Chapter 1- Ontogeny Flashcards
Structure and Function of the Skin
Initially the embryonic skin consists of how many layers and composed of what
single layer of ectodermal cells and a dermis containing mesenchymal cells in an interstitial ground substance
The ectodermal covering develops into what two layers as a second step in development?
- basal cell layer (stratum germinativum) 2. outer layer (periderm)
What is the layer that develops between the basal cell layer (Stratum germinativum) and the periderm?
stratum intermedium
What is the origin of melanocytes?
neural crest
What is the origin of Langerhans cells?
bone marrow
Fetal skin contains a large percentage of what type of collagen compared with the skin of an adult?
Fetal: Type III; Adult: Type I
Lipocytes develop from what type of precursor cells?
prelipoblasts
During what part of gestation do lipocytes form?
second half
Hair germs are AKA
primary epithelial germs
The embryonal stratum germinativum (basal cell layer) differentiates into ___germs that give rise to what three structures?
hair germs; 1. follicles 2. sebaceous glands 3. epitrichial (apocrine) sweat glands
Hair germs initially consist of an area of crowding of deeply _____cells in the____layer of the epidermis.
basophilic; basal
The areas of crowding in the basal layer of the epidermis become buds known as ______
epidermal placodes
Define epidermal placodes, what layer they come from, and what layer they protrude into
buds; protrude into the dermis form the epidermis
Where is the dermal condensate located and what structure is formed from it?
Located beneath each bud (epidermal placode); dermal hair papilla
The epidermal placode (Bud) develops into what three structures? What do each of these structures form?
Three epithelial cylinders. Inner cylinder: hair shaft; Outer cylinder: outer root sheath (ORS); middle cylinder (inner root sheath)
Three bulges appear as the hair peg lengthens and develops into a hair follicle and hair. The lowest (deepest) bulge develops into _____? The middle bulge becomes ____. The uppermost bulges becomes ____?
- attachment for the arrector pilli muscle 2. sebaceous gland 3. epitrichial (apocrine) sweat gland
Secondary hair follicles develop on what side of the primary hair follicles?
caudal side
The three appendages (Attachment for arrector pilli muscle, sebaceous gland, epitrichial sweat gland) develop on what side of the primary hair follicle?
cranial side
What are the first hairs to appear on the fetus?
Vibrissae and tactile or sinus hairs on the chin, eyebrows, upper lip
Where does general body hair first appear on the fetus? What direction does it progress?
The head; Caudally
At birth the majority of a dog’s hair follicles are primary or secondary?
Primary
Secondary follicles develop caudal to the primary hairs during which weeks of a dog’s life?
12 to 28 weeks
Another word for atrichial sweat gland
Eccrine sweat gland
What type of sweat gland germs also begin as areas of crowding of deeply basophilic cells in the basal layer of the epidermis?
atrichial (Eccrine) sweat gland germs
What are MORPHOGENS?
They control hair follicle development
Which six major morphogenic family systems are important in hair follicle development?
- genes of the Hox cluster 2. fibroblast growth factor (FGF) 3. transforming growth factor (TGF-Beta) 4. sonic hedgehog (shh) 5. Wingless or wnt pathway 6. neurotrophins
Epitrichial sweat glands are AKA_________
atrichial sweat glands are AKA ________
Apocrine (= epitrichial); Eccrine (=atrichial)
Which kind of sweat gland secrete substances indirectly?
apocrine (epitrichial)
Which kind of sweat gland secrete substances directly through a duct?
eccrine (atrichial)
Which kind of sweat gland occurs over most of the body and open directly onto the surface of the skin?
Eccrine (atrichial)
Which kind of sweat gland opens into the hair follicle, leading to the surface of the skin?
Apocrine (Epitrichial) glands
