DI

Integumentary system

Integumentary System Overview

  • Course: ANAT 200 - Human Morphology

  • Instructor: Pierre Lemelin, Ph.D.

  • Date: March 13, 2025

  • Major Components:

    • Skin (cutaneous membrane)

      • Epidermis (epithelium)

      • Dermis (connective tissue)

    • Accessory Structures:

      • Hair

      • Nails

      • Exocrine glands

Major Functions of the Integumentary System

  1. Physical and Immunological Protection

    • Quote: "...keeps the blood in, and the rain out." (Napier, 1993: 29)

  2. Thermoregulation

  3. Sensation

  4. Metabolic Functions:

    • Vitamin D synthesis

    • Stores energy as subcutaneous fat

Tissue Composition of the Integumentary System

  • All four tissue types are represented:

    1. Epithelium:

      • Covers surface

      • Forms boundary

    2. Connective Tissue:

      • Supports epithelium

      • Provides strength and resiliency

    3. Muscle (Smooth):

      • Controls diameter of blood vessels

      • Adjusts hair position

    4. Nerve:

      • Controls smooth muscle

      • Generates sensation (tactile, pressure, temperature, etc.)

      • Stimulates exocrine glands

Skin Characteristics

  • Largest organ system of the body:

    • Represents about 15% of total body mass

    • Covers an area of 2 m²

    • Thickness ranges from 0.5 mm to 4.0 mm (average = 1 to 2 mm)

Structure of Skin

  • Layered Structure:

    • Epidermis

    • Dermis

    • Hypodermis (subcutaneous layer)

Interface Between Epidermis and Dermis

  • Peak-and-Valley Interface:

    • Facilitates tight bonding between skin layers

    • Enables resistance to shearing stresses

Epidermis Structure

  • Comprised of several layers:

    1. Stratum Germinativum:

      • Basal layer with large stem cells that divide to produce keratinocytes

      • Firmly attached to basal lamina

    2. Stratum Spinosum:

      • Known as the "spiny layer"

      • Composed of keratinocytes with tonofilaments

      • Desmosomes attach keratinocytes together

    3. Stratum Granulosum:

      • Known as the "granular layer"

      • Produces keratohyalin and keratin

      • Forms water-repellent sealant

    4. Stratum Lucidum:

      • Known as the "clear layer"

      • Found only in volar skin (palmar and plantar areas)

    5. Stratum Corneum:

    • Composed of dead keratinocytes, providing a water-repellent barrier and protection

Thin vs. Thick Skin

  • Thin Skin:

    • Stratum corneum is much thinner

    • Less distinct epidermal layers

  • Thick Skin:

    • More developed dermal papillae and epidermal ridges

Dermis Structure

  • Papillary Layer:

    • Thinner layer made of areolar connective tissue

    • Contains nerve endings for touch, temperature, and pain

  • Reticular Layer:

    • Thicker layer with dense, irregular connective tissue

    • Provides skin extensibility and elasticity

Lines of Cleavage in the Dermis

  • Collagen fiber bundles align along lines of tension

  • Clinically significant for surgical procedures (cuts parallel heal better than those perpendicular)

Hypodermis Overview

  • Also known as superficial fascia

  • Stabilizes skin position relative to underlying tissues

  • Stores fat; distribution varies by sex

Specialized Skin Cells

  • Merkel Cells:

    • Least common, located in stratum germinativum

    • Important for touch sensation

  • Langerhans Cells:

    • Originate from bone marrow

    • Have phagocytic capabilities, vital for immune response

  • Melanocytes:

    • Produce melanin, about 8% of epithelial cells

    • Transfer melanin granules to keratinocytes

Anatomy of Skin Color

  • Influenced by:

    • Blood supply and hemoglobin levels

    • Thickness of stratum corneum

    • Pigments (carotene, melanin, pheomelanin)

Function of Melanin

  • Protects against UV radiation

  • Variations in melanin production affect skin tone

  • Fitzpatrick Scale: Classifies skin's response to UV exposure

UV-Induced Skin Damage

  • Leads to chromosomal damage (skin cancer), aging, and wrinkling in the dermis

Accessory Structures: Exocrine Glands

  1. Sweat Glands:

    • Secrete water and electrolytes

    • Merocrine (eccrine) secretion: Released without cell death

    • Sebaceous Glands: Distributed throughout the body, secrete sebum through holocrine secretion

Accessory Structures: Sweat Glands

  • Merocrine (Eccrine):

    • Widespread, regulate body temperature

  • Apocrine:

    • Specific to certain areas, secrete odiferous sweat during stress or arousal

Specialized Apocrine Glands

  • Ceruminous Glands: Secrete ear wax via merocrine secretion

  • Mammary Glands: Milk-producing, regulated by hormones

Accessory Structures: Hair

  • Approximately 5 million hairs (2% on head)

  • Functions:

    • UV protection

    • Thermal insulation

    • Particle filtration

Anatomy of Hair Follicle

  • Hair papilla, hair bulb, hair root, arrector pili muscle

Types of Hair

  1. Vellus: Fine hair over most of body

  2. Intermediate: Limb hair, varies with hormones

  3. Terminal: Heavier, found on scalp, eyebrows

Hair Growth Cycle

  • Anagen phase (growth): 2-6 years

  • Telogen (resting phase): 3 months

Accessory Structures: Nail Anatomy

  • Components: Free edge, lunula, eponychium, nail body, nail bed

Usage Guidelines

  • Students may display, download, or print materials for personal and educational use only, with restrictions on distribution and modifications.