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Dermatology > Physiology > Flashcards

Physiology Flashcards

1
Q

What percentage of the population have a skin condition?

A

> 25%

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2
Q

What is the skin?

A
  • epidermis
  • dermis
  • non hairy and hairy skin
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3
Q

Describe the structure of the epidermis

A
  • stratified cellular epithelium
  • outer layer
  • 95% of the epidermis is keratinocytes
  • movement from basement membrane
  • four defined layers
  • other cells; melanocytes, langerhans cells and merkel cells
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4
Q

Describe the structure of the dermis

A
  • beneath epidermis
  • connective tissue
  • thick coat of collagen fibres
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5
Q

What is the epidermis derived from?

A
  • ectoderm cells form a single layer periderm
  • gradual increase in layers of cells
  • periderm cells cast off
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6
Q

What is the dermis derived from?

A

Formed from mesoderm below ectoderm

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7
Q

What are melanocytes?

A

Pigment producing cells from neural crest

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8
Q

When does gastrulation take place?

A

Between days 7 and 10

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9
Q

Describe the skin development at four weeks

A
  • periderm
  • basal layer
  • dermis (corium)
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10
Q

Describe the skin development at 16 weeks

A
  • keratin layer
  • granular layer
  • prickle cell layer
  • basal layer
  • dermis
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11
Q

What are blaschkos lines?

A
  • developmental growth pattern of skin

- not following vessels, nerves of lymphatics

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12
Q

When a pattern runs across the blaschkos lines, what does this indicate?

A

It is a genetic problem, inborn error

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13
Q

What does the skin consist of?

A
  • epidermis
  • appendages; nail, hair, glands, mucosae
  • dermo-epidermal junction
  • dermis; connective tissue, less cellular
  • subcutis - predominantly fat
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14
Q

What is pilum?

A

Hair in latin

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15
Q

What is a pilosebaceous unit?

A

Hair and a sebaceous gland

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16
Q

What do keratinocytes contain?

A

Structural keratins

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17
Q

Name the four cell layers of the epidermis

A
  • keratin layer
  • granular layer
  • prickle cell layer
  • basal layer
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18
Q

Describe the structure of sebaceous glands

A

Torturous tubes filled with grease

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19
Q

Describe the regulation of epidermal turnover

A
  • balance between cells in and out
  • control by; growth factors, cell death, hormones
  • loss of control in; skin cancer, psoriasis
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20
Q

Most of the dermis is what?

A

Collagen fibres - produced by fibroblasts

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21
Q

Describe differentiation of the epidermis

A
  • keratinocytes migrate form basement membrane
  • continuous regeneration of epidermis
  • 28 days from bottom to top
  • they proliferate much faster in psoriasis
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22
Q

Describe the basal layer of the epidermis

A
  • usually one cell thick
  • small cuboidal
  • lots of intermediate filaments (keratin)
  • highly metabolically active
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23
Q

Describe the prickle cell layer of the epidermis

A
  • larger polyhedral cells
  • lots of desmosomes (connections)
  • intermediate filaments connect to desmosomes
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24
Q

What are desmosomes?

A

Cell to cell contacts that allow both adhesion (to impart stability) and flexibility (so cells can move upwards)

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25
Q

Describe the granular layer of the epidermis

A
  • 2 to 3 layers of flatter cells
  • large keratohyalin granules, contain structural filaggrin and involucrin proteins
  • odland bodies (lamellar bodies)
  • high lipid content
  • origin of cornified envelope
  • cell nuclei lost
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26
Q

Name the key feature of the short filaggrin breakdown products?

A

They retain water

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27
Q

Describe the keratin layer of the epidermis

A
  • corneocytes, overlapping non-nucleated cell remnants
  • insoluble cornified envelope
  • 80% keratin and filaggrin
  • lamellar granules release lipid
  • tight waterproof barrier
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28
Q

Human papilloma virus infection affects which type of skin cell?

A
  • keratinocytes

- virus infection of keratinocytes causes warts

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29
Q

Describe the mucosal membrane

A
  • highly specialised for function (eyes, mouth, nose, genito-urinary and GI tracts)
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30
Q

Describe the oral mucosa

A
  • masticatory; keratinised to deal with friction/ pressure
  • lining mucosa; non keratinised
  • specialised mucosa; tongue papillae, taste
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31
Q

Describe ocular mucosa

A
  • larcimal glands
  • eye lashes
  • sebaceous glands
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32
Q

True or false?

Mucosal surfaces can also be affected by skin diseases

A

True

Becomes white as keratin builds up

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33
Q

Name the epidermal cells

A
  • 95% of epidermal cells are keratinocytes
  • melanocytes (basal and suprabasal)
  • langerhans cells (suprabasal)
  • merkel cells (basal)
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34
Q

Where do melanocytes orginate?

