Ch-05-Integumentary-handout

Overview of the Integumentary System

• Largest and most accessible organ system of the human body

• Surface area: 1.5–2 m²

• Constitutes 16% of total body weight (approximately 10 to 13 kg)

• Commonly referred to as skin or integument

• Composed of:

  • Cutaneous membrane

  • Accessory structures

• Primary functions:

  • Provides physical protection

  • Facilitates thermoregulation

  • Engages in Vitamin D synthesis

  • Assists in excretion

  • Enables sensory reception

• Cyanosis: Bluish discoloration of skin indicating poor circulation or oxygenation of blood

Structure of the Cutaneous Membrane

• Epidermis: Composed of 4 to 5 layers

• Dermis: Divided into 2 layers

• Subcutaneous Layer: Also known as hypodermis

  • Composed of loose connective tissue

  • Not considered part of the integument

  • Contains major blood vessels

• Accessory Structures include:

  • Exocrine glands

  • Hair follicles

  • Nails

Dermal Layers and Circulation

• Papillary Layer:

  • Made of areolar connective tissue

  • Contains dermal papillae that interlock with epidermal ridges

  • Houses capillary loops for nutrient supply

• Reticular Layer:

  • Composed of dense irregular connective tissue (DICT)

  • Contains collagen and elastic fibers

  • Hosts cleavage lines and dermal circulation through the subpapillary and cutaneous plexus

Function and Composition of Epidermis

• Primary cell type: Keratinocytes

  • Produce keratin and store carotene

  • Involved in production of cholecalciferol (Vitamin D3)

• Merkel Cells: Sensory cells associated with fine touch/pressure

• Melanocytes: Produce melanin for skin pigmentation

  • Types of Melanin:

    • Eumelanin: Dark brown

    • Pheomelanin: Yellow to orange

• Dendritic Cells: Wandering phagocytic cells that initiate immune response

Layers of the Epidermis

• Stratum Basale:

  • Composed of one layer of cells anchored to the basement membrane

  • Contains basal cells, Merkel cells, and melanocytes

• Stratum Spinosum:

  • Consists of 8 to 10 cells thick, primarily keratinocytes

  • Produces a precursor to keratin

  • Connected by desmosomes

• Stratum Granulosum:

  • Made up of 3 to 5 cells thick

  • Keratinocytes begin to die and flatten

  • Features keratohyalin and lipoprotein for keratinization

• Stratum Lucidum:

  • Present only in thick skin (palmar/plantar regions)

  • Composes 3 to 5 cells thick of dead keratinocytes

• Stratum Corneum:

  • Thickest layer with 15 to 30 cells

  • Composed of dead, interlocked keratinocytes surrounded by lipoproteins

  • Provides protective barrier against dehydration and infection

Burns

• Severity classified by depth:

  • First-degree burn: Only upper epidermis is damaged

  • Second-degree burn: Upper part of dermis is also damaged, blisters appear

  • Third-degree burn: Consumes thickness of skin, may appear white, red, or blackened

• Rule of Nines: Estimation method for assessing the percentage of burned body surface area

Factors Determining Skin Color

• Skin Types:

  • Thick skin: Found in palmar/plantar regions with thicker stratum corneum

  • Thin skin: Covers the rest of the body with thinner stratum corneum

• Determinants include:

  • Melanin concentration: Influenced by melanocyte activity and UV exposure

  • Carotene concentration: Influenced by diet

  • Dermal circulation: Variation in hemoglobin influences skin color

  • Skin thickness: Impacts the persistence of pigments in the epidermis

Effects of Ultraviolet Radiation (UV Light)

• Increased melanocyte activity and melanin production with UV exposure

• Beneficial for Vitamin D synthesis by converting cholesterol to cholecalciferol

• Excessive UV exposure may cause skin damage, including collagen breakdown, mutations, and skin cancers (e.g., basal and squamous cell carcinoma, melanoma)

Accessory Structures

Glands of the Dermis

• Sebaceous Glands:

  • Widespread except on palms and soles

  • Functions: Holocrine secretion of sebum (lipids, proteins)

  • Can lead to acne when ducts are blocked

Sweat Glands

• Eccrine (Merocrine) Sweat Glands:

  • Most widely distributed; functions include thermoregulation and waste excretion

• Apocrine Sweat Glands:

  • Limited distribution, activated at puberty, secrete odorless fluid that can lead to body odor

Specialized Glands

• Mammary Glands:

  • Proliferate during pregnancy to produce milk

• Ceruminous Glands:

  • Located in the ear canal; produce cerumen (earwax)

Hair Structure

• Composed of hair follicle, hair shaft, medulla, cuticle, cortex, hair bulb, and hair papilla

• Types of Hair:

  • Lanugo: Fine hair on fetuses

  • Vellus: Thin, short hair

  • Terminal: Thick hair that develops at puberty

• Functions include protection, insulation, and sensation

Nails

• Structure:

  • Nail plate: Densely packed keratinocytes

  • Lunula: Crescent-shaped area of the nail root

  • Eponychium: Cuticle area

  • Function: Protection of fingertip

• Aging impacts the integument:

  • Thinning of epidermis, reduction in dendritic cells, decreased cholecalciferol and melanocyte activity, reduced glandular and hair follicle activity, and altered blood supply to dermis.