Structure and Function of the Skin

Question 1

• What are the functions of the skin?

Answer 1

Protective barrier, chemical barrier, inhibits infectious agents, sensory organ, prevents desiccation, photoprotection, immunosurveillance, temperature & blood pressure regulation, produces vitamin D, stores nutrients, absorptive surface

Question 2

• What are the 5 layers of epidermis (inner to outer)? stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

Answer 2

Stratum basale – single layer cuboidal cells, mitotically active at night, controlled by many growth factors (EGF, ILGF-1, KGF, bFGF, IL-1, IL-6, TGFα, vitamin D, retinoids
Stratum spinosum – 1 to 20 cells thick, prominent intracellular bridges (desmosomes)
Stratum granulosum – variably present in haired skin, slightly flattened cells, shrunken nuclei, contain intracellular keratohyaline granules containing profilaggrin, produce loricrin & keratin
Stratum lucidum – not present in haired skin, variably present in hairless thickened skin, slightly flattened cells, shrunk nuclei, contain intracellular keratohyalin & lipids
Stratum corneum – composed of anucleate flattened cells (squames), forms part of cornified envelope, squames contain intracellular proteins (involucrin, loricrin, keratolinin), extracellular lipids (mortar)

Question 3

• What three non-keratinocytes cell types are found in the epidermis?

Answer 3

Melanocytes – have many dendritic processes, derived from neural crest
Langerhans cells – antigen present cells, derived from bone marrow
Merkel cells – slow adapting mechanoreceptors, origin unknown

Question 4

• What is an epidermal melanin unit?

Answer 4

Melanocyte immersed in the epidermis with close contact with a defined number of keratinocytes

Question 5

• What are the two types of melanin?

Answer 5

Eumelanin black-brown & phaeomelanin reddish yellow

Question 6

• What are the functions of melanin?

Answer 6

Protection from UV light & free radical scavenger

Question 7

• What factors influence skin colour?

Answer 7

Carotenoids, oxyhaemoglobin, deoxyhaemoglobin, melanin

Question 8

• Where does hair pigment come from?

Answer 8

From melanocytes associated with hair matrix

Question 9

• What controls skin pigmentation?

Answer 9

Genetics, UV light & hormones (melanocyte stimulating hormone (MSH))

Question 10

• What is the function of the basement membrane?

Answer 10

Anchors the epidermis to the dermis

Question 11

• What is the main protein in hemidesmosomes?

Answer 11

Bullous pemphigoid antigen 1

Question 12

• What are the two layers of the dermis?

Answer 12

Superficial papillary layer & deeper reticular layer

Question 13

• What cell types can be found in the dermis?

Answer 13

Fibroblasts, mast cells, melanocytes, monocytes, lymphocytes

Question 14

• What sensory nerve endings are present in the skin?

Answer 14

Free nerve endings, Meissener’s corpuscles & Pacinian corpuscles

Question 15

• What do the adrenergic and cholinergic fibres supply?

Answer 15

Arterioles, atrichial (eccrine) and epitrichial (apocrine) sweat glands

Question 16

• Describe the vascular supply of the dermis

Answer 16

Superficial dermal vascular plexus, mid-dermal vascular plexus & deep dermal vascular plexus

Question 17

• What is the difference between a primary and a secondary hair follicle?

Answer 17

Primary – bulb in the deep dermis, have associated sebaceous glands, sweat glands & arrector pili muscles
Secondary – not as deep in the dermis, might have an associated sebaceous gland

Question 18

• What is the difference between a simple and a compound hair follicle?

Answer 18

Simple – single hair protrudes from the follicular orifice

Compound – multiple hairs use the same follicular orifice

Question 19

• What cells make up a sebaceous gland?

Answer 19

Layer of germinative basal cells, divide and differentiate towards large polygonal cells with abundant vacuolated cytoplasm containing sebum

Question 20

• What is sebum composed of?

Answer 20

Triglycerides, cholesterol, phospholipids, other lipids, transferring, IgG, IgA

Question 21

• What are the functions of sebaceous glands?

