Flashcards in Skin Deck (160):
In what ways does the macroscopic structure of human skin vary?
What causes variation in skin colour?
What causes variation in skin hairiness?
What areas of the body are hair free?
Palms, soles of feet, lips
How does body hair vary between sexes?
Facial and more profuse body hair growth in men
How does hair vary with age?
How does hair vary between ethnicity?
What causes variation in laxity of skin?
What is the importance in variations of macroscopic state of skin?
Influence on susceptibility or manifestations of skin disease
What is vitiligo?
What is the importance of ethnicity in vitiligo?
More psychosocial impact if affects visible areas of dark-skinned races
What is alopecia areata?
Autoimmune hair loss
What may affect the psychosocial impact of alopecia areata?
If it effects scalp, especially in women
How does the affect of UV-induced abnormalities differ between different skin types?
- Sunburn doesn’t occur in black skin
- Skin ageing in whites
- Skin cancer in whites
What skin cancers are more common in whites?
- Basal cell carcinoma
- Malignant melenoma
What is much of skin ageing and wrinkling due to?
UV induced injury to dermal and elastin
What is the problem with basal cell carcinomas?
Relatively benign cancer, but problematic if left because can cause ulcers
What is normal human skin made up of?
Epidermis and dermis
How does the dermis differ from the epidermis?
It is much thicker
What does the dermis contain?
- Blood vessels
- Arrector pilli muscles
- Sweat glands
What does the epidermis consist of?
- Stratum corneum
- Granular layer
- Prickle cell layer
- Basal layer
What does the epidermis have on the surface?
What does the stratum corneum consist of?
Layers of dead cells called corneocytes
What does the prickle cell layer do?
Interdigitates with the dermis
What kind of epithelium does the epidermis have?
Stratified squamous keratinised epithelium
What is the epidermis mainly made up of?
Keratinocytes and their products
What is keratinocytemitosis?
Where does keratinocytemitosis occur?
Mainly in the basal cell layer
What happens when daughter keratinocytes?
They move upwards to form the prickle cell layer
What happens as daughter keratinocytes move upwards?
Terminal differentiation begins
What happens when keratinocytes undergo terminal differentiation?
They lose their ability to divide
What to keratinocytes synthesise?
What are keratins?
Heterodimeric fibrous proteins
What do keratins contribute to?
The strength of the epidermis
What are keratins the main constituents of?
Hair and nails
What joins prickle cells
Prickle like desmosomes
What are desmosomes?
What are basal keratinocytes full of?
What happens to basal keratinocytes?
They undergo cell division
What abrupt changes occur in the granular layer?
What are the features of corneocytes?
What does the granular layer contain?
What is keratohyalin?
Aggregations of keratins, other fibrous proteins (e.g. filaggrin, involucrin) and enzymes
What does filaggrin do?
Helps aggregate keratin
What does involucrin do?
Forms major part of corneocyte envelope
What do the enzymes in keratohyalin do?
What are enzymes that degrade the phospholipid bilayer called?
What is the stratum corneum made up of?
Layers of flattened corneocytes
What is the major role of the stratum corneum?
Skin barrier formation
What is the barrier function of skin?
- Physical and chemical barrier
What is the transit time of a keranocyte from the basal layer to the stratum corneum?
What type of cells are melanocytes?
Where do melanocytes originate from?
Where do melanocytes occur?
At intervals along the basal layer of the epidermis
When are melanocytes difficult to see?
Without special stains
What do melanocytes produce?
What is melanin?
The main pigment that gives skin its colour
How do melanocytes differ in black/tanned skin?
They produce more melanin, but not an increased number of melanocytes
What kind of cells are Langerhans cells?
What is the origin of Langerhans cells?
Where are Langerhans cells found?
Scattered through the prickle cell layer
When is it difficult to see Langerhans cells?
Without special stains
What is the purpose of Langerhans cells
Highly specialised capacity to present antigens to T lymphocytes
What do Langerhans cells mediate?
Give an example of a stain that is used to show Langerhans cells and melanocytes?
S100 monoclonal antibodies stains
What happens to mature melanosomes?
They are transferred to neighbouring keratinocytes by pigment donation
What does pigment donation involve?
Phagocytosis of tips of dendritic processes
What do we need melanosomes for?
To protect DNA
Why is it important to protect DNA?
So we don’t get cancer
What do we need to balance DNA protection with?
The need for vitamin D
Where do melanosomes come to lie?
On the outer side of the cell
How does palmar skin differ from normal skin?
How does scalp skin differ from normal skin?
- Hair follicles and sebaceous glands
- Fat lobules
- Fibrous septae
Give 4 examples of disorders of epidermal components?
- Allergic contact dermatitis
- Malignant melanoma
What is psoriasis?
Abnormal epidermal growth and differentiation
What % of the population is affected by psoriasis?
What causes psoriasis?
What proves that psoriasis is influenced by genetic factors?
It runs in families
What is psoriasis associated with?
Extreme proliferation of epidermal basal layer
What does the extreme proliferation of the epidermal basal layer cause?
Gross thickening of prickle cell layer and production of excessive stratum corneum cells
How does psoriasis manifest clinically?
As excessive scaling
What may psoriasis involve?
Any area of skin, including the scalp
What can the effects of psoriasis be?
