Lecture 25-26: Integuement Flashcards
1
Q
Describe the general organization of the integuement
A
- Epidermis
- Basement membrane
- Dermis:
- Corresponds to lamina propria of a mucous membrane
- 0.5 to 3 mm thick
- Subcutaneous tissue (synonyms):
- SubQ
- Superficial fascia
- Hypodermis
2
Q
Name the four epidermal ridges
A
- Primary Dermal Ridge
- Secondary Dermal Ridge
- Interpapillary peg
- Dermal Papillae
- See Slide 7
3
Q
Describe the primary epidermal ridge
A
- Related to finger prints
- Found everywhere except forehead, external ear, perineum, and scrotum
- Formed during 3rd to 4th months of fetal life
- Subdivided into two secondary dermal ridges by interpapillary peg
4
Q
Describe the secondary dermal ridge
A
- Occur in double rows, branched
* Thin collagenous, reticular, and elastic fibers
5
Q
Describe the interpapillary peg
A
- Downward growth of epidermis along crest
6
Q
Describe the dermal papillae
A
- Upward Projections from the secondary dermal ridges
7
Q
Describe the Integumentary Functions
A
- Protection from mechanical injury
- Prevents desiccation
- Protects against foreign substances and microorganisms
- Protects against UV radiation
- Thermoregulation
- Regulation of blood pressure (via dermal capillary network)
- Excretion of metabolic waste products
- Synthesis of provitamin D
8
Q
Compare Thick Skin to Thin Skin
A
Thick and thin refer to the epidermis only.
- Thick skin:
- Occurs only on palms and soles and is hairless
- Epidermis varies from 0.4 to 0.6 mm thick.
- Displays all five epidermal layers
- Thin skin:
- Occurs over rest of body
- Epidermis varies from 75 to 150 μmm thick.
- Thinnest thin skin is on eyelids
- Thickest thin skin is on back
- Thicker on extensor surfaces than flexor surfaces
- Epidermal layers less distinct and lacking stratum lucidum
9
Q
List the Layers of the Epidermis
A
Stratified squamous epithelium:
- Derived from embryonic ectoderm
- Layers:
1. Stratum basale (germinativum) * - Deepest
2. Stratum spinosum*
3. Stratum granulosum: Refer to Figure 11-5. - Represented by only a few cells in thin skin
4. Stratum lucidum: - Absent in thin skin
5. Stratum corneum - Most superficial
- = stratum Malpighi
- See Slide 12-13
10
Q
Describe the stratum basale
A
- Deepest
- Columnar to high cuboidal keratinocytes
- Keratins 5 and 14 (low-molecular weight keratins)
- Single layer of cells
- Held together by desmosomes
- Hemidesmosomes hold layer to basal lamina
- High mitotic activity:
- Mitotic activity produces stem cells differentiating keratinocytes.
- Affected by chemotherapeutic and radiation treatments
- Keratinocytes are the major type of cell in the epidermis and are the cells that arise from the stratum basale and undergo keratinization.
11
Q
Describe the stratum Spinosum
A
- Polyhedral-shaped cells (prickle cells)
- Keratins 1 and 10 (high molecular weight keratins)
- Keratohyalin granules develop
- Membrane-coating granules first appear:
- Lamellar bodies: Contain lipid, carbohydrate, and hydrolytic enzymes
- Tonofibrils:
- Form intercellular bridges
- See Slide 17
12
Q
Describe the stratum granulosum
A
- Multilayered
- Keratins 2e and 9
- Flattened nucleated keratinocytes
- Keratohyalin aggregates:
- Fillagrin induces cross-linkage of keratin filaments by disulfide bonds
- No limiting membrane
- Membrane-coating granules (lamellar bodies)
- Acylglucosylceramide → intercellular spaces
- Tonofilaments
13
Q
Describe the stratum lucidum
A
- Flat keratinocytes lacking nuclei and organelles
- Only found in thick skin
- Contains eleiden
14
Q
Describe the stratum corneum
A
- Multilayered (5-50 layers)
- Thicker in thick skin
- Enucleated, flattened, dead keratinocytes
- Cytoplasm replaced by keratin
- Cytoplasm contains:
- Keratin cross-linked with filaggrin
- → cornified cell envelope
15
Q
Describe the cornified cell envelope
A
