Chapter 5 Review

Review Integumentary System

5.1 Structure of the Skin

  1. The integumentary system consists of the skin, hair, oil and sweat glands, nails, and sensory receptors.
  2. The skin is the largest organ of the body in weight. The principal parts of the skin are the epidermis (superficial) and dermis (deep).
  3. The subcutaneous tissue is deep to the dermis and not part of the skin. It anchors the dermis to underlying tissues and organs, and it contains lamellar corpuscles.
  4. The types of cells in the epidermis are keratinocytes, melanocytes, dendritic cells, and tactile epithelial cells.
  5. The epidermal layers, from deep to superficial, are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (in thick skin only), and stratum corneum (see Table 5.1). Epidermal stem cells in the stratum basale undergo continuous cell division, producing keratinocytes for the other layers.
  6. The dermis is composed of dense irregular connective tissue containing collagen and elastic fibers. It is divided into papillary and reticular dermis. The papillary dermis contains thin collagen and fine elastic fibers, dermal papillae, and tactile corpuscles. The reticular dermis contains bundles of thick collagen and some coarse elastic fibers, fibroblasts and macrophages, adipose tissue, hair follicles, nerves, sebaceous glands, and sudoriferous glands. (See Table 5.2.)
  7. Epidermal ridges provide the basis for fingerprints and footprints.
  8. The color of skin is due to melanin, carotene, and hemoglobin.
  9. In tattooing, a pigment is deposited with a needle in the dermis. Body piercing is the insertion of jewelry through an artificial opening.

5.2 Accessory Structures of the Skin

  1. Accessory structures of the skin—hair, skin glands, and nails—develop from the embryonic epidermis.
  2. A hair consists of a hair shaft, most of which is superficial to the surface, a hair root that penetrates the dermis and sometimes the subcutaneous tissue, and a hair follicle.
  3. Associated with each hair follicle is a sebaceous gland, an arrector muscle of the hair, and a hair root plexus.
  4. New hairs develop from division of hair matrix cells in the hair bulb; hair replacement and growth occur in a cyclical pattern consisting of growth, regression, and resting stages.
  5. Hairs offer a limited amount of protection—from the sun, heat loss, and entry of foreign particles into the eyes, nose, and ears. They also function in sensing light touch.
  6. Lanugo of the fetus is shed before birth. Most body hair on males is terminal (coarse, pigmented); most body hair on females is vellus (fine).
  7. Sebaceous glands are usually connected to hair follicles; they are absent from the palms, palmar surfaces of the digits, soles, and plantar surfaces of the soles. Sebaceous glands produce sebum, which moistens hairs and waterproofs the skin. Clogged sebaceous glands may produce acne.
  8. There are two types of sudoriferous glands: eccrine and apocrine. Eccrine sweat glands have an extensive distribution; their ducts terminate at pores at the surface of the epidermis. Eccrine sweat glands are involved in thermoregulation and waste removal and are stimulated during emotional stress. Apocrine sweat glands are limited to the skin of the axillae, groin, and areolae; their ducts open into hair follicles. Apocrine sweat glands are stimulated during emotional stress and sexual excitement. (See Table 5.3.)
  9. Ceruminous glands are modified sudoriferous glands that secrete cerumen. They are found in the external acoustic meatus.
    1. Nails are hard, dead keratinized epidermal cells over the dorsal surfaces of the distal portions of the digits. The principal parts of a nail are the nail plate, free edge, nail root, lunula, hyponychium, nail bed, eponychium, and nail matrix. Cell division of the nail matrix cells produces new nails.

5.3 Types of Skin

  1. Thin skin covers all parts of the body except for the palms, palmar surfaces of the digits, soles, and plantar surfaces of the toes.
  2. Thick skin covers the palms, palmar surfaces of the digits, soles, and plantar surfaces of the toes. (See Table 5.4.)

5.4 Functions of the Skin

  1. Skin functions include body temperature regulation, blood storage, protection, sensation, excretion and absorption, and synthesis of vitamin D.
  2. The skin participates in thermoregulation by liberating sweat at its surface and by adjusting the flow of blood in the dermis.
  3. The skin provides physical, chemical, and biological barriers that help protect the body.
  4. Cutaneous sensations include tactile sensations, thermal sensations, and pain.

5.5 Maintaining Homeostasis: Skin Wound Healing

  1. In an epidermal wound, the central portion of the wound usually extends down to the dermis; the wound edges involve only superficial damage to the epidermal cells.
  2. Epidermal wounds are repaired by enlargement and migration of epidermal stem cells, contact inhibition, and division of migrating and stationary basal cells.
  3. During the inflammatory phase of deep wound healing, a blood clot unites the wound edges, epithelial cells migrate across the wound, vasodilation and increased permeability of blood vessels enhance delivery of phagocytes, and mesenchymal cells develop into fibroblasts.
  4. During the migratory phase, fibroblasts migrate along fibrin threads and begin synthesizing collagen fibers and glycoproteins.
  5. During the proliferative phase, epithelial cells grow extensively.
  6. During the maturation phase, the scab sloughs off, the epidermis is restored to normal thickness, collagen fibers become more organized, fibroblasts begin to disappear, and blood vessels are restored to normal.

5.6 Development of the Integumentary System

  1. The epidermis develops from the embryonic ectoderm, and the accessory structures of the skin (hair, nails, and skin glands) are epidermal derivatives.
  2. The dermis is derived from mesodermal cells.

5.7 Aging and the Integumentary System

  1. Most effects of aging begin to occur when people reach their late 40s.
  2. Among the effects of aging are wrinkling, loss of subcutaneous adipose tissue, atrophy of sebaceous glands, and decrease in the number of melanocytes and dendritic cells.

Critical Thinking Questions

  1. The amount of dust that collects in a house with an assortment of dogs, cats, and people is truly amazing. A lot of these dust particles had a previous “life” as part of the home’s living occupants. Where did the dust originate on the human body?
  2. Josie reassures her mother that the tattoo she received at the tattoo parlor will eventually disappear. She knows this because she has learned in biology class that skin cells are shed every four weeks. Is Josie correct?
  3. Six months ago, Chef Eduardo sliced through the end of his right thumbnail. Although the surrounding nail grows normally, this part of his nail remains split and doesn’t seem to want to “heal.” What has happened to cause this?