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.
Where do hair follicles derive from?
Keratin.
What is the function of the arrector pili muscle on a hair follicle?
Goosebumps.
What does squalene do in hair follicles?
Lubrication, moisturization, barrier protection, and has antioxidant & anti-aging properties.
What is the physiological role of skin?
Lipid layer for waterproofing and UV protection from the top layer of epidermis.
What are Merkel cells?
Located in the basal layer of the epidermis (stratum basale). Function: Detect light touch and sustained pressure.
What are Meissner’s corpuscles?
Located in dermal papillae of hairless skin. Function: Detect changes in light touch and low-frequency vibration.
What are Pacinian corpuscles?
Located in deep dermis and subcutaneous tissue. Function: Detect deep pressure and high-frequency vibration.
What are Ruffini receptors?
Located in deep dermis. Function: Detect skin stretch and joint position sense (proprioception).
What are free nerve endings?
Widespread, found in the epidermis, dermis, and deeper tissues. Function: Detect pain, temperature, and chemical injury.
What are angiosomes?
Responsible for bright red face. Composite block of tissue supplied by underlying arterial flow and drained by venous flow.
How does the skin react to a skin burn?
The skin activates inflammatory responses and begins the healing process.
Describe angiosomes: Vascular territories in the skin.
Direct perfusion: Arteries specifically destined for the skin. Indirect perfusion: Arteries that supply deeper structures but also give off secondary branches for skin perfusion.
What is the clinical relevance of angiosomes?
Understanding angiosomes is crucial in surgical planning, such as in flap surgery and wound healing.
What are shunts and vascular plexi?
Shunts and plexi are components of the vascular system that aid in blood flow regulation.
What components of skin aid in thermoregulation?
Shunts and plexi, local, neural, and humoral control (vasodilation, hormones like adrenaline or thyroid hormones), and thermoregulatory feedback.
What is viscoelasticity?
Skin exhibits both elastic and viscous properties when force is applied. Function: Helps skin absorb mechanical stress and maintain integrity over time.
What are Langer’s lines?
Invisible lines in the skin that correspond to the natural orientation of collagen fibers in the dermis.
Why are Langer’s lines important?
Incisions made parallel to Langer’s lines heal better with minimal scarring, while perpendicular incisions create more tension, leading to wider scars and slower healing.
What is the relationship between the basal layer and viruses?
The basal layer can be a site of viral entry and replication, affecting skin health.
