Chapter 6.1

Skin and Subcutaneous Tissue

Why is the skin considered the body's most vulnerable organ?

It is directly exposed to radiation, trauma, infection, and chemicals.

What is Dermatology?

The scientific study and medical treatment of the integumentary system.

Why are skin, hair, and nail inspections an essential part of a physical exam?

They provide vital clues about a patient's overall health.

What does the integumentary system consist of?

Skin, hair, nails, and associated glands

[T/F] The skin (integument) is the body’s largest and heaviest organ that covers 1.5 to 2.0 m² and composes 8% of body weight

True

What tissue type makes up the epidermis vs. the dermis?

Epidermis is stratified squamous epithelium; Dermis is connective tissue.

Where is the hypodermis located, and is it a true skin layer?

Located below the dermis; it is not part of the skin but usually studied with it.

What is the general range of skin thickness, and which layer causes most of this variation?

0.5 to 6 mm; variation is mainly due to the dermis.

The classification of skin as thick or thin is based on the thickness of which layer?

The epidermis.

Where is thick skin located, and which glands does it feature or lack?

Palms, soles, fingers, and toes; features sweat glands but lacks hair follicles and oil glands.

How thick is the thick skin epidermis, and which specific stratum makes it so?

About 0.5 mm thick; primarily due to a thick stratum corneum.

Where is thin skin located, and what three structures does it possess?

Covers the rest of the body; possesses hair follicles, sebaceous (oil) glands, and sweat glands.

What is the average thickness of the thin skin epidermis?

About 0.1 mm thick.

Which specific protein in the skin provides physical protection against trauma?

Keratin.

What three components on the skin surface protect against bacterial infection?

Dermcidin, defensins, and the acid mantle.

What three environmental factors does the skin act as a barrier against?

Water, ultraviolet (UV) rays, and harmful chemicals.

Aside from trauma and infection resistance, what are the skin's other barrier functions?

Preventing excess water gain/loss and blocking UV radiation and harmful chemicals.

Which organ carries out the first step in Vitamin D synthesis and why does the body need Vitamin D synthesis?

The skin; for bone development and maintenance.

Which two organs complete the Vitamin D synthesis process after the skin starts it?

The liver and kidneys.

What is the body's most extensive sense organ?

The skin.

What seven stimuli do skin nerve endings react to?

Heat, cold, touch, texture, pressure, vibration, and tissue injury.

Where are sensory receptors most abundant vs. relatively few?

Abundant on face, palms, fingers, soles, nipples, genitals; few on back and overlying joints (knees/elbows).

How does the skin help with thermoregulation?

It alters blood flow to either release or retain body heat.

What are the terms for the narrowing vs. widening of skin blood vessels to control heat?

Cutaneous vasoconstriction (narrowing to retain heat) and cutaneous vasodilation (widening to release heat).

Anatomically, how do humans create subtle and varied facial expressions?

Complex skeletal muscles insert into the dermis and pull on the skin.

Why is the general appearance of skin, hair, and nails important beyond physiological function?

It is important for social acceptance, self-image, and emotional state.

What covers the surface of the epidermis, and what is it packed with?

Dead cells packed with tough keratin protein.

How does the avascular epidermis receive its nutrients?

By diffusion from the underlying connective tissue.

What type of nerve endings does the epidermis contain, and for what sensations?

Sparse nerve endings for touch and pain.

Which cell type makes up the great majority of epidermal cells?

Keratinocytes.

What is the primary function of keratinocytes?

To synthesize keratin.

What is the role of epidermal stem cells?

Undifferentiated cells that give rise to keratinocytes.

In which specific layer of the epidermis are stem cells located?

The deepest layer, the stratum basale.

What pigment do melanocytes synthesize, and what is its purpose?

Melanin; it shields cellular DNA from ultraviolet (UV) radiation.

Where are melanocytes located, and how do they distribute melanin to keratinocytes?

Located only in the stratum basale; they use branched processes to distribute melanin via melanosomes.

What are tactile cells, and where are they located?

Touch receptor cells associated with dermal nerve fibers; located in the basal layer of the epidermis.

What is a tactile disc?

The collective term for a tactile cell combined with its associated nerve fiber.

What is the function of epidermal dendritic cells?

Phagocytic immune cells that guard against toxins and microbes.

In which two strata (layers) of the epidermis are dendritic cells found?

Stratum spinosum and stratum granulosum.

What two cell types form a single layer resting on the basement membrane in the stratum basale?

Stem cells and keratinocytes.

Which two other cell types are found scattered throughout the stratum basale?

Melanocytes and tactile cells.

What type of cells make up the stratum spinosum, and how are they joined?

Several layers of living keratinocytes joined by desmosomes and tight junctions.

Why is the stratum spinosum named "spinosum"?

Because cells take on a spiny appearance after histological preparation.

Which immune cells are also found within the stratum spinosum?

Dendritic cells.

How many layers of cells make up the stratum granulosum, and what is their state?

Three to five layers of flat, living keratinocytes.

What type of granules do the cells in the stratum granulosum contain?

Dark-staining keratohyalin granules.

Where is the stratum lucidum found, and what does it look like?

A thin, pale layer found only in thick skin.

Keratinocytes in the stratum lucidum are packed with which clear protein?

Eleidin.

How many cell layers form the stratum corneum, and what is their state?

