Skin (integumentary system) Flashcards

To learn about the skin...

1
Q

What are the functions of the integumentary system?

A
  1. Maintain internal environment
  2. Protection from invaders and gross physical units
  3. Receive stimuli from environment
    4 Thermoregulation via sweat glands, fat deposits, blood vessels
  4. Excretory and photochemical functions
  5. Good source of diagnostic info
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2
Q

What is the embryonic origin of the epidermis?

A

Surface ectoderm.

- Initially a single layer, the epidermis reaches full thickness at birth

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3
Q

What is the embryonic origin of the dermis?

A

mesoderm

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4
Q

What is the embryonic origin of accessory structures (hair, sweat glands, mammary glands, etc)?

A

They are derivatives of epidermal cells and the epidermis originates in the surface ectoderm

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5
Q

What are the layers of the skin?

A

From the top:

  • Epidermis
  • Dermis
  • Hypodermis
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6
Q

Describe the structure of the epidermis?

A
  • Composed of keratinized, stratified squamous epithelium
  • forms outer layer of skin
  • predominantly keratinocytes and melanocytes (pigment cells)
  • Langerhans and Merkel cells also found there
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7
Q

What are Melanocytes?

A
  • Melanocytes are cells that create skin and hair pigmentation.
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8
Q

What are Langerhans Cells?

A

epidermal dendritic cells involved in signaling the the immune system

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9
Q

What are Merkel cells?

A

Cells associated with sensory nerve endings

  • They contain dense core neurosecretory granules
  • believed to be sensitive to tactile stimuli
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10
Q

From the dermis outward, what are the 5 layers of epidermis?

A
  1. Stratum basale (germinativum)
  2. Stratum spinosum
  3. Stratum granulosum
  4. Stratum lucidum (thick skin only)
  5. Stratum corneum
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11
Q

Describe the cells of the stratum basale (germinativum)

A
  • Basopihlic keratinocytes that are cuboidal to columnar
  • Cells have hemidesmosomal junctions with underlying basement membrane
  • Desmosomes bind cells to lateral and upper surfaces
  • mitotic figures are common as these cells are continuously renewing epidermal cells
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12
Q

Describe the cells of the stratum spinosum

A
  • polygonal or slightly flattened cells
  • prominent desmosomal attachments to adjacent cells
  • appear “spiny” in light microscope
  • cells contain abundant keratin filaments
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13
Q

Describe the cells of the stratum granulosum

A
  • Cells contain keratohyalin granules (not membrane bound)
  • these are basophilic granules, not to be confused with melanin granules (mostly found in basal layers of epidermis)
  • Cells have lamellar bodies
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14
Q

What are lamellar bodies?

A

Contribute to the formation of the intercellular epidermal water barrier
- ovid-shaped membrane bound organelles that hold a mixture of pro-barrier lipids and proteases used to form the epidermal water barier

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15
Q

Describe the cells of the stratum lucidum

A
  • thin layer of weakly eosinophilic, flattened cells specific to thick skin only
  • very few organelles or nuclei
  • abundant filaments in an electron dense amorphous matrix with no keratohyalin granules
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16
Q

Describe the cells of the stratum corneum

A
  • flattened, keratinized cells
  • plasma membranes are thickened by deposition of secretions from membrane-coating granules
  • strong barrier to movement of material across skin
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17
Q

Where is thin and thick skin present?

A

Thick skin: palms and soles of feet

Thin skin: everywhere else

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18
Q

What are the layers of the dermis?

A

Papillary layer

Reticular layer

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19
Q

Where are melanocytes found in the epidermis?

A

Beneath or between epithelial cells of the stratum basale and in hair follicles attached to basement membrane

20
Q

What is the origin of melanocytes?

A

They come from the neural crest and are responsible for synthesizing melanin granules

21
Q

What is albinism?

A

no melanin produced, usually due to absence of the enzyme tyrosinase

22
Q

How is melanin produced?

A

by oxidation of dihydroxy-phenylalanine (DOPA). DOPA is made from tyrosine by the enzyme tyrosinase

23
Q

How are melanin granules produced?

A

By the deposition of melanin onto a fibrous lattice, called the melanosome

24
Q

Why does pigment vary in individuals?

A

Pigment is determined by melanosome size, distribution, and density of pigment.

25
What is the process of melanin distribution throughout epidermal cells?
Melanin granules, made in melanocytes, are "injected" into keratinocytes. - melanocytes don't accumulate melanosomes, they continually transfer them. This process is known as cytocrine secretion.
26
What are free nerve endings?
Terminals of thinly myelinated or unmyelinated nerve fibers that penetrate the epidermis - responsible for sensing pain and temp changes
27
Describe the papillary layer
More cellular connective tissue than the reticular layer - contains fibroblasts, macrophages, mast cells, fine collagen fibers - Outstanding features: vascular papillae and Meissner's corpuscles
28
What are vascular papillae
In dermis, complementary to epidermal projections (rete ridges)
29
What are Meissner's corpuscles?
In dermis, encapsulated sensory receptors for light touch
30
Describe the reticular layer
In dermis, thick layer containing irregular dense connective tissue which has more fibers (and thicker ones) and fewer cells than papillary layer
31
Describe the subcutaneous tissue
Known as the hypodermis: - binds skin to subjacent organs - often contains adipose tissue, blood vessels, lymph vessels, and pacinian corpuscles
32
What are pacinian corpuscles?
endcapsulated, ovoid sensory receptors - sensitive to deep pressure - together with Meissner's corpuscles, they are responsible for vibratory sensation
33
What are the functions of blood supply in the skin?
- nourish epidermal structures | - termp regulation
34
Where are blood vessels found in the skin?
In dermis and hypodermis (few vessels found in reticular layer of dermis)
35
What are the structures of hair follicles?
Layers from inside out: 1. Matrix cells (including melanocytes) 2. Inner root sheath 3. Outer root sheath (source of new epidermal cells in wound healing) 4. Connective tissue sheath
36
What are the structures of a hair shaft after emerging from follicle?
1. Medulla - forms central axis 2. Cortex - multilayered structure containing pigment granules 3. Cuticle - thin protective covering
37
What are arrector pili?
bundle of smooth muscle fibers obliquely attached to hair follicle
38
What are sebaeous glands?
alveolar glands with excretory duct opening into hair shaft - secretes sebum (made of lipid rich cell debris) - these glands have no myoepithelial cells
39
What are nails composed of?
Keratinized plates which form a protective covering over the distal ends of digits
40
What is the nail bed?
the nail plate rests on the nail bed which consists of epithelial cells continuous with the epidermis
41
What is the nail matrix?
These cells produce the nail plate
42
What are myeoepithelial cells?
Cells that surround secretory cells and their contractions aid in movement of secretions toward the duct
43
What are dark cells?
Cells that border the lumen of secretory tubules and produce a mucoid substance Have abundant rER
44
What are clear cells?
Cells that rest on the basal lamina of secretory tubules and are involved in secretion of water and electrolytes Have abundant smooth ER
45
Describe sweat gland ducts.
Lined by stratified cuboidal epithelium, they recover sodium as sweat passes through the duct
46
Where does new growth occur when epidermis is removed by trauma (blisters, burns, scrapes...)?
From hair follicles and sweat glands
47
Where are stem cells located for the epidermis?
Midway along the hair follicle