Depending on severity, can have severe effects on quality of life, general health, occupation etc
When is psoriasis particularly disruptive?
When it affects the whole body
What is allergic contact dermatitis mediated by?
What are Langerhans cells responsible for?
Presentation of antigens to T lymphocytes and for cutaneous delayed-type hypersensitivity reactions
What causes a malignant melanoma?
Malignant growth of melonocytes
What do melonocytes do?
‘Feed out’ melanin to surrounding keranocytes through dendrites
What do melanocytes to with age?
Often stop functioning in hair follices
What is the result of cessation of function of melanocytes in hair follicles?
What is a malignant melanoma?
An agressive tumour (neoplasm) of melanocytes
What is the most common primary site of malignant melanomas?
What is associated with good prognosis for malignant melanomas?
Retention of the tumour cells above the epidermal basement membrane
What is it called when the malignant melanoma is retained above the epidermal basement membrane?
Superficial spreading melanoma
What is associated with poor prognosis with malignant melanomas?
More penetrating, ‘modular’ melanomas
What are common moles?
Benign growths of melanocytes
When are moles concerning?
When they have irregular colouration or an irregular surface
What is vitiligo?
An autoimmune disease in which immune system attacks melanocytes
How does vitiligo usually present?
In symmetrical, localised areas of skin, causing well-demarcated depigmentation
Where is vitiligo more visible?
In dark skin
What could be the cause of the symmetrical pattern of vitiligo?
Could be that the process is under neural control
Why would it make sense that vitiligo is under neural control?
Melanocytes are derived embryologically from the neural crest
Where is the dermo-epidermal junction?
The basement membrane zone, below the basal layer of the epidermis
What are the features of the dermis?
Tough, fibrous and vascular layer
What makes up the main part of the dermis?
What does the dermis extracellular matrix contain?
- Collagens, especially type I
- Other extracellular matrix components
Other than extracellular matrix, what are the other dermal components?
- Blood vessels
- Lymphatic vessels
- Mast cells
What forms of damage to collagen and elastin are there?
What causes solar elastosis?
Excessive UV exposure
What are stretch marks also known as?
What follows wounding?
What do scars compose of?
Main collagen synthesised by fibroblasts
What results from grossly excessive scar tissue production?
What type of blood vessels are there in the skin?
- Smaller blood vessels in superficial dermis- mainly capillaries, small venules and arterioles
- Interconnecting vesicles
- Larger blood vessels in deeper dermis
Give an example of a birthmark
Port wine stain
What causes a port wine stain?
Congenital malformation of blood vessels
How are tissue mast cells distributed in skin?
Around dermal blood vessels
What is the result of the release of histamine from mast cells?
Causes increased vascular permeability and leakage of plasma into extravascular sites, causing local oedema
What is oedema?
Swelling due to increased tissue fluid
What is the result of local oedema in the skin?
Causes urticaria and angio-oedema
Where may the release of histamine have serious consequences?
In vital structures such as the upper respiratory tract
Where are cutaneous sensory nerves of critical importance?
In transmitting sensation
Give 4 skin appendages
- Hair follicles
- Sebaceous glands
- Sweat glands
What do the hair follicles and the sebaceous glands form?
What kind of sweat glands are there?
Describe the structure of a pilosebaceous unit?
What is the hair sheath?
The projection of epidermis surrounding the hair follicle
What is typically true of sebaceous glands in the adult human face?
The are large and produce sebum
What do sebaceous gland ducts lead to?
How do sebaceous glands secrete?
What is acne?
A skin disease affecting sebaceous glands
What causes acne?
When do the changes in sebaceous glands causing acne occur?
Where are sebaceous glands most abundant?
What is hyperhidrosis?
What causes hyperhidrosis?
What may hyperhidrosis exclusively affect?
Palms and soles
Why is hyperhidrosis often a substantial problem?
How big are apocrine sweat glands?
Where are apocrine sweat glands most abundant?
Axillae, genital and submammary areas
What is the functional value of apocrine sweat glands?
What do apocine sweat glands produce?
Odourless, protein rich, apocrine secretion
What digests the secretions of apocrine sweat glands?
What is the result of the digestion of the secretion of apocrine sweat glands?
What are the main functions of skin?
- Barrier function
- Psychosexual communication
What forms the major barrier function of skin?
The stratum corneum
What does the stratum corneum form?
Major barrier preventing percutaneous absorption of exogenous substances
When must the skin barrier be overcome?
During percutaneous administration of drugs
When may be the barrier function of skin be seriously disrupted?
Diseases such as widespread scaling rashes
What does poor barrier function of skin lead to?
When may skin sensation be lost?
What is critically important in maintenance of body temperature?
What may happen if thermoregulation fails?
What happens in vascular thermoregulation?
What does dilation of skin blood vessels lead to?
What does constriction of skin blood vessels lead to?
- Heat conservation
What may cause a failure of vascular thermoregulation?
- Widespread vasodilation of erythyrodermic psoriasis
- Inability to vasoconstrict in a cold environment
What may be the result of failure to vasoconstrict in a cold environment?
Leads to heat loss, causing the patient to become shivery and potentially hypothermic
How does thermoregulation by eccrine sweating work?
Evaporation of eccrine sweat causing cooling