Anatomy of the Skin: Epidermis, Dermis, and Hypodermis | Quizlet

Epidermis

The outermost layer of the skin, made of keratinized stratified squamous epithelium. It is avascular, meaning it lacks blood vessels and relies on the dermis for nutrients.

Functions of the Epidermis

Protects against pathogens, water loss, UV radiation, and provides sensation.

Keratin

A tough, fibrous protein that strengthens and waterproofs the skin.

Avascular

The epidermis has no blood vessels, so it depends on diffusion from the dermis for nutrients.

Mitosis in the Epidermis

Occurs in the stratum basale and lower stratum spinosum. Mitosis slows with age.

Keratinocytes

The most abundant cells in the epidermis. They produce keratin, which provides strength and protection.

Stem Cells

Undifferentiated cells found in the stratum basale that divide to form new keratinocytes.

Melanocytes

Found in the stratum basale; they produce melanin, which protects the skin from UV radiation.

Tactile (Merkel) Cells

Sensory receptors for touch found in the stratum basale. They are connected to nerve endings.

Dendritic (Langerhans) Cells

Immune cells found in the stratum spinosum and granulosum. They protect the skin by detecting pathogens and foreign invaders.

Stratum corneum

The outermost layer, made of dead, keratinized cells that continuously shed to protect the skin.

Stratum lucidum

Found only in thick skin (palms, soles). It is a clear, featureless layer of densely packed keratinocytes.

Stratum granulosum

Contains 2 to 5 layers of keratinocytes with keratohyalin granules that help with waterproofing.

Stratum spinosum

Several layers of keratinocytes connected by desmosomes, giving them a spiny appearance. Contains dendritic cells for immune protection.

Stratum basale

The deepest layer of the epidermis. It contains stem cells, melanocytes, and tactile cells and is the site of mitosis (cell division).

Dermis

The connective tissue layer beneath the epidermis. It contains blood vessels, nerve endings, glands, hair follicles, and collagen fibers.

Composition of the Dermis

Made up of collagen, elastic fibers, reticular fibers, and fibroblasts.

Function of the Dermis

Provides strength, flexibility, blood supply, and sensory reception to the skin.

Hair Follicles & Nail Roots

Both are embedded in the dermis.

Facial Expressions

The skeletal muscles attach to dermal collagen fibers, allowing movement such as smiling, frowning, and raising eyebrows.

Dermal Papillae

The upward projections of the dermis into the epidermis. These interlock with the epidermis to prevent slipping and form fingerprints.

Papillary Layer

The superficial (top) layer of the dermis. It consists of loose areolar connective tissue and contains capillaries and immune cells. It extends upward into the epidermis as dermal papillae.

Reticular Layer

The deeper, thicker layer of the dermis. It consists of dense irregular connective tissue with thick collagen fibers that provide strength and elasticity.

Friction Ridges

Form fingerprint patterns, caused by dermal papillae.

Stretch Marks (Striae)

Form when collagen fibers tear due to rapid skin stretching (e.g., pregnancy, obesity).

Blisters

Occur when fluid accumulates between the epidermis and dermis due to friction, burns, or pressure.

Hypodermis

The deepest layer of the skin, also called subcutaneous tissue. It consists of areolar and adipose tissue and connects the skin to muscles and bones.

Functions of the Hypodermis

Acts as a shock absorber, energy storage site, and insulator to help regulate body temperature.

Subcutaneous Fat

A fat layer that provides padding and insulation. It is thicker in the abdomen, hips, thighs, and breasts.

Gender Differences in Subcutaneous Fat

Women have about 8% more subcutaneous fat than men.

Age-Related Changes

Infants and elderly people have less subcutaneous fat, making them more sensitive to cold.

Drug Absorption

The hypodermis is highly vascular, making it an ideal site for injections (e.g., insulin, vaccines).