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

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