Lecture 21 - Skin Structure & Function

Question 1

What are the 3 primary layers of the skin from bottom to top?

Answer 1

• Hypodermis
• Dermis
• Epidermis

Question 2

Where is the location of the hypodermis?
What does it contain?
What are its functions?
Where does thickness of this layer differ?

Answer 2

• Hypodermis is the lowest layer of skin (AKA: sub-cutaneous layer)
• Mostly adipose tissue as well as loose connective tissue
• Provides energy store, insulator (for underlying muscle), shock absorber, connects skin to underlying muscles/bone and makes hormones (e.g.: leptin).
• In men thickest in abdomen and shoulders, in women thickest in hips, thighs, buttocks.

Question 3

Where is the location of the dermis?
What does it contain?
What are its functions?
What is thinning of this layer responsible for?

Answer 3

• In-between the hypo and epidermis
• A lower reticular layer and an upper papillary layer with interdigitating dermal papillae of various thickness.
• Thermoregulation (contains hairs/sweat glands), special senses (contains sensory structures), gives structure to skin.
• Skin wrinkling in old age due to loss of collagen & elastin.

Question 4

Where is the location of the epidermis?
What is its structure & held together by?
What are its functions?

Answer 4

• Outermost layer of skin made from keratinised stratified squamous epithelium.
• 4 layers (thin skin) or 5 layers (thick skin), held together laterally by adherens junctions, vertically by desmosomes. Has NO blood vessels.
• Prevent water loss, entry of bacteria, contains langerhans cells, synthesis of keratin and prevents underlying tissue loss.

Question 5

What are the 5 layers in the epidermis and what are their features?

Answer 5

1) Stratum corneum (corny layer) - made of dead keratinocytes, thick on palms and soles of feet and shed.
2) Stratum lucidum (transparent layer) - only on palms and soles of feet (thick skin)
3) Stratum granulosum (granular layer) - stratified squamous epithelium where keratin is synthesised & secreted.
4) Stratum spinosum (spinous layer) - cuboidal epithelium in 3 layers held together by desmosomes
5) Stratum basale (basal layer) - columnar epithelial cells, constantly renew keratinocytes and home to melanocytes.

Question 6

What is keratin synthesised by?
What is keratin the main constituents for?
What is the transit time of the cell that makes it from the basal layer to the corny layer?
What are 2 diseases associated with keratin?

Answer 6

• Keratinocytes
• Hair, nails and animal horns
• 28-40 days
• Psoriasis (transit time reduced to 2-3 days) to corny layer produced in abundance leading to silvery scales
• Hyperkeratosis - too much keratin on surface of skin (particularly on hands and feet).

Question 7

What are 3 other cell types found in the epidermis?

What are their roles?

Answer 7

1) Melanocytes - produce melanin which protect against UV rays.
2) Langerhans - present antigens to T-lymphocytes and mediate immune reactions.
3) Merkels - Contain mechanoreceptors associated with sensory nerve endings.

Question 8

What are the 2 main types of skin?

Answer 8

1) Thick (non-hairy)
2) Thin (hairy)

NB: exceptions to this rule include lips, back of the ear, some areas of external genitalia.

Question 9

Describe the location, structure and function of thick (non-hairy) skin.

Answer 9

• Palmar surface of hand/plantar surface of foot & webs of fingers and toes.
• Same as rest of the body, except no arrector pili muscles, hairs or sebaceous glands. Thicker corny layer and thinner dermis.
• Prevents tissue loss by abrasion, increased sensation (due to mechanoreceptor population).

Question 10

What are the main differences between thick (non-hairy) and thin (hairy) skin?

Answer 10

• No arrector pili, hairs or sebaceous glands in thick, all 3 present in thin.
• Bigger ridges and furrows on surface of thick
• Starum lucidum often seen in thick, but absent in thin

Question 11

What are the 3 main skin-associated structures? (appendages)

Answer 11

Hair, arrector pili muscles, nails

• also sebaceous and sweat glands but we’re looking at these 3 above.

Question 12

What are the 3 main types of hair and their features?

Answer 12

1) Lanugo -covers developing fetus
2) Vellus - replaces lanugo, short, thin, light coloured
3) Terminal - adult hair, long, wide, dark, produced by actions of testosterone.

Question 13

What are the 4 main functions of hair?

Answer 13

1) Thermoregulation - hairs erect when cold, arrector pili muscles contract by sympathetic stimulation.
2) Sexual attraction - apocrine glands secrete pheromones which attract opposite sex.
3) Sensation - hairs have sensory nerve endings in bulb which provides sensory awareness
4) Protection - e.g.: eyelashes and nasal hair from pathogens, eyebrows from swear etc.

Question 14

What do arrector pili muscles consist of?

When are they used?

Answer 14

• Smooth muscle fibres attached to papillary region of dermis and hair bulb
• During ‘fight or flight’ response, or contraction when cold (goose bumps!)

Question 15

Describe the location, structure and function of nails.

Answer 15

• Distal surface of phalanges
• Consist almost entirely of alpha-keratin
• Protect distal phalanx from injury, enhances precise delicate movements, enhances sensitivity of finger tip, and enables the “extended precision grip”.

Question 16

Summarise the key functions of skin

Answer 16

1) Protection and repair - by epidermis, papillary dermis and hypodermis
2) Thermoregulation
3) Lubrication
4) Storage
5) Vit D synthesis
6) Absorption
7) Aesthetics
8) Sensation