ANHB2212 - Fate of the Germ Layers

What are the 3 main types of ectoderm?

• neural tube ectoderm

• surface ectoderm

• neural crest ectoderm

Epithelial-to-Mesenchymal Transition

Neural crest cells undergo an epithelial-to-mesenchymal transition as they leave the neuroectoderm to facilitate their migration

Mesenchyme

loosely organized embryonic tissue composed of fibro-blast like cells and extracellular matrix (regardless of cell origin)

Derivatives of the neural tube ectoderm

• Neurons of the CNS

• Supporting cells of the CNS

• Somato-motor neurons of the PNS

• Presynaptic autonomic neurons of PNS

• Sensory epithelium of the ear, nose and eye (retina)

• Posterior part of the pituitary gland

What germ layer forms the neurons and supporting cells of the CNS?

neural tube ectoderm

What germ layer forms the somato-motor neurons of the PNS?

neural tube ectoderm

What germ layer forms the presynaptic autonomic neurons of the PNS?

neural tube ectoderm

What germ layer forms the sensory epithelium of the ear, nose and eye?

neural tube ectoderm

What germ layer forms the posterior pituitary?

neural tube ectoderm

What are the derivatives of surface ectoderm?

• Epidermis of skin (protection, waterproofing)

• Epidermal appendages: hair & sebaceous glands, sweat glands, mammary glands, nails

• Enamel of the teeth

• Lens of the eye

• Organs of inner ear (hearing & balance)

• Anterior pituitary gland (from Rathke’s pouch)

What germ layer forms the skin epidermis?

surface ectoderm

What germ layer forms the epidermal appendages (hair, sebaceous glands, sweat glands, mammary glands, nails)

surface ectoderm

What germ layer forms teeth enamel?

surface ectoderm

What germ layer forms the eye lens?

surface ectoderm

What germ layer forms the organs of the inner ear?

surface ectoderm

What germ layer forms the anterior pituitary?

surface ectoderm

Describe the formation of the pituitary gland.

At week 3, the infundibulum (posterior pit) migrates towards Rathke’s pouch (anterior pit). As they begin to fuse, the stalk of Rathke’s pouch regresses and the infundibular stalk forms.

What are the derivatives of the neural crest cells?

• Dorsal root ganglia and sensory neurons of the PNS

• Sympathetic chain and preaortic ganglia

• Parasympathetic (enteric) ganglia of the gastrointestinal tract

• Schwann cells (neurolemmocytes – produce myelin)

• Arachnoid and pia mater of meninges (leptomeninges) (Dura mater - from mesoderm)

• Adrenal medulla

• Melanocytes of the skin and hair follicle

What germ layer forms the dorsal root ganglia and PNS sensory neurons?

neural crest cells

What germ layer forms the sympathetic chain and preaortic ganglia?

neural crest cells

What germ layer forms the parasympathetic ganglia of the gastrointestinal tract?

neural crest cells

What germ layer forms schwann cells?

neural crest cells

What germ layer forms the arachnoid and pia mater?

neural crest cells

What germ layer forms the dura mater?

mesoderm

What germ layer forms the adrenal medulla?

neural crest cells

What germ layer forms melanocytes of skin and hair follicles?

neural crest cells

What are the derivatives of endoderm?

• Gastrointestinal tract

• Trachea, bronchi, lungs

• Liver and pancreas

• Urinary bladder and allantois

What germ layer forms the gastrointestinal tract?

endoderm

What germ layer forms the lining of the anus?

surface ectoderm

What germ layer forms the hard palate?

surface ectoderm

What germ layer forms the anterior 2/3 of the tongue?

surface ectoderm

What germ layer forms the trachea, bronchi and lungs?

endoderm

What germ layer forms the liver?

endoderm

What germ layer forms the pancreas?

endoderm

What germ layer forms the urinary bladder?

endoderm

What germ layer forms the allantois?

endoderm

What are the 4 types of intraembryonic mesoderm?

• Axial mesoderm

• Paraxial mesoderm

• Intermediate mesoderm

• Lateral plate mesoderm

What germ layer forms the notochord?

axial mesoderm

What is the function of the notochord?

Main role is to induce development in:

• Ectoderm (neurulation)

• Paraxial mesoderm (Somites)

Makes a contribution to the intervertebral disc (nucleus pulposus)

What germ layer forms the somites?

paraxial mesoderm

What are the 3 components of the somites?

• sclerotome

• dermatome

• myotome

What are derivatives of sclerotome?

• vertebral column

• ribs

What germ layer gives rise to the ribs and vertebral column?

sclerotome (paraxial mesoderm)

Dermomyotomes

dermatomes + myotomes = dermomyotomes

Dermomyotomes divide into dorsal and ventral components:

• Dorsal = epimere (epi = above, mere = segment)

• Ventral = hypomere (hypo = below

What are the derivatives of the epimere (myotome component)?

intrinsic back muscles (epaxial muscles) and dorsal rami of spinal nerves

What are derivatives of epimere (dermatome component)?

dermis covering the intrinsic back muscles

What are derivatives of hypomere (myotome component)?

• body wall

• limb muscles

• extrinsic back muscles (hypaxial muscles)

What happens to the hypomere (dermatome component)?

disintegrates

What germ layer forms the dermis of the body wall and limbs?

lateral plate mesoderm

What are derivatives of intermediate mesoderm?

paired glands and associated structures such as:

• kidneys

• ureters

• gonads + ducts + accessory glands

• adrenal cortex

What germ layer forms the kidneys and ureters?

intermediate mesoderm

What germ layer forms the gonads?

intermediate mesoderm

What germ layer forms the adrenal cortex?

intermediate mesoderm

What forms primordial germ cells?

epiblast

• First located in yolk sac close to the allantois

• Migrate along the wall of the hindgut and the dorsal mesentery into the genital ridge

• Give rise to male and female gametes (sex cells)

What are derivatives of lateral plate mesoderm?

• somatopleure (appendicular skeleton, bones, tendons, dermis)

• splanchnopleure ( mesenteries, viscera connective tissue and muscle, cardiovascular system, spleen)

• pleura, pericardium & peritoneum (lining of the coelomic cavity)

• serous membranes of these body cavitie

What germ layer forms the appendicular skeleton (limbs + girdles)

lateral plate mesoderm (somatopleure)

What germ layer forms tendons?

lateral plate mesoderm (somatopleure)

What germ layer forms the dermis?

lateral plate mesoderm (somatopleure)

What germ layer forms the mesenteries of the gut wall?

lateral plate mesoderm (splanchnopleure)

What germ layer forms tissue and muscle of the viscera?

lateral plate mesoderm (splanchnopleure)

What germ layer forms the cardiovascular system?

lateral plate mesoderm (splanchnopleure)

What germ layer forms the spleen?

lateral plate mesoderm (splanchnopleure)

What germ layer forms the pleura, pericardium and peritoneum?

lateral plate mesoderm

What germ layer forms serous membranes?

lateral plate mesoderm

What are the derivatives of the extraembryonic mesoderm?

placenta and umbilical cord

What are derivatives of the intraembryonic coelom?

• pericardial cavity

• pleural cavity

• peritoneal cavity

What component of the mixed spinal nerve innervates the hypaxial muscles?

ventral rami

What component of the mixed spinal nerve innervates the epaxial muscles?

dorsal rami