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Organisation of the Body: Tissues > Skin > Flashcards

Skin Flashcards

1
Q

Main Functions of skin

A

Protection, sensory, thermoregulatory, metabolic and absorptive

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2
Q

Protective function explained

A

provides a physical barrier against pathogens and friction. Pathogens that do get in alert antigen presenting cells in the skin which initiate an immune response. Melanin protects nuclei from UV radiation. Prevents excessive water loss.

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3
Q

Sensory function explained

A

contains many sensory receptors and mechanoreceptors

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4
Q

thermoregulatory function explained

A

Fatty layer- helps maintain heat, hair follicles, sweat production

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5
Q

metabolic function explained

A

cells of skin synthesise vitamin D needed in calcium metabolism and bone formation

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6
Q

Absorptive function

A

skin patches can be placed, containing nicotine, hormone replacements, steroids etc.

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7
Q

3 main layers of skin

A

epidermis, dermis and hypodermis

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8
Q

What type of epithelium is the epidermis?

A

Stratified squamous

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9
Q

4 main epidermal layers

A

Basal layer (stratum basale), spinous layer (stratum spinosum), granular layer (stratum granulosum) and stratum corneum

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10
Q

Stratum Basale location

A

between the dermis and stratum spinosum. Bound to the basal lamina via hemidesmosomes

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11
Q

Stratum Basale cell type

A

simple cuboidal or columnar

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12
Q

How is the stratum basale characterised?

A

Intense mitotic activity. Contains progenitor cells for the epidermal layers and basal stem cells for the keratinocytes.

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13
Q

What sorts of keratin is expressed?

A

cytoskeletal keratins are 10 nm in diameter.

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14
Q

How often are the stratum basale epithelial cells renewed?

A

25-30 days

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15
Q

What is normally the thickest layer in the epidermis?

A

Stratum spinosum

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16
Q

What are the prickles on the stratum spinosum cells?

A

Tonofibrils assembled from keratin fibre bundles that terminate at numerous desmosomes, holding the cell layers together.

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17
Q

Where will epidermis have a larger stratum spinosum?

A

Skin where there is a lot of friction, such as the foot sole

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18
Q

What type of cells are in the basale granulosum?

A

flattened

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19
Q

What process are they undergoing?

A

Terminal differentiation process of keratinisation

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20
Q

What is the cytoplasm of the basale granulosum cells filled with?

A

basophilic keratohyaline granules

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21
Q

What are keratohyaline granules?

A

dense, non- membranous bound masses of filaggrub and other proteins associated with keratin

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22
Q

Keratohyaline granule functions

A

cross link proteins together in a big mass, forming a cornfield layer

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23
Q

What else occurs in the basle granulosum?

A

small keratinosomes are released, filled with lipids producing water proofing

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24
Q

What cells are present in the stratum corneum?

A

15-20 layers of squamous cells, that have been squashed and migrated from the stratum basale’s cuboidal cells

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25
Q

What is the stratum corneum?

A

The most superficial layer of the epidermis, containing remnants of dead keratinocytes, including desmosomes, monofilaments and cornified cell envelope.

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26
Q

What is the cornified cell envelope?

A

A structure formed beneath the plasma membrane in terminally differentiating stratified squamous epithelia that provides a physical barrier and consists of a thick layer of highly cross linked insoluble proteins.

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27
Q

What are the fully keratinised cells called?

A

squames

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28
Q

What is the process of cornification?

A

Metabolism ceases. Cells completely filled with keratin that forms the cytoskeleton by binding to desmosomes, hemidesmosomes and cell junction plaques. Loses nuclei.

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29
Q

What is keratin + structure?

A

Fibrous, insoluble scleroprotein. Two strands of alpha keratin parallel to each other wrap around one another fro form a supercoil.

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30
Q

Cells present in epidermis

A

keratinocytes, melanocytes, Langerhan’s, Merkel Cells

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31
Q

Function of keratinocytes

A

Constitute 90% of the cells of the epidermis. Form a barrier against environmental damage such as heat, UV light, water loss and pathogens.

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32
Q

Keratinocyte maturation stages

A
  1. Keratinocytes in the stratum basale begin to differentiate and migrate superficially
  2. Keratinocytes then permanently withdraw from the cell cycle
  3. Begin expressing different keratin molecules, such as 1, 5, 10 and 14.
  4. eventually become corneocytes, when the keratinocytes lose their nucleus and organelles, once differentiation has completed, forming the stratum corneum.
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33
Q

Melanocytes function

A

Melanocytes produce melanin in melanosomes. It’s different forms are responsible for different colours of hair and skin.

