Skin - Structure And Function

Question 1

What is the integumentary system of the body?

Answer 1

Skin, Hair and Nails

Question 2

List some features of the integumentary system

Answer 2

• Largest organ of the body
• Heaviest organ of the body: 15% of adult body weight
• Much GP time

Question 3

What are the 3 layers of the skin?

Answer 3

• Epidermis
• Dermis
• Hypodermis

Answer 4

Hair, Skin glands, Nails and sensory receptors

Question 5

What are the functions of the skin?

Answer 5

• Barrier protection: Dehydration, Infection, Injury, Solar radiation
• Thermoregulation
• Sensation
• Repair
• Vitamin D production

Question 6

Describe the Epidermis layer of the skin

Answer 6

• Most superficial
• Gives skin it’s colour
• Protection from pathogens and environment
• Vitamin D production
• Made up of multiple layers of differentiating keratinocytes

Question 7

List the 4 main layers of the Epidermis

Answer 7

• Stratum Corneum
• Stratum Granulosum
• Stratum Spinosum
• Stratum Basale

Question 8

Describe the Stratum Basale: Basal Layer

Answer 8

• 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

Question 9

Describe the Stratum spinosum: Spiny layer

Answer 9

• Cells (Keratinocytes) have many desmosomes (junctions) visible as spines between the cells
• Strong bonds holding the epidermis together

Question 10

Describe the Stratum Granulosum: Granular layer

Answer 10

• 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

Question 11

Describe the Stratum Corneum: Cornified layer

Answer 11

• 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

Question 12

What is Keratin also the main components of?

Answer 12

Horns, Hair, Nails, Claws and hoofs

Question 13

List some other epidermal cell types

Answer 13

• Melanocytes (pigment)
• Langerhans cells (defence)
• Merkal cells (sensation)

Question 14

How are melanocytes viewed under a microscope?

Answer 14

Via a special DOPA stain for melanin which shows their denitrification form

Question 15

What are Melanocytes?

Answer 15

• They synthesise melanosomes
• Transfers them to basal keratinocytes through long dendrites

Question 16

How is melanin arranged in the pigment?

Answer 16

• 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

Question 17

What are Merkal cells?

Answer 17

• 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

Question 18

Describe the Langerhans cells

Answer 18

• Function: Immune system, Seeks and deals with invading microbes
• Antigen presenting cells (like macrophages)
• They are dendritic cells, forming a network

Question 19

Describe the Vitamin D production in the skin

Answer 19

• 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

Question 20

Describe the dermis layer of the skin

Answer 20

• Found below the epidermis
• Has 2 layers
• Tensile strength & elastic
• Contains blood vessels, skins glands & sensory receptors

Question 21

Describe what the dermis layer is made from

Answer 21

• 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

Question 22

What are the two layers of the dermis?

Answer 22

• Thin papillary layer
• Deeper reticular layer

Question 23

Briefly describe the dermis

Answer 23

• Dense irregular connective tissues
• Dense = full of collagen fibres
• Irregular = Fibres run in all directions (not parallel)

Question 24

What are the functions of the dermis?

Answer 24

• 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

Question 25

Describe the Dermal Epidermal border

Answer 25

- 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

Question 26

Which dye is used on the Dermis? What does it show?

Answer 26

- Verhoeff Van gieson stain (VVG) - Shows the collagen fibres in red

Question 27

What is one effect of ultraviolet light on skin?

Answer 27

- One effect is damage/loss of Elastic fibres - This results in the loss of elasticity causing wrinkles

Question 28

Describe the Hypodermis layer

Answer 28

- Below the dermis - Helps insulate the deeper tissue - Anchors skin to the muscle with connective tissue

Question 29

What is the Hypodermis made up of?

Answer 29

- 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

Question 30

What is the Hypodermis composed of?

Answer 30

- 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

Question 31

Describe the hair

Answer 31

- 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

Question 32

Describe the Hair follicles in detail

Answer 32

- 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

Question 33

Describe the bulb of the hair

Answer 33

- 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

Question 34

Describe the follicular keratinocytes

Answer 34

- 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

Question 35

List the different types of skin glands

Answer 35

- Eccrine Sweat glands - Apocrine Sweat glands - Sebaceous gland

Question 36

Briefly describe Eccrine sweat glands

Answer 36

- Normal sweat glands - Watery secretion on to skin surface - Cools the body down by evaporation

Question 37

Describe the Apocrine sweat glands

Answer 37

- 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

Question 38

Describe Sebaceous gland

Answer 38

- Secrete oily sebum (lanolin) into hair follicle - Conditioner for hair and skin - Prevents dryness and flaking - Only present after puberty

Question 39

Describe the Nails: Nail folds and Eponyvhium

Answer 39

- 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

Question 40

Describe the Nail matrix

Answer 40

- 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

Question 41

Where does the older and youngest keratinocytes go after keratinisation?

Answer 41

- Youngest keratinocytes go to the nail matrix - Older cells go to the Keratinize which form the nail plate

Question 42

Describe the sensory receptors

Answer 42

- 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.