Integumentary system

What are the two types of skin?

Thin skin, found on most of the body, and thick skin, found only on the palms of the hands and soles of the feet.

Which layer is present only in thick skin?

The stratum lucidum.

What are the layers of the epidermis from superficial to deep?

Stratum corneum, stratum lucidum (in thick skin), stratum granulosum, stratum spinosum, and stratum basale.

What is the mnemonic for the epidermal layers?

"Come Let’s Get Sun Burned" — Corneum, Lucidum, Granulosum, Spinosum, Basale.

What type of epithelium makes up the epidermis?

Keratinized stratified squamous epithelium.

Where is the epidermal water barrier located?

Mainly in the stratum granulosum layer.

What forms the epidermal water barrier?

Lipids secreted by dying keratinocytes.

Why is the epidermal water barrier important?

It prevents dehydration by retaining body water and cutting off nutrients to upper cells, which then die and exfoliate.

What is dander?

Dead skin cells that flake off from the epidermis.

What is dandruff?

Clumps of dander stuck together by sebum (oil) from sebaceous glands.

What is the dermis composed of?

Mainly collagen with elastic and reticular fibers, fibroblasts, blood vessels, sweat and sebaceous glands, and nerve endings.

What structures are embedded in the dermis?

Hair follicles, nail roots, and smooth piloerector muscles.

What are piloerector muscles?

Smooth muscles that contract in response to cold, fear, or touch, causing goosebumps.

What are dermal papillae?

Extensions of the dermis into the epidermis that form friction ridges and fingerprints.

What is the papillary layer of the dermis?

The superficial zone made of areolar connective tissue rich in small blood vessels.

What is the reticular layer of the dermis?

The deeper and thicker layer composed of dense irregular connective tissue.

What causes stretch marks (striae)?

Tears in collagen fibers of the reticular layer due to overstretching from pregnancy or obesity.

What is the hypodermis?

A subcutaneous tissue layer beneath the dermis composed of areolar and adipose tissue that pads the body and binds skin to underlying structures.

Why are drugs often injected into the hypodermis?

Because it is highly vascular and absorbs substances quickly.

What are the functions of subcutaneous fat?

Energy storage, thermal insulation, and cushioning; typically thicker in women.

What pigment gives skin a pinkish hue?

Hemoglobin in red blood cells.

What pigment gives skin a yellow tone?

Carotene, obtained from foods like egg yolks and orange vegetables, accumulates in the stratum corneum and fat.

What determines skin color differences?

The amount and type of melanin produced by melanocytes, not the number of melanocytes.

Where are melanocytes located?

In the stratum basale of the epidermis.

What is cyanosis?

Bluish skin color caused by oxygen deficiency, often from airway blockage, heart failure, or lung disease.

What is erythema?

Abnormal redness of the skin due to dilated blood vessels, caused by heat, exercise, or emotions like embarrassment.

What is pallor?

Paleness caused by reduced blood flow, low blood pressure, cold, or anemia.

What is albinism?

A genetic lack of melanin due to nonfunctional tyrosinase enzyme, causing white skin and hair and pink eyes.

What is jaundice?

Yellowing of skin and eyes due to excess bilirubin from liver dysfunction.

What is a hematoma?

A bruise caused by clotted blood showing through the skin.

What is vitiligo?

Idiopathic loss or dysfunction of melanocytes, leading to irregular depigmented patches; may be autoimmune.

What environmental factor heavily influences skin color evolution?

Exposure to ultraviolet radiation (UVR).

What are the harmful effects of UV radiation?

Causes skin cancer and destroys folic acid, which is needed for cell division and fetal development.

What is a beneficial effect of UV radiation?

Stimulates vitamin D synthesis, aiding calcium absorption.

Why do people near the equator have darker skin?

To protect from excessive UV radiation.

Why do people from higher latitudes have lighter skin?

To allow more UV light to penetrate for vitamin D production.

What are friction ridges?

Raised skin markings on fingertips that form fingerprints and improve grip.

What are flexion lines?

Skin creases on palms, wrists, and joints caused by repetitive flexing.

What are freckles and moles?

Freckles are flat melanized patches; moles (nevi) are elevated patches that may have hair.

What are hemangiomas?

Benign skin discolorations caused by tumors of dermal blood capillaries, commonly called birthmarks.

What are the three types of human hair?

Lanugo (fine fetal hair), vellus (fine, pale body hair), and terminal (coarse, pigmented hair on scalp, face, and body).

Where is terminal hair found?

On the scalp, eyebrows, eyelashes, and after puberty in axillary and pubic regions (and face/trunk in males).

What are the three parts of a hair?

Bulb (base with living cells), root (within follicle), and shaft (above the skin surface).

What is the dermal papilla in hair?

A vascular connective tissue at the bulb that supplies nutrients to the hair.

What is the hair matrix?

The region of actively dividing cells above the papilla that produces new hair.

What are the three layers of a hair in cross-section?

