Integumentary

Integumentary System Overview

  • Definition: Covers the body and consists of skin and accessory tissues (nails, hair, sweat and sebaceous glands).

  • Integument: Refers to skin, which is also called the cutaneous membrane.

  • Functions: Acts as a barrier to the outside world, is a visual indicator of physiological health, and is the subject of dermatology.

Composition and Functions of the Integument

Layers of the Integument

  • Epidermis:

    • Composed of stratified squamous epithelium.

    • Main protective layer of the skin.

  • Dermis:

    • Deeper layer made of primarily dense irregular connective tissue.

  • Subcutaneous Layer (Hypodermis):

    • Situates deep to the dermis and consists of areolar and adipose connective tissues; not part of the integumentary system.

Key Structures in the Integument

  • Hair Follicles: Site where hair grows.

  • Glands: Include sweat glands, sebaceous (oil) glands, which are vital for skin moisture and temperature regulation.

  • Sensory Receptors: Allow for the detection of environmental stimuli.

Epidermis Structure

Layers of the Epidermis (Superficial to Deep)

  • Stratum Corneum: The outer protective layer of dead keratinized cells.

  • Stratum Lucidum: Thin, translucent layer found only in thick skin (palms, soles).

  • Stratum Granulosum: Where keratinization begins; keratinocytes start to die.

  • Stratum Spinosum: Contains several layers of keratinocytes connected by desmosomes; houses immune cells.

  • Stratum Basale: Deepest layer; contains stem cells that divide to regenerate the epidermis; includes keratinocytes, melanocytes, and tactile cells.

Cell Types in the Epidermis

  • Keratinocytes: Produce keratin, a protein that strengthens the epidermis.

  • Melanocytes: Produce melanin, providing color to the skin and protecting from UV radiation.

  • Tactile Cells (Merkel Cells): Sensitive to touch and aid in sensory reception.

Skin Color and Variations

  • Factors Influencing Skin Color:

    • Hemoglobin: Contributes to red color in the skin.

    • Melanin: Dark pigment produced in response to UV exposure; varied amounts result from genetic factors.

    • Carotene: Yellow-orange pigment found in certain vegetables.

  • Skin Markings:

    • Nevus (Mole): Overgrowth of melanocytes; monitored for changes.

    • Freckles: Localized increase in melanocyte activity.

    • Friction Ridges: Contribute to fingerprints, unique to individuals.

Dermis Structure

Components of the Dermis

  • Papillary Layer: Superficial layer with areolar tissue; contains dermal papillae.

  • Reticular Layer: Deeper layer composed of dense irregular connective tissue; houses most structures of the skin.

  • Tactile Receptors: Sensory nerves are present for touch perception.

Dermis Functionality

  • Collagen and Elastic Fibers: Arranged to resist stress and influence healing; incisions parallel to cleavage lines heal better.

  • Lines of Cleavage: Orientation of fiber bundles in the dermis that dictate scar formation under stress or injury.

Subcutaneous Layer (Hypodermis)

  • Not actually part of the integument; consists of areolar and adipose tissues.

  • Functions in protection, energy storage, and insulation, and serves as a common site for drug injection due to high vascularity.

Functions of the Integument

Protection and Barrier Function

  • Protects against injury, harmful substances, and microbial invasion.

  • Acts as a barrier to prevent water loss; epidermis is water-resistant.

Metabolic Functions

  • Produces vitamin D3, which is essential for calcium absorption.

Sensory Reception and Thermoregulation

  • Contains nerve endings for temperature regulation and sensory input.

  • Blood vessels utilize vasoconstriction and vasodilation for heat control.

Integumentary Structures Derived from Epidermis

Nails

  • Structure: Modified stratum corneum; provides protection to digit tips and assists in grasping.

  • Components: Nail plate (body, root, free edge), nail matrix (growth area), and various folds (cuticle, etc.).

Hair

  • Types: Includes lanugo (fetal), vellus (fine hair), and terminal hair (coarse and pigmented).

  • Structure & Follicles: Hair bulb (growth), root, and shaft; hair matrix is where new cells are formed.

Exocrine Glands of the Skin

Sweat Glands

  • Types:

    • Merocrine: Widely distributed; involved in temperature regulation.

    • Apocrine: Found in specific areas; secrete a thicker, odor-causing fluid in response to hormonal changes.

Sebaceous Glands

  • Produce sebum, an oily substance that lubricates skin and hair; becomes active during puberty.

Other Glands

  • Ceruminous: Produce earwax to protect the ear canal.

  • Mammary: Specialized for milk production in lactating females.

Repair and Regeneration of the Integumentary System

Healing Process

  • Two primary methods: regeneration (replacement with same cell type) and fibrosis (scarring).

  • Stages:

    1. Hemostasis and clot formation.

    2. Inflammation with leukocyte activity.

    3. Granulation tissue formation and epithelial regeneration.

Clinical Views

Skin Conditions

  • Psoriasis: Autoimmune condition causing rapid skin cell turnover leading to scaly patches.

  • Burns: Classified by depth (first, second, third-degree).

  • Skin Cancer: Common types include basal cell carcinoma (most common), squamous cell carcinoma (second most common), and melanoma (most dangerous).

Melanoma Detection** (ABCD Rule)

  • Asymmetry, Border irregularity, Color variation, Diameter larger than 6 mm, Evolving nature.