective barrier that protects against abrasion, penetration, environmental damage, and water loss.

Name the layers of the dermis and describe the functions of each layer.

The dermis has a papillary layer and a reticular layer. The papillary dermis contains dermal papillae, capillary loops, pain receptors, and touch receptors. The reticular dermis contains collagen fibers for strength and resiliency and elastic fibers for stretch and recoil.

Describe the factors that normally contribute to skin color.

Skin color is mainly influenced by melanin, carotene, and hemoglobin. Melanin is produced by melanocytes, carotene is a yellow-orange pigment obtained from the diet, and hemoglobin gives the skin a pinkish hue.

Briefly describe how changes in skin color may be used as clinical signs of certain disease states.

Cyanosis is a bluish-gray color caused by poorly oxygenated hemoglobin. Pallor is pale skin caused by reduced blood flow, low blood pressure, or anemia. Erythema is redness caused by increased blood flow. Jaundice is yellow skin and eyes caused by bilirubin buildup and may indicate liver disease or biliary obstruction. Ecchymosis or hematoma is bruising caused by blood leaking into tissues. Acanthosis nigricans is dark, thickened skin in folds associated with endocrine disruption and poorly regulated blood glucose.