The Skin Flashcards
Describe the skin
Part of the integumentary system
A sensory organ
Largest organ in the body
Thinnest over eyelids and thickest on palms and soles
Most parts of the body are accessory structures
Superficial layer is epidermis
Layer below is dermis
What are the two major classes of skin
Hirsute - thin, hairy skin which covers grater parts of the body
Glabrous - which covers the surfaces of palms, soles and flexor surfaces of the digits
What are the 5 layers of the epidermis
Stratum basale ( lowest )
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum ( most superficial )
Describe the stratum lucidum
Smooth almost translucent layer, only found in thick skin
The keratinocytes & dead and flattened, the keratinocytes are packed with eledin ( clear protein rich in lipids which provides a barrier to water
Keratinocytes- produce keratin which helps protect the skin and underlying tissue from heat, microbes and chemicals and lamellar granules which release a waterproof sealant
Contains the precursor to keratin
Describe the stratum corneum
Most superficial epidermal layer
25 30 layers of keratinocytes, they are dry & dead filled with keratin and surrounded by lipids, help prevent microbes & dehydration of deeper tissues
Provides a mechanical and protective layer against abrasion, light, heat and chemicals
Regular shedding of cells and replaced by new cells that are pushed upwards
Lamellar granules in this layer help make the skin water repellent
Describe keratinisation and growth of the epidermis
Stem cells divide to produce keratinocytes
As keratinocytes are pushed up towards the surface, they fill with keratin
Keratinisation is replacement of cell contents with the protein keratin - occurs as cells move to the skin surface over 2-4 weeks in 1mm of skin
Epidermal growth factor ( EGF ) and other hormone like proteins play a role in epidermal growth
Nutrients & oxygen diffuse to the avascular epidermis from blood vessels of dermis
Describe the dermis
Dermal papillae anchor the epidermis and dermis - blisters occur when trauma separates these 2 layers and serous fluid collects between them
In the fingers, soles and feet it’s arranged in parallel lines giving a ridged appearance = fingerprints
Tough and elastic - connective tissue & collagen fibres interlaced with elastic fibres, ruptures of these fibres = stretch marks
Dermal cells - fibroblasts, macrophages & mast cells
Dermal structures- small blood & lymph vessels, sensory nerve endings, sweat glands and ducts
Sub- cutaneous layer is under the dermis
Describe the sensory receptors in the skin
Meissner’s corpuscle - light pressure
Pacinian corpuscle - deep pressure
Free nerve ending pain
Information travels from these receptors to the spinal cord by sensory nerves & conducted to the sensory area of the cerebrum where they are perceived
Describe the sweat glands
Eccrine - open, watery substance, not fully active in infants, present on palms, soles of feet, axillae and groins
Apocrine - sweat glands develop/activate during puberty and secrete alongside hair follicles, mix with bacteria on skin= body odour
Sebaceous glands - secrete into hair follicles, scalp, face, axillae and groin, waterproof barrier, bacterial and fungicidal, prevents cracking and drying on exposure to heat and sunlight, less active in elderly and infants
What are the functions of the skin
Protection
Regulation of body temperature
Formation of vitamin D
Cutaneous sensation
Excretion
Absorption
Describe the protection function of skin
Forms a relatively waterproof layer, provided mainly by its superficial keratinised layer, which protects the deeper, more delicate structures
Acts as a barrier against - invasion by microorganisms, physical agents, chemicals and dehydration
Contains Langerhans cells
Melanocytes secrete the pigment melanin, which protects against harmful ultraviolet rays of sunlight
Abundant sensory nerve endings in the dermis enable very accurate perception
Describe regulation of body temp function of skin
Maintaining constant temp
Heat production- when metabolic rate increases, body temp rises ; when it decreases, body temp falls, Some energy released during metabolic activity is in the form of heat ; the most active organs produce most heat
Heat loss - radiation ( radiate heat away from body temperature), evaporation ( body cools down), conduction ( objects take up heat) and convection ( air passes over exposed parts of the body)
Describe formation of vitamin D function of skin
A lipid based substance present in the skin called 7-dehydrocholesterol is converted to vitamin D by sunlight
Describe cutaneous sensation function of skin
Sensory receptors including some specialised structures e.g. pacinian corpuscles
Stimulation generates impulses in sensory nerves, which are transmitted to the cerebral cortex where they are perceived
Some areas have more abundant sensory receptors than others, causing them to be especially sensitive e.g. lips and fingertips, collectively the sensory receptors enable fine discrimination between wide- ranging sensations on very specific areas of the skin
Describe absorption function of skin
Property is limited but substances that can be absorbed include:
Some drugs when applied as a transdermal patches e.g. nicotine patches
Some toxic chemicals e.g. mercury
Some medications e.g. chemotherapy
Describe excretion function of the skin
Minor excretory organ for some substances, including:
Sodium chloride in sweat
Urea, especially when kidney function is impaired
Aromatic substances e.g. garlic and other spices
Describe the association with skin and aging
Changes may be caused by genetics, sun and weather exposure
Aging = both the skin & mucous membranes become thin & fragile, the dermis is thinner & subcutaneous tissue is diminished
Fewer capillaries & cell proliferation is decreased, resulting in slower wound healing & atrophy of the glands
Number of sensory receptors in the skin and mucosa decline
The skin is often dry & appears wrinkled as elastic fibres are reduced & collagen fibres become less flexible
Melanocytes decrease causing greying of hair & skin
Describe wound healing
Is a complex process that occurs naturally when the skin is damaged
This can take from 3 days to many months dependent on the severity and nature of the damage
What can inhibit = disease, infection, stress, poor nutrition, medication, pre-existing medical conditions and lifestyle
Describe the 1st stage of wound healing
Inflammation- within the 1st few hours the wound surfaces became inflamed, a blood clot ( mainly fibrin ) and cell debris fill the gap between them
Describe second stage of wound healing
Proliferation:
Epithelial cells proliferate across the wound, the epidermis meets & grows upwards until full thickness is restored, the clot above the new tissue becomes the scab, which separates after 3- 10 days
Granulation tissue, consisting of new capillary buds, phagocytes & fibroblasts develop invading the clot & restoring blood supply to the wound
Fibroblasts continue to secrete collagen fibres as the clot & bacteria are removed by phagocytosis, when granulation tissue reaches the level of the dermis, epithelial cells at the edges proliferate and grow towards the centre
Describe 3rd stage of wound healing
Maturation:
The granulation tissue is gradually replaced by fibrous scar tissue
Rearrangement of collagen fibres occurs & the strength of the wound increases
In time the scar becomes less vascular
During fibrosis scar tissue replaces granulation tissue, usually over several months, until the full thickness of the skin is restored
Scar tissue is shiny, no sweat glands, hair follicles or sebaceous glands
Describe the pressure damage
Pressure ulcers can develop when a large amount of pressure is applied to an area of skin a short period of time, they can also occur when less pressure is applied over a longer period of time
The extra pressure disrupts the flow of blood through the skin, without a blood supply, the affected skin becomes starved of O2 and nutrients and begins to break down, leading to an ulcer forming
Pressure ulcers tend to affect people with health conditions that make it difficult to move, especially those confined to lying in a bed or sitting for prolonged periods of time
