Integumentary System Lecture Notes

Integumentary System

Overview

• The integumentary system, also known as the integument, is the largest system in the body.

• It includes two major parts:

  • Cutaneous membrane (skin): the largest organ consisting of the epidermis and dermis.

  • Accessory structures: hair, nails, and glands.

Components

• Cutaneous Membrane (Skin)

  • Largest organ of the body.

  • Layers:

    • Epidermis

    • Dermis

• Accessory Structures

  • Originate in the dermis and extend through the epidermis to the skin surface.

  • Include:

    • Hair and hair follicles (composed mainly of keratin).

    • Exocrine glands (sebaceous/oil glands and sudoriferous/sweat glands).

    • Nails (made of hard keratin).

    • Arrector pili muscle (causes goosebumps, a vestigial trait).

• Sensory Receptors

  • Detect temperature, pain, touch, and pressure.

Medical Terminology

• Skin: derma

• Hair: trinco

• Nails: onycho

• Examples:

  • Dermatitis: affects the dermis layers.

  • Psoriasis and eczema: affect the epidermis (genetic and autoimmune).

Subcutaneous Layer (Hypodermis)

• Not technically a layer of the skin.

• Composed of loose connective tissue (e.g., areolar tissue containing collagen) and adipose tissue (fat).

• Located below the dermis.

Cutaneous Layers

• Epidermis: 5 layers (thick skin), 4 layers (thin skin); avascular (no blood vessels).

• Dermis: papillary layer and reticular layer; vascular (contains blood vessels).

Sites of Injections

• Epidermis: subcutaneous.

• Hypodermis: intramuscular or hypodermic.

Functions of Integumentary System

• Protection:

  • Underlying tissues and organs.

  • Barrier against trauma, infection, dehydration, and UV radiation.

• Excretion:

  • Salts, water, and organic wastes (mainly through sweat glands).

• Thermoregulation:

  • Maintenance of normal body temperature.

• Production of Melanin

• Production of Keratin:

  • Hair and nails.

• Synthesis of Vitamin D3:

  • Allows humans to absorb more calcium.

• Storage of Lipids

  • Adipose tissue; long-term energy, insulation, and cushioning.

• Detection of Touch, Pressure, Pain, etc.:

  • Sensory receptors.

• Coordination of Immune Response:

  • Epidermis (Langerhans cells).

Epidermis

• Stratified squamous epithelial tissue.

• Avascular (no blood vessels).

• Nutrients and oxygen diffuse from capillaries in the dermis.

• Outermost layer: stratum corneum (made of dead keratin cells).

• Contains keratinocytes (keratin cells).

Keratinocytes

• Most abundant epithelial cells in the body.

• Contain large amounts of keratin (tough, fibrous, water-resistant protein).

Types of Skin

• Thin Skin:

  • Covers most of the body.

  • Has four layers of keratinocytes.

• Thick Skin:

  • Covers palms of the hands and soles of the feet.

  • Has five layers of keratinocytes.

Strata (Layers) of Keratinocytes in Thick Skin (from basement membrane to free surface)

• Stratum Basale (Base):

  • Deepest layer.

  • Contains melanocytes (pigmentation) and sensory input (touch, pressure, pain).

• Stratum Spinosum:

  • Keratin production starts here.

  • Contains Langerhans cells (immunity).

• Stratum Granulosum

• Stratum Lucidum:

  • Clear layer.

  • Only in thick skin.

• Stratum Corneum:

  • Horny layer.

  • Outermost layer of dead keratinized cells.

Perspiration

• Insensible Perspiration:

  • Invisible passive loss of water.

  • Water diffuses across stratum corneum and evaporates from skin.

• Sensible Perspiration:

  • Water excreted by sweat glands.

  • Noticeable, active loss of water.

  • Occurs during heat exposure, physical activity, and stress.

Sensory Receptors

• Light touch: tactile (Meissner) corpuscles in dermal papillae.

• Deep pressure and vibration: lamellar (Pacinian) corpuscles in reticular layer.