Up to 30 layers of dead, scaly, keratinized cells.

What three specific things does the stratum corneum resist?

Abrasion, penetration, and water loss.

Where does keratinocyte mitosis occur?

In the stratum basale or the deepest part of the stratum spinosum.

Mitosis requires an abundant amount of what?

Oxygen and nutrients.

Why does keratinocyte mitosis stop as cells migrate upward?

They move away from the blood vessels of the dermis, losing necessary oxygen and nutrients.

As new keratinocytes push older ones toward the surface and get flatten, what two things do the older cells produce?

More keratin and lipid-filled lamellar granules.

How long does it take a keratinocyte to reach the surface, and what is it called when it exfoliates?

30 to 40 days; it flakes off as dander.

What is dandruff?

Clumps of dander combined with sebum (oil).

How does the speed of keratinocyte multiplication change in old age vs. injured skin?

Slower in old age; faster in injured/stressed skin.

What are calluses or corns?

Thick accumulations of dead keratinocytes caused by mechanical stress on hands or feet.

In what layer of the epidermis do the four important events of keratinocyte life history occur?

Stratum granulosum.

What protein is released by keratohyalin granules, and what is its function?

Filaggrin; it binds keratin into tough bundles.

Where do keratinocytes produce tough envelope proteins?

Directly beneath their cell membranes.

What do membrane-coating vesicles release to waterproof the cell surface?

A lipid mixture.

What happens to keratinocyte organelles in the stratum granulosum?

They degenerate, causing the cells to die and leave behind a waterproof sac.

What components form the epidermal water barrier?

The stratum granulosum processes combined with tight junctions between keratinocytes.

What is the primary function of the epidermal water barrier?

It helps prevent dehydration.

Does the epidermal water barrier prevent the stratum corneum from absorbing water in a bath?

No; absorption there is what causes "prune fingers."

What is the general thickness range of the dermis connective tissue layer?

0.2 mm to 4 mm thick.

What fiber type mainly composes the dermis?

Collagen (it also contains elastic and reticular fibers).

What 6 anatomical structures are housed within the dermis?

Blood vessels, sweat glands, sebaceous glands, nerve endings, and hair follicles and nail roots.

Which muscles attach directly to the dermis to produce facial expressions?

Skeletal muscles of facial expression.

What are dermal papillae?

Upward, finger-like extensions of the dermis into the epidermis.

What are epidermal ridges?

Downward waves of the epidermis into the dermis.

What type of tissue makes up the papillary layer, and where is it located?

Areolar tissue; located in and near the dermal papillae.

What is the primary function of the areolar tissue in the papillary layer?

It allows for the mobility of leukocytes and other defense cells.

What type of tissue composes the reticular layer of the dermis?

Dense irregular connective tissue.

What are stretch marks (striae) anatomically?

Tears in the collagen fibers of the reticular layer due to skin stretching.

How is a blister formed?

Damaged dermal blood vessels leak serous fluid, which seeps out between the dermis and epidermis.

Which two tissue types are found in greater abundance in the hypodermis than in the dermis?

Areolar and adipose tissue.

What are the two primary functions of the hypodermis layer?

It pads the body and binds skin to underlying tissues.

Why is the hypodermis a common site for drug injections?

It contains many blood vessels, allowing for quick absorption.

What is subcutaneous fat, and what are its two functional roles?

Hypodermis comprised mostly of adipose tissue; acts as an energy reservoir and provides thermal insulation.

How does subcutaneous fat thickness vary across demographics?

Thicker in women; thinner in infants and the elderly.

What clinical procedure is often required to treat third-degree burns?

Skin grafts.

What is an autograft?

Skin tissue taken from another location on the same person's body.

What is an allograft?

Skin tissue taken from an unrelated person (usually a deceased donor).

Variations in skin and hair color are primarily due to what two factors?

The type and amount of melanin pigment.

What are the two main types of melanin and their general colors?

Eumelanin (dark: brown/black) and pheomelanin (reddish-yellow).

What three other factors contribute to skin color variations?

Dermal vessel show-through, carotene pigment accumulation, and UV radiation exposure.

From where does the body accumulate carotene pigment?

Yellow and orange vegetables.

Do people of different skin colors have a different number of melanocytes?

No; they have the same number but vary in melanin production and longevity.

What four features characterize melanin in darker skin?

Greater quantities produced, slower breakdown, granules more spread out, and visible throughout the epidermis.

What two features characterize melanin in lighter skin?

Melanin is clumped near the nucleus and little is seen beyond the stratum basale.

What is cyanosis and its physiological cause?

Blueness of the skin due to an oxygen deficiency.

What is erythema and its physiological cause?

Redness of the skin due to increased blood flow.

What is pallor and its physiological cause?

Paleness of the skin due to decreased blood flow.

What is albinism and its physiological cause?

White skin due to a genetic lack of melanin.

What is jaundice and what organ malfunction does it typically signal?

Yellowing of skin due to bilirubin buildup; signals compromised liver function.

What is a hematoma anatomically?

A bruise caused by clotted blood under the skin.

What are friction ridges, and what are their two main functions?

Markings on fingertips that leave oily fingerprints; they enhance sensitivity and improve grip.

When are friction ridges formed, and do identical twins share them?

Formed during fetal development (remain unchanged for life); not even identical twins have identical patterns.