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System that includes the skin and its derivatives
What the derivatives of skin?
Epithelial layer of skin
Layer of connective tissue, nerve & muscle
What is the Subcutaneious tissue (subQ or hypodermis)?
A layer of adipose & areolar tissue located below the dermis
Composed of keratinized stratified squamous epithelium
Contains no blood vessels
4 types of cells in it
Has 4/5 distinct strata (layers) of cells
What are the four cell types of the epidermis?
- 1. Keratinocytes (90%)
- 2. Melanocytes
- 3. Langerhan cells
- 4. Merkel cells
Produces melanin pigment
How is melanin transferred to other cells?
With long cell processes
From bone marrow (modified monocytes)
Provide immunity (ingest bacteria and viruses)
In deepest layer
Form touch receptor with sensory neuron
Deepest single layer of cells
Called stratum germinativum
Combination of merkel cells, melanocytes, keratinocytes & stem cells that divide repeatedly
Cells attached to each other and to basement membrane
8-10 cell layers held together by desmosomes
What happens to the cells during slide preparation?
Cells shrink and look spiny
Stratum Spinosum: How is melanin taken in?
By phagocytosis from nearby melanocytes
3-5 layers of flat dying cells
Show nuclear generation
Contain dark-staining keratohylin granules
3-5 layers of clear, flat, dead cells
Contains precursor of keratin
Seen in thick skin on palms & soles of feet
25-30 layers of flat dead cells filled with keratin and surrounded by lipids
Barrier to light, heat, water, chemicals & bacteria
Friction stimulates callus formation
What are the two types of skin?
Describe thin skin (3 points)
- Covers most of body
- Thin epidermis that lacks stratum lucidum
- Lacks epidermal ridges, has fewer sweat gladns and sensory receptors
Describe thick skin (3 points)
- Only on palms and soles
- Thick epidermis with distinct stratum lucidum & thick stratum corneum
- Lacks hair follicles and sebaceous glands
Describe the process of Keratinization & Epidermal Growth
- 1. Stem cells divide to produce keratinocytes
- 2. As keratinocytes are pushed up towards the surface, they fill with keratin
- 3. 4 week journey unless outer layers removed in abrasion
Connective tissue layer composed of collagen & elastic fibers, fibroblasts, macrophages & fat cells
Contains hair follicles, glands, nerves & blood vessels
What are the 2 major regions of dermis?
- Papillary region
- Reticular region
Top 20% of dermis
Composed of loose CT & elastic fibers
Finger like projections called dermal papillae
What are the 3 functions of the papillary region?
- 1. anchors epidermis to dermis
- 2. contains capillaries that feed epidermis
- 3. contains Meissner’s corpuscles (touch) & free nerve endings (pain and temperature)
Dense irregular connective tissue
Contains interlacing collagen and elastic fibers
Packed with oil glands, sweat gland ducts, fat & hair follicles
Provides strength, extensibility & elasticity to skin– stretch marks are dermal tears from extreme stretching
Where do epidermal ridges form?
In fetus as epidermis conforms to dermal papillae
What do epidermal ridges give us? (2 things)
- 1. Fingerprints are left by sweat gladns open on ridges
- 2. Increase grip of hand
What are the 7 functions of skin?
- Regulation of body temperature
- Blood reservoir
- Synthesis of vitamin D
What is Thermoregulation?
- Releasing of sweat onto the skin
- -perspiration and its evaporation lowers body temperature
Adjusting flow of blood to body surface:
What happens during moderate exercise?
More blood brought to surface helps lower temperature
Adjusting flow of blood to the body surface:
What happens with extreme exercise?
Blood is shunted to muslces and body temperature rises
What do humans do to raise internal body temperature as needed?
Shiver and constrict surface vessels
How does skin provide protection? (4 points)
- Physical, chemical and biological barrier:
- 1. Tight cell junctions prevent bacterial invasion
- 2. Lipids released retard evaporation
- 3. Pigment protects somewhat against UV light
- 4. Langerhans cells alert immune system (antigen presenting to T-lymphocytes
Touch, temperature, pressure, vibration, tickling and pain sensations arise from the skin
Only a minor role is played by the skin
400 mL of water evaporates from it daily
Small amounts salt, CO2, ammonia and urea are excreted
Lipid soluble substances can be absorbed through the skin
– vitamins A, D, E and K, Oxygen and CO2
– acetone and dry-cleaning fluid, lead, mercury, arsenic, poisons in poison ivy and oak
Blood can be stored in venous vessels located in the dermis and hypodermis
Describe the synthesis of Vitamin D?
- 1. Sunlight activates a precursor to vitamin D
- 2. Enzymes in the liver and kidneys transform that molecule into calcitriol (most active form of vitamin D)
Why is vitamin D important?
Necessary vitamin for absportion of calcium from food in the gastrointestinal tract
How are hair, oil glands, sweat glands and nails formed?
Cells sink inward during development
What are the 4 functions of hair?
- 1. Prevents heat loss
- 2. Decreases sunburn
- 3. Eyelashes help protect eyes
- 4. Touch receptors (hair root plexus) senses light touc
What are the 3 parts of the hair shaft?
- 1. Medulla
- 2. Cortex
- 3. Cuticle
What ar the 3 part so the hair structure?
- Shaft (visible)
- Root (below the surface)
- Folllicle (surrounds root)
What is the base of the follicle called and what does it have?
- -blood vessels
- -germinal cell layer
What is the difference between the external root sheath and the internal root sheath?
Smooth muscle in dermis contracts with cold or fear
Forms goosebumps as hair is pulled vertically
Detects hair movement
Hair root plexus
How does hair have color?
Result of melanin produced in melanocytes in hair bulb
True or false: Dark hair contins true melanin
What does blonde and red hair contain?
Melanin with iron and sulfur added
Why does hair go grey?
Result of decline in melanin production
Why does hair go white?
White hair has air bubbles in the medullary shaft
Secretory portion in the dermis
Located on most of body except palm of hands and sole of feet
Most open onto hair shafts
Combination of cholesterol, proteins, fats & salts
Keeps hair and skin soft & pliable
Inhibits growth of bacteria & fungi(ringworm)
Holocrine type of excretion
Bacterial inflammation of glands
Secretions stimulated by hormones at puberty
Most areas of skin
Secretory portion in dermis with duct to surface
Regulate body temperature with perspiration
Eccrine-Merocrine (sweat) glands
Armpit and pubic region
Secretory portion in dermis with duct that opens onto hair follicle
Secretions more viscous
Apocrine (sweat) glands
What are the two types of sweat glands?
- Eccrine-Merocrine glands
- Apocrine glands
What are nails composed of?
Tightly packed keratinized cells
What is the nail body pink?
- Visible portion pink due to underlying capillaries
- Free edge appears white
Which part of the nail is...
Buried under skin layers
Lunula is white due to thickened stratum basale
Which part of the nail is...
Stratum corneum layer
What are the 4 functions of nails?
- 1. Enhance grasping
- 2. Manipulate objects
- 3. Protection against trauma to ends of digits
- 4. Scratching body part