Extracellular: - Multi-lamellar lipid layer covalently linked to involucrine Intracellular: - Involucrine - Small proline-rich proteins - Loricrin - Fillagrin and keratin complexes
- See Slides 25-26
16
Q
Describe the characteristics of dermis
A
- Dense fibrous irregular connective tissue layer beneath epidermis
- Derived from embryonic mesoderm
- Induces development of epidermis and epidermal derivatives
- Supports epidermis
17
Q
Describe the characteristics of hypodermis
A
- Loose connective tissue that underlies dermis
- Corresponds to superficial fascia of gross anatomy
- Technically not part of skin
- May contain fat cells that can form a thick layer called the panniculus adiposus
18
Q
Describe the two layers of the dermis
A
- Papillary layer (closest to epidermis):
- Loose CT
- Separated from epidermis by basal lamina
- Network of fine elastic fibers and abundant capillaries
- Reticular layer
- Dense irregular CT
- Includes fibrocytes, macrophages, and adipocytes
19
Q
Describe Langerhan Cells
A
= dendritic cells
- From monocytes
- Antigen-presenting cells
- Primarily in stratum spinosum
- Migrate from epidermis to lymph nodes
- Birbeck granules
- See Slide 30
20
Q
Describe Merkel Cells
A
- Mechanoreceptors
- May also act as diffuse neuroendocrine cells
- Usually in stratum germinativum
- Contain catecholamine-like granules
- See Slide 31
21
Q
Describe Melanocytes
A
- Derived from melanoblasts
- Do not form desmosome attachments in epidermis
- Inject melanin granules into keratinocytes
- Pathway for melanin formation:
Tyrosine → 3,4-dihydroxyphenylalanine (DOPA) → dopaquinone→ melanin - Requires tyrosinase
- See Slide 32
22
Q
Explain the embryonic origins of the epidermis and dermis.
A
- Epidermis starts as a single layer of ectodermal cells.
- Divide during sixth week to form:
- Periderm: Sloughs off to form vernix caseosa
- Inner cuboidal germinal layer: continues to proliferate to form adult layers of the epidermis and derivatives:
- – 10 weeks: fingernails
- – 12 weeks: hair buds and toenails
- Dermis is derived from mesoderm
23
Q
Describe Sebaceous Glands
A
- Holocrine glands
- Branched acinar glands with short ducts
- Found everywhere except palms and soles
- Continuously produce sebum
- Released into hair follicle
- Growth is stimulated at puberty by sex hormones
- See Slide 6
24
Q
Describe sweat (sudoriferous) glands
A
- Both merocrine and apocrine glands
- Merocrine glands:
- Coiled, simple tubular secretory portions:
- Lined by simple epithelium
- Apical dark secretory cells secrete glycoproteins
- Basal clear cells secrete water and electrolytes
- Myoepithelial cells
- Duct system consists of stratified cuboidal epithelium except in epidermis.
- Cholinergic endings
- Apocrine glands:
- Found in labia majora, areola, and axillary and anal regions.
- Secretions are thicker and more viscous than merocrine types.
- Excretory duct opens into hair follicle.
- Adrenergic innervation
- Inactive until puberty
- Special types:
- Ceruminous glands
- Glands of Moll
- See slide 8-9
25
Describe hair follicles
* Develop from epidermis as elastic, keratinized threads:
- Components of follicle:
- - Root sheaths (external and internal)
- - Hair shaft
- - Hair bulb
- Sebaceous glands and arrector pili muscles are associated with hair follicles.
- Hair bulb:
- - Expanded lower part of hair follicle
- - Matrix
- - Vascularized dermal papilla
* External root sheath:
- Down growth of epidermis
* Internal root sheath:
- Generated by bulb matrix
- Layers:
- - Henle’s layer (outermost)
- - Huxley’s layer
- - Cuticle: Interlocks with cuticle of hair shaft
* Hair Shaft
- Layers:
- - Medulla (innermost)
- - Cortex
- - Cuticle
26
Describe Keratinocyte Stem Cells
* These cells can reestablish epidermis in severely burned patients.
* Migration pathways:
- Bulb-epidermis stem cell pathway
- Bulb-sebaceous gland stem cell pathway
- Bulb-hair stem cell pathway
* Signaling pathways:
- Wnt signaling pathway
- Notch signaling pathway
- See Slide 16