Medulla (core), cortex (bulk), and cuticle (outer overlapping cells).

What is the follicle?

A diagonal tube extending into the dermis or hypodermis that encloses the hair root.

What are hair receptors?

Nerve fibers that wrap around hair follicles and detect hair movement.

What is the piloerector muscle?

A small smooth muscle attached to each hair follicle that causes hairs to stand up when contracted.

What determines hair color?

The ratio of eumelanin (brown-black pigment) to pheomelanin (yellow-red pigment) and air spaces in the cortex.

What are the stages of the hair cycle?

Anagen (growth, 6–8 years), catagen (degeneration, 2–3 weeks), and telogen (rest, 1–3 months).

How much scalp hair is lost daily on average?

About 50–100 hairs per day.

What is alopecia?

Thinning or loss of hair.

What is pattern baldness?

Genetic and hormonal hair loss localized to certain areas of the scalp, triggered by high testosterone levels.

What is hirsutism?

Excessive or abnormal hair growth in areas not typically hairy.

What is the nail matrix?

The thickened area at the base of the nail responsible for nail growth.

What is the eponychium?

The cuticle — the nail fold that overlaps the base of the nail.

What is the hyponychium?

The area beneath the free edge of the nail where dirt may accumulate.

Why do nails appear pink?

Due to underlying capillaries.

What is the lunule?

The white crescent at the base of the nail caused by the thickened nail matrix.

What are the two types of sweat glands?

Merocrine (eccrine) and apocrine glands.

What are merocrine (eccrine) glands?

Simple tubular glands that secrete watery sweat to cool the body; found all over the skin surface.

What are myoepithelial cells?

Cells in sweat glands that contract to squeeze perspiration out of ducts.

Where are apocrine sweat glands found?

In the axilla, groin, anal region, areola, and bearded areas of adult males.

What do apocrine glands secrete?

Thicker, milky sweat containing fatty acids that respond to stress and sexual stimulation.

What are pheromones?

Chemicals secreted in apocrine sweat that influence the behavior or physiology of others.

What is bromhidrosis?

Body odor caused by bacterial breakdown of apocrine sweat.

What is the composition of sweat?

Mostly water (99%) with small amounts of ions, urea, lactic acid, and ammonia; slightly acidic (pH 4–6).

What is the acid mantle?

A thin acidic film on the skin surface that inhibits bacterial growth.

What is insensible perspiration?

500 ml/day of unnoticeable water loss through the skin.

What is diaphoresis?

Visible sweating during exercise or heat, up to one liter per hour.

What are sebaceous glands?

Holocrine glands that secrete sebum (oil) into hair follicles to lubricate and waterproof the skin and hair.

What is sebum?

An oily mixture of lipids and cell debris that keeps hair and skin soft and prevents cracking.

What are ceruminous glands?

Glands in the ear canal that produce cerumen (earwax) by combining sebum and dead cells.

What are the functions of earwax (cerumen)?

Waterproofs and protects the ear canal, kills bacteria, and traps foreign particles.

What are mammary glands?

Modified apocrine glands that produce milk during pregnancy and lactation.

What are polymastia and polythelia?

Polymastia is the presence of extra breasts; polythelia is the presence of extra nipples along the milk line.

What is dermatitis?

Inflammation of the skin — a symptom, not a disease.

What is ringworm?

A fungal infection of the skin caused by the Tinea species.

What are UVA and UVB rays?

UVA are “tanning rays” and UVB are “burning rays”; both can cause skin damage and cancer.

Why has skin cancer increased despite sunscreen use?

Certain sunscreen chemicals can damage DNA and generate free radicals.

What is the ABCDE rule for skin cancer detection?

A = Asymmetry, B = Border irregularity, C = Color variation, D = Diameter >6 mm, E = Elevation/Evolution.

What is basal cell carcinoma?

The most common and least dangerous skin cancer; arises from stratum basale and rarely metastasizes.

What is squamous cell carcinoma?

Skin cancer arising from keratinocytes of the stratum spinosum; may metastasize to lymph nodes.

What is malignant melanoma?

The most dangerous skin cancer arising from melanocytes, often in preexisting moles; highly metastatic and resistant to chemotherapy.

What is the leading cause of death from burns?

Fluid loss, infection, and toxic effects of dead tissue (eschar).

What are first-degree burns?

Burns affecting only the epidermis; cause redness and pain; heal in a few days.

What are second-degree burns?

Burns involving the epidermis and part of the dermis; blistering, very painful, and may scar.

What are third-degree burns?

Full-thickness burns destroying epidermis, dermis, and sometimes deeper tissues; require grafts and fluid replacement.

What is debridement?

Removal of burned, dead tissue (eschar) to prevent infection.

What is the Rule of Nines?

A method to estimate the extent of burns by dividing the body into areas that are approximately 9% each of total surface area.

When are burns considered critical?

If over 25% of the body has second-degree burns, over 10% has third-degree burns, or if third-degree burns affect the face, hands, or feet.