Integument

Question 1

What are the functions of the integument?

What are the epidermal derivatives contained within the integument?

Answer 1

• barrier for protection, sensation, excretion, thermoregulation, and vitamin D3 synthesis
• contains hair, nails, sebaceous and sweat glands

Question 2

What are the layers of integument?

Answer 2

• epidermis: epithelial layer (ectoderm derived)
• dermis: layer of CT (paraxial mesoderm > dermatome derived)
• hypodermis (subcutaneous): loose CT layer, binds the skin to underlying tissue and corresponds to the superficial fascia

Question 3

What epithelium type is the epidermis?

What are the main types of cells within the epidermis?

Answer 3

• epidermis consists mainly of stratified squamous keratinized epithelium
• composed mostly of keratinocytes; less abundant are melanocytes, Langerhands cells, and Merkel cells

Question 4

• irregular projections at epidermal-dermal junction
• interdigitate w/ epidermal ridges to strengthen adhesion = increased anchoring of epidermis to dermis

Answer 4

dermal papillae

Question 5

What are the two types of skin?

Answer 5

• thick (400-1400 μM): palms and soles, fiver layers (w/ stratum lucidum), fingerprints
• thin (75-150 μM): widespread on body, four layers, glands and hair follicles

Question 6

What are the 4-5 layers of skin?

Answer 6

• stratum corneum (SC)
• stratum lucidum (not shown in image)
• stratum granulosum (SGr)
• stratum spinosum (SS)
• stratum basale (SB)

*know these in order, know distinguishing features, be able to identify them individually*

Question 7

• 15-20 layers of squamous, keratinized cells of the epidermis, filled w/ filamentous keratins
• cells are anucleate (more space for keratin) and coated by an extracellular layer of lipids (from granules of SGr)
• fully keratinized “cornified” cells, squames, are continuously shed as desmosomes break down

Answer 7

stratum corneum

Question 8

• layer of the epidermis found only in thick skin
• thin, translucent layer of flattened eosinophilic keratinocytes
• held together by desmosomes
• nuclei and organelles have been lost
• cytoplasm is almost exclusively keratin filaments

Answer 8

stratum lucidum

Question 9

• three to five layers of flattened cells of the epidermis
• filled w/ keratohyaline granules (granules = tonofibrils + filaggrin (bundling protein)): undergoing terminal differentiation of keratinization, stain intensely basophilic
• also include lamellar granules (small, ovoid structures containing lipids and glycolipids): undergo exocytosis and produce lipid-rich, impermeable layer that protects against water loss
• keratinization + lipid-rich layer = almost impenetrable skin barrier

Answer 9

stratum granulosum

Question 10

• typically the thickest layer of epidermis
• polyhedral cells w/ central nuclei and spiny processes
• keratin filaments assemble here into microscopically visible bundles called tonofibrils (a/w desmosomes > result in spiny appearance ‘prickle layer’)

Answer 10

stratum spinosum (remember ‘spiny’)

Question 11

• layer of the epidermis
• single-layer of keratinocytes w/ stem cells interspersed
• mitotically active, cuboidal/low columnar cells
• contains melanin and melanocytes
• bound apically by desmosomes
• bound basally by hemidesmosomes

Answer 11

stratum basale

Question 12

What does the mnemonic C’mon Let’s Get Sun Burn stand for?

Answer 12

(layers of the epidermis from apical to basal)

• Corneum
• Lucidum
• Granulosum
• Spinosum
• Basale

Question 13

• predominant cell type of the epidermis
• produce keratins, 85% of cells within the epidermis
• participate in the epidermal water barrier
• will produce “cornified” cells (full of keratin)
• stratum corneum is when keratinocytes are most mature
• outermost layer of skin, we lose these with abrasion
• undergo keratinization and desquamation (loss of cells)

Answer 13

keratinocytes

Question 14

• type of cell within the epidermis
• produce melanin and transfer it to keratinocytes
• melanin: pigment protein that protects nuclei from UV radiation
• neural crest-derived, scattered along stratum basale
• epidermal-melanin unit: one melanocyte maintains an association w/ a specific number of keratinocytes (1:10)

Answer 14

melanocytes

Question 15

Describe the process of melanin production:

Answer 15

• tyrosinase coverts tyrosine > DOPA (3,4-dihydroxyphenylalanine)
• DOPA is polymerized to melanin
• reactions occur in membrane-bound organelles, premelanosomes
• as melanin increases in premelanosomes, a melanosome is produced
• melanosomes are transferred to keratinocytes (pigment donation)
• creates a melanin umbrella that shields the nucleus

Question 16

Why is melanoma such a dangerous skin cancer?

Answer 16

• melanoma is derived from melanocytes, which are derived from neural crest cells
• the transition of melanocytes to cancer and uncontrolled growth, converts the cells to be able to access embryonic genes that are migratory (aka it can migrate anywhere in the body)

Question 17

• antigen presenting cells (APCs) that provide defense against pathogens (develop from monocyte precursor)
• identifiable in stratum spinosum
• pale cytoplasm w/ long processes
• antigen is phagocytized and displayed on the cell surface
• cell migrates to a nearby lymph node to activate lymphocytes

Answer 17

Langerhans cells

Question 18

How are epidermal cells differentiated and replaced?

