Integument: Epidermis, Dermis and Hypodermis

• The integument consists of the epidermis and dermis.
• The epidermis is the outermost layer, composed of stratified squamous epithelium.
• The dermis is the deeper layer, composed of connective tissue.
• The hypodermis (subcutaneous layer) lies beneath the dermis and it primarily consists of adipose and areolar connective tissue.
• The hypodermis provides insulation, cushioning, energy reserve, and anchors skin to underlying structures

Dermis Structure

• The dermis consists of dense irregular connective tissue with collagen and elastic fibers.
• The dermis contains blood vessels, nerve endings, hair follicles, sebaceous glands, and sweat glands.
• The dermis has two layers: papillary and reticular.
• The papillary layer is the superficial layer with loose connective tissue and capillaries.
• The reticular layer is the deeper, thicker layer with dense connective tissue, larger blood vessels, and collagen fibers.

Cells Found in the Dermis

• Fibroblasts produce collagen and elastin fibers.
• Macrophages are immune cells that engulf pathogens.
• Mast cells are involved in inflammatory responses and release histamine.

Papillary Layer Structure

• The papillary layer is the dermis's superficial layer and consists of loose areolar connective tissue.
• It contains dermal papillae: projections extending into the epidermis, increasing surface area for nutrient exchange.
• Dermal papillae contain capillaries, nerve endings, and Meissner's corpuscles (touch receptors).

Friction Ridges

• Friction ridges are raised patterns on the skin (fingerprints).
• Friction Ridges enhance grip and tactile sensation.
• They are formed by the dermal papillae interacting with the epidermis.

Reticular Layer Structure

• The reticular layer is the dermis' deepest layer and consists of dense irregular connective tissue.
• It contains collagen and elastin fibers for strength and flexibility.
• It houses blood vessels, sweat and sebaceous glands, hair follicles, and Pacinian corpuscles (deep pressure receptors).

Epidermis

• The epidermis consists of keratinized stratified squamous epithelium.

Epidermis Cells

• Keratinocytes produce keratin for protection.
• Melanocytes produce melanin (pigment).
• Dendritic (Langerhans) cells provide immune response.
• Tactile (Merkel) cells are touch receptors.

Keratinocytes

• Keratinocytes produce keratin, which strengthens the skin and provides a waterproof barrier.

Melanocytes

• Melanocytes produce melanin, which protects skin cells from UV damage.

Melanosomes

• Melanosomes are organelles inside melanocytes that synthesize and store melanin.
• Melanin is deposited on the nucleus of keratinocytes to shield DNA from UV damage.

Dendritic Cells

• Dendritic cells are star-shaped immune cells.
• Their function is to detect pathogens and activate the immune response.
• They are located in the stratum spinosum.

Tactile Cells

• Tactile cells are small, oval cells connected to nerve endings.
• Their function is to sense touch.
• They are located in the stratum basale.

Epidermis Layers

• Thick skin (palms, soles) contains five layers.
• Thin skin (everywhere else) contains four layers.
• Thick skin has five layers, including the stratum lucidum, and is found on palms and soles, while thin skin lacks the stratum lucidum and has hair follicles and sebaceous glands.

Epidermis Layers Described

• Stratum basale consists of a single layer of basal cells and is the site of mitosis.
• Stratum spinosum consists of several layers of keratinocytes connected by desmosomes.
• Stratum granulosum is where cells begin to die and accumulate keratohyalin.
• Stratum lucidum (only in thick skin) is a thin, clear layer of dead keratinocytes.
• Stratum corneum consists of 20-30 layers of dead, flat keratinized cells.

Melanin

• Melanin is a pigment ranging from yellow to brown to black, protecting against UV damage, and contributes to skin color.

Carotene

• Carotene: an orange-yellow pigment from diet (carrots, sweet potatoes) stored in the skin, contributes to skin color

Hemoglobin

• Oxygen-rich hemoglobin gives a pinkish hue to fair skin and contributes to skin color.

Skin Color Alterations

• Cyanosis (blue) indicates low oxygen.
• Pallor (pale) indicates anemia or low blood pressure.
• Jaundice (yellow) indicates liver disease.
• Erythema (red) indicates fever or inflammation.

Sudoriferous Glands

• Sudoriferous glands are sweat glands.
• Eccrine glands function in thermoregulation.
• Apocrine glands are found in the axillae and groin and become active after puberty.

Eccrine Glands

• Eccrine sweat glands are located all over the body, especially on the palms, soles, and forehead.

Sensible vs Insensible Sweating

• Sensible sweating is visible sweat.
• Insensible sweating is the evaporation of moisture from the skin.

Blood Vessels and Temperature Regulation

• Vasodilation (widening) cools the body.
• Vasoconstriction (narrowing) retains heat.

Integumentary System

• The integumentary system acts as a blood reservoir.
• The dermis holds about 5% of the body's blood and can redirect it when needed.

Skin Cancer

• The most important risk factor for developing skin cancer is UV radiation, which damages DNA and can lead to mutations.

Three Major Forms of Skin Cancer

• Basal cell carcinoma is the least dangerous and most common form of skin cancer.
• Squamous cell carcinoma can metastasize if left untreated.
• Melanoma is the most aggressive form of skin cancer and spreads quickly.

ABCD Rule

• A stands for Asymmetry
• B stands for Border irregularity
• C stands for Color variation
• D stands for Diameter >6mm

Burns

• First-degree burns affect the epidermis only.
• Second-degree burns affect the epidermis and dermis and cause blisters.
• Third-degree burns destroy all layers and cause no pain due to nerve damage.

Consequences of Burns

• The life-threatening consequences of burns include dehydration, infection, and shock.