Structure, Function and Disorders of Epidermis, Dermis and Adnexa 12% Flashcards
Describe Vitamin D production in the epidermis
- Provitamin D3 (7-dehydrocholesterol) forms Vitamin D3 (cholecalciferol) via Previatmin D3 on exposure to sunlight
- Vitamin-D binding protein in plasma translocates Vitamin D3 from the skin to circulation
- Vitamin D3 is then hydroxylated in the liver to 25-hydroxyvitamin D3
- 25-hydroxyvitamin D3 is then hydroxylated in the kidney to form 1, 25-dihydroxyvtamin D3
Fetal skin contains a large percentage of type a)_____ collagen whereas adult skin contains a large percentage of type b)______ collagen
a) III
b) I
Transglutaminase
- Marker of early anagen hair follicles
- important in protein cross-linking that contributed to shape and strength of hair
In dogs and cats, which hairs are medullated?
Both primary (outercoat, guard) and secondary (undercoat)
Lanugo
non-medullated hair shaft
What are the three types of hairs seen in cats?
1) Guard hairs (thickest, straight, evenly tapered to a fine tip)
2) Awn hairs (thinner, possessing subapical swelling below the hair tip)
3) Down hairs (thinnest, evenly crimped or undulating)
Trichoglyphics
The study of hair tract patterns.
List how the trophic effects of cutaneous nerves are exerted on follicular growth
- regulation of vascular tone (and nutrient/oxygen supply)
- neuropeptide stimulation of receptors on follicular keratinocytes and dermal papilla fibroblasts
- modulation of macrophages and mast cells activities
List several factors that control the hair cycle
- Photoperiod (hair growth responds predominately to photoperiod)
- Ambient temperature
- Nutrition
- Hormones
- General state of health
- Genetics
- Poorly understood intrinsic factors (growth factors, cytokines produced by the hair follicle, dermal papilla and other cells)
- Sinus hairs are not subjected to a seasonal shedding and are shed continuously as single hairs
What are the transient portions of the hair follicle?
- Matrical cells
- dermal papilla cells (mesenchymal component)
What is an agouti-type hair?
Seen in the German Shepherd or Norwegian elkhound
- the tip is white or light
- The heavy body is pigmented brown or black
- The base is light yellow or red-brown
Eumelanin
- The black-brown pigment
- Activation of the melanocortin 1 receptor (MC1R) on melanocytes leads to production of eumelanin
- The shade of eumelanin is controlled by tyrosinase related protein 1 gene (TYRP1)
Pheomelanin
- The red-brown pigment
- Inhibition of the melanocortin 1 receptor (MC1R) on melanocytes leads to production of pheomelanin
List the 13 genes involved in coat coloration of dogs
1) A - agouti; agouti signaling protein (ASIP)
2) B - brown; tyrosinase related protein 1 gene (TYRP1)
3) C - colored/albino
4) D - blue dilution; melanophilin (MLPH)
5) E - extension; melanocortin 1 reception (MC1R)
6) G - graying
7) H - Harlequin
8) I - phaeomelanin dilution
K - black; beta defensin 103 gene
9) M - merle, SILV
10) P - dilute
11) R - roaning
12) S - white spotting, micropthalmia-associated transcription factor (MITF)
13) T - ticking
What is the underlying mechanism of pointed hair coats seen in Siamese, Himalayan-Persian, Balinese and Burman cats?
- There is a temperature dependent enzyme that converts melanin precursors into melanin by a process of oxidation.
- With high temperatures, the hair coat is lighter
- With low temperatures, the hair coat is darker
- Inflammation and hyperemia cause more lightly colored new hair
- Poor peripheral circulation the accompanies senility and shaving to remove hair often results in more darkly colored new hair
- Expression of this enzyme is controlled by the colorpoint restriction gene (C, tyrosinase gene, TYR)
Tortoioseshell pattern
occurs in females or in males with two XX chromosomes
What breeds of cat are characterized by a curly hair coat?
- Devon Rex: has primary hairs that resemble secondary hairs; whiskers are either absent or stubbled
- Cornish (German) Rex: lacks primary hairs, whiskers are often short and curly
- Both breeds partially or completely molt during estrus or pregnancy that result in a symmetric alopecia that may be mistaken for an endocrine alopecia
What are voight lines?
- boundaries of the areas of distribution the main cutaneous nerve stems
What are langer lines?
Reflect the course of blood vessels or lymphatics
What are blaschko lines?
- Form the pattern assumed by many different nevoid and acquired skin disease
- reflect a mosaic condition deriving from either a single mutated clone of cells originating from a post zygotic mutation or from an x-linked mutation made evident by lyonization
- These lines form a V shape or the spine, S shape on the abdomen, and axial distribution on the limbs and a wavy pattern down the forehead, over and below the eyes, over the upper lip and behind the eyes
- The black lines in a Brindle coat follow Blaschko lines
What are the four cell types found in the epidermis?
- Keratinocytes (85%)
- Merkel cells (~2%): associated with tylotrich pads
- Melanocytes (~5%)
- Langerhans cells (3-8%)
From outside to inside, label the layers of the epidermis
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
What kind of keratinocytes make up the stratum basale?
Single row of columnar - cuboidal cells
Where are the presumed sited of epidermal and hair follicle stem cells in humans and rodents?
- The tips of the deep epidermal rete ridges in glabrous skin
- The bulge (Wulst) region of the hair follicle (i.e. the site attachment of the arrector pili muscle
- Dogs and cats do not have a hair follicle bulge