The Skin Flashcards
Identify the structure making up the skin
Part of the integumentary system (consists of the skin, hair, nails and exocrine glands)
A sensory organ
Largest organ of the body
Thinnest over eyelids; thickest over palms and soles
Two major classes of skin:
Hirsute- thin, hairy skin which covers the greater part of the body
Glabrous- which covers the surfaces of palms, soles and flexor surfaces of the digits
Name the 5 layers of skin
- Stratum basale (stratum germinativum)
- Stratum spinous
- Stratum granulosum
- Stratum lucidum
- Stratum corneum
Describe the 5 layers of the skin
Stratum basale (lowest):
-deepest layer
-attaches the epidermis to the basal lamina, below this lies the layers of the dermis
-this attachment occurs through cells in the stratum basale (dermsomes and hemi dermosomes) bonding via intertwining collagen fibres referred to as the basement membrane. Finger-like folds known as dermal papilla are found in the superficial portion of the dermis and help increase the connection and strength between the epidermis and dermis
-this stratum basale is a single layer of cells- basal cells, these are cuboidal- shaped stem cells that is the precursor of the keratinocytes of the epidermis. Keratinocytes and stem cells divide repeatedly.
-other cells- merkel cells- receptors are responsible for stimulating sensory nerves that the brain perceives as touch (manu in the soles of the feet and palms of hands)
-melanocytes- produces melanin, giving skin and hair it’s pigment and helps project the DNA in the nuclei of living cells of the epidermis from UV damage
Stratum spinosum:
-provides strength and flexibility to the skin
-8-10 layers of keratinocytes formed because of cell division in the Stratum Basale
-the keratinocytes begin the synthesis of keratin and release of water- repelling glycolipid (making the skin relatively waterproof)
-as new keratinocytes are pushed up from the stratum basale into the stratum spinosum, the keratinocytes in the stratum spinosum are moved into the stratum granulosum
-amongst the keratinocytes are dendritic cells called Langerhans cell- functions as a macrophage engulfing bacteria, foreign particles, and damaged cells. Langerhans cells- derived from bone marrow- participate in immune response
Stratum granulosum:
-represents the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata
-3-5 layers of flat dying cells that show nuclear degeneration
-contains lamellar granules that release lipid that repels water
-contains dark-staining ketatohyalin granules, ketatohyalin converts tonofilaments into keratin (which gives the grainy appearance)
Stratum lucidum:
-smooth almost translucent layer. Only found in the thick skin of palms, digits and soles of feet
-the keratinocytes and dead and flattered. The keratinocytes are packed with eleidin- a clear protein rich in lipids produced from ketatohyalin and provides a barrier to water
-keratinocytes- produce the protein 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
Stratum corneum:
-most superficial epidermal layer
-25-30 layers of keratinocytes, they are dry and dead filled with keratin and surrounded by lipids, help prevent microbes and 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 the dermis
Dermal papillae anchor the epidermis and dermis- blisters occur when trauma separates these 2 layers and serious fluid collects between them.
In the fingers, soles and feet dermal papillae are arranged in parallel lines given a ridged appearance = finger prints
Touch and elastic - connective tissue and collages fibres interlaced with elastic fibres. Rupture of these fibres = stretch marks
Dermal cells- fibroblasts, macrophages and mast cells- all found in the dermis
Dermal structures- small blood and lymph vessels, sensory nerve endings, sweat glands and ducts, hairs, arrector pili muscles and sebaceous glands
Sub- cutaneous layer is under the dermis
Describe the sensory receptors in the skin
Meissner’s corpuscle- light pressure
Pacunian corpuscle- deep pressure
Free nerve ending pain
Ruffinis, krauses(bulbs) and merkel discs
Information travels from these receptors to the spinal cord by sensory nerves and conducted to the sensory area of the cerebrum where they are perceived
Describe sweat glands
Eccrine- open, watery substance (develop during 4th month of gestation), 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 the hair follicles, scalp, face, axillae and groin. Waterproof barrier, bacterial and fungicidal, prevent cracking and drying on exposure to heat and sunlight. Less active in elderly and infants = skin prone to maceration from moisture
List the functions of the skin and their importance in health
- Protection
-has a waterproof layer, provided by its superficial keratinised layer, which protects the deeper, more delicate structures. It’s an important non-specific defence mechanism which acts as a barrier against:
—invasion by microorganisms
—physical agents e.g. mild trauma, ultraviolet
—chemicals
—dehydration
-the dermis contains melanocytes and specialised immune cells called dendrites (langerhans) cells
