Learn: Integumentary System: Skin Structure, Cells, and Functions

What are the two primary layers of the skin?

Epidermis and dermis

What lies beneath the skin?

Hypodermis

What is the integumentary system?

The skin and its appendages, including hair, nails, and glands

What are the major functions of the integumentary system?

Protection, temperature regulation, sensation, vitamin D synthesis, and prevention of water loss

Approximately how large is the surface area of the average human skin?

Nearly 2 square meters (20 square feet)

How much can skin thickness vary?

From less than 0.05 cm to slightly more than 0.3 cm

What are the major cell types found in the epidermis?

Keratinocytes, melanocytes, dendritic cells, and Merkel cells

What percentage of epidermal cells are keratinocytes?

Over 90%

What do keratinocytes produce?

Keratin

What is keratin?

A tough, fibrous protein that helps protect the skin

What is one major function of keratin?

It helps make the skin water-resistant and prevents fluid loss

What do melanocytes do?

Produce pigments that give the skin its color

How does melanin protect the skin?

It reduces potentially dangerous ultraviolet radiation and protects the nucleus of keratinocytes

What do dendritic cells do?

Identify invading bacteria and other foreign substances and present them to the immune system

Where are Merkel cells found?

In the deepest layer of the epidermis

What do Merkel cells form?

Merkel discs

What do Merkel discs function as?

Receptors for light touch

How many distinct strata does thick epidermis have?

Five

What are the five layers of the epidermis from deepest to most superficial?

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum

What is the stratum basale?

The base layer of the epidermis consisting of a single layer of columnar cells that produces the other epidermal cells

What happens in the stratum basale?

Cells continuously undergo mitosis and produce new epidermal cells

What is the stratum spinosum?

The spiny layer containing about 8-10 layers of cells

What holds cells of the stratum spinosum together?

Desmosomes

Why does the stratum spinosum appear spiny?

The cells are attached by desmosomes that create a spiny appearance

What is the stratum granulosum?

The granular layer containing 2-5 layers of dying, flattened cells

What happens to the nuclei in the stratum granulosum?

They disappear

What is the stratum lucidum?

A clear layer of squamous cells found in thick skin

What is found inside cells of the stratum lucidum?

A substance needed to produce surface keratin

Where is the stratum lucidum found?

In thick skin, such as calloused areas

What is the stratum corneum?

The horny layer consisting of several layers of very thin, dead squamous cells

What forms the tough, waterproof barrier of the stratum corneum?

A dense network of keratin fibers

What happens to epidermal cells as they move toward the surface?

They become increasingly keratinized, die, and eventually are shed

What must happen for epidermal growth and repair?

New cells must be formed in the stratum basale at the same rate that old keratinized cells flake off

What are calluses?

Areas of thickened skin that form because of constant friction

What is the dermoepidermal junction (DEJ)?

A specialized interface that anchors the epidermis to the dermis and resists friction and shearing forces

What provides structural support at the dermoepidermal junction?

The basement membrane and anchoring fibers

What happens when the epidermis separates from the dermis?

A blister can form

What fills the space in a blister?

Extracellular fluid

What can prolonged pressure without relief cause?

Pressure sores

What are the two layers of the dermis?

Papillary layer and reticular layer

What is the dermis sometimes called?

The "true skin"

What type of tissue makes up the dermis?

Connective tissue

What is the papillary layer?

The superficial layer of the dermis

What are dermal papillae?

Nipple-like projections of the papillary layer

What is the reticular layer?

The deeper, thicker layer of the dermis

What types of fibers are found in the reticular layer?

Collagen and elastic fibers

What is the major structural role of collagen fibers in the dermis?

They provide mechanical strength and help the skin handle force

What are somatic sensory receptors?

Specialized networks of nerves and nerve endings in the dermis

What sensations can the sensory receptors of the dermis detect?

Pain, pressure, touch, and temperature variation

What are major functions of the dermis?

Protection, fluid storage, muscle attachment, sensation, and repair

How does the dermis protect the body?

