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Physiology 2 : skin > Skin structure and function > Flashcards

Skin structure and function Flashcards

1
Q

Epidermis

A

The outer layer of the skin: stratified, squamous, keratinized epithelium.

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2
Q

Dermis

A

The second skin layer: fibrous, dense connective tissue

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3
Q

Hypodermis or subcutis

A

the third layer, of fatty connective tissue

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4
Q

Cutis

A

cutaneous) – Epidermis + dermis

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5
Q

Keratin

A

A protein made inside keratinocytes; the main component of hair, hooves, horns, nails and the outer epidermis, giving strength and (in large masses) hardness.

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6
Q

Keratinocytes

A

epithelial cells, main cells composing the epidermis

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7
Q

Melanocytes

A

Cells that make melanin, the pigment of skin, hair and eyes

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8
Q

Collagen

A

A strong, fibrous, extracellular protein, main component of the dermis (and of leather)

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9
Q

Fibroblasts

A

Main cell type of the dermis (and other soft connective tissue), generating the extracellular matrix including collagen

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10
Q

Sebaceous gland

A

Gland producing oily conditioning fluid (sebum) for skin and hair

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11
Q

Eccrine sweat gland

A

Produces normal sweat

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12
Q

Apocrine sweat gland

A

Produces different sweat in armpits etc, after puberty

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13
Q

The skin

A

is the largest and heaviest organ of the body - ~15% of adult body weight

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14
Q

3 Layers of the skin

A 
•	Epidermis
•	Dermis
•	Hypodermis
Also 
•	Hair, skin glands, nails and sensory receptors.
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15
Q

The skin functions

A 
•	Barrier (protection) against:
Dehydration
Infection
Injury/abrasion
Solar radiation
•	Thermoregulation
•	Sensation
•	Repair 
•	Vitamin D production
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16
Q

Hypodermis Can be the

A

thickest layer depending on the part of the body

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17
Q

Epidermis

A

Outer epithelial layer

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18
Q

Dermis

A

Middle connective/ collagen layer

and inner fatty layer

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19
Q

Epidermis in more detail

A 
•	Most superficial
•	Gives skin its colour
•	Protection from 
-	Pathogens
-	Environment
•	Vitamin D production
•	Made up of multiple layers of differentiating keratinocytes.
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20
Q

Keratinocytes

A

Flat pancake-shaped cells that are named for the keratin -producing capabilities.

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21
Q

4 main layers of the epidermis

A 
Cornified layer (stratum corneum)
Stratum lucidium (clear layer and is only in thick soles of feet and palms)
Granular layer - stratum granulosum 
Spiny layer (stratum spinosum)
Basal layer (stratum basale)
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22
Q

Basal layer [b] (stratum basal)

A

First single layer, containing stem cells, and attached to dermis.

Stem cells constantly proliferate.

Dynamic - Daughter cells constantly move “up” (distally) through the epidermis, differentiating as they go, until they are shed from the outer surface. This takes ~20-50 days.

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23
Q

Spiny layer (Stratum spinosum)

A

Cells (keratinocytes) have many desmosomes, (junctions) here visible as “spines” between the cells. Strong bonds holding the epidermis together.

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24
Q

Granular layer [G] (Stratum granulosum)

A

• 1-4 layers of cells containing prominent granules of “keratohyalin” – precursor of the protein keratin. Also contain lamellar bodies containing lipids (seen by TEM). Cells are differentiating to form the outermost layer.

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25
Q

Cornified layer [C] (Stratum corneum)

A
  • The outer protective layer of the epidermis.
  • Cell are keratinised (cornified) – cytoplasm full of “horny” keratin (from keratohyalin granules), thus tough and resistant to injury.
  • Cells are flattened and have lost their nuclei…
  • Nonpolar lipids (waterproof) are between the cells – from lamellar bodies.
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26
Q

Other epidermal cell types

A
  • Melanocytes (Pigment)
  • Langerhans cells (defense)
  • Merkel cells (sensation)
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27
Q

Melanocytes

A

Melanocytes as viewed through thin sheets of human epidermis.
Special (DOPA) stain for melanin shows their dendritic form.

28
Q

Melanin (pigment)

A

Keratinocytes arrange melanin pigment in a cap distal to the nucleus (sunny side).
Especially in basal layer (stem cells).
UV protection - black-skinned people have only about 10% as many skin cancers as white people with the same lifestyle.

29
Q

Merkel cells

A

Touch sensors

30
Q

Langerhans cells

A

Function: Immune system. Seeks and deals with invading microbes.
Antigen-presenting cells (like macrophages).
They are dendritic cells, forming a network – seen here with immunoperoxidase staining.

31
Q

Langerhans cells

H and E appearance

A

Small, pale cells in non-basal layers of epidermis. Hard to see with H&E only.

32
Q

Melanocytes H and E white skin

A

– pale cells, in or protruding from basal layer.

Some pale cells in basal layer are Merkel cells: touch-sensors.
Hard to tell difference with H and E alone.