A

Migrate from the neural crest to the epidermis in the first 3 months of foetal development

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35
Q

Where are melanocytes found?

A

Basal layer and above

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36
Q

Describe the function and structure of melanocytes

A
  • pigment producing dendritic cells
  • contains organelles; melanosomes
  • convert tyrosine to melanin pigment; eumelanin (brown or black), phaeomelanin (red, yellow)
  • melanin absorbs light (neutral density filter)
  • full melanosomes (melanin granules) transferred to adjacent keratinocyte via dendrites
  • form protective cap over nucleus
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37
Q

Melanin is derived from what?

A

Tyrosine

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38
Q

Melanin is hormonally driven by what?

A
  • alpha melanocyte stimulating hormone (aMSH)
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39
Q

What is vitiligo?

A

An autoimmune disease with loss of melanocytes

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40
Q

What is albinism?

A

A genetic disorder where there is a genetic partial loss of pigment production

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41
Q

What is nelsons syndrome?

A

A disorder in which melanin stimulating hormone is produced in excess by the pituitary

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42
Q

What is a malignant melanoma?

A

A tumour of the melanocyte cell line - always deadly if not treated

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43
Q

Describe langerhans cells of the skin

A
  • mesenchymal origin; bone marrow
  • prickle cell level in epidermis
  • also found in dermis and lymph nodes
  • involved in the skin immune system; antigen presenting cells, pick up antigen in skin and circulate to lymph nodes via lymphatic system - a type of dendritic cell
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44
Q

Describe merkel cells

A
  • basal
  • between keratinocytes and nerve fibres
  • mechanoreceptors
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45
Q

What is merkel cell cancer?

A
  • rare

- caused by viral infection - high mortality

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46
Q

Describe pilosebaceous units (hair follicles)

A
  • epidermal component plus dermal papilla
  • specialised keratins
  • adjacent sebaceous gland
  • hair pigmentation via melantocytes above dermal papilla
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47
Q

What is natures own emollent?

A

Sebum greasy wax (ceramides), greases the epidermis

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48
Q

What are the three phases of growth of hair follicles?

A
  • anagen; growing
  • catagen; involuting
  • telogen; resting
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49
Q

Name the types of hair follicle

A
  • lanugo (in utero)
  • vellus
  • terminal
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50
Q

Name some hormonal influences on hair growth

A
  • thyroxine

- androgens

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51
Q

Is human hair growth synchronous or asynchronous?

A

Asynchronous

52
Q

What is hirutism?

A

Virilisation due to excess androgen from a tumour

53
Q

What is alopecia areata?

A

Autoimmune hair loss

54
Q

Describe the structure of nails

A
  • specialised keratins
  • nail matrix / root similar to hair bulb
  • growth rate 0.1mm per days
  • some drugs increase nail / hair growth
55
Q

Where is the nail matrix located?

A

Underneath the nail proximal to the bed

56
Q

Describe the cuticle

A

A protective layer

57
Q

What is luluna?

A

Keratin

58
Q

What does clubbing of the nails affect?

A

Stem cells affected in the keratin layer

59
Q

Where are the stem cells located in the nail

A

In the nail matrix

60
Q

What are the three plates of nail growth?

A
  • dorsal
  • intermediate
  • ventral
61
Q

What are the divisions of the matrix?

A
  • dorsal
  • intermediate
  • ventral
62
Q

Describe the dermo-epidermal junction

A
  • interface between epidermis and dermis
  • key role in epithelial - mesenchymal interactions
  • support, anchorage, adhesion, growth and differentiation of basal cells
  • semi-permeable membrane acting as barrier and filter
63
Q

The dermis contains what?

A
  • ground substance
  • cells; mainly fibroblasts, macrophages, mast cells, lymphocytes and langerhans cells
  • fibres; collagen, elastin
  • muscles; blood vessels, lymphatics, nerves
64
Q

What percentage of the dermis is collagen based?

A

90%

65
Q

Describe the flow of blood vessels

A
  • arteriole
  • precapillary sphincters
  • arterial
  • venous capillaries
  • post capillary venules
  • collecting venules
66
Q

Where are deep vessels found?

A

In the subcutaneous fat

67
Q

The papillary dermis supplies what with blood?

A
  • the epidermis

- materials diffuse across the dermis epidermis junction

68
Q

Describe the lymphatic vessels

A
  • sub epidermal meshed networks
  • smaller noncontractile vessels&raquo_space;> larger contractile lymphatic trunks
  • continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
  • important immune functions; immune surveillance by circulating lymphocytes and langerhans cells, channelling of micro-organisms / toxins
69
Q

What are the special receptors of the skin?