-melanocytes secrete the pigment melanin, which protects against harmful ultraviolet rays in sunlight
-abundant sensory nerve endings in the dermis enable very accurate perception, discriminate and location of internal and external stimuli. This allows responses to changes in the environment, e.g. by reflect action (withdrawal) to unpleasant or painful stimuli, protecting it from further injury - Regulation of body temperature
-core body temp = 36.8 to ensure the optimal range for enzyme active required for metabolism. To maintain this, negative feedback system regulates the balance between heat produced in the body and heat lost to the environment
-heat production- when metabolic rate increases, body temp increases and vice versa. Some of the energy released during metabolic activity is in the form of heat; the most active organs produces most heat (live, skeletal muscle)
-heat loss- four mechanisms of heat loss- radiation (main mechanism) when exposed parts of the body radiate heat away from the body; evaporation- when body is cooled as body heat converts the water in sweat to water vapour; conduction- when clothes and other objects in direct contact with the skin take up heat; convection- when air passing over exposed parts of the body is heated and rises, and cool air replaces it, setting up convection currents. Convection also cools the body when clothes are worn, except when they are windproof - Formation of vitamin d:
-lipid based substance in skin called ‘7-dehydrocholesterol’ is converted to vitamin d by sunlight- its used with calcium and phosphate formation in the bone - Cutaneous sensation:
-dermis has sensory receptors which are sensitive to touch, pressure and temp or pain
-some areas have more abundant sensory receptors than others, causing them to be more sensitive like lips and fingertips - Absoption:
-some drugs when applied as transdermal patches, e.g. nicotine as an aid to smoking cessation, hormone replacement therapy during menopause
-some toxic chemicals e.g. mercury
-some medications: such as chemotherapy and also analgesia (pain relief) - Excretion:
-skin is a minor excretory organ for some substances like sodium chloride in sweat (excess sweating may lead to low blood sodium levels- hyponatraemia), urea (esp when kidney function is impaired), aromatic substances (garlic/ other spices) - Movement and growth
Describe the changes in skin from preterm to old age
Old age:
-these changes can be through genetics, sun and weather exposure
-aging = both the skin and mucous membranes become thin and fragile. Dermis is thinner and subcutaneous tissue is diminished
-fewer capillaries and cell proliferation is decreased, resulting in slower wound healing and atrophy of the glands
-the numbers of sensory receptors in the skin and mucosa decline = increased susceptibility to injury, bruising occurs frequently and the mucosal membranes become inflamed or ulcerated
-skin is often dry and appears wrinkled as elastic fibres are reduced and collagen fibres become less flexible
-melanocytes decrease causing greying of hair and skin
Developing foetus:
-the epidermis develops from a single layer of ectoderm to which other layers are added
-by the end of 4 weeks, a thin outer layer of flatter ended cells covers the embryo. Further development continues until 24 weeks
-brown adipose tissue (BAT) develops from 17-20 weeks’ gestation- very important for thermoregulation post birth
-post 18 weeks, the foetus is covered with a white, creamy substance called vernix caseosa- a protective layer
-hair begins to develop-9th-12th week. By 20 weeks, the foetus is covered with a fine downy hair called lanugo; including hair on eyebrows and head
-languo is shed from 36 weeks and by term, there is little left
-fingernails > 10 weeks, toenails - 18 weeks. At term, the nails can extend beyond the fingertips
Describe the mechanism of wound healing
- Inflammation
-within the first few hours, the wound surfaces become inflamed, a blood clot (mainly fibrin) and cell debris fill the gap between them - Proliferation
-epithelial cells proliferate across the wound. The epidermis meets and grows upwards until 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 and fibroblasts, develop, invading the clot and restoring blood supply to the wound
-fibroblasts continue to secrete collagen fibres as the clot and 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 - Maturation
-the granulation tissue is gradually replaced by fibrous scar tissue. Rearrange of collagen fibres occurs and 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 pressure ulcers
Aka pressure tissue damage
-pressure ulcers can develop when a large amount of pressure is applied to an area of skin over 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 oxygen 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
-conditions that affect the flow of blood through the body, such as type 2 diabetes can also make a person more vulnerable to pressure ulcers
-pressure sores can occur at the back of head/ears, shoulder, elbow, lower back and buttocks, hip, inner knees, heel
-4 stages. Stage 1 shows reddening/darkening and non-blanching erythema
