Skin - Structure And Function Flashcards
1
Q
What is the integumentary system of the body?
A
Skin, Hair and Nails
2
Q
List some features of the integumentary system
A
- Largest organ of the body
- Heaviest organ of the body: 15% of adult body weight
- Much GP time
3
Q
What are the 3 layers of the skin?
A
- Epidermis
- Dermis
- Hypodermis
4
Q
A
Hair, Skin glands, Nails and sensory receptors
5
Q
What are the functions of the skin?
A
- Barrier protection: Dehydration, Infection, Injury, Solar radiation
- Thermoregulation
- Sensation
- Repair
- Vitamin D production
6
Q
Describe the Epidermis layer of the skin
A
- Most superficial
- Gives skin it’s colour
- Protection from pathogens and environment
- Vitamin D production
- Made up of multiple layers of differentiating keratinocytes
7
Q
List the 4 main layers of the Epidermis
A
- Stratum Corneum
- Stratum Granulosum
- Stratum Spinosum
- Stratum Basale
8
Q
Describe the Stratum Basale: Basal Layer
A
- First single layer contains stem cells arranged to the dermis
- Stem cells constantly proliferate
- Are dynamic: Daughter cells constantly move “up” (distally) through the epidermis, differentiating as they go
- Until they are shed from the outer surface.
- This takes 20-50 days
9
Q
Describe the Stratum spinosum: Spiny layer
A
- Cells (Keratinocytes) have many desmosomes (junctions) visible as spines between the cells
- Strong bonds holding the epidermis together
10
Q
Describe the Stratum Granulosum: Granular layer
A
- 1-4 layers of cells containing granules of kreatohyalin: a precursor of the protein keratin
- Also contain lamellar bodies containing lipids (seen by TEM)
- Cells are differentiating to form the outermost layer
11
Q
Describe the Stratum Corneum: Cornified layer
A
- The outer protective layer of the epidermis
- Cells are keratinised (cornified), Cytoplasm full of horny keratin (keratohyalin granules)
- Thus tough and resistant to injury
- Cells are flattened and lost their nuclei
- Nonpolar lipids (waterproof) are between the cells from lamellar bodies
12
Q
What is Keratin also the main components of?
A
Horns, Hair, Nails, Claws and hoofs
13
Q
List some other epidermal cell types
A
- Melanocytes (pigment)
- Langerhans cells (defence)
- Merkal cells (sensation)
14
Q
How are melanocytes viewed under a microscope?
A
Via a special DOPA stain for melanin which shows their denitrification form
15
Q
What are Melanocytes?
A
- They synthesise melanosomes
- Transfers them to basal keratinocytes through long dendrites
16
Q
How is melanin arranged in the pigment?
A
- Keratinocytes arrange melanin pigment in a cap distal to the nucleus (sunny side)
- Especially in the Basal layer (Stem cells)
- UV protection: black ppl only have about 10% as many skin cancers as white ppl with the same lifestyle
17
Q
What are Merkal cells?
A
- Some pale cells in the basal layer are Merkal cells
- These are touch sensors
- Hard to tell the difference with H&E alone which is white skin, pale cells in or protruding from basal layer
18
Q
Describe the Langerhans cells
A
- Function: Immune system, Seeks and deals with invading microbes
- Antigen presenting cells (like macrophages)
- They are dendritic cells, forming a network
19
Q
Describe the Vitamin D production in the skin
A
- Vitamin D3 is made in the epidermis layer
- Mostly in the basal cells but also in the Stratum spinosum
- Requires UV light
- Requires more UV light in dark skin (melanin barrier)
- Converted to active form in liver in the liver and kidney
- Commonly deficient in the UK
20
Q
Describe the dermis layer of the skin
A
- Found below the epidermis
- Has 2 layers
- Tensile strength & elastic
- Contains blood vessels, skins glands & sensory receptors
21
Q
Describe what the dermis layer is made from
A
- Made up of layers of connective tissue
- Characterised by interconnected mesh of elastin and collagen fibres
- produced by dermal fibroblasts
- Fibroblasts are the principal cell of the dermis
22
Q
What are the two layers of the dermis?
A
- Thin papillary layer
- Deeper reticular layer
23
Q
Briefly describe the dermis
A
- Dense irregular connective tissues
- Dense = full of collagen fibres
- Irregular = Fibres run in all directions (not parallel)
24
Q
What are the functions of the dermis?
