64: Phylogeny and development of the skin

Question 1

What is the origin of the epidermis?

Answer 1

Ectoderm.

Question 2

What are the derivatives of the epidermis?

Answer 2

Feathers, hairs, and skin glands.

Question 2

What are the characteristics of the epidermis?

Answer 2

Composed of keratinized, stratified squamous epithelium.

Question 3

What is the origin of the dermis?

Answer 3

Mesoderm.

Question 4

What are the characteristics of the dermis?

Answer 4

Made up of reticular connective tissue.

Question 5

What is the origin of the hypodermis (tela subcutanea)?

Answer 5

Mesoderm.

Question 6

What are the characteristics of the hypodermis?

Answer 6

Consists of reticular and adipose tissues.

Question 7

What is keratin?

Answer 7

A fibrous structural protein forming the primary constituent of scales, nails, hooves, and horns in vertebrates.

Question 8

What are corneous (horny) scales?

Answer 8

Found in reptiles like lizards and snakes; provide protection and assist in locomotion.

Question 9

What are corneous (horny) plates?

Answer 9

Found in reptiles and some mammals, serving as armor.

Question 10

What are feathers and their functions?

Answer 10

Exclusive to birds, crucial for flight, insulation, and display.

Question 11

What are hairs (fur) and their functions?

Answer 11

Present in mammals, offering insulation, protection, and sensory functions.

Question 12

What are placoid scales and where are they found?

Answer 12

Found in sharks, made of dentin covered by enamel, enhancing hydrodynamics and protection.

Question 13

What are ganoid scales?

Answer 13

Present in certain ancient and living fishes, characterized by a rhombus shape and a hard enamel-like surface.

Question 14

What are bony plates?

Answer 14

Dermal appendages that provide structural protection.

Question 15

Define skin.

Answer 15

The soft, flexible outer tissue covering the body of vertebrate animals.

Question 16

What are the functions of the skin?

Answer 16

• Protection: Shields against mechanical damage and pathogens.
• Hydration: Acts as a semi-impermeable barrier against excessive water loss.
• Thermoregulation: Provides insulation and regulates body temperature.
• Sensation: Contains nerve endings sensitive to various stimuli.
• Synthesis and Storage: Facilitates water retention, lipid synthesis, and production of Vitamin D.
• Respiratory Function: In some amphibians, serves as the primary respiratory organ.

Question 17

What is the initial stage of epidermis development?

Answer 17

Starts as a single layer called the surface ectoderm.

Question 18

What happens during periderm formation in epidermis development?

Answer 18

The surface ectoderm cells multiply and form the periderm, a temporary cover for the developing skin.

Question 19

What occurs during stratification in the epidermis?

Answer 19

The epidermis starts layering, forming multiple layers of specialized cells.

Question 20

What is cornification in epidermis development?

Answer 20

Cells at the outermost layer die, turning into a tough layer made of keratin and lipids, forming the protective barrier.

Question 21

How does the permeability of fetal skin change during development?

Answer 21

Initially very permeable, it becomes impermeable post-cornification, sealing off the fetus from the surrounding fluid.

Question 22

What are the key pathways in epidermal development?

Answer 22

• FGFs: Promote neural induction.
• BMPs and Wnt: Drive epidermal fate determination.
• Retinoic Acid and Sonic Hedgehog: Involved in epidermal cell fate decisions.
• Notch Signaling: Regulates the commitment between hair follicles and interfollicular epidermal lineages.

Question 23

Describe the cellular hierarchy in epidermal development.

Answer 23

Stem cells (SCs) in the basal layer lead to committed progenitor cells (CPs), which further differentiate into terminally differentiated cells (TDs).

Question 24

What do the Lines of Blaschko represent?

Answer 24

The pattern of developmental growth and epidermal cell migration, distinct from vascular, lymphatic, or nervous structures of the skin.

Question 25

What characterizes the epidermis of fish (Pisces)?

Answer 25

Stratified epithelium with multiple cell layers.

Question 26

What are the features of the dermis in fish (Pisces)?

Answer 26

• Single-celled mucous glands.
• Chromatophores.
• Dermal scales (bony and placoid).
• Ganoid scales.

Question 27

Describe the epidermis of amphibians.

Answer 27

Features protective layers such as the stratum corneum and stratum germinativum.

Question 28

What is the structure of the dermis in amphibians?

Answer 28

• Contains stratum spongiosum and stratum compactum.
• Multicellular glands (mucous, seromucous, and poison).
• Functions in evaporation prevention and respiratory exchange.

Question 29

What characterizes the epidermis and dermis in reptiles?

Answer 29

• Epidermis: Well-developed stratum corneum with epidermal scales.
• Dermis: Thick with chromatophores, bony plates, skin glands near jaws and cloaca, and sometimes venom glands.

Question 30

What is molting in reptiles?

Answer 30

Occurs in one piece or in patches, facilitating growth and renewal.

Question 31

Describe the epidermis and dermis in birds (Aves).

Answer 31

• Epidermis: Thin, with beaks, claws, and leg scales.
• Dermis: Contains muscular fibers, uropygial gland, and various feather types (contour, down, filoplumes).

Question 32

What are the layers of the epidermis in mammals?

Answer 32

Stratum corneum, lucidum, granulosum, and spinosum.

Question 33

What are the features of the dermis in mammals?

Answer 33

• Contains stratum papillae and stratum reticulare.
• Includes CT-fibers, nerve endings, blood vessels, and various glands (sweat, sebaceous, mammary).

Question 34

What are keratin structures in mammals?

Answer 34

Claws, nails, hooves, and horns.

Question 35

What are the sources of origin for dermis development?

Answer 35

• Dorsal Trunk: From dermatomes of somites.
• Ventral/Lateral and Limbs: From lateral mesoderm.
• Cranial Skin and Anterior Neck: From neural crest cells.

Question 36

Describe the formation process of the dermis.

Answer 36

• Starts with loosely aggregated mesenchymal cells.
• These cells secrete a matrix rich in hyaluronic acid and glycogen.

Question 37

How do mesenchymal cells differentiate in dermis development?

Answer 37

• Mesenchymal cells transform into fibroblasts.
• Fibroblasts produce collagen (types I and III) and elastic fibers.

Question 38

What is the structure of the mature dermis?

Answer 38

• Becomes a fibroelastic connective tissue, rich in blood vessels.
• Divided into two layers: the upper papillary layer and deeper reticular layer.

Question 39

What is papillae formation in the dermis?

Answer 39

• Papillae, or dermal thickenings, extend into the epidermis.
• Contain capillaries and sensory nerve endings like Vater-Pacini, Meissner, and Kraus corpuscles.

Question 40

What is alopecia in abnormal skin development?

Answer 40

Can be linked to the absence of sebaceous glands.

Question 41

What is polythelia in abnormal skin development?

Answer 41

The presence of extra nipples, more than typically found in mammals.

Question 42

What is polymastia in abnormal skin development?

Answer 42

Appearance of additional mammary glands beyond the normal number.