BIOL1019 Chap.7 The Integumentary System
The Integumentary System
The skin is an organ with jobs well beyond covering the body: it protects, excretes salts and water, helps regulate temperature, synthesises vitamin D3, stores lipids and detects touch, pressure, pain and temperature. This chapter stacks the epidermal strata from the dead keratinocytes of the stratum corneum down to the dividing cells of the stratum basale, then the papillary and reticular dermis and the hypodermis.
It compares apocrine and merocrine sweat glands, explains skin colour, the vitamin D pathway, epidermal and deep wound healing and burn depth, and finishes with thermoregulation, where the skin works through the sympathetic nervous system and the hypothalamus.
The course's practice short answers on this topic ask how the skin regulates temperature with help from other systems and how the skin and nails reveal clinical information, so both appear here as worked answers and practice questions with their marking points.
What this chapter covers
- 01
Functions of the integument
- 02
Epidermal strata and cell types
- 03
Papillary and reticular dermis
- 04
Melanin, carotene and skin colour
- 05
Hair, sebaceous and sweat glands, nails
- 06
Wound healing and burns
- 07
Thermoregulation and perspiration
- 08
Vitamin D synthesis and rickets
Worked example · free
Why the skin turns blue and the nails change
- +1Cyanosis: a reduced oxygen supply makes the skin look bluish because less oxygenated haemoglobin colours the blood.
- +1Skin turgor: the elasticity of the dermis lets skin spring back, so a slow return suggests dehydration.
- +1Nail changes: clubbing can point to lung, cardiovascular or inflammatory bowel disease, and blue nails to cyanosis.
Key terms
- Stratum basale
- The deepest epidermal layer, holding dividing stem cells, melanocytes and Merkel cells.
- Merocrine sweat gland
- A widespread gland that secretes water and ions onto the skin surface for cooling.
- Insensible perspiration
- Water lost by evaporation of interstitial fluid through the stratum corneum, without sweat gland activity.
- Skin turgor
- The ability of skin to return to its shape after pinching, used to assess hydration.
- Cleavage lines
- Parallel bundles of dermal collagen and elastic fibres that determine how a cut gapes and heals.
- Melanocyte
- An epidermal cell that makes melanin and transfers it to keratinocytes to protect DNA from sunlight.
- Calcitriol
- The active form of vitamin D, made in the kidney, that increases calcium and phosphate absorption from the gut.
The Integumentary System FAQ
Why does it take about four weeks to replace the epidermis?
New keratinocytes are produced by stem cells in the stratum basale and are pushed upward through the spinosum and granulosum, where they make keratin and begin to die, before reaching the stratum corneum and being shed. The course gives about four weeks for a cell to travel from the basale to the surface.
What is the difference between UVA and UVB damage?
UVA triggers melanin production, which is tanning, and adds to skin damage over the long term. UVB is the chief cause of sunburn and damages the DNA of epidermal cells, which can disable tumour-suppressor genes and lead to uncontrolled cell division. Melanin passed to keratinocytes is the skin's own shield for that DNA.
How serious is a burn of a given depth?
The course grades burns by depth. Superficial burns cause discomfort and heal in days, partial-thickness burns are painful and take weeks, and full-thickness burns bring complications and take months or years. Burns covering more than 20% of the body surface can be life-threatening, and burns on areas such as the hands, feet or major joints need medical care.
Why do apocrine glands cause body odour while merocrine glands do not?
Apocrine sweat glands, found in the armpits, around the nipples and in the groin, open into hair follicles and secrete a sticky, cloudy fluid that can produce odour, and they only become active at puberty. Merocrine glands are spread widely, especially on the palms and soles, and release watery, salty sweat directly onto the skin for cooling.
Exam move
Draw the skin from surface to fat and label each stratum with one feature and one cell type, then add the receptors of the dermis. Make two comparison tables, sweat glands and burn depths, and practise the deep wound healing phases as a numbered sequence. Finish by writing a thermoregulation answer that names the receptors, the hypothalamus, the sympathetic nerves and every effector.
Before Test 1, practise a three-mark thermoregulation answer and a two-mark answer on clinical signs, timing each one, since these mirror the shape of the short answers the course publishes.
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