The skin Flashcards
What is epidermis?
Outermost layer of skin.
Consists of stratum corneum, stratum lucidum (lips, palms and soles), stratum granulosum, stratum spinosum, and stratum basale.
What is the dermis?
Layer under the epidermis.
What is subcutaneous layer?
Subcutaneous tissue = fatty tissue supporting the skin.
What does the basal layer (stratum basale) consist of?
Single layer of columnar-like keratinocytes attached to the basement membrane. Cells adhere to each other by connections at the desmosomes. The cells are mitotically active but the rate of cell division is relatively slow. There is a group of stem cells within the tissue that can self-renew and generate new cells when needed.
Where should cellular reproduction occur in the skin layers?
Cellular reproduction occurs in the basal layer (stratum basale) of the epidermis. The stratum basale contains mitotically active keratinocytes and stem cells, which divide to produce new skin cells. These new cells migrate upwards through the epidermal layers in a process called keratinization. The turnover cycle from basal layer to shedding in the stratum corneum takes ~28 days under normal conditions.
What do keratinocytes do?
Keratinocytes are the primary cells of the epidermis that produce keratin, a protein that helps protect the skin.
What affects the rate of cell division?
UV exposure and injury.
What is the time period for keratinocytes migration through the epidermis?
Once keratinocytes are produced in the basal layer, they begin a 14-day migration through the epidermis until they reach the stratum corneum. After reaching the stratum corneum, the keratinocytes remain for another 14 days, during which they continue to mature and eventually desquamate (shed). This results in a total turnover time of ~28 days.
What is a hyperproliferative skin condition?
The basal layer undergoes increased cell division, leading to thicker epidermis; instead of being a single cell layer, the basal layer becomes 2-3 cells thick.
Why do hyperproliferative skin conditions cause scaling, flaking, and abnormal epidermal structure?
Because the basal layer becomes 2-3 cells thick. This accelerates the process of keratinocytes migrating through the epidermis to the stratum corneum, from 28 days to 3-7 days, leading to incomplete maturation of keratinocytes.
What are the thickness, structure, and cell types of the stratum spinosum?
Thickness: Composed of 5–10 layers of keratinocytes. Structure: Cells are larger and more irregularly shaped compared to the basal layer. They contain desmosomes, which give them a ‘spiny’ appearance under a microscope. Cell Types: Basal melanocytes and Langerhans cells.
What is the structure and function of the stratum granulosum?
Cells become flattened as they begin the process of terminal differentiation. The cytoplasm contains keratohyaline granules, important for skin barrier formation and hydration. Cells discharge lipid components that form a hydrophobic barrier, preventing water loss and protecting against external irritants and microbes.
What is the structure and function of the cornified layer (stratum corneum)?
Composed of dead, flattened keratinocytes (corneocytes) that have lost their nuclei. Function: Mechanical protection, barrier to water loss, and barrier to invasion.
Describe a melanocyte.
Dendritic, protein-synthesizing cells that produce melanin. They originate from the neural crest and reside in the stratum basale, where they transfer melanin to keratinocytes.
Describe Langerhans cells.
Dendritic immune cells that are antigen-presenting cells (APCs) that detect pathogens and activate the immune system. Primarily found in the stratum spinosum.
Describe Merkel cells.
Oval-shaped mechanoreceptors that detect light touch and pressure. Located in high-sensitivity areas such as digits, lips, and oral cavity.
What are the two layers in the dermis?
Thin upper layer: papillary dermis. Thick lower layer: reticular dermis.
What are the components of the papillary dermis?
Connective tissue and vasculature that supply the epidermis.
What are the components of the reticular dermis?
Vasculature, hair follicles, oil and sweat glands, and nervous system.
What are the three types of sweat glands?
Eccrine, apocrine, and apoecine.
Describe eccrine sweat glands.
Most prominent on soles of feet, least plentiful on back. Primary role in thermoregulation.
Describe apocrine sweat glands.
Apocrine glands release scent and open into pilosebaceous follicles.
Describe apoecine sweat glands.
Similar to eccrine but found in axillae.
What are the components of sweat?
Sodium (0.9 gram/liter), potassium (0.2 g/l), calcium (0.015 g/l), magnesium (0.0013 g/l), trace lactic acid, and urea.