Epidermal Growth Factor (EGF)

• Used in laboratories to grow skin grafts for burn victims and patients with chronic wounds.

• Functions:

  • Promotes division of basal cells (stem cells of the epidermis).

Dermis

• Located between the epidermis and subcutaneous layer.

• Anchors epidermal accessory structures.

• Two components:

  • Outer papillary layer: nourishes and anchors the epidermis.

  • Deeper reticular layer: contains hair follicles, glands, and nerve endings.

  • Vascular

Dermal Strength and Elasticity

• Collagen fibers:

  • Protein; strong and resists stretching.

• Elastic fibers:

  • Made of elastin; permit stretching and recoil to original length.

• Fibers and water provide flexibility and resilience.

• Skin turgor: indicates hydration status and elasticity.

Dermal Blood Supply

• Cutaneous plexus: deep network of arteries along the reticular layer.

• Contusion (bruise) / (brain) concussion: caused by damage to blood vessels in the dermis; blood leaks out of the vessels and into the skin.

• Colors: start red, blue, purple, heal green and yellow.

• Sensory receptors respond to stimuli; found in fingers (digits/phalanges).

Hypodermis (Subcutaneous Layer)

• Primarily adipose tissue + areolar tissue.

• Large arteries and veins are in the superficial region (vascular).

• Distribution of subcutaneous fat is determined by sex hormones.

Skin Color Influences

Pigments in the Epidermis

• Melanin (produced by melanocytes):

  • Eumelanin (brown/black)

  • Pheomelanin (yellow/red)

  • Protects against UV radiation; excess can cause melanoma.

• Carotene:

  • Yellow-orange color

  • Produces vitamin A

• Genetics determine skin, hair, and eye color.

Illness and Skin Color

• Jaundice:

  • Build-up of bile produced by the liver (e.g., hepatitis);

  • Skin and whites of eyes turn yellow (sclera).

• Pituitary tumor:

  • Hyperpigmentation (skin gets dark).

• Addison's disease:

  • Bronze skin.

• Vitiligo:

  • Loss of melanocytes, causing loss of color (depigmentation);

  • White patches on the skin.

Vitamin D3 (Cholecalciferol)

• Produced by epidermal cells in the presence of UV radiation.

• Liver and kidneys convert vitamin D3 into calcitriol, a hormone that increases calcium levels.

• Insufficient vitamin D3 can cause rickets (common in children).

• Fat-soluble vitamins: A, D, E, and K.

• Water-soluble vitamins: B and C.

Hairs

• Two types:

  • Terminal hairs: heavily pigmented with melanin.

  • Vellus hairs: lack pigmentation (peach fuzz).

Hair Follicles

• Produce and support hair growth.

• Give rise to non-living hairs.

• Located at the surface of the skin.

Hair Structure (3 Layers)

• Medulla: inside (central core).

• Cortex: middle (intermediate layer).

• Cuticle: outside (surface layer).

• Hairs are made of keratin.

Exocrine Glands

• Sebaceous glands (oil glands; secrete sebum):

  • Inhibits bacterial growth (antibacterial properties).

• Sweat glands:

  • Apocrine sweat glands: found in armpits and groin (limit bacterial growth; cause body odor when sweat interacts with bacteria).

  • Eccrine sweat glands: found in palms, soles, and forehead (thermoregulation).

Types of Sebaceous Glands

• Simple branched alveolar glands.

• Most common: associated with hair follicles.

• Sebaceous follicles: discharge sebum directly onto the skin surface; not attached to hair.

Nails

• Made of dead cells packed with hard keratin.

• Parts:

  • Nail plate

  • Nail bed

  • Nail matrix

  • Lunula

  • Cuticle

• Pitted nails: dimples in nails (defects in keratinization).

• Fungal infections in nails: onychomycosis.

• Nails (medical term): onycho

Hyponychium

• Skin beneath the distal free edge of the nail.

• Portion of the nail that is trimmed or filed.

• Serves as a protective layer for the nail and nail bed.