A
- Collagen provides tensile strength hence protection against abrasion and impact
- Also contains elastin providing elasticity
- Carries blood and nerve supply for epidermis
- Rich in blood vessels, sensory receptors and skin glands
25
Describe the Dermal Epidermal border
- Often wavy which helps resist shear forces
- Has Dermal papillae: Finger like protrusions of dermal connective tissue into epidermal layer
- rete ridges: Extension of epidermis into the dermal layer
- Most apparent in thick skin of hands = fingerprints as well as feet
26
Which dye is used on the Dermis?
What does it show?
- Verhoeff Van gieson stain (VVG)
- Shows the collagen fibres in red
27
What is one effect of ultraviolet light on skin?
- One effect is damage/loss of Elastic fibres
- This results in the loss of elasticity causing wrinkles
28
Describe the Hypodermis layer
- Below the dermis
- Helps insulate the deeper tissue
- Anchors skin to the muscle with connective tissue
29
What is the Hypodermis made up of?
- Made up of well vascularised, loose, areoles connective tissue and adipose tissue
- Functions as a mode of fat storage
- Provides insulation and cushioning for the integument
30
What is the Hypodermis composed of?
- Composed of fat containing glands, hair follicles, nerves, blood vessels
- Often the thickest layer of skin. Thickness varies with age
- This is where you put a hypodermic needle for a subcutaneous injection
31
Describe the hair
- Found on nearly every part of the skin except the palms, soles and lips
- Every strand of hair is composed of the shaft, root and bulb that sits in a pouch like structure called the hair follicle
32
Describe the Hair follicles in detail
- The hair follicle is epidermal tissue that dips down into the dermis
- Interacts with other structures like apocrine glands, sebaceous glands, the affector pili muscle and nerve receptors
33
Describe the bulb of the hair
- Bulb contains the hair matrix: active site of hair growth and pigmentation
- Contains different cell types: Follicular keratinocytes and Melanocytes
- Follicular keratinocytes produce hard keratin = hair
34
Describe the follicular keratinocytes
- Keratinocytes filled with hard flatten out and are slowly pushed up the follicle resulting in root and shaft formation
- Follicular keratinocytes at the bulb replicate only a set number of times
- After the hair follicles stops growing and fall out leading to baldness
- Overtime these melanocytes stop producing melanin which is why hair turns white as ppl age
35
List the different types of skin glands
- Eccrine Sweat glands
- Apocrine Sweat glands
- Sebaceous gland
36
Briefly describe Eccrine sweat glands
- Normal sweat glands
- Watery secretion on to skin surface
- Cools the body down by evaporation
37
Describe the Apocrine sweat glands
- Secrete into hair follicles
- Found in the armpits and anogenital region
- Oily fluid in humans
- Function is unclear (contains pheromones)
- Source of body odour after bacterial action
- Only present after puberty
38
Describe Sebaceous gland
- Secrete oily sebum (lanolin) into hair follicle
- Conditioner for hair and skin
- Prevents dryness and flaking
- Only present after puberty
39
Describe the Nails: Nail folds and Eponyvhium
- Nail folds: Where the skin seals of the edges of the nail
- Eponychium: Proximal skin fold that gives rise to the cuticle
- Which is a semi circular layer of dead skin keratinocytes that covers where the nail enters the skin
- Preventing the entry of pathogens
40
Describe the Nail matrix
- Creates the nail plate, The hard part of the nail as well as the free edge that hangs over the skin
- Special epidermal tissue that contains nerves, lymphatics and blood vessels that support the nail
- Contain modified keratinocytes that replicate and undergo the process of keratinisation
41
Where does the older and youngest keratinocytes go after keratinisation?
- Youngest keratinocytes go to the nail matrix
- Older cells go to the Keratinize which form the nail plate
42
Describe the sensory receptors
- Free nerve endings -> nociception, thermal sensation, light touch
- Encapsulated endings
- Pacinian corpuscles (rapidly adapting) → vibration or brief touch
➢Merkel's discs (slowly adapting) → sustained touch/pressure e.g. skin indentation
➢Meissner's corpuscles (rapidly adapting) → moving touch or vibration
➢Ruffini endings (slowly adapting) → steady pressure
➢Root hair plexus (rapidly adapting) → hair displacement.
➢Krause end bulbs → touch/pressure, possibly thermoreceptors.
