Notes
Structure
- The skin has a stratified squamous epidermis (avascular) and a connective tissue dermis (vessels, nerves, glands). The hypodermis lies deep to the skin.
- Epidermal layers from deep to superficial: basale, spinosum, granulosum, lucidum (thick skin only), corneum. Melanocytes make melanin.
- Accessory structures: hair, nails, eccrine and apocrine sweat glands, sebaceous glands.
Functions
- Protection, temperature regulation (vasodilation and sweating versus vasoconstriction), sensation, vitamin D synthesis, blood reservoir and excretion.
Injury and disease
- Burns are first-, second- or third-degree by depth. The rule of nines estimates burned area. Fluid loss and infection are the greatest threats.
- Healing involves a clot, granulation tissue, regeneration and fibrosis. Skin cancers: basal cell, squamous cell and melanoma (ABCDE).
Topics in this unit
Each topic has its own short notes and practice.
Practice
Constricted vessels reduce blood flow to the skin, so less heat is lost.
The stratum lucidum is a thin clear layer present in thick skin.
Blistering and partial dermal involvement indicate a second-degree (partial thickness) burn.
Loss of the skin barrier causes rapid water and electrolyte loss and exposes the body to microbes.
Eccrine glands secrete sweat across most of the body.
Keratin is the tough, waterproof structural protein in hair, nails and the stratum corneum.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A lifeguard spends summer days in strong sunlight. Her skin becomes darker, and after one long day she gets a red, painful, non-blistered sunburn. At a check-up, a doctor finds a mole that is asymmetrical, has an irregular border, and has grown over the last two months.
(a) Explain why the skin darkens with sun exposure and what advantage this gives.
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Melanocytes in the stratum basale make more melanin when exposed to UV light. Melanin absorbs UV radiation and protects the DNA in skin cells from damage.
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(b) Classify the sunburn by degree and identify the layer involved.
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It is a first-degree burn involving only the epidermis.
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(c) Which ABCDE features does the mole show, and what should the lifeguard do?
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It shows asymmetry (A), irregular border (B) and evolving change (E). These are warning signs of melanoma, so she should have it evaluated promptly by a doctor, such as with a biopsy.
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