A
  • pacinian (pressure) corpuscles

- meissners (vibrations) corpuscles

70
Q

Are pacinian and meissners corpuscles somatic sensory or autonomic nerve supply?

A

Somatic sensory

71
Q

What type of nerve senses light touch sensation?

A

Free nerve endings

72
Q

Give an example of a condition where the free nerve endings grow without ingivition

A

Neurofibromatosis

73
Q

Which cells give pigmentation?

A

Melanocytes above the dermal papilla

74
Q

Name a specialised keratin

A

Adjacent sebaceous gland

75
Q

Where are the largest and most abundant pilo-sebaceous units found

A

In the face, upper back and upper chest

76
Q

Describe involuted hairs

A

Hairs that are still embedded but are not growing

77
Q

Describe a condition in which there is an attack on anagen hairs

A

Alopecia areata

78
Q

What are the three skin glands?

A
  • sebaceous
  • apocrine
  • eccrine
79
Q

Which glands are involved in acne?

A

Sebaceous glands

80
Q

Describe apocrine glands

A
  • feed into the hair follicle
  • most likely linked to pheromones
  • develop as part of pilosebaceous unit
  • axillae and perineum
  • androgen dependent
  • produce oily fluid&raquo_space;> odour after bacterial decomposition
81
Q

Which glands play a role in thermoregulation?

A

Eccrine glands

82
Q

Describe sebaceous glands

A
  • holocrine secretion opening into pilary canal
  • widely distributed; largest glands face and chest
  • hormone sensitive; quiescent pre-puberty
  • produce sebum; squalane, wax esters, TG and FFA
  • functions; control moisture loss, protection from fungal infection
83
Q

Describe eccrine sweat glands

A
  • whole skin surface; palms, soles and axillae in particular
  • sympathetic cholinergic nerve supply; mental, thermal and gustatory stimulation
  • ultrafiltration; can be >10L per day, NaCl and HCO3 reabsorbed, hypotonic fluid
  • functions; cooling by evaporation, moisten palms and soles to aid grip
84
Q

Name the functions of the skin

A
  • barrier function
  • metabolism and detoxification
  • thermoregulation
  • immune defence
  • communication
  • sensory functions
85
Q

Describe the barrier function of skin

A
  • two way barrier; epidermis
  • physical; friction, mechanical trauma, UV radiation
  • chemical; irritants, allergens, toxins
  • pathogens; bacteria, viruses, fungi
86
Q

Which UV causes the most damage?

A

UVA and UVB

87
Q

What is the role of the superior cap of melanin pigment in basal cells?

A

Melanin absorbs UV rays to protect DNA in the cells nuclei

88
Q

Describe metabolism and detoxification of the skin

A
  • skin is metabolically active
  • vitamin D metabolism
  • thyroid hormone metabolism
  • defence against chemicals, drugs, pollutants and sunlight
89
Q

Vitamin D3 is stored as what in the liver?

A

Hydroxycholecalciferol

90
Q

Vitamin D3 is converted to what in the kidney?

A

1,25-dihydroxycholecalciferol

91
Q

Cholecalciferol is converted to vitamin D3 at what UV wavelength?

A

290 to 320nm

92
Q

Where does thyroid hormone metabolism take place?

A

20% occurs in thyroid gland

80% in peripheral (to thyroid) tissues including skin

93
Q

If there is less blood in the superficial plexus what is retained?

A

Heat

94
Q

Name the sensory functions of the skin

A
  • touch, pressure, vibration
  • pain and itch
  • heat and cold
  • nerve endings and receptors in skin
95
Q

Name the basic tissue groups found in the skin

A
  • epithelium
  • nervous tissue
  • glands
  • muscle
  • hair
  • adipose tissue
  • connective tissue
96
Q

The skin consists of what type of epithelium?

A

Stratified squamous epithelium

97
Q

Blood vessels are lined with which type of epithelium?

A

Simple squamous epithelium

98
Q

What gland is described?

Derived from epidermis. Lobulated masses in dermis which usually secrete an oily substance into hair follicle to coat hair and skin. Not present in palm and sole skin

A

Sebaceous glands

99
Q

What gland is described?

Found over the whole body except the lips and genital. Coiled tubular structures which regulate heat and salt loss

A

Eccrine glands

100
Q

What gland is described?

Limited to axillae/nipple/genitals. Develop at puberty and open into hair follicles

A

Apocrine glands

101
Q

What is attached to hair follicles and can pull the hair perpendicular to the skin during cold

A

Arrector pilli

also present in the walls of blood vessels

102
Q

What provides tensile strength and the elastic qualities of the skin?

A

Collagen fibres and elastic fibres present in the dermis

103
Q

Where are meissners corpuscles found?

A

Present in the dermis, just beneath epidermis and abundant in tactile areas of fingers and toes

104
Q

Where are pacinican corpuscles located?