Answer 21

Lubricates the hair & secrets pheromones

Question 22

• Give examples of other specialised sebaceous type glands in other locations

Answer 22

Meibomian gland (eyelid)
Circumanal gland (hepatoid gland) is a modified sebaceous gland
Supracaudal gland of dogs and cats
Submental glands in cats
Preputial glands in horses
Infraorbital, inguinal, interdigital in sheep

Question 23

• What is the difference between apocrine (epitrichial) & eccrine (atrichial) sweat glands?

Answer 23

Apocrine – associated with hair follicle, apical bleb of cytoplasm lost when secretion occurs
Eccrine – not associated with a hair follicle, no cytoplasm lost when secretion occurs

Question 24

• Describe the structure of a sweat gland

Answer 24

Double layer of cuboidal cells in the duct, one layer of cuboidal cells and one layer of myoepithelium in the coiled secretory part

Question 25

• What are the two main types of atrichial secretion?

Answer 25

Atrichial (eccrine) apocrine secretion – mammary glands, external ear canal, eyelids, anal sacs
Atrichial (eccrine) merocrine secretion – nasolabial region of ruminants and pigs, footpads of dogs and cats

Question 26

• What are the three stages of the hair cycle?

Answer 26

Anagen (growth phase), catagen (transitional-involuting phase) & telogen (resting phase)

Question 27

• What regulates the hair cycle?

Answer 27

Photoperiod, temperature, hormones (thyroid, growth hormone, oestrogen, corticosteroids), nutritional status, general health

Question 28

• What growth factors are involved?

Answer 28

FGF, EGF, IGF-1, TGFb, TGFa, KGF, HGF, PDGF

Question 29

• What does the duration of anagen phase determine?

Answer 29

Length of the hair

Question 30

• What are the six layers of the hair (inner to outer)?

Answer 30

Medulla, cortex, cuticle of the hair, Huxley layer, Henle layer (inner root sheath), outer root sheath, classy membrane

Question 31

• What happens during the catagen phase?

Answer 31

Involution of the hair bulb and dermal papilla, upwards migration of the follicle and papilla, loss of the internal root sheath & development of a thick glassy membrane above the bulb of the follicle

Question 32

• Describe the appearance of hair in the telogen phase

Answer 32

Bulb at the level fo the attachment of the arrector pili muscle, hair surrounded by the external root sheath which terminates at sebaceous gland level, hair bulb separated from the dermal papilla by thick basement membrane

Question 33

• What are the two types of specialised hairs?

Answer 33

Vibrissae (sinus hairs) – simple follicles with blood-filled sinus between the inner and outer layers of the dermal sheath, mechanoreceptors
Tylotrich hairs – simple follicles in amongst body hairs, mechanoreceptors

Question 34

• What does abnormal lipid metabolism result in?

Answer 34

Deficient fatty acids in ‘mortar’ layer

Question 35

• What does abnormal protein metabolism result in?

Answer 35

Deficient keratin ‘brick’ layer

Question 36

• What is seborrhea?

Answer 36

Excessive discharge of sebum from the sebaceous glands

Question 37

• Which hormones affect hair growth?

Answer 37

Thyroid hormones & growth hormones stimulate hair growth

Adrenal cortical hormones & oestrogen decrease hair growth

Question 38

• What are the causes and symptoms of atrophic dermatosis?

Answer 38

Causes – endocrine, chronic skin disease, chronic systemic disease
Symptoms – thinning of the epidermis, loss of hair follicles and adnexal structures (sebaceous and sweat glands), all of the hair follicles in telogen, no inflammation

Question 39

• What does increased corticosteroids result in?

Answer 39

Gluconeogenesis, lipolysis, protein catabolism, anti-inflammatory effects, increased appetite and thirst, hepatomegaly fat and glycogen deposition, centripetal redistribution of fat, atrophy of appendicular and abdominal muscles, atrophy of and changes in dermal collagen and glycosaminoglycan matrix

Question 40

• What are T3 and T4 responsible for?

Answer 40

Make glucose available to meet metabolic needs, stimulate glycolysis, gluconeogenesis, glucose absorption, protein synthesis & lipolysis

Question 41

• What does a lack of T3 and T4 result in?

Answer 41

Alopecia, hyperpigmentation, seborrhea, atrophy of adnexae, possibly myxoedema, epidermal atrophy or hyperplasia, possibly secondary pyoderma