Skin Structure & Function Flashcards
(97 cards)
1
Q
What cells of the embryo do the... - epidermis - dermis - melanocytes ... originate from?
A
- Epidermis = single layer of ectoderm cells (periderm)
- Dermis = mesoderm (below ectoderm)
- Melanocytes = neural crest
2
Q
What are the 4 layers of the epidermis?
A
Basal layer
Prickle cell layer
Granular layer
Keratin layer
3
Q
Give 4 examples of appendages in the epidermis
A
Melanocytes
Sebaceous glands
Arector pili muscles
Hair follicles
4
Q
What are Blaschko’s lines?
A
Developmental growth patterns of the skin due to migration of the cells from the centre to the outside of the foetus during development
5
Q
How can Blaschko’s lines signify a congenital problem?
A
If the daughter cell of the line is affected, all migrating/ descending cells along the line will also be affected
6
Q
What is found between the dermis and epidermis?
A
A basement membrane called the dermo-epidermal junction
7
Q
What is the…
- dermis
- subcutis
… mainly composed of?
A
Dermis - connective tissue
Subcutis - fat
8
Q
The dermis is thicker/thinner than the epidermis
A
Thicker
9
Q
What is the epidermis mainly composed of?
A
Composed of stratified squamous epithelium - 95% is keratinocytes
10
Q
How thick is the epidermis?
A
~ 1.5mm
11
Q
What is epidermal turnover regulated by?
A
Growth factors
Cell death
Hormones
12
Q
Loss of regulation of epidermal turnover can lead to…
A
Skin cancer
Psoriasis
13
Q
How long does it usually take for skin cells to differentiate and migrate from the basement membrane to the keratin layer?
A
Around a month/ 28 days
14
Q
Describe the basal layer of the epidermis
A
- Small cuboidal cells
- Usually 1 cell thick
- Contains lots of keratin (intermediate filaments)
- Highly metabolically active
15
Q
Describe the prickle cell layer of the epidermis
A
- Larger polyhedral cells
- Lots of cell-to-cell connections (desmosomes) allow them to migrate up the epidermis
- Intermediate filaments connect to desmosomes
16
Q
Describe the granular layer of the epidermis
A
- 2-3 layers of flatter cells
- The cell nuclei is lost
- Contain large granules containing filaggrin and involucrin proteins
- Contain Odland bodies (which process lipids)
- High lipid content
17
Q
What is the function of filaggrin and involucrin proteins in the granular layer?
A
The proteins are released from the granules and are cut into amino acids
These amino acids bind water molecules to prevent water from leaving the body
18
Q
What would happen in the absence of filaggrin proteins from the granular layer?
A
Water would be able to leave the body and the skin would become very dry
19
Q
What is the No.1 risk factor for eczema and atopic dermatitis?
A
Absence of filaggrin proteins
20
Q
Describe the keratin layer of the epidermis
A
- Corneocytes (overlapping non-nucleated cell remnants) form an insoluble cornified envelope
- 80% keratin & filaggrin
- Lamellar granules release lipids
- Forms a tight waterproof barrier
21
Q
Which layer of the epidermis is most commonly affected by skin conditions?
A
The keratin layer
22
Q
The subcutis/? is mostly composed from ?
A
Hypodermis
Fat
23
Q
What is the function of fat in the subcutis?
A
- Energy storage
- Movement of the skin
24
Q
What is panniculitis?
How does it relate to skin conditions?
A
- Panniculitis = infection of fat
- It restricts skin movement
25
What is acne caused by?
Bacteria that clog the hair shafts and feed on fatty acids/ grease produced by the sebaceous glands
26
95% of epidermal cells are keratinocytes.
| Name 3 other epidermal cells
- Melanocytes
- Langerhans cells
- Merkel cells
27
What are melanocytes?
| Where are they found?
- Pigment producing dendritic cells
| - Found in the basal layer and above (basal & suprabasal)
28
Where do melanocytes originate from during foetal development?
Migrates from the neural crest to the epidermis in the first 3 months of development
29
How do melanocytes produce pigment?
They contain melanosomes that produce melanin pigment
Dendrites pass full melanosomes to adjacent keratinocytes
Melanin is distributed evenly over the keratinocytes to give the skin colour
30
What is another function of melanocytes? (besides pigmentation)
They form a protective cap over the nucleus of the cells in the basal layer of the epidermis
31
Which hormone stimulates melanocyte production?
Alpha melanocyte stimulating hormone = alpha-MSH = ACTH
32
What is vitiligo?
An autoimmune disease characterised by loss of melanocytes (patches of white skin in a brown-skinned person)
33
What is albinism?
A genetic condition characterised by partial loss of pigment production
34
The immune system can kill melanocytes - this can be taken advantage of to help fight malignant melanomas.
Why can stimulating the immune system like this lead to further problems?
