Chapter # 5: Integumentary System

What structures are included in the integumentary system?

Skin, sweat glands, oil glands, hair, nails.

How thick is skin?

1.5 – 4.0 mm.

What are the 2 main layers of skin?

1. Epidermis (epithelial tissue)

2. Dermis (dense connective tissue).

What is the hypodermis and its functions?

Subcutaneous layer beneath dermis; made of adipose tissue; anchors skin, shock absorber, insulator.

What type of tissue makes up the epidermis?

Keratinized stratified squamous epithelium.

What are the 4 main cell types in the epidermis?

1. Keratinocytes

2. Melanocytes

3. Dendritic (Langerhans) cells

4. Tactile (Merkel) cells.

Function of keratinocytes?

Most abundant cell; produce keratin for protection; connected by desmosomes; renew every 25–45 days.

What happens to keratinocytes in areas of constant friction?

Epidermis thickens, forming a callus.

Function of melanocytes?

Produce melanin for UV protection; located in deepest epidermal layer; melanin transferred to keratinocytes.

Function of dendritic (Langerhans) cells?

Immune defense; ingest foreign substances; come from bone marrow.

Function of tactile (Merkel) cells?

Sensory receptors for touch; found at epidermis/dermis junction; form Merkel’s discs with nerve endings.

Where is thick skin found?

Palms, fingertips, and soles of feet.

What are the 5 layers of thick skin (superficial to deep)? *Come Lets Get Sun Burned!

1. Startum Corneum

2. Stratum Lucidum

3. Startum Granulosum

4. Startum Spinosum

5. Stratum Basale.

How does thin skin differ from thick skin?

Same layers but no stratum lucidum and all layers are thinner.

Does thick vs thin skin refer to the whole skin?

No, only the epidermis.

What is the stratum basale also called and why?

Stratum germinativum; continuous cell division of stem cells.

What cells are found in the stratum basale?

Stem cells and 10–25% melanocytes.

What characterizes the stratum spinosum?

Several layers of “prickle cells” connected by desmosomes; contains melanin granules & dendritic cells.

What happens in the stratum granulosum?

1–5 layers; keratinization begins; cells flatten, organelles disintegrate; keratohyaline & lamellar granules form.

What is the function of keratohyaline granules?

Help form keratin in upper epidermal layers.

What is the function of lamellar granules?

Release water-resistant glycolipid into extracellular space → reduces water loss.

Why do cells above the stratum granulosum die?

They are too far from dermal capillaries for nutrients, and glycolipids block nutrient diffusion.

Where is the stratum lucidum found?

Only in thick skin (palms of hand, soles of feet, and fingertips).

What does the stratum lucidum look like and consist of?

A translucent band above granulosum; 2–3 layers of clear, flat dead keratinocytes with indistinct boundaries.

What is the structure of the stratum corneum?

Outermost layer; 20–30 layers of flat, dead, anucleate keratinocytes filled with keratin; ~¾ of epidermis.

What functions does the stratum corneum provide?

Protection against abrasion & penetration; waterproof barrier from glycolipids; overall surface protection.

How much skin does the average person shed?

bout 50,000 dead cells per minute and ~40 lbs in a lifetime.

What lies beneath the epidermis?

Dermis.

What type of tissue makes up the dermis?

Strong, flexible connective tissue.

What cells are found in the dermis?

Fibroblasts, macrophages, mast cells, white blood cells.

What important structures are in the dermis?

Blood supply, nerve fibers, lymphatic vessels, hair follicles, oil glands, sweat glands.

What are the two layers of the dermis?

Papillary dermis and reticular dermis.

What tissue type is in the papillary dermis?

Areolar connective tissue with thin collagen and elastic fibers.

What structures are found in dermal papillae?

Capillary loops, free nerve endings, and Meissner’s (tactile) corpuscles.

What do dermal ridges in thick skin form?

Epidermal ridges (friction ridges) → fingerprints

What is the function of friction ridges?

Enhance grip and sense of touch.

What percentage of the dermis is the reticular dermis?

About 80%.

What type of tissue makes up the reticular dermis?

Dense irregular connective tissue.

What are cleavage (tension) lines in the skin?

Less dense regions of collagen bundles; important for surgical healing.

What functions do collagen fibers provide in the dermis?

Strength, resiliency, and water binding for hydration.

What functions do elastic fibers provide in the dermis?

Stretch and recoil properties.

What are flexure lines?

Dermal folds at or near joints where dermis is tightly anchored to deeper structures.

What are the 3 main pigments that determine skin color?

1. Melanin

2. Carotene

3. Hemoglobin

What enzyme do melanocytes use to produce melanin?

Tyrosinase.

What determines skin color differences between individuals?

Activity of tyrosinase and number of melanosomes produced (not number of melanocytes).

What is the main function of melanin?

Protection from UV radiation.

