Lecture 25-26: Integuement Flashcards Preview

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Flashcards in Lecture 25-26: Integuement Deck (26):
1

Describe the general organization of the integuement

* 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

Name the four epidermal ridges

* Primary Dermal Ridge
* Secondary Dermal Ridge
* Interpapillary peg
* Dermal Papillae

- See Slide 7

3

Describe the primary epidermal ridge

* 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

Describe the secondary dermal ridge

* Occur in double rows, branched
* Thin collagenous, reticular, and elastic fibers

5

Describe the interpapillary peg

* Downward growth of epidermis along crest

6

Describe the dermal papillae

* Upward Projections from the secondary dermal ridges

7

Describe the Integumentary Functions

* 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

Compare Thick Skin to Thin Skin

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

List the Layers of the Epidermis

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

Describe the stratum basale

* 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

Describe the stratum Spinosum

* 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

Describe the stratum granulosum

* 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

Describe the stratum lucidum

* Flat keratinocytes lacking nuclei and organelles
* Only found in thick skin
* Contains eleiden

14

Describe the stratum corneum

* 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

Describe the cornified cell envelope

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

Describe the characteristics of dermis

* Dense fibrous irregular connective tissue layer beneath epidermis
* Derived from embryonic mesoderm
* Induces development of epidermis and epidermal derivatives
* Supports epidermis

17

Describe the characteristics of hypodermis

* 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

Describe the two layers of the dermis

* 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

Describe Langerhan Cells

= dendritic cells
- From monocytes
- Antigen-presenting cells
- Primarily in stratum spinosum
- Migrate from epidermis to lymph nodes
- Birbeck granules
- See Slide 30

20

Describe Merkel Cells

* Mechanoreceptors
* May also act as diffuse neuroendocrine cells
* Usually in stratum germinativum
* Contain catecholamine-like granules
- See Slide 31

21

Describe Melanocytes

- 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

Explain the embryonic origins of the epidermis and dermis.

* 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

Describe Sebaceous Glands

* 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

Describe sweat (sudoriferous) glands

* 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