Stimulating the immune system to kill the melanocytes can lead to other autoimmune diseases e.g., vitiligo
35
What are langerhans cells and where are they found?
Dendritic cells found in the prickle cell layer of the epidermis (suprabasal)
(Also found in the dermis and lymph nodes)
36
What do langerhans cells do?
They are involved in the skin immune system as antigen presenting cells (dendrites!)
They pick up antigens (e.g., microbes) and circulate to lymph nodes
37
What are Merkel cells?
Mechanoreceptors in the epidermis
38
How do Merkel cells allow us to experience touch?
They are connected to nerve endings which are connected to the CNS
39
Where are Merkel cells found in the epidermis?
The basal layer (basal)
40
Describe Merkel cell cancer
- Rare
- Caused by viral infection
- Very high mortality - nearly all patients die
41
Name the components that make up the structure of hair follicles (pilo-sebaceous units)
- Dermal papilla of hair follicle
- External and internal root sheaths
- Cortex
- Medulla
- Hair shaft
- Sebaceous glands
- Arrector pili muscle
42
Describe the embryological development of hair
- Hair bud branches from the epidermis
- Hair shaft grows from the bud
- Hair papilla comes from the dermis
- Smooth muscle fibres join to form arrector pili muscle
- Sebaceous gland develops
43
What do the sebaceous glands do?
Produce a fatty oil (sebum) that is released onto the skin
44
What do arrector pili muscles do?
Contract to lift the hairs when it is cold
45
Describe the cycle of hair follicle growth (3 steps)
- Anagen -> growing
- Catagen -> growth stops and the outer root sheath shrinks i.e., the hair is starting to die
- Telogen -> shedding phase, the hair remains in the follicle but comes out easily
46
Why does different people's hair grow at different rates?
The length of the anagen (growing) phase can vary from weeks to years
47
What stage of the hair follicle growth cycle are most hairs in?
Anagen (90%)
The other 10% are in telogen
48
How long are hair follicles in catagen for?
Around a month for most people (3-4 weeks)
49
What are the functions of the dermo-epidermal junction aka basement membrane?
- Anchors epidermis to dermis (support)
- Growth and differentiation of basal cells
- Semi-permeable membrane acts as a barrier and filter for proteins to filter across to the epidermis
50
What are the 3 layers of the dermo-epidermal junction? (from top to bottom)
- lamina lucida
- lamina densa
- sub-lamina densa zone
51
Give 2 examples of diseases targeting the dermo-epidermal junction
- Bullous pemphigoid (autoimmune disease)
| - Epidermolysis bullosa (rare inherited disorder involving defects in DEJ proteins)
52
What is the function of the dermis?
It is a connective tissue support structure for the skin
53
List the components of the dermis
- Ground substance
- Cells (fibroblasts, macrophages, lymphocytes, langerhans cells)
- Fibres (collagen and elastin)
- Muscle, blood vessels, lymphatics, nerves
54
What is the function of fibroblasts?
Production of collagen and elastin fibres
55
Why do individuals with darker skin tend to 'age better'?
Thicker collagen in darker skin offers more protection and more macrophages
56
The papillary dermis is above/below the reticular dermis
Above
57
What is the difference between intrinsic and extrinsic skin aging?
- Intrinsic skin ageing happens to everyone
| - Extrinsic skin ageing is more pronounced in sun lovers and smokers
58
What is the difference between hypertrophic and atrophic photoaging?
Hypertrophic -> deep furrows and leathery appearance
Atrophic -> thin, smooth appearance
59
Describe the structure of blood vessels in the dermis
Vessels in the subcutis form horizontal plexuses in the dermis
These reach up to supply the epidermis
60
Why does the dermis have a blood supply greater than its metabolic needs?
The vessels also supply the epidermis
61
What is angioma?
Benign dilatation of the blood vessels in dermal tissue
These are friable and bleed easily
62
Where are lymphatic vessels of the skin found?
As meshed networks in the dermis
63
What are the functions of lymphatic vessels in the skin?
- Drain cell debris
- Drain toxins/ pathogens
- Take part in immune surveillance via circulating lymphocytes and Langerhans cells
64
Give 3 examples of somatic sensory nerves found in the dermis
- Free nerve endings in the higher dermis (touch)
- Pacinian corpuscles in the deep dermis (specialised pressure receptors)
- Meissners corpuscles in the deep dermis (specialised vibration receptors)
65
In the dermis, what do the autonomic nerves supply?
- Blood vessels
- Nerves
- Glands
66
In a biopsy, Pacinian corpuscles look like...
Onion rings
67
What are the 3 main segments of a hair follicle?
- Infundibulum (upper part)
- Isthmus (where sebaceous glands join and stem cells are located)
- Hair bulb (where the papilla is found)
68
The arrector pili muscle gets its nerve supply from...
The sympathetic nervous system
69
African individuals have strong/fragile hair
Fragile
70
Hairs in anagen are hard/easy to pull out
Hard
71
What is the most common hair loss condition?
