6.1 - Anatomy of the Skin Flashcards
What is the largest organ of the body?
The skin is the largest organ in the human body and comprises approximately 8% of total body mass.
What are the functions of the skin?
Protection:
- Part of innate immune system = barrier to infection.
- Keratinised stratified epithelium.
- Low moisture content and low pH.
- Antimicrobials: sebum and sweat.
- Normal microflora at specific sites.
- Regular sloughing off of surface layer.
- Abrasion/trauma.
- Infection.
- UV light - Pigmentation provides a protection against UV exposure.
- Dehydration.
- Water resistant (not water proof).
Thermal regulation:
- Insulation (fat keeps you warm) - Subcutaneous fat reduces heat loss.
- Cooling
- Sweat cools you down = evaporative cooling.
- Acetylcholine-releasing sympathetic nerve fibres stimulate sweat secretion.
- If body temperature is too high inhibitory signals are sent to sympathetic centres leading to vasodilation of skin blood vessel.
- If body temperature is too low stimulatory signals are sent to the same sympathetic centres leading to vasoconstriction of skin blood vessels.
Sensory reception.
- Mechanoreceptors: fire when surrounding tissue experiences a mechanical force (e.g. pressure, stretch, touch, irritation, vibration).
- Thermoreceptors: sensitive to changes over a range of temperatures.
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Nociceptors: pain receptors. Respond to:
- Tissue damage.
- Extremes of temperatures.
- Excess mechanical stimuli.
- Inflammation.
Vitamin D Production
- In the skin: 7-dehydrocholesterol is converted to vitamin D3 (cholecalciferol) by UV irradiation.
- In the liver: vitamin D3 is hydroxylated to 25-OH D3
- In the kidney: 25-OH D3 is hydroxylated to 1, 25-OH D3 which is 1000-fold more potent than its precursors.
Communication - e.g. blushing, raised eyebrows.
What are the 3 distinct layers of the skin?
Three distinct layers:
- Epidermis
- Dermis
- Hypodermis
What are 4 cells in the epidermis?
- What is cornification?
Epidermis
The epidermis is the most superficial layer of the skin, and is largely formed by layers of keratinocytes undergoing terminal maturation. This involves increased keratin production and migration toward the external surface, a process termed cornification.
There are also several non-keratinocyte cells that inhabit the epidermis:
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Melanocytes – responsible for melanin production and pigment formation.
- Note – individuals with darker skin have increased melanin production, not an increased number of melanocytes.
- Langerhans cells – antigen-presenting dendritic cells.
- Merkel cells – sensory mechanoreceptors.
What are the 5 layers of the epidermis?
- In which layer does mitosis of keratinocytes occur?
- In which layer do the keratinocytes lose their nucleus?
- What happens in the stratum corneum?
- How long for keratinocyte to transverse layers?
The epidermis can be divided into layers (strata) of keratinocytes – this reflects their change in structure and properties as they migrate towards the surface. From deepest to most superficial, these layers are:
- Stratum basale – mitosis of keratinocytes occurs in this layer.
- Stratum spinosum – keratinocytes are joined by tight intercellular junctions called desmosomes.
- Stratum granulosum – cells secrete lipids and other waterproofing molecules in this layer.
- Stratum lucidum – cells lose nuclei and drastically increase keratin production.
- Stratum corneum – cells lose all organelles, continue to produce keratin.
A keratinocyte typically takes between 30 – 40 days to travel from the stratum basale to the stratum corneum.
Which layer of the skin gives it its strength?
The epidermis is the layer that gives strength to the skin.
What is the blood supply to the epidermis?
NONE = It is avascular.
What layer of the skin are Merkel cells in?
Merkel cells reside in the stratum basale of the epidermis
Where are Langerhan’s cells found?
Stratum spinosum of epidermis
Where are melanocytes found?
Melanocytes = stratum basale of epidermis
What are the 2 layers of the Dermis?
What are 4 cells/structures in the dermis?
- Fibroblasts – these cells synthesise the extracellular matrix, which is predominantly composed of collagen and elastin.
- Mast cells – these are histamine granule-containing cells of the innate immune system.
- Blood vessels and cutaneous sensory nerves
- Skin appendages – e.g. hair follicles, nails, sebaceous and sweat glands. Although present in the dermis, these structures are derived from the epidermis which descend into the dermis during development.
What are 2 types of deep pressure receptors of the Dermis?
The dermis has deep pressure receptors:
Pacinian corpuscle: nerve receptors in the dermis for vibration and pressure.
Meissner’s corpuscle: nerve receptors in the dermis for light touch.
What is the Hypodermis?
3 functions?
What is the structure of a hair follicle?
Describe the Cross-section of a hair.
Hair Follicle Structure
- Shaft: superficial portion.
- Root: below the surface.
- Cuticle: outermost layer of hair.
- Hair develops in follicles (downward continuation of epidermis).
In which layer of the skin are the appendages located?
= Reticular dermis (deepest dermal layer)
What are 3 types of corpuscles of the dermis and their functions?
How do hairs grow?
Hair Growth
- At the base of the follicle = hair papilla.
- Contains blood vessels and nerves (nourishes hair).
- Bulb: contains matrix – epithelial cells responsible for growth.
- Contains melanocytes.
What is the embryological origin of skin?
Epidermis = Ectoderm
Dermis & Subcut = Mesoderm
Nails = Ectoderm
What are the 2 types of hair follicles? Where do each of them grow?
Vellus = short & fine - most of body
Terminal = longer, thicker, coarse = pubis, scalp, beard, eyelashes
What 3 things form the pilosebaceous unit?
The pilosebaceous unit is composed of a hair follicle, arrector pili muscle, and sebaceous gland.
- What are the 2 types of sweat glands?
- Functions of each?
- Where are each located?
- What do they secrete?
- Which are associated with a hair follicle?
- When do apocrine glands form?
- Eccrine glands – the major sweat glands of the human body. They release a clear, odourless substance, comprised mostly of sodium chloride and water – which is involved in thermoregulation.
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Apocrine glands – larger sweat glands, located in the axillary and genital regions. These apocrine glandular products can be broken down by cutaneous microbes, producing body odour.
- Develop at puberty
Understand the nature and clinical importance of relaxed skin tension lines.
