Ectodermal Placode

What are ectodermal placodes?

Thickenings in the surface ectoderm that give rise to sensory structures and other tissues.

What is the origin of the epidermis?

The epidermis originates from ectodermal cells.

What is the role of BMPs in epidermis development?

BMPs promote epidermal specification and block the neural pathway.

What structures do cranial placodes develop into?

Cranial placodes develop into sensory tissues, including the lens of the eye and olfactory epithelium.

What is the function of the adenohypophyseal placode?

It will become the anterior lobe of the pituitary gland.

What does the olfactory placode develop into?

It develops into the first cranial nerve (CN I) and contributes to the sense of smell.

What is the trigeminal placode responsible for?

It contributes to the 5th cranial nerve (CN V) and the nasal cavity.

What does the otic placode give rise to?

It gives rise to the sensory epithelium of the inner ear and the 8th cranial nerve, involved in hearing and balance.

What are the epibranchial placodes associated with?

They are associated with taste buds, tonsils, and sensory functions in the heart, lungs, and GI tract.

What is the basal layer of the epidermis called?

The stratum basale (germinavitium).

What happens to cells in the stratum basale?

They are asymmetrical stem cells that rise to upper layers of the skin, becoming more keratinized and flat.

What are ectodermal appendages?

Structures such as hair, teeth, sweat glands, and mammary glands that develop from ectodermal epithelium.

How do ectodermal appendages form?

They require interaction between ectodermal epithelium and mesenchyme.

What are the major subdivisions of embryonic ectoderm?

Cranial sensory placodes and epidermal placodes.

What is the significance of cranial sensory placodes?

They are local thickenings of ectoderm that contribute to sensory organs like eyes, nose, and ears.

What induces cranial placodes?

They are induced by neighboring tissues and signaling pathways such as FGF and Wnt.

What is the role of FGF in cranial placode development?

FGF helps convert neural crest cells into pre-neural cells and induces placode formation.

What is the function of the otic placode?

It gives rise to mechanosensory hair cells and neurons for hearing and balance.

What is the most superficial layer of the skin?

The stratum corneum.

What happens to cells as they move from the stratum basale to the surface?

They become more keratinized, flatten, and eventually die.

What is the embryonic origin of the lens of the eye?

It originates from the lens placode.

What do sensory placodes give rise to?

They give rise to structures such as nasal organs and olfactory epithelium.

What is the relationship between the neural crest and cranial placodes?

Cranial placodes have contributions from the cranial neural crest but primarily generate peripheral neurons.

What are cranial sensory placodes?

Epithelial thickenings that give rise to sensory neurons and other structures in the head.

What role do the neurons from the olfactory placode play in reproduction?

They are involved in the production of testosterone, estrogen, and progesterone.

What does the trigeminal placode give rise to?

The distal end of the trigeminal ganglion, which gathers sensory stimuli from the head and face.

What sections of the trigeminal nerve are associated with the trigeminal placode?

The ophthalmic and maxilla-mandibular sections.

What is unique about the lens placode?

It does not form neurons and is a precursor to the lens.

What do lens fiber cells provide?

A transparent and refractive medium for light to pass to the retina.

What sensory neurons do the epibranchial placodes give rise to?

Sensory neurons of the facial, glossopharyngeal, and vagal nerves.

What functions do the glossopharyngeal nerves serve?

They are involved in swallowing (gag reflex) and taste (posterior 1/3 of the tongue).

What is the epidermis?

A tough, elastic, water impermeable membrane originating from ectodermal cells.

What induces the formation of the epidermis?

Bone Morphogenetic Proteins (BMPs) induce surface ectoderm to form epidermis instead of neural tissue.

What are the main components of mammalian skin?

Stratified epidermis and an underlying dermis composed of loosely packed fibroblasts.

What role do melanocytes play in the epidermis?

They provide pigmentation and are derived from neural crest cells.

What is the significance of the basal layer of the epidermis?

It contains epidermal stem cells and is the only layer that is mitotically active.

What happens to the outer layer of the epidermis during development?

It becomes the periderm, a temporary layer that is shed.

What is the inner layer of the epidermis called?

The basal layer or stratum germinativum.

What pathway facilitates the division of cells in the epidermis?

The Notch pathway.

What occurs if the Notch pathway is inhibited?

Hyperproliferation of dividing cells may occur.

What is the characteristic of the skin's renewal process?

The skin is constantly being renewed by a population of epidermal stem cells.

What is the primary function of cell division in the basal layer of the epidermis?

To produce younger cells that push older cells to the skin surface.

What are keratinocytes?

Differentiated epidermal cells that produce a water-impermeable seal of lipids and proteins.

What happens to keratinocytes as they reach the skin surface?

They become dead, flattened sacs of keratin protein.

What is the cornified layer of the epidermis called?

Stratum corneum.

What role do BMPs play in epidermal development?

BMPs induce the p63 transcription factor in the basal layer, required for keratinocyte proliferation and differentiation.

What is the function of the Notch activator Jagged in the epidermis?

Jagged activates the Notch protein on adjacent cells to prevent further cell division.

What is the significance of Notch signaling in epidermal cells?

It is necessary for transitioning cells from the basal layer to the spinous layer.

What occurs to epidermal cells as they transition to the stratum corneum?

They become metabolically inert and lose cytoplasmic organelles.

What are epidermal placodes?

Ectodermal appendages formed from interactions between mesenchymal dermis and ectodermal epidermis.

What do epidermal placodes give rise to?

Hairs, scales, scutes, teeth, sweat glands, mammary glands, and feathers.

What is the hair placode's role in development?

It develops into the hair follicle bud, with connective tissues derived from mesoderm.

What is the dental lamina?

An epidermal thickening that develops into separate tooth placodes in each jaw.

What is the fate of mammary placodes in humans?

Only one pair survives, forming mammary glands, while in mice, five pairs typically survive.

What happens during the bud stage of epidermal placode development?

Ectoderm grows into the mesenchyme, with superficial cells contracting and intercalating.

What is the role of inductive interactions between epithelium and mesenchyme?

They are specific and determine the ability of tissues to form structures like teeth and hair.

How does dental mesenchyme influence tooth formation?

It can induce tooth formation when combined with dental epithelium from the jaw of a mouse embryo.

What is the outcome when dental epithelium is combined with non-dental mesenchyme?

It can still cause tooth formation, demonstrating the specificity of inductive interactions.

What is the significance of keratin expression in epidermal cells?

It marks the transition to terminal differentiation as cells migrate through the granular layers.

What happens to epidermal cells during the apoptotic-like destructive phase?

They become metabolically inert and lose their organelles, including the nucleus.

What is the primary goal of the epidermal transition process?

To push older cells towards the surface to become part of the stratum corneum.

What is the role of keratin-building proteins in the epidermis?

They are expressed as cells migrate through the granular layers, contributing to the cornified envelope.

What type of protein is Jagged?

A juxtacrine protein that activates the Notch signaling pathway in keratinocyte differentiation.