64: Phylogeny and development of the skin Flashcards
What is the origin of the epidermis?
Ectoderm.
What are the derivatives of the epidermis?
Feathers, hairs, and skin glands.
What are the characteristics of the epidermis?
Composed of keratinized, stratified squamous epithelium.
What is the origin of the dermis?
Mesoderm.
What are the characteristics of the dermis?
Made up of reticular connective tissue.
What is the origin of the hypodermis (tela subcutanea)?
Mesoderm.
What are the characteristics of the hypodermis?
Consists of reticular and adipose tissues.
What is keratin?
A fibrous structural protein forming the primary constituent of scales, nails, hooves, and horns in vertebrates.
What are corneous (horny) scales?
Found in reptiles like lizards and snakes; provide protection and assist in locomotion.
What are corneous (horny) plates?
Found in reptiles and some mammals, serving as armor.
What are feathers and their functions?
Exclusive to birds, crucial for flight, insulation, and display.
What are hairs (fur) and their functions?
Present in mammals, offering insulation, protection, and sensory functions.
What are placoid scales and where are they found?
Found in sharks, made of dentin covered by enamel, enhancing hydrodynamics and protection.
What are ganoid scales?
Present in certain ancient and living fishes, characterized by a rhombus shape and a hard enamel-like surface.
What are bony plates?
Dermal appendages that provide structural protection.
Define skin.
The soft, flexible outer tissue covering the body of vertebrate animals.
What are the functions of the skin?
- 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.
What is the initial stage of epidermis development?
Starts as a single layer called the surface ectoderm.
What happens during periderm formation in epidermis development?
The surface ectoderm cells multiply and form the periderm, a temporary cover for the developing skin.
What occurs during stratification in the epidermis?
The epidermis starts layering, forming multiple layers of specialized cells.
What is cornification in epidermis development?
Cells at the outermost layer die, turning into a tough layer made of keratin and lipids, forming the protective barrier.
How does the permeability of fetal skin change during development?
Initially very permeable, it becomes impermeable post-cornification, sealing off the fetus from the surrounding fluid.
What are the key pathways in epidermal development?
- 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.
Describe the cellular hierarchy in epidermal development.
Stem cells (SCs) in the basal layer lead to committed progenitor cells (CPs), which further differentiate into terminally differentiated cells (TDs).
What do the Lines of Blaschko represent?
The pattern of developmental growth and epidermal cell migration, distinct from vascular, lymphatic, or nervous structures of the skin.
What characterizes the epidermis of fish (Pisces)?
Stratified epithelium with multiple cell layers.
What are the features of the dermis in fish (Pisces)?
- Single-celled mucous glands.
- Chromatophores.
- Dermal scales (bony and placoid).
- Ganoid scales.
Describe the epidermis of amphibians.
Features protective layers such as the stratum corneum and stratum germinativum.
What is the structure of the dermis in amphibians?
- Contains stratum spongiosum and stratum compactum.
- Multicellular glands (mucous, seromucous, and poison).
- Functions in evaporation prevention and respiratory exchange.
What characterizes the epidermis and dermis in reptiles?
- Epidermis: Well-developed stratum corneum with epidermal scales.
- Dermis: Thick with chromatophores, bony plates, skin glands near jaws and cloaca, and sometimes venom glands.
What is molting in reptiles?
Occurs in one piece or in patches, facilitating growth and renewal.
Describe the epidermis and dermis in birds (Aves).
- Epidermis: Thin, with beaks, claws, and leg scales.
- Dermis: Contains muscular fibers, uropygial gland, and various feather types (contour, down, filoplumes).
What are the layers of the epidermis in mammals?
Stratum corneum, lucidum, granulosum, and spinosum.
What are the features of the dermis in mammals?
- Contains stratum papillae and stratum reticulare.
- Includes CT-fibers, nerve endings, blood vessels, and various glands (sweat, sebaceous, mammary).
What are keratin structures in mammals?
Claws, nails, hooves, and horns.
What are the sources of origin for dermis development?
- Dorsal Trunk: From dermatomes of somites.
- Ventral/Lateral and Limbs: From lateral mesoderm.
- Cranial Skin and Anterior Neck: From neural crest cells.
Describe the formation process of the dermis.
- Starts with loosely aggregated mesenchymal cells.
- These cells secrete a matrix rich in hyaluronic acid and glycogen.
How do mesenchymal cells differentiate in dermis development?
- Mesenchymal cells transform into fibroblasts.
- Fibroblasts produce collagen (types I and III) and elastic fibers.
What is the structure of the mature dermis?
- Becomes a fibroelastic connective tissue, rich in blood vessels.
- Divided into two layers: the upper papillary layer and deeper reticular layer.
What is papillae formation in the dermis?
- Papillae, or dermal thickenings, extend into the epidermis.
- Contain capillaries and sensory nerve endings like Vater-Pacini, Meissner, and Kraus corpuscles.
What is alopecia in abnormal skin development?
Can be linked to the absence of sebaceous glands.
What is polythelia in abnormal skin development?
The presence of extra nipples, more than typically found in mammals.
What is polymastia in abnormal skin development?
Appearance of additional mammary glands beyond the normal number.
