General Skin Structure & Function (Noland)

Question 1

Describe the general migration pathway of melanoblasts to the skin.

Answer 1

Melanoblasts originate from neural crest cells at the dorsal neural tube, delaminate, and migrate dorsolaterally between the somite and ectoderm to reach the skin, where they differentiate into melanocytes.

Question 2

What are the four broad categories of tissues?

Answer 2

• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nervous tissue

Question 3

Identify the germ layers from which the components of the skin are derived.

Answer 3

The three embryonic germ layers include the endoderm, mesoderm, and ectoderm.

The epidermis of the skin is derived from the ectoderm. The dermis and subcutis of the skin are derived from the mesoderm.

Question 4

Epidermis of the skin is derived from the ________.

Answer 4

ectoderm

Question 5

The dermis and subcutis of the skin are derived from the __________.

Answer 5

mesoderm

Question 6

Main types of epithelia of the skin?

Answer 6

• Keratinized stratified squamous
• Stratified cuboidal
• Simple cuboidal
• Simple columnar

Question 7

Describe the development of the integument system

Answer 7

The epidermis of the skin is derived from the ectoderm, while the dermis and subcutis are derived from the mesoderm.

Question 8

Identify the germ layers from which the components of the skin are derived

Answer 8

Epidermis → ectoderm
Dermis & subcutis → mesoderm

Question 9

Describe the general migration pathway of melanoblasts to the skin — Origin

Answer 9

Melanocytes arise from neural crest cells, derived from the neuroectoderm on the dorsal surface (roof plate) of the neural tube.

Question 10

Identify epidermal, dermal, and subcutaneous layers of skin on a microscopic slide/image.

Answer 10

Question 11

Describe the general migration pathway of melanoblasts to the skin — Delamination & Specification

Answer 11

Neural crest cells detach (delaminate) from the neural tube, forming migratory bipotent precursor cells that divide into melanoblasts.

Question 12

Describe the general migration pathway of melanoblasts to the skin — Migration Route

Answer 12

Melanoblasts migrate along a dorsolateral pathway between the somite and ectoderm toward developing skin.

Question 13

Describe the general migration pathway of melanoblasts to the skin — Destination

Answer 13

Melanoblasts reach the skin, proliferate, and differentiate into melanocytes in the basal layer of the epidermis and hair follicles.

Question 14

Name the four broad categories of tissues

Answer 14

Epithelial, connective, muscle, and nervous.

Question 15

Name all the types of epithelia of the skin.

Answer 15

• Simple/stratified squamous
• Simple/stratified cuboidal
• Transitional
• Simple/stratified columnar
• Pseudostratified columnar

Question 16

Differentiate non-keratinized vs keratinized stratified squamous epithelium

Answer 16

Non-keratinized retains nuclei; keratinized loses nuclei and forms a protective outer layer.

Question 17

Name the areas of the body with thick vs thin skin (grossly)

Answer 17

Thick (dermal):

• dorsum
• lateral limbs (high friction)

Thin (dermal):

• ventral abdomen/thorax
• medial limbs
• axilla
• inguinal
• eyelids
• muzzle

Question 18

Name the areas where thick skin (microscopically) can be found

Answer 18

Paw pads, nose, and lip regions.

Microscopically thick = thick epidermis, usually hairless.

Question 19

Differentiate microscopic vs gross thick and thin skin

Answer 19

Microscopic = epidermal thickness
Clinical = dermal thickness

Thick epidermis → paw pads/nose/lips
Thick dermis → dorsum/lateral limbs

Question 20

Identify the layer of the skin where melanocytes reside

Answer 20

Basal layer of the epidermis.

Question 21

Identify a melanocyte within a microscopic slide or image

Answer 21

Question 22

Describe how the skin functions as a protective barrier — overview

Answer 22

Highly impermeable

Prevents chemical penetration, water loss, and pathogen entry via immune surveillance.

Question 23

Explain the brick and mortar analogy of the skin barrier

Answer 23

Bricks = corneocytes

Mortar = lipid bilayers surrounding corneocytes (stratum corneum)

Question 24

Name the immune system cell involved in the skin barrier

Answer 24

Langerhans cells — antigen-presenting immune cells in the epidermis.