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34
Q

Two types of melanin + colour

A

Eumelanins (black/brown pigments) produced by eumelanosomes and phenomelanins (red pigments) produced by phenomelanosomes

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35
Q

Melanocytes origin and location

A

Neural-crest cell derivatives that migrate into embryonic epidermis’ stratum basale. One melanocyte accumulates for every 5/6 keratinocytes

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36
Q

melanocyte structure

A

Rounded cell bodies attached to the basal layer by hemidesomosomes, but lack attachments to keratinocytes. Contains several long cytoplasmic extensions that penetrate the epidermis and run parallel to the basal and spinous layers of cells

37
Q

Melanin synthesis stages

A
  1. Tyrosinase enzymes, transmembrane enzymes in vesicles, convert tyrosine to 3,4-dihydroxyphenylalanine which is then further transformed into different melanin molecules.
  2. Melanin pigment, linked to the matrix and structural proteins, accumulates in the vesicles until they form mature elliptical granules called melanosomes.
  3. Melanosomes are then transported via kinesin to the tips of the cytoplasmic extensions
  4. Neighbouring keratinocytes phagocytose the dendrite tips, take in the melanosomes and then transport them by dynein towards their nuclei.
  5. Form a supranucledar cap surrounding the nucleus, protecting DNA from UV radiation
38
Q

Langerhan’s cell function

A

Bind, process and present antigens to T lymphocytes, becoming antigen presenting cells that initiate an immune response.

39
Q

Langerhan’s cell location and structure

A

Most clearly seen in the stratum spinosum layer. Cytoplasmic processes extend from the dendritic cells between keratinocytes.

40
Q

Merkel cells function

A

Low threshold mechanoreceptors, essential for sensing gentle touch

41
Q

Merkel cell structure

A

joined by desmosomes to keratinocytes of the basal epidermal layer. Same structure as keratinocytes however have no melanosomes. Contain small, Golgi derived, dense core granules in areas near the basolateral surface where the cells have synaptic contact with nerves.

42
Q

Merkel cell location

A

Abundant in highly sensitive skin, such as the fingertips

43
Q

What is the dermis?

A

Layer of connective tissue that supports the epidermis and binds it to the subcutaneous hypodermic layer

44
Q

Two dermis sublayers

A

Upper papillary layer and lower reticular layer

45
Q

Papillary layer components

A

Loose connective tissue, collagen fibres, fibroblasts, mast cells, dendritic cells and leukocytes

46
Q

Structure of papillary

A

Contains dermal papillae which are projections that interdigitate with invagination epidermal ridges. Anchoring fibrils of Type VII collagen insert into the basal lamina, helping bind the dermis to the epidermis

47
Q

What is the function of the epidermal ridges and dermal papillae?

A

Increase the strength of adhesion between the epidermis and dermis

48
Q

Structure and components of reticular layer

A

Thicker layer, consists of dense irregular connective tissue with more fibres and less cells than the papillary layer. Network of elastic fibres also present, provide elasticity to the skin.

Between collagen fibres and elastic fibres there are a large number of proteoglycans rich in dermatan sulphate.

49
Q

Which layer of the skin contains a rich network of blood and lymphatic vessels?

A

Dermis

50
Q

Two Major plexuses

A

Subpapillary plexus and deep plexus

51
Q

Location of subpapillary plexus

A

Between the papillary and reticular Demis layers. Capillaries branch off and extend into the dermal papillae

52
Q

What sort of blood vessels are present in the subpapillary plexus?

A

A nutritive capillary network

53
Q

Deep plexus location

A

Near the interface of the dermis and the hypodermis

54
Q

What sort of vessels in the deep plexus?

A

Larger blood vessels and lymphatic vessels

55
Q

Anteriovenous anastomoses function

A

The shunts decrease blood flow to the papillary layer to minimise heat loss and increase flow to maximise heat loss.

56
Q

Location of the arteriovenous anastosomes

A

Between the the deep and subpapillary plexuses

57
Q

Where are nerve fibres found?

A

Sensory afferent nerve fibres form a network in the papillary dermis and around hair follicles ending at dermal and epithelial receptors.

Autonomic effector nerves to dermal sweat glands. Smooth muscle fibres in the skin of some areas are postganglionic fibres of sympathetic ganglia.

58
Q

What type of innervation is not present?

A

Parasympathetic

59
Q

Hypodermis structure

A

loose connective tissue and adipocytes. Extensive vascular supply.

