Integumentary System
The integumentary system includes skin, hair, nails, glands, sensory
receptors, and fascia. This system plays crucial roles in protection,
thermoregulation, sensation, metabolism, and immune response.
1. Skin Structure
The skin, or cutaneous membrane, is the body's largest organ and consists
of three primary layers:
Epidermis:
Outermost, avascular layer composed of stratified squamous epithelium.
Cell Types:
Keratinocytes: The most common, produce keratin.
Melanocytes: Produce melanin, found in the basal layer.
Langerhans Cells: Immune cells derived from bone marrow.
Merkel Cells: Sensory receptors for touch.
Layers of the Epidermis:
Stratum Basale (Basal Layer): Single layer of cells, including stem cells for
keratinocyte production. Mitotic activity is high here.
Stratum Spinosum (Prickle Cell Layer): Provides structural support with
intermediate filaments.
Stratum Granulosum: Keratinocytes contain keratohyalin granules for
waterproofing.
Stratum Lucidum: Only in thick skin; a thin, clear layer for extra protection.
Stratum Corneum: The outermost layer, consists of dead, keratinized cells
that continuously shed.
Dermis:
Dense connective tissue layer rich in collagen and elastic fibers.
Layers of the Dermis:
Papillary Layer: Contains loose connective tissue, capillaries, and
Meissner’s corpuscles; responsible for forming fingerprints.
Reticular Layer: Thicker, denser layer with collagen bundles that provide
tensile strength.
Contains blood vessels, nerve endings, hair follicles, sweat glands, and
sebaceous glands.
Hypodermis (Subcutaneous Layer):
Composed of loose connective tissue and adipose tissue, connecting skin to
underlying structures.
Functions in insulation, shock absorption, and energy storage.
2. Fascia
The fascia is an integral part of the body’s connective tissue framework,
often studied alongside the integumentary system.
Superficial Fascia:
Lies directly beneath the dermis, often considered part of the hypodermis.
Composed of loose connective tissue and adipose tissue.
Allows skin mobility over underlying structures and provides thermal
insulation.
Contains cutaneous vessels, nerves, and lymphatics.
Deep Fascia:
Dense, fibrous connective tissue surrounding muscles, bones, nerves, and
blood vessels.
Functions:
Provides structural support and compartmentalizes muscles.
Pathway for nerves and blood vessels.
Contributes to venous return by exerting pressure on veins during muscle
contraction.
Forms specialized structures:
Retinacula: Bands around tendons, prevent bowstringing.
Aponeuroses: Flattened tendinous sheets that connect muscles to the parts
they move.
3. Skin Appendages
Hair:
Structure:
Shaft: Visible part of hair above the skin.
Root: Embedded in the dermis, extending into a bulb.
Hair Follicle: Invagination of the epidermis surrounding the hair.
Growth Phases: Anagen (growth), Catagen (regression), Telogen (resting).
Functions: Insulation, sensory input, protection.
Associated Structures: Arrector pili muscle (causes "goosebumps"),
sebaceous glands.
Nails:
Structure: Composed of keratinized cells; parts include nail plate, nail bed,
lunula, and eponychium (cuticle).
Functions: Protects fingertips, assists in grasping objects.
Glands:
Sebaceous Glands: Produce sebum, lubricating hair and skin, found
primarily in association with hair follicles.
Sweat Glands:
Eccrine Glands: Widely distributed; play a major role in thermoregulation
by excreting sweat.
Apocrine Glands: Found in axillary and genital areas; activated by stress,
producing an odor when metabolized by skin bacteria.
Ceruminous Glands: Located in the ear canal; produce cerumen (earwax)
for protection.
Mammary Glands: Modified sweat glands that produce milk in lactating
females.
4. Skin Pigmentation
Melanin: Produced by melanocytes in the stratum basale; protects skin
from UV radiation.
Carotene: Yellow-orange pigment found in stratum corneum and adipose
tissue.
Hemoglobin: Oxygenated blood gives a reddish hue, particularly visible in
lighter skin.
5. Sensory Receptors
The skin is rich in specialized sensory receptors to detect various stimuli:
Meissner’s Corpuscles: Light touch receptors located in the papillary layer.
Pacinian Corpuscles: Detect deep pressure and vibration; found in the
deeper dermis.
Merkel Cells: Located in the stratum basale, sensitive to steady pressure.
Free Nerve Endings: Detect pain, temperature changes, and itch sensations.
6. Functions of the Skin
Protection: Acts as a physical, chemical, and biological barrier.
Thermoregulation: Sweating and vasodilation/vasoconstriction help
maintain body temperature.
Sensation: Receptors for touch, temperature, pain, and pressure provide
environmental awareness.
Metabolism: Synthesizes Vitamin D when exposed to sunlight.
Excretion: Sweat glands help in the excretion of salts, water, and some
waste.
Immune Function: Langerhans cells in the epidermis are involved in
immune defense.
7. Skin Healing and Repair
Regeneration: Epidermal cells regenerate to restore damaged areas.
Fibrosis: Scar formation occurs when damage extends to the dermis.
Healing Stages:
Inflammation: Increased blood flow to the injury site.
Proliferation: New tissue formation (granulation).
Maturation: Collagen remodeling restores tensile strength.
8. Clinical Conditions
Burns: Classified by degree (first, second, third) based on depth.
Skin Cancers: Basal cell carcinoma, squamous cell carcinoma, and
melanoma, each differing in severity and origin.
Dermatitis: Inflammatory conditions including eczema and psoriasis.
Aging and Skin Changes: Thinning of skin, loss of elasticity, decrease in
glandular activity
