4.2 - Skin Flashcards
List 3 functions of melanocytes.
- Pigmentation
- Protection from UV radiation
- Antigen-presenting (dendritic)
Why do Caucasians have lighter skin?
Melanocytes produce less melanin
Note: Caucasians and POC have the same NUMBER of melanocytes
List 4 conditions fair-skinned people are more susceptible to.
- Sunburn
- Freckling
- Aging
- Skin cancer
What is the most common skin cancer?
Basal cell carcinoma
What causes basal cell carcinoma?
Neoplasm of basal cells
What causes malignant melanoma?
Neoplasm of melanocytes
What causes moles?
Benign growths of melanocytes
What causes vitiligo?
Auto-immune destruction of melanocytes
Why might vitiligo have a symmetrical nature?
Melanocytes all derive from the neural crest
What causes alopecia?
Auto-immune destruction of hair follicles
What causes male-pattern hair loss?
Auto-immune destruction of hair follicles in response to testosterone
Compare alopecia areata, alopecia totalis, and alopecia universalis
Areata: spots of hair loss
Totalis: total scalp hair loss
Universalis: loss of all body hair
What causes scarring alopecia?
Damage to stem cells in hair follicles as a result of scarring
Describe the appearance of actinic keratosis.
Rough, scaly patches of skin; pre-cancerous
What causes actinic keratosis?
Dysplasia of keratinocytes due to sun exposure
What causes psoriasis?
Extreme proliferation of the basal layer reduces cell turnover to 3-7 days, manifesting as scaling
What causes freckles?
UV-induced hyper-production of melanin
What causes actinic lentigo (a.k.a. age spots or liver spots)?
UV-induced hyperplasia of melanocytes
Why do freckles fade while liver spots do not?
Freckles: same number of melanocytes transiently produce more melanin
Liver spots: number of melanocytes increases
What causes sunburn?
Keratinocyte apoptosis due to sun exposure
List 2 symptoms of sunburn.
- Reddening
2. Swelling
List 4 skin conditions associated with long-term sun exposure.
- Actinic keratosis
- Squamous cell carcinoma
- Basal cell carcinoma
- Malignant melanoma
What are 2 treatments for psoriasis?
- Vitamin D analogues (promote differentiation)
2. Steroids (suppress inflammation)
List 4 functions of skin.
- Barrier
- Sensation
- Thermoregulation
- Psychosexual communication
What are the skin’s 2 means of thermoregulation?
- Vascular (i.e., dilation and constriction of blood vessels)
- Sweating (i.e., evaporation of sweat causes cooling)
What component of the skin allows it to perform its sensory function?
Sensory nerves
What layer of the skin provides a barrier against exogenous materials?
Stratum corneum
What are the 4 main layers of the epidermis?
- Stratum CORNEUM
- Stratum GRANULOSUM
- Stratum SPINOSUM
- Stratum BASALE
Which epidermal layer is only present in the palms and soles?
Stratum LUCIDUM
What shape are the cells of the stratum basale?
Columnar or cuboidal
What shape are the cells of the stratum spinosum?
Irregular polyhedral
What holds the cells of the stratum spinosum together?
Desmosomes
What shape and colour are cells of the stratum granulosum?
Squamous
Dark (due to granules of keratohyalin)
What shape and colour are the cells of the stratum lucidum?
Squamous
Translucent
What is the predominant cell type in the epidermis?
Keratinocytes
What do keratinocytes produce?
Keratins
What is the function of keratins?
Strength
Where do keratinocytes divide?
Stratum basale
Where do keratinocytes lose their ability to divide and begin to differentiate?
Stratum spinosum
Where do keratinocytes lose their plasma membranes and begin to differentiate into corneocytes?
Stratum granulosum
Where would you find keratohyallin granules?
Stratum granulosum
List 5 components of keratohyallin granules.
- Keratins (intermediate filaments)
- Phospholipases (degrade plasma membrane)
- Fillaggrin (binds keratins)
- Involucrin (forms cornified envelope)
- Transglutaminases (cross-link proteins)
What is the role of filaggrin?
Binds keratins in the skin
Remember: filament aggregating
What layer contains flattened corneocytes?
Stratum corneum
How long does it take for a keratinocyte to travel from the basal layer to the stratum corneum?
28 days
What happens to keratinocytes in the stratum basale?
Divide
What happens to keratinocytes in the stratum spinosum?
Stop dividing
Begin to differentiate
What happens to keratinocytes in the stratum granulosum?
Lose their cell membranes
Begin to differentiate into corneocytes
What is the main cell type found in the stratum corneum?
Flattened corneocytes
How do corneocytes break down?
Desmosomes weaken
Corneocytes sloughed off as squames (a.k.a. scales)
What thickens the cornified layer of skin?
Exposure to abrasion
Describe the process of keratinocyte differentiation.