60
Q

Hypodermis function

A

Bind loosely to the skin of subjacent organs making it possible for the skin to slide over them.

61
Q

Two types of skin glands

A

Sebaceous and sweat glands

62
Q

Sebaceous glands location

A

Embedded in the dermis all over the body apart from the soles and palms

63
Q

Structure of sebaceous glands

A

Branched acinar glands with several acini converging at a short duct that usually empties into the upper portion of a hair follicle. In hairless regions, the sebaceous ducts open directly onto the epidermal surface

64
Q

Pilosebaceous unit definition

A

a hair follicle and its associated sebaceous glands

65
Q

What form of secretion occurs at acini?

A

Holocrine, where cells undergo terminal differentiation and form lipid producing sebocytes filled with small fat droplets. Eventually cells undergo autophagy and release the lipids called sebum.

66
Q

What does sebum cover?

A

surface of epidermis and hair shafts

67
Q

Continents of sebum

A

mixture of lipids that includes wax esters, squalene, cholesterol and hydrolysed triglycerides.

68
Q

Sweat gland structures

A

Long epidermal invaginations embedded in the dermis

69
Q

Two types of sweat gland

A

eccrine and apocrine

70
Q

Eccrine sweat gland location

A

Mainly sole of foot

71
Q

Three cell types in secretory part of gland and function

A

Clear cells, located on basal lamina and produce sweat.

Dark cells, filled with strongly eosinophilic granules line the lumen and do not contact basal lamina. Granules undergo merocrine secretion of glycoproteins with bactericidal action

Myoepithelial cells, on basal lamina contract to move watery secretion into duct

72
Q

How is sweat produced?

A

Interstitial fluid from capillary rich dermis around the gland is transported through the clear cells into the gland’s lumen

73
Q

Adaptations to the duct to minimise sodium ion loss

A

Ducts of eccrine sweat glands have two layers of acidophillic cells linked with mitochondria and cell membranes rich in the sodium potassium ATPase. Duct cells thus absorb sodium ions from the secreted water.

74
Q

How is sweat lost from the gland?

A

Duct merges with stratum basale and sweat floes through a spiralling channel to an excretory sweat pore on the skin’s surface where it then quickly evaporates upon release.

75
Q

Under what control is release from eccrine glands?

A

cholinergic sympathetic control

76
Q

Apocrine sweat gland location

A

skin on the axillary and perineal regions

77
Q

Under what control is release from apocrine glands?

A

adrenergic sympathetic control

78
Q

What type of secretion occurs at apocrine glands?

A

merocrine secretion from secretory granules that undergo exocytosis into the lumen

79
Q

What is secreted?

A

Viscous milky secretion which may acquire a distinctive door as a result of bacterial activity

80
Q

What is hair?

A

elongated keratinised structures that form within epidermal invaginations, hair follicles. Keratin is harder and more compact than that of the stratum corneum

81
Q

What is the hair shaft surrounded by?

A

A hair follicle, an epidermal downgrowth

82
Q

Hair location

A

Bulb in dermis, however hair shaft in epidermis, so is an epidermal structure

83
Q

What inserts into the base of the hair bulb + function?

A

Dermal papillae, containing a capillary network. Also covered in a layer of keratinocytes which form the matrix of the elongating hair root.

84
Q

Cells in the hair root matrix + functions

A

keratinocytes - divide rapidly around dermal papillae, undergo keratinisation, melanin accumulation and terminal differentiation.

melanocytes- transfer melanosomes to epithelial cells which will later differentiate into hair cells

85
Q

What are arrector pili muscles?

A

small bundles of smooth muscle cells that extend from midpoint of fibrous sheath to the dermal papillary layer.

86
Q

Arrector pili muscle function

A

Contract to pull the hair shaft into a more effect position

87
Q

What are nails?

A

Hard plates of keratin on the dorsal surface of each distal phalanx

88
Q

Structure of nail

A

Nail root- at bottom of the nail covered by a fold of skin called the eponychium (proximal nail fold).

Cuticle- extension of epidermal stratum corneum

Nail plate bound to a nail bed, which contains only the basal and spinous epidermal layers

89
Q

Brief nail growth

A

Nail root continuously forms from nail matrix containing keratinising cells that mature and harden. Continuous growth of the matrix pushes the nail plate forward over the nail bed. Epidermal fold at the tip of the finger is called the hyponychium (lateral nail fold)

Organisation of the Body: Tissues (10 decks)

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