Integumentary System Overview

Integumentary System

• The integument, or skin, is a barrier between the internal and external environments.
• It contains accessory structures.
• Major functions:
  • Barrier to environmental microbes
  • Prevents water loss
  • Thermoregulation
  • Detecting sensations
  • Vitamin D synthesis
  • Excretion

Learning Objectives

• List major functions of the skin.
• Identify tissue types of the epidermis, papillary layer, reticular layer of the dermis, and subcutaneous tissues.
• List five layers of the epidermis and describe their structural and functional differences.
• Explain thick skin and its differences from thin skin.
• Describe functions of each type of cell in the epidermis.
• Describe factors contributing to skin color and alterations.
• Explain the anatomical basis for fingerprints.
• Describe structural and functional differences of two dermis layers.
• Describe secondary structures of the skin (sensory structures, exocrine glands, hair, and nails).
• Explain short-term and long-term burn dangers and degree determination.
• Explain the significance of the Rule of Nines.
• Relate three types of skin cancer to the epithelial layers.
• Describe tissue repair process for superficial wounds.

Layers of the Skin

• Epidermis:
  • Keratinized stratified squamous epithelium
• Dermis:
  • Papillary layer (20%)
    • Areolar loose connective tissue
  • Reticular layer (80%)
    • Dense irregular connective tissue
• Subcutaneous Layer (Hypodermis):
  • Adipose loose connective tissue

Epidermis

• The outermost layer of skin.
• Keratinocytes in strata (layers):
  • Stratum corneum (top layer)
  • Stratum lucidum (middle layer in thick skin)
  • Stratum granulosum (middle layer)
  • Stratum spinosum (middle layer)
  • Stratum basale (bottom - germ layer)
• Cells:
  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells

Strata of the Epidermis

• Stratum basale:
  • Deepest layer
  • Closest to capillaries
  • Keratinocyte mitosis
  • Melanocytes producing melanin
  • Merkel cells (sensory nerve cells)
• Stratum spinosum:
  • Spiny cell junctions (desmosomes)
  • Langerhans cells
  • Melanin granules

Stratum Granulosum

• Lamellar granules (dark spots)
• Prevent water loss
• Keratinization begins

Stratum Corneum

• Outermost layer of dead cells
• Keratinization for abrasion and microbe protection
• Constant shedding and replacement

Stratum Lucidum

• Clear layer
• Only in thick skin
• Between stratum corneum and granulosum

Cells of the Epidermis

• Keratinocytes:
  • Most abundant
  • Replenish epithelium
  • Produce keratin
  • Mitosis in stratum basale
  • Dead in outer layers
• Langerhans cells:
  • Immune system of epidermis
  • Phagocytize foreign substances
  • Migrate to epidermis from red bone marrow
• Melanocytes:
  • Melanin-producing cells
  • Provide skin pigmentation
• Merkel cells:
  • Rare; specialized sensory receptors
  • Detect touch and proprioception

Skin Pigments

• Melanin: Reddish-yellow/brownish-black pigment from melanocytes
  • Exposure to UV stimulates melanocyte activity
• Carotene: Yellow/orange pigment from plants
  • Accumulates in stratum corneum
• Hemoglobin: Leads to red/pink color from red blood cells in dermis

Alterations to Skin Color

• Erythema: Redness due to increased blood flow
• Pallor: Paleness due to decreased blood flow
• Bruising: Changing color due to pooling blood
• Jaundice: Yellowing due to liver malfunction
• Cyanosis: Blueness due to low oxygenated blood
• Albinism: Lack of melanin production
• Vitiligo: Loss of melanin in certain areas
• Addison's Disease: Bronze patches due to adrenal gland malfunction

The Dermis

• Thickest layer
• Papillary layer (superficial)
  • Loose areolar connective tissue
• Reticular layer (deep)
  • Dense irregular connective tissue
• Contains blood vessels, nerves, lymphatic vessels

The Papillary Layer

• Ridges with collagen fibers and nervous structures
• Determine fingerprint pattern (friction ridges)

The Reticular Layer

• Dense irregular connective tissue
• Collagen fiber orientations (cleavage lines)
• Locations of cleavage lines

Secondary Structures

• Sensory receptors (detect different kinds of information)
• Location can predict information they collect
  • Free nerve endings (pain, temperature)
  • Merkel's discs (touch)
  • Meissner's corpuscles (touch)
  • Hair follicle receptors (touch)
  • Pacinian corpuscles (vibration and pressure)
  • Ruffini's endings (stretch)
• Exocrine glands
  • Eccrine (watery sweat, thermoregulation)
  • Apocrine (protein- and lipid-rich sweat, body odor, reproductive signaling)
  • Sebaceous (sebum, lubricates and waterproofs hair and skin)

Sebaceous Gland Malfunctions

• Whiteheads/blackheads: Blocked sebaceous glands
• Pimples, Cysts: Infected sebaceous glands

Anatomy of Hair

• Composed of dead keratinized cells
• Grows out of hair follicles
• Functions:
  • Detecting sensations
  • Protection against heat loss and sunlight
  • Eye protection (eyelashes)
  • Terminal hairs (coarse)
  • Vellus hairs (fine)

Fingernails

• Extension of epidermis
• Harder keratin proteins than keratinocytes
• Grow from nail matrix
• Blood capillaries under nail bed lead to pink color

Skin Cancer

• Types:
  • Basal cell carcinoma (most common, least dangerous)
  • Squamous cell carcinoma (may spread)
  • Malignant melanoma (most deadly)
• Risk factor: UV exposure

The ABCDEs of Detecting Melanoma

• Asymmetry (uneven shape)
• Border (irregular or uneven edges)
• Color (various shades or uneven coloration)
• Diameter (larger than 1/4 inch)
• Evolving (changes over time)

Burns

• Damage to skin by heat, electricity, chemicals, or radiation
• Protein denaturation and cell death occur
• Protective layer compromised (water loss, electrolyte/protein loss, septicemia, bacterial infection)

Degrees of Burns

• First-degree: Epidermis only damaged (redness, swelling, pain)
• Second-degree: Epidermis and upper layers of the dermis damaged (blisters appear)
• Third-degree: All layers of the skin are damaged (full thickness)

Treating Burns

• Critical situation for 2nd-degree burns (> 30%) or 3rd-degree burns (> 20%)
• Initial concern: Fluid and protein replacement
• Next: Infection and sepsis prevention
• Finally: Skin grafts create barrier (necessary for 3rd-degree burns)

The Rule of Nines

• Estimation of burned skin surface area
• Each body area approximately 9% plus genital region (1%)

Stages of Tissue Repair

• Inflammation: Blood flow increases and blood clots form.
• Granulation (scar tissue): Granulation replaces clots, fibroblasts produce collagen, epithelium regenerates, and macrophages clean up debris.
• Wound Closure: Fibrosis pulls the area closed, epithelium thickens, and scabs detach; underlying scar tissue may remain.