Skin (Structure & Function)

Question 1

What are the 3 main layers of the skin?

Answer 1

Epidermis-squamous keratinised epithelium
Dermis-irregular dense connective tissue
Hypodermis -adipose tissue

Question 2

How does thickness of the Hypodermis vary?

Answer 2

Thickness varies in different regions of body and can vary between people

In men-its thickest in abdomen and shoulders

In women-its thickest in hips, thighs and buttocks (milk storage areas)

In both sexes it is thick on the palms of hands and soles of feet to act as a shock absorber

Question 3

What is the location and structure of the Hypodermis?

Answer 3

Location=lowest layer of skin (also known as sub-cutaneous)

Structure=mainly adipose tissue (some neuromuscular bundles + lymphatics), some loose connective tissue (fibroblasts/macrophages/collagen fibres/mast cells)

Question 4

What is the function of the Hypodermis?

Answer 4

Provides energy store-to generate heat
Insulator for underlying muscle heat generation
Shock absorber-impact cushion + protect structures)
Connects skin to underlying muscle and bone
Makes hormones (Leptin made when cells expand to control eating)

Question 5

What is the location and structure of the dermis?

Answer 5

Location=between epidermis and hypodermis

Structure=3 layers Papillary (upper), Reticular (lower) and Dermal Papilae (interdigitating). Variable thickness (0.6mm on eyelid, 3mm on hands/feet’s). Made of Dense Irregular connective Tissue

Question 6

What is the function of the Dermis?

Answer 6

Contains hairs + sweat glands for thermoregulation
Contains sensory structures-touch
Gives structure to skin and so body shape

Question 7

What is the location and structure of the Epidermis?

Answer 7

Location=outermost layer of skin, made of keratinocytes

Structure=Thin skin has 4 layers, thick skin has 5 layers. Held together by lateral adhesion junctions, has some terminal nerve endings but no blood vessels. Respires by diffusion.

Question 8

What are the 4/5 layers of the epidermis?

Answer 8

1) Stratum Corneum (squamous/dead keratinocytes, continuously sheds)
2) Stratum Lucidum (transparent keratin, 1 cell thick, palms and soles ONLY-THICK SKIN)
3) Stratum Granulosum (stratified squamous epithelium, lamellar granules secrete keratin, Tonofibrils (bundle of keratin) made by lamellar bodies)
4) Stratum Spinosm (cuboidal epithelium in 3 layers, held by desmosomes, produce lamellar bodies (keratin factory’s), first time Golgi Apparatus appears)
5) Stratum Basale (tall columner epithelial cells, constantly renew keranicytes by division, as cells differentiate they move away from epidermis-dermis junction, make keratin filaments, home to melanocytes)

Question 9

Describe the keratin synthesis pathway.

Answer 9

Rises from tonofilaments to the spinous cell which have the keratin forming factory in them. Then rise to Tonofibrils and this is where apoptosis is fist seen. The apoptosis cells are held together by desmosomes, the desmosomes are broken by enzymes to release the top squamous cells and prevent excessive build-up

Question 10

What are the main constitutes of hair, nails and animal horns?

Answer 10

Keratin

Question 11

What cells synthesise keratin?

Answer 11

Keratinocytes synth the keratin that contribute to epidermis strength.

Question 12

What is psoriais?.

Answer 12

The transit time of keratinocytes from the basal layer to Stratum corneum is reduced from 28-40 days to only 2-3. The skin appears as silvery scales. The immune cells are exposed, and mast cells degenerate causing redness and itching

Question 13

What is Hyperkeratosis?

Answer 13

Too much keratin is put on the surface of the skin (esp hands/feet). It causes drying out and cracking allowing pathogens to enter.

Question 14

What pigment-giving cell an be found in the epidermis and how does it move?

Answer 14

Mature melanasomes contain melanin (the pigment of skin. These can be transferred to neighbouring keratinocytes by pigment donation. This involves phagocytosis of the tips of the dendritic processes of the cell.

Question 15

Give an example of an immune cell can be found in the epidermis

Answer 15

Langerhan’s cells can be found in the epidermis. They act as macrophages to any foreign bodies. They present antigens to T-lymphocytes to mediate an immune response (ie allergic contact dermatitis)

Question 16

What are Merkel Cells?

Answer 16

Can be found in epidermis.
Mechanoreceptor cells associated with sensory nerve endings. Make up 6-10% of cells in epidermis, the darker the skin the more merkel cells are present.

Question 17

Why are black people better suited for sunny climates?