33
Q

Vitamin D production

A

• Vitamin D3, made in the epidermis.
• Mostly basal cells, also stratum spinosum.
• Requires UV light.
• Converted to active form in liver and kidney: 1,25 dihydroxyvitamin D3.
Commonly deficient in UK.

34
Q

Vit D

A

Vitamin D3 (cholecalciferol) is synthesized in the skin by the reaction of 7-dehydrocholesterol with UVB radiation, present in sunlight with an UV index of three or more.

35
Q

The dermis

A
  • Below the epidermis
  • Two layers
  • Blood vessels, skin glands & sensory receptors
  • Made up of layers of connective tissue characterized by interconnected mesh of elastin and collagen fibres, produced by dermal fibroblasts.
  • Fibroblasts are the principal cell of the dermis.
36
Q

Reticular meaning

A

containing branching fibres of connecting tissue.

37
Q

Functions of dermis

A

Collagen provides tensile strength, (strength when pulled), hence protection against abrasion and impact.

Also contains elastin, a protein complex that provides elasticity.
Dermis also carries blood and nerve supply for the epidermis. Rich in blood vessels, sensory receptors and skin glands.

38
Q

Dense (dermis)

A

Full of collagen fibres;

39
Q

Irregular (dermis)

A

Fibres run in all directions (not parallel)

40
Q

Dermal- epidermal border

A

• The dermal-epidermal border is often wavy, to resist shear forces (rubbing sideways).

41
Q

Dermal papillae

A

Finger-like protrusions of dermal connective tissue into the epidermal layer.

42
Q

Reteridges

A

Extensions of the epidermis into the dermal layer

More apparent in thick skin of hands = fingerprints, as well as feet

43
Q

The hypodermis

A
  • Below the dermis
  • Helps insulate deeper tissue.
  • Anchors skin to the muscle with connective tissue.
44
Q

Fascia or subcutis

Cutis = epidermis + dermis

A

• Made up of well-vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.

45
Q

Fascia/subcutis pt 2

A
  • Composed of fat, containing glands, hair follicles, nerves, blood vessels.
  • Often the thickest layer of skin. Thickness varies with age, body site, nutrition etc.
46
Q

Function of subcutis

A

provides insulation, cushioning and energy storage.

• Where you put a hypodermic needle, for a subcutaneous injection.

47
Q

Hair

A

Found on nearly every part of skin except the palms, soles and lips.
Every strand of hair is composed of the shaft, root, and bulb that sits in a pouch like structure called the hair follicle.
The hair follicle is epidermal tissue that dips down into the dermis, and interacts with other structures like apocrine glands, sebaceous glands, the arrector pili muscle, and nerve receptors.

48
Q

Sebaceous gland

A

Secrete oily sebum (“lanolin”) into hair follicle. Conditioner for hair and skin, prevents dryness and flaking. Only present after puberty.

49
Q

Eccrine sweat gland

A

Normal sweat glands. Watery secretion on to skin surface, cools body by evaporation.

50
Q

Apocrine sweat gland

A

Secrete into hair follicles. Found in armpits and anogenital region. Oily fluid in humans, function unclear (contains pheromones in some mammals). Source of body odour after bacterial action. Only present after puberty.

51
Q

Nail folds

A

where the skin seals of the edges of the nail

52
Q

Eponychium

A

Proximal skin fold that gives rise to the cuticle, a semi-circular layer of dead skin keratinocytes that covers the junction where the nail enters the skin, preventing the entry of pathogens.

53
Q

Nail matrix

A

creates the nail plate, which is the hard part of nail we can see as well as the free edge that hangs over the skin.

54
Q

The nail matrix is made up of

A

Special epidermal tissue that contains nerves, lymphatics, and blood vessels that support the nail.

modified keratinocytes that replicate and undergo the process of keratinisation. The youngest keratinocytes are in the nail matrix, and older cells keratinize, and form the nail plate.

55
Q

Free nervous endings

A

nociception, thermal sensation, light touch

56
Q

Pacinian corpuscles (rapidly adapting)

A

Vibration or brief touch

57
Q

Merkel’s discs (slowly adapting)

A

Sustained touch/pressure e.g. skin indentation

58
Q

Meissner’s corpuscles (rapidly adapting)

A

Moving touch or vibration

59
Q

Ruffini endings (slowly adapting)

A

Steady pressure

60
Q

Root hair plexus (rapidly adapting)

A

Hair displacement.

61
Q

Krause end bulbs

A

Touch/pressure, possibly thermoreceptors

62
Q

Nociception

A

Detection of noxious stimuli (painful, harmful)

63
Q

Why does it take longer for darker skin to absorb Vit D?

A

More UV light is needed as melanin blocks the UV rays

64
Q

Function of the dermis

A

Provides Tensile strength and elasticity

65
Q

2 layers of the dermis

A

Papillary layer

Deeper reticular layer

66
Q

How melanin travels to the basal layer?

A

Synthesizes melanosomes
(pigment granules)
and transfers them to basal keratinocytes through long dendrites.

Physiology 2 : skin (2 decks)

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