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.