A

Located in deep dermis and frequently seen in finger pulp sections

105
Q

What senses;

  1. tactile sensation
  2. deep pressure
  3. pain
A
  1. meissners corpuscle
  2. pacinian corpuscles
  3. free nerve endings
106
Q

What is a hair follicle?

A

An invagination of the epidermis

107
Q

Describe hair structure

A
  • central medulla containing soft keratin
  • outer cortex and cuticle of hard keratin
  • papilla (bulge at base) contains multiple vascular channels
  • the hair bulb at the base of the follicle contains the hair matrix and dermal papilla
108
Q

Nails are plates of cells filled with what?

A

Hard keratin

109
Q

Describe the structure of nails

A
  • nail plate; sits on the nail bed
  • matrix; cells divide and then produce hard keratin
  • cuticle; extension of the skin fold covering the nail root
  • hyponychium; secures the free nail edge
110
Q

Skin failure has what consequences?

A
  • loss of thermoregulation; may contribute to cardiovascular instability
  • increased risk of infection; bacterial and yeast infections may result in overwhelming sepsis
  • failure of homeostatic function; enormous fluid and electrolyte losses, may result in cardiovascular instability
111
Q

Name the requirements for healthy skin

A
  • intact physical barrier ie good hydration, not broken infected or injured
  • functioning immune system, both innate and adaptive
  • functioning vasculature / adequate supply and drainage large and small arterial vessels - for oxygenation
  • functioning venous return and lymphatic system, to avoid stasis
  • means of temperature regulation; capillary dilatation / constriction, functioning sweat glands
  • normal sensory nerve function to warn us about injury
  • adequate nutrition
112
Q

Many surgical wounds heal by means of what?

A
  • primary intention
  • the edges are approximated (brought together) by stitches leading to rapid healing
  • can be compromised by haematoma, infection, poor suture technique or dehiscence
113
Q

What is secondary intention healing?

A
  • generally used for larger wounds that are too tight to stitch, or areas where direct closure would cause significant distortion of surrounding tissue
  • has three stages
114
Q

Name the three stages of secondary intention healing

A
  • inflammation
  • proliferation and tissue remodelling
  • tissue remodelling
115
Q

Describe the inflammatory phase of secondary intention healing

A
  • platelets form the initial clot and release inflammatory mediators
  • leucocytes debride the wound bed by phagocytosing bacteria and scavenging cellular debris
  • inflammation gradually decreases as keratinocyte proliferation and new tissue formation become predominant
116
Q

Describe the proliferation and tissue remodelling phase of secondary intention healing

A
  • cells divide (proliferate) to re-epithelialise the wound surface
  • granulation tissue formation is stimulated
  • fibroblasts lay down matrix, and contract the wound (fibroplasia)
  • endothelial cells develop into new blood vessels (angiogenesis)
117
Q

Describe the tissue remodelling phase of secondary intention healing

A
  • new tissue is converted into mature scar tissue over a period of months
  • fibroblasts lay down collagen to improve the tensile strength of the scar and restore the normal dermal matrix
118
Q

First degree burns affect which layer of skin?

A

Epidermis only

119
Q

Second degree burns affect which layer(s) of the skin?

A

Epidermis and dermis

120
Q

Third degree / full thickness burns affect which layer of the skin?

A

Goes beyond the dermis

121
Q

Describe superficial burns

A
  • erythematous
  • wet
  • extremely painful
122
Q

Describe deep burns

A
  • white or black and charred
  • dry
  • numb
123
Q

Chronic wounds often exhibit surface what?

A

Slough - a mixture of dead cells, polymorphs and bacteria. It is yellow green in colour and may be quite adherent to the underlying tissue. Has an inhibitory effect on healing

124
Q

How do chronic wounds tend to heal?

A
  • from the edges

- increased risk of infection and slow resolution

125
Q

What factors contribute to pressure sores?

A
  • prolonged pressure over bony area
  • lack of blood flow
  • friction from bedding / clothing
  • irritation from sweat / blood / urine / faeces
126
Q

Describe the four stages of pressure sore development

A
  1. skin is unbroken but shows a pink or reddened area, may look like a mild sunburn. skin may be tender, itchy or painful
  2. skin is red, swollen and painful. blisters that may be broken or intact may be present. upper layers of skin begin to die
  3. sore has broken through the skin and wound extends down to deeper layers of skin tissue. crater-like ulcers are present. wound is prone to infection
  4. sore extends past the skin and into fat, muscle and bone tissue. blackened dead tissue called eschar may be seen in deep opened wounds
127
Q

How might you ensure good healing of a laceration on a hand?

A
  • clean wound (check for nerve / tendon / vessel damage)
  • suture
  • consider antibiotics
  • tetanus prophylaxis

Dermatology (10 decks)

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