Answer 18

• replacement is initiated by the division of stem cells in the stratum basale
• new cells undergo divisions in the stratum basale
• move upward as they differentiate into keratinized cells
• eventually are lost by exfoliation on skin surface

Question 19

• uneven boundary with finger-like dermal papillae that project into epidermis
• complemented by epidermal protrusions, epidermal ridges
• increased in size/number at sites of mechanical stress
• hemidesmosomes provide tight interface
• focal adhesions are also present

Answer 19

dermal-epidermal junction

Question 20

What are the 2 layers of the dermis?

Answer 20

• papillary layer: loose CT immediately beneath epidermis, vasculature and nerve endings present
• reticular layer: deep to papillary layer, dense irregular CT w/ coarse elastic fibers, form regular lines of tension (Langer’s lines) that are important for surgical purposes

Question 21

What are the 2 plexuses of the dermis?

Answer 21

• subpapillary plexus: rich, nutritive capillary network located between papillary and reticular layers
• deep plexus: lies near dermis-subcutaneous layer interface

Question 22

• loose CT that binds the skin loosely to the subjacent organs
• adipocytes vary in number and size based on body regions/nutritional state
• extensive vasculature promotes rapid uptake of insulin or drugs injected into this tissue

Answer 22

hypodermis (subcutaneous fascia)

Question 23

• epithelial tactile cells that function as low threshold mechanoreceptors essential for sensing gentle touch
• abundant in highly sensitive skin (fingertips, hair follicles)
• resemble surrounding keratinocytes but lack melanosomes
• contain small, golgi-derived granules concentrated near basolateral surface

Answer 23

Merkel cells

Question 24

• rare, aggressive and difficult to treat form of skin cancer
• 40x less common than malignant melanoma, but 2x mortality rate

Answer 24

Merkel cell carcinoma

Question 25

- located in the papillary dermis and extending into lower epidermal layers - respond primarily to high and low temperatures, pain, and itching - may also function as tactile receptors

Answer 25

free nerve endings

Question 26

- encapsulated receptors responsive to light touch or low frequency stimuli - perpendicular to the epidermis (located in the tip) in the dermal papillae - numerous in fingertips, palms, and soles

Answer 26

Meissner's capsule

Question 27

- large, encapsulated, oval structures found deep in the reticular dermis and hypodermis - specialized for sensing coarse touch, pressure (sustained touch), and vibration - also found in CT of visceral organs (wall of rectum and urinary bladder) to produce pressure sensations when distorted

Answer 27

lamellated (pacinian) corpuscle

Question 28

- type of gland - secretion delivered via membrane bound vesicles and undergo exocytosis

Answer 28

merocrine gland

Question 29

- type of gland - secretion accumulates within cell, apoptosis secretion and cell debris released

Answer 29

holocrine gland

Question 30

- type of gland - release of apical portion of the cell, surrounded by cytoplasm within a plasma membrane

Answer 30

apocrine gland

Question 31

- several glands per follicle - abundant on face and scalp - produce a lipid mixture, **sebum** via **holocrine secretion** - waxy mix of trigs and cholesterol (lubricates and softens skin, waterproofs skin) - sebum discharged into hair follicle

Answer 31

sebaceous glands

Question 32

- simple, coiled glands found extensively throughout skin - duct is stratified cuboidal - **myoepithelial cells** facilitate expulsion of secretions via **merocrine glands** - temperature regulation via cooling (evaporation of H2O from sweat on body surface) - sweat components: H20, salt, ammonia, uric acid, and mucinogen granules

Answer 32

eccrine sweat glands

Question 33

- large lumen, tubular glands - duct is stratified cuboidal - **myoepithelial cells** facilitate expulsion of secretions via **merocrine secretion** - protein, carbohydrates, and ammonia rich secretion - odorless until mixed w/ bacteria - become functional at puberty and is what makes pubescent kids smelly

Answer 33

apocrine sweat glands

Question 34

What is the structure of hair follicles?

Answer 34

- hair follicle has a terminal dilation called a **hair bulb** - dermal papilla inserts into hair bulb, provides nutrients via capillaries - keratinocytes form the **hair matrix**: continuous w/ epidermis, divide and differentiate which creates hair growth - **follicular bridge**: contains epidermal stem cells, near insertion of arrector pilli M. - arrector pilli M.: small bundle of smooth muscle that extends from midpoint of hair root to papillary layer (dermis); goose bumps = contracting muscle distorts attached dermis

Question 35

What is the structure of nails?

Answer 35

- highly keratinized cells on a bed of epidermis (nail bed) - **nail root**: most proximal region, covers the nail matrix - **nail matrix**: stem cells divide and form keratinocytes (nail plate remains attached to nail bed, pushed forward by continuous growth) - **lunula**: crescent-shaped white area near nail matrix - **cuticle** (eponychium): extension of skin covering nail root

Question 36

What is the concern of black or dark purple striping/coloring of the nail w/o associated injury/damage?

Answer 36

melanoma of nail