Hair and Skin Biology Quiz

Structure and Function of Hair and Skin

• Melanin synthesis is accelerated by the faster repair rate of DNA damaged by sunlight.
• Skin color is determined by melanin, carotene, and hemoglobin.
• Carotene, found in plant products like carrots, accumulates in the skin and can be converted to vitamin A.
• The pinkish hue of fair skin is due to the oxygenated pigment hemoglobin in the red blood cells.
• Skin appendages, including hair, nails, sweat glands, and sebaceous glands, are part of the integumentary system.
• Hair is composed of dead, keratinized cells and has a root and shaft with three layers: medulla, cortex, and cuticle.
• Hair color is determined by different concentrations of melanin, or a related pigment called pheomelanin for red hair.
• Hair follicles extend from the epidermis into the dermis and subcutaneous tissue, with a hair bulb at the base.
• The hair follicle contains sensory nerve endings, a papilla with capillaries, and a peripheral connective tissue sheath.
• Hair grows as cells in the follicle bulb divide rapidly, with new cells produced by stem cells near the skin surface.
• Each hair follicle is associated with an Arrector Pili muscle that can cause goosebumps and force sebum out of hair follicles.
• Hairs are classified as vellus (pale, fine hair) or terminal (coarse, pigmented hair), with different growth cycles.

The Structure of the Skin

• Melanocytes are spider-shaped cells in the deepest layer of the epidermis that produce melanin in membrane-bound granules called melanosomes.
• Melanin is transferred from melanocytes to nearby keratinocytes, forming a pigment shield that protects the nucleus from UV radiation.
• Dendritic cells, also known as Langerhans cells, are star-shaped cells that ingest foreign substances and activate the immune system in the epidermis.
• Tactile epithelial cells, or Merkel cells, function as touch sensory receptors at the epidermal-dermal junction.
• The dermis consists of the papillary dermis, which is areolar connective tissue with blood vessels and sensory receptors, and the reticular dermis, which is dense irregular connective tissue with collagen fibers.
• Papillary dermis contains dermal papillae with capillary loops, nerve endings, and touch receptors, contributing to grip and touch sensations.
• Reticular dermis makes up about 80% of the dermis thickness and contains collagen fibers that give skin strength and resiliency.
• Melanin, carotene, and hemoglobin determine skin color, with melanin being synthesized by melanocytes and transported to basal keratinocytes.
• Differences in skin color distribution are related to the kind and amount of melanin produced and retained by melanocytes.
• Freckles and pigmented nevi are local accumulations of melanin, while prolonged sun exposure causes substantial melanin buildup to protect skin cells from UV radiation.
• Melanin synthesis depends on an enzyme called Tyrosinase, and its two forms range in color from reddish yellow to brownish black.
• Skin color differences reflect the kind and amount of melanin made and retained, with darker-skinned individuals producing more and darker melanosomes and retaining melanin longer than fair-skinned individuals.