Chapter 1- Ontogeny Flashcards

Structure and Function of the Skin

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1
Q

Initially the embryonic skin consists of how many layers and composed of what

A

single layer of ectodermal cells and a dermis containing mesenchymal cells in an interstitial ground substance

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2
Q

The ectodermal covering develops into what two layers as a second step in development?

A
  1. basal cell layer (stratum germinativum) 2. outer layer (periderm)
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3
Q

What is the layer that develops between the basal cell layer (Stratum germinativum) and the periderm?

A

stratum intermedium

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4
Q

What is the origin of melanocytes?

A

neural crest

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5
Q

What is the origin of Langerhans cells?

A

bone marrow

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6
Q

Fetal skin contains a large percentage of what type of collagen compared with the skin of an adult?

A

Fetal: Type III; Adult: Type I

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7
Q

Lipocytes develop from what type of precursor cells?

A

prelipoblasts

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8
Q

During what part of gestation do lipocytes form?

A

second half

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9
Q

Hair germs are AKA

A

primary epithelial germs

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10
Q

The embryonal stratum germinativum (basal cell layer) differentiates into ___germs that give rise to what three structures?

A

hair germs; 1. follicles 2. sebaceous glands 3. epitrichial (apocrine) sweat glands

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11
Q

Hair germs initially consist of an area of crowding of deeply _____cells in the____layer of the epidermis.

A

basophilic; basal

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12
Q

The areas of crowding in the basal layer of the epidermis become buds known as ______

A

epidermal placodes

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13
Q

Define epidermal placodes, what layer they come from, and what layer they protrude into

A

buds; protrude into the dermis form the epidermis

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14
Q

Where is the dermal condensate located and what structure is formed from it?

A

Located beneath each bud (epidermal placode); dermal hair papilla

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15
Q

The epidermal placode (Bud) develops into what three structures? What do each of these structures form?

A

Three epithelial cylinders. Inner cylinder: hair shaft; Outer cylinder: outer root sheath (ORS); middle cylinder (inner root sheath)

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16
Q

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 ____?

A
  1. attachment for the arrector pilli muscle 2. sebaceous gland 3. epitrichial (apocrine) sweat gland
17
Q

Secondary hair follicles develop on what side of the primary hair follicles?

A

caudal side

18
Q

The three appendages (Attachment for arrector pilli muscle, sebaceous gland, epitrichial sweat gland) develop on what side of the primary hair follicle?

A

cranial side

19
Q

What are the first hairs to appear on the fetus?

A

Vibrissae and tactile or sinus hairs on the chin, eyebrows, upper lip

20
Q

Where does general body hair first appear on the fetus? What direction does it progress?

A

The head; Caudally

21
Q

At birth the majority of a dog’s hair follicles are primary or secondary?

A

Primary

22
Q

Secondary follicles develop caudal to the primary hairs during which weeks of a dog’s life?

A

12 to 28 weeks

23
Q

Another word for atrichial sweat gland

A

Eccrine sweat gland

24
Q

What type of sweat gland germs also begin as areas of crowding of deeply basophilic cells in the basal layer of the epidermis?

A

atrichial (Eccrine) sweat gland germs

25
Q

What are MORPHOGENS?

A

They control hair follicle development

26
Q

Which six major morphogenic family systems are important in hair follicle development?

A
  1. 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
27
Q

Epitrichial sweat glands are AKA_________

atrichial sweat glands are AKA ________

A

Apocrine (= epitrichial); Eccrine (=atrichial)

28
Q

Which kind of sweat gland secrete substances indirectly?

A

apocrine (epitrichial)

29
Q

Which kind of sweat gland secrete substances directly through a duct?

A

eccrine (atrichial)

30
Q

Which kind of sweat gland occurs over most of the body and open directly onto the surface of the skin?

A

Eccrine (atrichial)

31
Q

Which kind of sweat gland opens into the hair follicle, leading to the surface of the skin?

A

Apocrine (Epitrichial) glands