Question 25

Describe the function of Langerhans cells

Answer 25

Capture antigens from skin and present them in lymph nodes (dendritic cell function).

Question 26

Name the general pH of dog skin

Answer 26

More neutral (vs human skin, which is acidic).

Question 27

Explain how pH affects the dog skin barrier

Answer 27

Neutral pH supports a healthy microbiome and prevents pathogen infection.

Question 28

Describe the general process of melanogenesis — overview

Answer 28

Melanocytes produce melanin when triggered by UV light, hormones, or genetics.

Question 29

Describe the enzymatic steps of melanogenesis

Answer 29

Tyrosinase converts tyrosine → DOPA → dopaquinone. With cysteine → pheomelanin (yellow-red). Without cysteine → eumelanin (brown-black).

Question 30

Explain how melanin is transported to keratinocytes

Answer 30

Melanin travels via microtubules/actin to melanocyte dendrite tips, then transferred to surrounding keratinocytes.

Question 31

Name the major enzyme in melanogenesis

Answer 31

Tyrosinase — rate-limiting enzyme in melanin synthesis.

Question 32

Explain how lack or mutation of tyrosinase presents clinically

Answer 32

Causes pigmentation defects (congenital or acquired), possibly affecting skin, eyes, ears, and nervous system.

Question 33

Name the two melanin pigments produced in domestic species

Answer 33

Eumelanin (black/brown) and Pheomelanin (red/yellow).

Question 34

Explain how melanin protects from UV damage

Answer 34

Melanosomes cluster above keratinocyte nuclei forming a perinuclear cap that shields DNA from UV.

Question 35

Explain the skin’s role in thermoregulation

Answer 35

* Vasoconstriction retains heat * Vasodilation promotes heat loss * Adipose tissue provides insulation and heat production

Question 36

Describe the Vitamin D synthesis pathway involving the skin

Answer 36

UVB light exposure converts 7-dehydrocholesterol (in plasma membrane of epidermal keratinocytes) → Pre-D3 undergoes hydroxylation either spontaneously or by additional UVB light exposure → Cholecalciferol (Vitamin D3, inactive form).

Question 37

Describe how the skin functions as a sensory organ

Answer 37

Detects touch, pressure, temperature, pain, proprioception, hair follicle receptors, and itch.

Question 38

Identify the four mechanoreceptors in skin

Answer 38

Encapsulated nerve ending-mechanoreceptors (x3): 1. Pacinian corpuscles 2. Meissner’s corpuscles 3. Ruffini’s corpuscles Unencapsulated free nerve endings (x1): 4. + Merkel cells

Question 39

Pacinian corpuscle — function and location

Answer 39

Detects vibration and pressure changes. Located in deep dermis/hypodermis (paw pads, joints) and firbrous tissue surrounding a nerve.

Question 40

Meissner’s corpuscle — function and location

Answer 40

Detects light/fine touch. Found in papillary dermis (paw pads, lips, muzzle).

Question 41

Ruffini’s corpuscle — function and location

Answer 41

Senses skin stretch and joint angle changes via displacement of collagen bundles. Located in reticular/deep dermis (joint capsules, paws, skin over joints).

Question 42

Unencapsulated free nerve endings — function and location

Answer 42

Sense fine touch, temperature, and pain. Extend into epidermis and hair follicle epithelium.

Question 43

Merkel cells — function and location

Answer 43

Detect fine touch, pressure, texture. Located in basal epidermis and tylotrich pads.

Question 44

What do Pacinian Corpuscles look like histologically?

Answer 44

## Footnote Pacinian corpuscles = onion-like rings

Question 45

What do Meissner Corpuscle look like histologically?

Answer 45

## Footnote Meissner corpuscle = encapsulated in dermal papillae

Question 46

What do Tylotrich Pads look like histologically?

Answer 46

## Footnote Tylotrich pad = raised epidermal mound

Question 47

Describe how the skin functions as a behavioral organ

Answer 47

Skin influences agonistic and sexual behaviors (e.g., piloerection, horn display, sexual dimorphism).