Answer 17

They have more marked constitutional pigmentation, more melanin in their skin. Reduced chances of getting skin cancer, however is still possible.

Question 18

What are the 2 types of skin and what are the exceptions to this?

Answer 18

Hairy-Thin skin
Non-hairy thick skin

The exceptions are the back of the ear, the lips and some areas of external genitalia

Question 19

What is the location and structure of Non-hairy thick skin?

Answer 19

Location=Plamar surface of hand, plantar surface of foot, area between fingers and toes

Structure=same as rest of body except: No hair, arrector pili muscles, no sebaceous glands. Thicker stratus corneum, thinner dermis, increased density of mechanoreceptors.

Question 20

What is the function of non-hairy thick tissue?

Answer 20

Prevent tissue loss due to abrasion, increased friction between skin and surface (palm vs back of hand), increased sensation

Question 21

Compare the histology of thin (hairy) and thick (non-hairy) skin.

Answer 21

Thick-no hair follicles, Thin-hair follicles
Thick-no sebaceous glands, Thin-sebaceous glands
Thick-no arrector pilli muscle, Thin-arrector pilli muscles
Thick-pronounced ridges + furrows, Thin-small ridges+furrows
Thick-regular dermal papillae, Thin-irregular dermal papillae
Thick-Stratum lucidium seen, Thin-stratum lucidum absent

Question 22

List some skin appendages.

Answer 22

Hairs
Arrector pilli 
Sebaceous glands 
Sweat glands 
Nails

Question 23

What are the 3 types of hair and when/where are they present?

Answer 23

Lanugo-covers developing foetus (then falls out, occasionally seen at birth)

Vellus-replaces lanugo (short,thin,light colour, soft, not connected to sebaceous gland) back of hand etc.

Terminal-head (scalp, eyebrows, nasal passage), axillae, external genitals, long, wide, dark coloured coarse, produced by actions of testosterone.

Question 24

What is the thermoregulation function of hair?

Answer 24

Hair lays flat when normal or elevated
Hair stands erect when cold (arrector pilli muscle contract, stimulated by sympathetic fibres from autonomic nervous system)

Also acts as partial UV barrier (scalp)

Question 25

Describe the sexual attraction function of Hair.

Answer 25

Hair style can be alluring

Apocrine sweat glands secrete oils (pheromones) that attract opposite sex, the hairs trap these oils to accentuate pungency

Question 26

Describe the sensation function of hair.

Answer 26

Hairs have sensory nerve endings within the bulb
(Air movement, physical interaction, vibrations transmitted to the bulb sensed and transmitted to CNS, provides sensory awareness)

Question 27

Describe the protective function of hair.

Answer 27

Eyelashes and nasal hair prevent dust and pathogens entering body.

Eyebrows reduce amount of light + sweat from entering eyes

Axilla hair acts as a conduit to conduct sweat away from body

Question 28

What is the arrector pili muscle?

Answer 28

Consists of smooth muscle fibres attached to papillary region of the dermis (origin) and hair bulb (insertion)

Fight or flight response or cold causes involuntary contraction-‘goose bumps”

May also induce sebum release from sebaceous gland-as bulb moves it compresses sebum gland, oil slides up hair, fight/flight “slipper” harder to catch.

Question 29

What mechanoreceptors are present in the skinlayers and what do they detect?

Answer 29

End bulb=thermoreceptor

Free nerve endings=nociceptor (pain)

Tactile disks=vertical dimpling of skin-attach to basal layer keratinocyte-sense touch, pressure and texture. In non hairy skin=merkel disc, in hairy skin= Meissner disk

Meissner corpuscle-tapping+flickering movements

Pacinian corpuscle-vibrations

Ruffini’s corpuscle-joint movement and tissue stretch

Root hair plexus-vibration in hair shaft

Question 30

What is the location and structure of nails?

Answer 30

Location=distal surface of phalanges (finger+toes)

Structure=solely alpha keratin. Has nail plate, nail matrix and nail bed below it, grooves surround it.

Question 31

What is the function of nails?

Answer 31

Protection of distal Phalenx and surrounding soft tissue from injury.
Enhances precise delicate moment of distal digit through counter pressure on pulp of finger
Enhances sensitivity of finger tip (nail has n nerve endings)
Useable as a tool “extended precision grip” scraping action etc

Question 32

What are all the overall functions of the skin?

Answer 32

Protection + repair 
Thermoregulation + waste excretion 
Lubrication 
Storage 
Vitamin D synthesis 
Absorption 
Aesthetics 
Sensation