Alopecia areata
| an autoimmune disease targeting patches of hair papilla, hair isthmus isn't targeted so hair can grow back
72
What is hirsutism?
Inappropriate growth of hair (in women) -> can be physiological or caused by excess androgen hormones
73
What are the 3 skin glands found in the dermis?
- Sebaceous
- Apocrine
- Eccrine
74
Describe sebaceous glands
- Start producing an oily sebum during puberty
- Holocrine secretions sent into pilary (hair) canal
- Found everywhere but the palms and soles
- Largest glands in the face, chest and upper back
- Function is to control moisture loss and protect from fungal infection
- Can lead to acne if they produce excess sebum
75
Describe apocrine sweat glands
- Empties oily fluid into pilary (hair) canal
- May be involved in sex hormone secretion but function is unknown
- Androgen dependent
- Found in the axillae, groin, eyelids, ears, mammary and perineal regions
76
Describe eccrine sweat glands
- These are the true sweat glands
- Found on all skin surfaces except lips and genitals
- Functions include cooling by evaporation and moistening of the palms and soles for gripping
- Sympathetic supply can be stimulated by mental, thermal or taste cues
77
What are the 6 main functions of the skin?
- Barrier function
- Metabolism & detoxification
- Thermoregulation
- Immune defence
- Communication
- Sensory functions
78
What may the skin be a barrier against?
- Physical: trauma, friction, UV radiation
- Chemical: irritants, allergens, toxins
- Pathogens: bacteria, viruses
79
How do melanocytes help protect against UV radiation?
Melanin pigment in basal cells absorbs UV rays to protect DNA in the cell's nuclei
80
Give 2 examples of metabolism via the skin
- Ultraviolet B acts on a precursor (7-dehydrocholesterol) to produce vitamin D3 in the skin
- Thyroid hormone T4 is converted to more metabolically active T3
81
How is the skin involved in thermoregulation?
- Protects against heat and cold via sweating and vasodilation/contraction
- Warm/ cold thermoreceptors
82
When the body is too hot, the superficial/deep vascular plexus in the dermis will be more dilated
Superficial (to lose heat)
83
When the body is too cold, the superficial/deep vascular plexus in the dermis will be more dilated
Deep (to conserve heat)
84
How is the skin involved in immune defence?
- Non-specific responses e.g., itching to remove a parasite
| - Specific cellular immune responses (see immunology)
85
Why is the skin thought to be involved in communication between individuals?
Skin colour, smell, anomalies and level of exposure influence how other people view an individual
86
What different sensory functions does the skin have?
Touch, pressure, vibration, pain, itch, heat, cold
87
What is meant by the pilosebaceous unit?
The hair follicle and the surrounding accessory appendages
88
What is bullous pemphigoid?
An autoimmune disease which targets proteins in the dermo-epidermal junction, resulting in the formation of blisters
89
Describe the structure of the nails:
- Nail plate =
- Matrix =
- Cuticle =
- Hyponychium =
- Nail plate = plate of cells filled with hard keratin sit on the nail bed
- Matrix = found beneath the nail and epidermis, cells divide then produce hard keratin
- Cuticle = extension of the skin fold covering the nail root
- Hyponychium = secures the free nail edge
90
What is the difference between primary and secondary intention wound healing?
Primary wound healing -> the edges of the wound are connected, e.g., by a suture, usually resulting in more rapid wound healing
Secondary wound healing -> the edges of the wound cannot practically be joined together so the wound is left open to heal on its own
91
What are the 3 stages of wound healing?
1. Inflammation - platelets form initial clot, leucocytes phagocytose bacteria
2. Proliferation - granulation tissue forms, fibroblasts lay down matrix and contract wound, angiogenesis occurs
3. Tissue remodelling - new tissue becomes scar tissue as fibroblasts lay down collagen
92
What is the difference between the appearance of superficial and deep burns?
Superficial - erythematous, wet, painful, blistering
Deep - white or black/charred, dry, numb
93
Which layers of the skin are affected by 1st-3rd degree burns?
1st -> epidermis
2nd -> epidermis and dermis
3rd -> extends beyond the dermis (full thickness burn)
94
What factors can delay wound healing?
- Infection
- Poor arterial supply
- Poor venous return
- Repeated trauma/friction
- Poor nutrition
- Underlying disease e.g., diabetes, anaemia
95
What are the 4 stages of pressure sore development?
1. Skin is unbroken but reddened and tender
2. Skin is swollen and blisters may be present
3. Sore breaks through the skin and crater-like ulcers are present. The wound is prone to infection
4. Sore extends deep into fat, muscle and bone tissue. Eschar may be seen
96
What is eschar?
Blackened dead tissue in deep open wounds
97
What do Odland bodies in the granular layer do?
Process lipids destined for the epidermal permeability barrier