Stratum basale: cells divide
Stratum spinosum: cells stop dividing and begin to differentiate
Stratum granulosum: cells lose their plasma membranes and begin to differentiate into corneocytes
Stratum corneum: flattened corneocytes form a barrier
What is the function of dendritic cells?
Antigen-presenting
What are melanocytes?
Dendritic cells of neural crest origin found in the stratum basale
What is the origin of melanocytes?
Neural crest
Where are melanocytes found?
Stratum basale
What is melanin?
Pigment produced by melanocytes
What are Langerhans cells?
Dendritic cells of bone marrow origin found in the stratum spinosum
What is the origin of Langerhans cells?
Bone marrow
Where are Langerhans cells found?
Stratum spinosum
Compare melanocytes and Langerhans cells.
Melanocytes: dendritic, neural crest origin, found in the stratum basale
Langerhans cells: dendritic, bone marrow origin, found in the stratum spinosum
What are Merkel cells?
Mechanoreceptors receptors located in the stratum basale
In which part of the body are Merkel cells (mechanoreceptors) particularly abundant?
Fingertips
How would you determine the prognosis in malignant melanoma?
Depth of malignant cell penetration
Note: neoplasm above the basement membrane is associated with good prognosis
What is the prognosis for a malignant melanoma with a Breslow thickness of < 1 mm?
5-year survival rate of 95-100%
What is the prognosis for malignant melanoma with a Breslow thickness of > 4 mm?
5 year survival rate of < 50%
What are the ABCD’s of melanoma and what are they used for?
- Asymmetry
- Border
- Colour
- Diameter
Used to distinguish melanomas from benign moles
What causes moles?
Benign growths of melanocytes
What is the dermo-epidermal junction?
The area where the basement membrane anchors the epidermis to the underlying dermis
What is epidermolysis bullosa?
A group of inherited disorders that cause the skin to blister
Remember: “butterfly children”
What causes epidermolysis bullosa?
Defects in type VII collagen synthesis weakens anchoring at the dermo-epidermal junction
What type of connective tissue is the dermis?
Dense irregular
Which layer gives the skin its resilience?
Dermis
What is the characteristic structure of the dermis? (Hint: must resist shear in multiple planes.)
Basket-weave
The dermis consists of ECM and cellular structures. List 6 of its cellular structures.
- Blood vessels
- Lymph vessels
- Nerves
- Fibroblasts
- Adipocytes
- Immune cells
How are keloids (lumpy scars) formed?
Excessive fibroblast activity following wounding
What is hyperhidrosis?
Excessive sweating
Where would you find sebaceous glands?
At the base of hair follicles
What type of secretion would you find in sebaceous glands?
Holocrine
What causes acne?
Obstruction of sebaceous glands
Why is acne more common in the face?
Sebaceous glands are large and abundant
List 3 triggers for acne.
- Increased sebum production at puberty
- Infection by normally harmless skin bacteria
- Abnormal differentiation of sebaceous glands, leading to their obstruction
Compare intrinsic and extrinsic aging of the skin.
Intrinsic: chronological
Extrinsic: caused by sun exposure
What causes solar elastosis?
Excess elastic fibre deposition in the dermis due to UV exposure
What causes stretch marks?
Collagen fibres oriented along stress lines in the dermis
What causes hair to stand on end?
Contraction of arrector pilli mucles
Where would you find eccrine (i.e., merocrine) sweat glands?
Most of the skin
Where would you find apocrine sweat glands? (Nb apocrine sweat glands use MEROCRINE secretion.)
Armpits, nipples, genitals, anus
Compare the function of eccrine sweat glands and apocrine sweat glands.
Eccrine: thermoregulation
Apocrine: odour production
Compare the secretions of eccrine sweat glands and apocrine sweat glands.
Eccrine: watery
Apocrine: protein-rich
Sweat itself is odorless. How may it cause body odour?
Proteins in sweat from apocrine glands are broken down by bacteria on the skin surface, releasing odor
What causes port wine stains?
Malformed capillaries
How might mast cells cause local edema?
Release of heparin, histamine, and cytokines increases blood flow to the area
What is the effect of allergens on mast cells?
Trigger de-granulation, releasing heparin, histamine, and cytokines to launch an immune response
Compare urticaria and angioedema.
Urticaria: allergic response, edema of the upper dermis
Angioedema: allergic response, edema of the lower dermis
What is the effect of leprosy on nerves?
Damage and inflammation
List 2 causes of diabetic foot ulcers following injury.
- Damage to nerves impedes SENSATION
2. Damage to vasculature impedes HEALING
What are the 4 mechanoreceptors of the skin?
- Pacinian corpuscles
- Meissner’s corpuscles
- Ruffini’s corpuscles
- Merkel cells
What happens in Raynaud’s phenomenon?
Cold-induced spasm of arteries blocks blood flow to the fingers and toes
