Chapter 1- Ontogeny

Question 1

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

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

stratum intermedium

Question 4

What is the origin of melanocytes?

Answer 4

neural crest

Question 5

What is the origin of Langerhans cells?

Answer 5

bone marrow

Question 6

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

Answer 6

Fetal: Type III; Adult: Type I

Question 7

Lipocytes develop from what type of precursor cells?

Answer 7

prelipoblasts

Question 8

During what part of gestation do lipocytes form?

Answer 8

second half

Question 9

Hair germs are AKA

Answer 9

primary epithelial germs

Question 10

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

Answer 10

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

Question 11

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

Answer 11

basophilic; basal

Question 12

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

Answer 12

epidermal placodes

Question 13

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

Answer 13

buds; protrude into the dermis form the epidermis

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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 ____?

Answer 16

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

Question 17

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

Answer 17

caudal side

Question 18

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

Answer 18

cranial side

Question 19

What are the first hairs to appear on the fetus?

Answer 19

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

Question 20

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

Answer 20

The head; Caudally

Question 21

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

Answer 21

Primary

Question 22

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

Answer 22

12 to 28 weeks

Question 23

Another word for atrichial sweat gland

Answer 23

Eccrine sweat gland

Question 24

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

Answer 24

atrichial (Eccrine) sweat gland germs

Question 25

What are MORPHOGENS?

Answer 25

They control hair follicle development

Question 26

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

Answer 26

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

Question 27

Epitrichial sweat glands are AKA_________

atrichial sweat glands are AKA ________

Answer 27

Apocrine (= epitrichial); Eccrine (=atrichial)

Question 28

Which kind of sweat gland secrete substances indirectly?

Answer 28

apocrine (epitrichial)

Question 29

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

Answer 29

eccrine (atrichial)

Question 30

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

Answer 30

Eccrine (atrichial)

Question 31

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

Answer 31

Apocrine (Epitrichial) glands