Integumentary System

Integumentary System Overview

Course Reference

BIOL 2610: Human Anatomy and Physiology I

Learning Objectives

• Identify and describe structures related to the integumentary system.

• Describe organs and functions of the integumentary system.

• Understand the three layers of skin: epidermis, dermis, hypodermis.

• Describe the cells of the epidermis and their functionalities.

Introduction to Integumentary System

Organs Involved

• Skin (integument): The largest organ of the body, encompassing a diverse range of functions and structures.

• Hair: Provides protection and contributes to thermal regulation and sensory perception.

• Nails: Protect the tips of fingers and toes and assist in grasping.

• Cutaneous glands: Secretory glands involved in homeostasis, including sweat and sebaceous glands.

Functions of the Integumentary System

1. Protection:

   • Acts as a barrier to protect underlying tissues from mechanical injuries, pathogens, and harmful chemicals.

   • Keratinocytes produce keratin, contributing to skin toughness; desmosomes strengthen cell adhesion, enhancing skin's resistance to tearing and microbial invasion.

2. Water Retention:

   • The integumentary system helps prevent dehydration by minimizing water loss.

   • The stratum corneum layer is particularly crucial as it contains lipids that reduce trans-epidermal water loss, preventing excessive absorption during activities like swimming.

3. Thermoregulation:

   • Regulates body temperature through mechanisms such as:

     • Vasoconstriction: Constricts blood vessels in cold temperatures to retain heat.

     • Vasodilation: Expands blood vessels in high temperatures to dissipate heat through increased blood flow to the skin's surface.

4. Vitamin D Synthesis:

   • The skin, when exposed to UV radiation, initiates the synthesis of vitamin D, which is vital for calcium absorption and bone health. This process involves the kidneys and liver for final activation.

5. Cutaneous Sensation:

   • Houses a network of sensory receptors for touch, temperature, pain, and pressure. This sensory information is crucial for the perception of the environment, with a concentration of receptors found in regions such as the fingertips, face, and soles of the feet.

6. Nonverbal Communication:

   • The skin facilitates emotional expression through its structure; movements and changes in the skin's surface can convey emotions like anger, happiness, or sadness.

Characteristics of Skin

• Largest Organ: Constitutes approximately 15% of total body weight, indicating its extensive role and importance in overall physiology.

• Thickness Variation: Skin thickness ranges from as little as 0.5 mm on eyelids to as much as 6 mm between the shoulder blades, primarily resulting from differences in dermal layer thickness.

• Types of Skin:

  • Thick Skin: Found on areas requiring added protection such as palms and soles.

  • Thin Skin: Covers the majority of the body's surface, providing flexibility and sensitivity.

Layers of the Skin

1. Epidermis: The outermost layer, providing the first line of defense against environmental factors.

2. Dermis: The underlying layer containing collagen and elastin fibers, offering strength and elasticity.

3. Hypodermis: Subcutaneous layer, primarily composed of adipose tissue, serving to insulate and bind skin to underlying structures, as well as acting as an energy reserve.

Cells of the Epidermis

Types of Cells

• Stem Cells: Undifferentiated cells capable of continuous division leading to the formation of keratinocytes.

• Keratinocytes: Predominantly make up the epidermis, responsible for forming the protective barrier and producing keratin.

• Tactile (Merkel) Cells: Act as mechanoreceptors, essential for perceiving touch and texture.

• Melanocytes: Produce melanin, which protects against UV radiation and determines skin pigmentation. Different types of melanin:

  • Eumelanin: Produces brownish-black coloration.

  • Pheomelanin: Imparts a reddish-yellow hue.

• Dendritic (Langerhans) Cells: Part of the immune response, detecting pathogens and initiating immune reactions.

Layers of the Epidermis

1. Stratum Basale: Composed of the deepest layer with actively dividing stem cells continuously generating new keratinocytes.

2. Stratum Spinosum: Known as the thickest layer with keratinocytes that are beginning to flatten and lose water, containing desmosomes that provide structural stability.

3. Stratum Granulosum: Contains keratinocytes that are undergoing keratinization; keratohyalin granules accumulate to facilitate the loss of water and permeability.

4. Stratum Lucidum: A clear layer only present in thick skin, composed of dead keratinocytes.

5. Stratum Corneum: The outermost layer comprised of layers of dead, flattened keratinized cells that form a barrier against environmental hazards.

Life History of a Keratinocyte

• Keratinocytes typically migrate from the stratum basale to the surface in about 30-40 days, undergoing transformation and eventually being shed during the process of desquamation.

• Factors such as age and environmental stressors can influence the turnover rate and overall health of the skin.

Dermis Overview

Layers of the Dermis

• Papillary Layer: Characterized by loose areolar connective tissue with an abundance of blood vessels, enhancing nutrient exchange and temperature regulation.

• Reticular Layer: Composed of dense irregular connective tissue, contributing to the structural integrity and elasticity of the skin.

Sensory Receptors:

• Meissner's Corpuscles: Sensitive to light touch, concentrated in areas such as fingers and lips.

• Pacinian Corpuscles: Respond to pressure and vibration, found deeper in the dermis or hypodermis.

Hypodermis Overview

• Known as subcutaneous tissue, mainly consisting of adipose tissue that serves various roles:

  • Binds the skin to underlying tissues and muscles,

  • Provides insulation and energy storage,

  • Facilitates movement of the skin over underlying structures.

  • Common site for hypodermic injections due to its rich blood supply that allows for rapid absorption of administered substances.

Skin Color Factors

• Variations in skin color are primarily due to levels of melanin, affected by genetics and environmental factors. UV exposure can stimulate increased melanin production, leading to tanning.

• Hemoglobin: Contributes a pinkish hue, especially prominent in areas such as the lips and cheeks.

• Carotene: A pigment contributing a yellowish coloration, found in certain foods and stored in the skin.

• Abnormal skin colors such as cyanosis (bluish tint), jaundice (yellowish), or redness may indicate underlying medical conditions that necessitate further investigation.

Accessory Organs of the Skin

Hair

• Composed of keratinized cells; undergoes continual growth and cycles of shedding. Variations in hair composition lead to differences in texture, color, and functions such as insulation and protection against mechanical injury.

• Hair follicles are complex structures containing a bulb (where hair growth occurs), a matrix (site of active cell division), and a root surrounded by dermal papilla, which supplies blood, nutrients, and signals necessary for hair growth.

Nails

• Comprised of hard keratin, the growth of nails originates from the nail matrix, contributing to mood and dexterity; useful for grasping and protecting the tips of fingers and toes. Fingernails typically grow at a rate of around 1 mm per week.

Cutaneous Glands

• Glandular structures that play crucial roles in maintaining homeostasis:

  • Sweat Glands:

    • Merocrine (Eccrine): Surface-level glands that secrete sweat to help cool the body through evaporation.

    • Apocrine: Found in specific regions, such as the armpits, associated with scent production.

  • Sebaceous Glands: Produce sebum, an oily substance that helps to keep the skin and hair moisturized.

  • Ceruminous Glands: Produce cerumen (earwax), providing a protective barrier in the ear canal.

  • Mammary Glands: Specialized glands involved in the production of milk during lactation.

Resources

• References for further reading include works by Marieb, Hoehn, Saladin, and Silverthorn that delve deeper into human anatomical structures and physiological functions.