The Integumentary System

• Components of the Integumentary System

  • Skin
  • Hair
  • Nails
  • Sweat and oil glands
  • Sensory receptors
  • Vascular network
• Skin

  • Composed of two distinct layers: Epidermis and Dermis
  • Epidermis is the thinnest and outermost protective shield of the body, composed of keratinized epithelial cells
  • Dermis is a deep thicker layer, tough, leathery, composed mostly of dense connective tissue
• Keratinocytes


  Produce keratin, arise in the stratum Basale, undergo continuous mitosis, form scale-like flat sacs filled with keratin
• Melanocytes


  Produce melanin, found in the deepest layer of the epidermis, form a pigment shield protecting the nucleus from UV radiation
• Dendritic/Langerhans cells

  Arise from bone marrow, migrate to the epidermis, help activate the immune system
• Tactile epithelial/Merkle cells


  Found in the epidermal-dermal junction, sensory receptor aiding in the sense of touch
• Epidermis layers

  Stratum Basale, Stratum Spinosum, Stratum Granulosum, Stratum Lucidum, Stratum Corneum
• Stratum Basale


  Deepest epidermal layer, actively mitotic stem cells, contains melanocytes
• Stratum Spinosum


  Several layers thick, contains Langerhans cells, spinelike extensions of keratinocytes
• Stratum Granulosum

  1 to 5 layers thick, undergoing keratinization, contains keratohyaline and lamellar granules
• Stratum Lucidum

  Only found in thick skin, thick band of dead, flat keratinocytes
• Stratum Corneum

  Most superficial layer, contains 20-30 layers of dead, flat keratinocytes, sheds regularly
• Dermis layers

  Superficial papillary dermis, Deep Reticular dermis
• Superficial papillary dermis

  Thin layer of areolar connective tissue, contains dermal papillae with capillary loops, nerve endings, and touch receptors
• Deep Reticular dermis

  Dense irregular connective tissue, contains blood vessels, glands, hair follicles, pressure receptors, collagen fibers for strength and resiliency
• Collagen fibers in the dermis

  Give skin strength and resiliency, form cleavage (tension) lines in the skin
• Melanin is a polymer made of an amino acid called tyrosine, produced by melanocytes in the stratum Basale, protects skin cells' DNA from UV radiation
• Colors of skin


  • Reddish yellow to brownish black
• Melanin production

  Produced by melanocytes in the striatum Basale, then transported to the basal keratinocytes
• Stimulation of melanocytes

  When skin is exposed to sunlight, keratinocytes secrete chemicals that stimulate melanocytes to produce melanin, protecting skin cells' DNA from UV radiation
• Skin pigments

  • Carotene
  • Hemoglobin
• Carotene


  Yellow to orange pigment found in certain plants, accumulates in the stratum corneum and subcutaneous tissue, can be converted to vitamin A
• Hemoglobin


  Pinkish hue in fair-skinned people due to small amounts of melanin and transparency of skin, causes blueness or cyanosis when poorly oxygenated, redness or erythema due to various factors, pallor or blanching due to emotional stress or health issues, yellowness indicates liver disorder
• Skin discolorations


  • Red/purple/green/yellow marks (bruises or ecchymoses)
• Hair


  Millions of hairs distributed over skin surface, except for palms, soles, lips, nipples, parts of external genitalia, serves a protective function
• Structure of hair (Pili)

  • Flexible strands produced by hair follicles, consist of dead, keratinized cells, shaft and root parts, subdivided into medulla, cortex, cuticle
• Hair Colour


  • Made by melanocytes at the base of hair follicle, different proportions of melanins produce different hair colors, red hair produced by pheomelanin, grey hair due to decreased melanin production
• Structure of hair follicle

  • Extend from epidermis into dermis, hair bulb at deep end, hair matrix cells responsible for growth, hair follicle wall consists of outer peripheral connective tissue sheath, glassy membrane, inner epithelial root sheath, arrector pili muscle
• Parts of hair follicle

  • External parts
  • Internal parts
• Arrector pili muscle


  Bundle of smooth muscle cells associated with each hair follicle
• Hair position

  Hair is normally at an angle to the skin surface
• Contraction of arrector pili


  Causes hair to stand up, i.e., goose bumps
• Types of hair and growth

  • Vellus hair - Pale and fine, e.g., body hair of children and adult females
  • Terminal hair - Coarser, longer, e.g., hair of eyebrows and scalp, may be darker
• At puberty

  Terminal hair appears in axillary and pubic regions of both sexes and on face and chest of males, grow in response to androgens, e.g., testosterone
• Hair grows approximately 2mm per week, widely varies with sex and age
• Follicle growth cycle


  Active phase (new hair pushes out old hair) and resting phase (matrix is inactive and follicle shrinks)
• Life span of hair - scalp follicles stay active for ~4 years, eyebrow follicles are active for only a few months
• Cycles of adjacent hair follicles are not synchronized, therefore we only lose a small percentage of hairs at a time
• Skin Derivative - Nails

  • Root, Nail plate/body, Free edge, Nail bed, Nail matrix, Lunula, Nail folds, Cuticle
• Skin Derivative - Glands

  • Sudoriferous glands, Erricrine sweat glands, Apocrine sweat glands, Ceruminous glands, Mammary glands, Sebaceous/oil glands