Skin DSL

Question 1

What are functions of the skin?

Answer 1

• protection from external damage
• sensation (touch, heat, pressure, pain)
• thermoregulation
• metabolic functions (subcutaneous adipose tissue is a major store of energy (triglycerides). Vitamin D is synthesised in the epidermis supplementing dietary sources)

Question 2

What are the 2 main and variable 3rd layer of the skin?

Answer 2

epidermis, dermis and the subcutis

Question 3

What type of cell forms the epidermis?

Answer 3

Stratified squamous keratinizing epithelium - main cell type is keratinocyte.

Question 4

What are the 4 morphological layers of the epidermis?

Answer 4

• stratum corneum (cornified layer)
• surface keratin constantly lost from wear and tear
• stratum granulosum (granular cell layer)
• prod surface keratin, waterproof substances - prolongued exposure will wash away these leaving keratin to absorp water and swell/soften
• stratum spinosum (prickle cell layer)
• keratinocytes above basal layer, prickle cells form bridges (prickles), formed from cytoplasmic projections
• stratum basale
• deepest cell layer responsbile for constant production of keratinocytes

Question 5

Describe the structure between the dermis and epidermis and how it minimised the risk of dermo-epidermal separation by shearing forces

Answer 5

• tethering fibres connect dermis and epidermis to intervening basement membrane
• basal cell membrane of individual basal cells, and underlying basement membrane are convoluted

Question 6

What are rete ridges and where are they highly developed?

Answer 6

Downgrowths of epidermis into the dermis - they are highly developed in areas constantly exposed to shearing stress - eg. fingers, palms and soles

Question 7

What factors cause basal blisters?

Answer 7

• excessive shearing force (eg tight fitting shoes)
• structural abnormality (primary or secondary)

Question 8

What is an example of primary structural abnormalities causing basal blisters?

Answer 8

Rare inherited skin disease epidermolysis bullosa, the dermo-epidermal junction is intrinsically weak and unable to resist even a minimal shearing trauma

Question 9

What is an example of a secondary cause for basal blisters?

Answer 9

More common than primary, result from inflammatory skin disease damaging basal layer and underlying basement membrane - eg. pemphigold and dermatitis herpetiformis

Question 10

Describe the function and location of melanocytes

Answer 10

Produce protective pigment melanin, responsible for skin colour and minimises tissue damage by UV radiation.

Derived from neuroectoderm and located in the basal layer of keratinocytes in contact with basement membrane.

Uncontrolled proliferation can result in melanoma

Question 11

Describe the function and location(s) of Langerhan’s cells

Answer 11

• antigen recognition cells, important for immune system
• located in all layers of epidermis but easily seen in prickle cell layer (stratum spinosum)

Question 12

In which conditions are Langerhan’s cells increased?

Answer 12

• in chronic inflammatory disorders esp those with an allergic or immune aetiology eg. atopic dermatitis

Question 13

What do Merkel cells do and where are they found?

Answer 13

• sensory receptors in the epidermis
• found in basal layer and form synaptic junctions with peripheral nerve endings at base of cells
• form small desmosomal attachments to adjacent keratinocytes

Question 14

What is the composition of the dermis?

Answer 14

• fibroblasts, fibrocytes + their extracellular products
• epidermal appendages
• collagen + elastic fibres
• glycosaminoglycan-containing matrix
• blood vessels + nerves
• macrophages, lymphocytes, mast cells

Question 15

What are the two distinct zones of the dermis?

Answer 15

1) upper narrow papillary dermis (close to dermo-epidermal junction)
2) thicker reticular dermis (between papillary dermis and subcutaneous adipose tissue)

Question 16

What is the general blood supply of the skin?

Answer 16

Located within the dermis, arises from larger vessels in subcutaneous fat. Two plexues:

1) deep vascular plexus in lower reticular dermis close to border with subcutis
2) superficial vascular plexus in upper reticular dermis close to junction with papillary dermis

Question 17

Do blood vessels penetrate the epidermis?

Answer 17

No - loops of small vessels from the superficial vascular plexus can run up into the papillary dermis lying CLOSE to epidermal basement membrane but not into actual epidermis.

Question 18

Describe the components of the nerve supply of the skin in the dermis and what they control

Answer 18

• rich non-myelinated supply derived from sympathetic ANS which controls skin appendages and vascular flow
• afferent myelinated and non-myelinated system detecting cutaneous sensation by variably specialised nerve endings

Question 19

What are some variably specialised nerve endings detecting cutaneous sensation in the afferent system?

Answer 19

• free nerve endings (pain, temp)
• pacinian corpuscles (pressure, vibration)
• meissner’s corpuscles (touch)
• merkel cells (slowly adapting touch receptors)

Question 20

Describe the structure of subcutaneous tissue

Answer 20

• largely adipose
• adipose separated by fibrocollagenous septa, contains main blood vessels and nerves from, supplying dermis
• an effective heat insulator, food store + shock absorber
• may contain extensions of skin structuress eg hair follicles, apocrine/eccrine glands

Question 21

What are some common skin appendages?

Answer 21

• hairs
• sebaceous glands
• sweat glands

Question 22

What is hair?

Answer 22

Hairs are highly modified keratinised structures, produced by hair follicles which are essentially cylindrical downgrowths of surface epithelium ensheathed by collagenous tissue.

Question 23

How are goose bumps formed?

Answer 23

Arretctor pilli muscles (smooth) are attched to follicular sheath, inserted into dermal papillary zone. Contraction of arrector pili causes hair to become erect and pulls down its point of insertion

Activated by cold or fear.

Question 24

What is the value of arrector pili contraction in humans?

Answer 24

Play some part in expulsion of sebum from sebaceous glands

Question 25

What do sebaceous glands do?

Answer 25

Secrete oily substance called sebum onto hair surface of upper part of follicle, acts as waterproofing and moisturising agent for hair and skin surface.

Question 26

In which places are sebaceous glands indepedent of hair follicles, secreting directly onto skin surface?

Answer 26

lips, eyelids, glans penis, labia minora and nipples

Question 27

What is the process by which sweat is enacted in most areas directly onto skin?

Answer 27

merocrine secretion - coild tubular glands (same as eccrine)

Question 28

What type of sweat gland is found in the skin of axilla and genital regions?

Answer 28

Apocrine sweat glands - produce viscid secretion into hair follicles rather than directly onto surface

Question 29

What is the difference in innveration between eccrine and apocrine sweat glands?

Answer 29

apocrine - adrenergic fibres of SNS

eccrine - cholinergic fibres of SNS

Question 30

What is the difference between the following types of skin:

• Thin
• Thick sole
• Scalp
• Fingertip
• Axillary

Answer 30

• Thin - thin epidermal and keratin layers, poorly developed rete ridge system, few hair follicles, variable number of eccrine glands (eg on back)
• Thick - thick epidermis + keratin layers, well developed rete ridge system + numerous eccrine glands and ducts
• Scalp - tightly packed pilosebaceous units of scalp skin
• Fingertip - thick epidermis, well developed rete ridge system, compact protective keratin, dermis contains glomus body + abundant eccrine sweat glands + ducts
• Axillary - abundant apocrine glands, oblique hair follicles + thin epidermis