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Chapter 4: The Integumentary System – Vocabulary Flashcards

Introduction

  • The integumentary system (integument) is composed of skin, hair, nails, sweat, oil, and mammary glands.
  • Skin tells clinicians about the overall health of the body and can be used to detect some internal problems.

Integumentary Structure and Function

  • Functions of the integument:
    • Physical protection
    • Regulation of body temperature
    • Excretion (secretion)
    • Nutrition (synthesis)
    • Sensation
    • Immune defense
  • Skin structure and subdivisions:
    • Skin (cutaneous membrane) has two subdivisions:
    • Epidermis: stratified squamous epithelium
    • Dermis: underlying loose connective tissue
    • Deep to the dermis is the subcutaneous layer (hypodermis)
    • Accessory structures include hair, nails, and many multicellular exocrine glands

The Epidermis

  • Keratinocytes are the most abundant cells in the epidermis.

  • The epidermis typically has at least four cell layers in most areas.

  • Other epidermal cell types:

    • Melanocytes: pigment cells found deep in the epidermis
    • Merkel cells: sensory cells
    • Langerhans cells: fixed macrophages

  • Epidermal layers (from deep to superficial):

    • Stratum germinativum (basal layer):
    • Innermost, basal layer
    • Attached to basal lamina
    • Contains epidermal stem cells, melanocytes, and Merkel cells
    • Stratum spinosum:
    • Keratinocytes bound together by macula adherens attached to tonofibrils of the cytoskeleton
    • Some keratinocytes divide in this layer
    • Stratum granulosum:
    • Keratinocytes produce keratohyalin and keratin
    • Keratin fibers develop as cells become thinner and flatter
    • Stratum lucidum (glassy layer):
    • Appears as a "glassy" layer in thick skin only
    • Stratum corneum:
    • Multiple layers of flattened, dead, interlocking keratinocytes
    • Typically relatively dry
    • Water resistant, but not waterproof
    • Permits slow water loss by insensible perspiration

  • Additional notes:

    • Langerhans cells and melanocytes are often present in the epidermal layers.
    • Melanocytes are pigment cells located deep in the epidermis; Merkel cells are associated with sensation.

  • The epidermis also includes keratinocytes that produce keratohyalin and keratin; keratin fibers develop as cells move toward the surface.

The Dermis and the Subcutaneous Layer

  • The dermis is the deeper, supporting layer of connective tissue beneath the epidermis.
  • The subcutaneous layer (hypodermis) lies deep to the dermis.
  • Accessory structures (hair follicles, glands, and associated structures) are associated with the dermis.
  • Lines of cleavage (Langer’s lines) in the skin reflect the orientation of collagen fibers and influence wound healing and surgical incisions.

Accessory Structures

  • Hair and hair follicles:
    • Hair is a nonliving keratinized structure that extends beyond the surface of the skin in most areas of the body.
    • Approximately 98% of the 5 million hairs on the body are not on the head.
    • Hair follicles are the organs that form hairs.
  • Hair anatomy and related structures (as depicted in the figures):
    • Hair shaft, root hair, cortex, medulla, cuticle, external root sheath, internal root sheath, glassy membrane, connective tissue sheath, hair papilla, matrix, subcutaneous adipose tissue, and root hair plexus.
    • Hair growth involves the hair papilla and matrix within the follicle.
    • Arrector pili muscle is associated with hair follicles.
    • Sebaceous glands secrete oily sebum into the follicle.
  • Exocrine glands of the skin:
    • The skin contains exocrine glands categorized in diagrams (e.g., Figure 4.12).
    • Sweat glands are shown in two main types:
    • Apocrine sweat glands: depicted with lumen, duct, myoepithelial cells, and gland cells; associated with hair follicles in some regions.
    • Merocrine (eccrine) sweat glands: depicted with lumen and gland cells; ducts transport sweat to the surface.
    • Myoepithelial cells assist in expelling sweat from gland acini.
  • Structure of a nail:
    • The nail is shown in a dedicated figure illustrating the nail structure (e.g., nail plate, nail bed, and related components).

Accessory Structures (continued): Special notes

  • Hair follicles consist of external root sheath and internal root sheath surrounding the hair shaft; the glassy membrane separates the follicle from surrounding connective tissue.
  • The hair follicle environment includes a root hair plexus (nerve endings) and a vascular supply via hair papilla.

Local Control of Integumentary Function

  • The integument can respond independently of the endocrine system and nervous system.
  • Mechanical stress can trigger stem cell divisions, leading to the formation of calluses.
  • Regeneration occurs after damage to the integument.
  • Severe damage may not fully heal and can result in acellular scar tissue (scar tissue lacking normal cellular components).

Aging and the Integumentary System

  • The skin aging process is described in Figure 4.16, illustrating changes over time.
  • Practical implications include how aging affects skin function, wound healing, and barrier properties (not detailed in the provided content but implied by the aging figure).

Connections and Implications

  • Diagnostic relevance: the skin reflects overall health and can indicate internal disease or nutritional status.
  • Clinical relevance: understanding epidermal layers and dermal structures informs wound care, dermatology, and surgical practices.
  • Practical considerations: proper wound management depends on regeneration capacity and avoidance of scar tissue when possible.
  • Philosophical/ethical note: the skin as a window into health underscores the importance of noninvasive diagnostic observations and patient care.