Where does carotene accumulate in the body?

Stratum corneum and fatty areas of hypodermis.

What is carotene converted into and what is it used for?

Vitamin A; important for vision and epidermal health.

What gives skin its pinkish hue?

Oxygenated hemoglobin in red blood cells in dermal capillaries.

Is hair dense enough for warmth?

No, it’s mainly for detection of things on the skin.

What are the protective role of scalp hair?

Protects against trauma, heat loss, and sunlight

What is the protective role of eyelash hair?

Protect eyes

What are the protective role of nose hair?

Filter dust

What produces hair?

Hair follicles

What is hair mostly made of?

Dead, keratinized cells with hard keratin (tougher, more durable, doesn’t flake).

What are the 2 main regions of hair?

1. Shaft (keratinization complete)

2. Root (keratinization ongoing).

How far does the shaft extend?

From outside scalp to about halfway into the skin.

What determines hair texture?

Shape of the shaft:

• Flat/ribbonlike → kinky

• Oval → silky & wavy

• Round → straight & coarse

What are the three concentric layers of hair?

Medulla (inner), Cortex (middle), Cuticle (outer).

What is the medulla?

Large cells with soft keratin & air spaces; absent in fine hairs.

What is the cortex?

Several layers of flattened cells.

What is the cuticle?

A single layer of overlapping, most keratinized cells; provides strength & compacts layers.

Where is hair pigment produced?

By melanocytes at the base of the hair follicle.

How is hair color determined?

Various proportions of melanins transferred to cortical cells.

Where does the hair follicle originate?

Epidermis folding into dermis and even hypodermis.

What is the hair bulb?

Base of follicle, expanded, contains CT papilla with capillaries & nerve endings.

What is the follicle receptor (hair root plexus)?

Nerve endings around the bulb, sensitive to hair movement.

What are the components of the follicle wall?

• Peripheral CT (fibrous sheath, dermis-derived)

• Glassy membrane (thickened basal lamina)

• Inner epithelial root sheath (from epidermis, internal & external parts)

What is the hair matrix?

Actively dividing cells around papilla that form new hair.

What happens to matrix cells as they move away from the bulb?

They keratinize & die.

What muscle is attached to hair follicles?

Arrector pili (smooth muscle); contracts for goosebumps in cold or fear.

What are the two main types of hair?

Vellus (fine; children & adult females) and Terminal (coarse; eyebrows, scalp, axillary & pubic regions).

What influences terminal hair growth at puberty?

Androgens (esp. in males).

What factors influence hair growth & density?

Nutrition and hormones.

What are the three phases of the hair growth cycle?

1. Active phase (weeks–years, cells divide)

2. Regressive phase (matrix cells die, bulb shrinks)

3. Resting phase (1–3 months, then new hair grows)

How long do scalp hairs last vs eyebrow hairs?

Scalp: 6–10 years;

Eyebrows: 1–3 months.

Why does hair thin with age?

Follicles have a limited number of cycles.

What causes male pattern baldness?

Genetic, sex-influenced condition where follicles become hypersensitive to DHT (testosterone metabolite); growth cycles shorten, preventing hair development.

What is the lunule?

Pale area over the thick nail matrix.

What is the eponychium (cuticle)?

Proximal nail fold projecting over nail body.

What is the hyponychium?

Thickened region beneath the free edge; secures nail to finger/toe.

What can yellow or spoon-shaped nails indicate?

Yellow → respiratory/thyroid issue;

thick yellow → fungal infection;

spoon-shaped → iron deficiency.

What are the two types of sweat glands?

1. Eccrine (merocrine)

2. Apocrine.

What are myoepithelial cells?

Cells that contract to push sweat into the gland duct and onto the skin surface.

Where are eccrine glands most numerous?

Palms, soles of feet, forehead.

What is eccrine sweat composed of?

99% water, salts (NaCl), vitamin C, antibodies, dermcidin, metabolic wastes (urea, uric acid, ammonia).

What regulates eccrine sweat glands?

Sympathetic nervous system; used for thermoregulation.

What is cold sweat and where does it occur?

Sweat from fear/nervousness; occurs in palms, soles, axillae.

Where are apocrine glands located?

Axillary and anogenital regions.

How do apocrine secretions differ from eccrine?

Includes fatty substances & proteins; viscous; odorless until bacteria act → musky odor.

When are apocrine glands activated?

Puberty (androgens), sympathetic NS during pain/stress; not for temperature regulation.

What are ceruminous glands?

Modified apocrine glands in external ear canal; secrete cerumen (earwax) with sebum to block foreign material.

Where are sebaceous glands found?

Most body surface except thick skin areas; mostly attached to hair follicles.

What type of secretion do sebaceous glands use?

Holocrine secretion (cells burst and are replaced).

What is sebum and its function?

Oily substance; lubricates hair, slows water loss from skin, has bactericidal properties.