It resists mechanical injury, pressure, and compression

What does the dermis store?

Water and electrolytes

What is the role of the dermis in muscle attachment?

It provides attachment for smooth muscle fibers and other structures

How does the dermis contribute to sensation?

It contains numerous sensory receptors and nerve endings

Does the dermis continuously replace itself like the epidermis?

No

How does the dermis respond to injury?

It regenerates by forming new connective tissue to repair the wound

What happens if normal dermal tissue is not fully restored?

A scar remains

What is the hypodermis?

The region below the dermis filled with adipose and loose fibrous connective tissue

What is another name for the hypodermis?

The subcutaneous layer or superficial fascia

Is the hypodermis part of the skin proper?

No

What is the main role of the hypodermis?

It connects the skin to underlying structures of the body

Where is the hypodermis located?

Deep to the dermis

What secures the skin to underlying structures?

Fibrous bands

What happens to adipose cells with weight gain or loss?

They increase or decrease in size/amount

What is a subcutaneous (SQ) injection?

An injection delivered into the subcutaneous tissue

What is an intradermal (ID) injection?

An injection delivered into the dermis

What are examples of substances or procedures delivered subcutaneously?

Medications such as Ozempic and some vaccines

What are examples of uses for intradermal injections?

TB testing, allergy skin testing, Botox, and fillers

What does "thick skin" refer to?

Thicker epidermal layers, not necessarily a thicker entire skin structure

Where is thin skin found?

Over most of the body's surface

Where is thick skin found?

On the palms, fingertips, soles of the feet, and other areas subject to friction

Does thick skin contain hair?

No, it is hairless

What are friction ridges?

Finger-like projections of dermal papillae that extend upward from the dermis

What do friction ridges create?

Unique fingerprints and footprints

What are the five epidermal strata in order from deep to superficial?

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

What are the two layers of the dermis?

Papillary layer and reticular layer

What is located below the dermis?

The hypodermis

What is melanin?

A pigment that determines skin color

Where are melanocytes located?

Within the stratum basale

What factors influence skin pigmentation?

The density of melanocyte projections, the transport of melanosomes, and the distribution of melanosomes within keratinocytes

What are melanosomes?

Tiny pigmented granules containing pigment

What causes variation in skin color?

Differences in pigment production and the type and distribution of melanosomes

What happens to melanin production after prolonged exposure to ultraviolet radiation?

Melanocytes increase melanin production

Why is melanin protective?

It protects the nucleus of keratinocytes from ultraviolet radiation

What is beta-carotene?

A pigment important for skin growth that is stored in skin tissue and can be converted into vitamin A

How can deoxygenated hemoglobin affect skin color?

It can cause the skin to appear bluish

What is cyanosis?

A bluish appearance of the skin caused by a high proportion of deoxygenated hemoglobin

Why does deoxygenated hemoglobin cause a bluish appearance?

It reflects light differently from oxygenated hemoglobin

What is the surface film of the skin?

A film produced from residues and secretions of sweat and sebaceous glands mixed with dead epithelial cells

What are functions of the skin's surface film?

Lubrication, hydration, buffering against irritants, and blocking toxic agents

What is the acid mantle?

The slightly acidic surface created by the combination of sweat and sebum

Why is the acid mantle useful?

The slightly acidic environment makes it more difficult for some bacteria to grow

What is the protective function of skin?

It protects underlying tissues from microorganisms, harmful chemicals, and mechanical injury

How does the skin protect against microorganisms?

It acts as a physical barrier and contains defensive cells

How does the skin protect against harmful chemicals?

It helps prevent many chemicals from entering the body

How does the skin contribute to sensation?

Sensory receptors respond to touch, pressure, vibration, pain, and temperature

What allows skin to stretch and recoil?

Collagen and elastic fibers

What is the flexibility function of skin?

It allows changes in body contour without tearing

How does the skin contribute to excretion?

Sweat helps regulate the volume and chemical content of fluid lost from the body

What substances are found in sweat?

Salts/electrolytes and urea