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Flashcards in Gastrulation and Neurulation Deck (38):

What is the form of the disk at the end of week 2?

Bi-laminar disc (epiblast and hypoblast)


What happens at the beginning of week 3?

Gastrulation begins


What are the key structures on the bi-laminar disc as gastrulation begins?

+ Anterior visceral endoderm of hypoblast defines anterior

+ Primitive streak (groove on epiblast)

+ Primitive pit and associated primitive node


What happens at the streak and node during gastrulation when the endoderm is formed?

Epiblast cells stream into the embryo along the primitive streak/node and replace hypoblast cells


What happens during gastrulation when the mesoderm is being formed?

+ Epiblast cells stream into the embryo along the primitive streak between the two layers

+ In front of the node a specialised mesoderm structure called the notochord forms between the two layers


What is the notochord?

+ An important signalling structure

+ Primitive beginning to the spine

+ Appears in embryos as a small flexible rod made from mesoderm cells


What is neurulation?

+ The folding process in vertebrate embryos, - transformation of the neural plate into the neural tube

+ The embryo at this stage is termed the neurula


What does the primitive node/notochord organise?

Dorsal structures


Why is the notochord an important signalling structure?

It releases factors (chordin, noggin, follistatin) which block the effects of BMP, allowing neural tissue to form instead of skin


What happens to the neural plate at around 19 days?

+ Neurulation induced by notochord (deep to neural epithelium)

+ Epithelial cells become columnar

+ The plate will form a tube (neurulation)

+ Day 19+ a midline groove becomes apparent


What happens around 20-21 days (end of third week)?

+ Cells on plate edge thicken and form neural folds and a neural groove


What happens during day 22+ of the fourth week?

There is fusion in the cervical region of the neural folds and neural tube beings to form


What causes the curvature of the columnar cells to form the tube?

Actin rings around apex of columnar cells constricts


Approx. how long does it take for the rostral/nose-end to close?

25 days


What forms at the rostral/nose-end?

rostral neuropore


Approx. how long does it take for the caudal/tail-end to close?

27 days


What forms at the caudal/tail-end?

Caudal neuropore


What happens if the rostral neuropore fails to close?

- brain fails to develop


What happens if the caudal neuropore fails to close?

Some forms of spina bifida
- neural tissue remain open to the environment


Name cells which are derived from neural crest cells

+ Cranial nerve ganglia
+ Dorsal root ganglia
+ Autonomin ganglia
+ Adrenal medulla
+ Schwann cells

+ Peripheral glial

+ Smooth muscle of cardiac flow

+ Odontoblasts
+ Craniofacial skeleton

+ Thyroid parafollicular (C) cells
+ Melanocytes



What are two possible syndromes that can develop due to defective neural crest development?

+ Waardenburg's Syndrome (1/50,000)

+ Treacher Collins Syndrome (autosomal dominant 1/50,000)


What are features of Waardenburg's Syndrome?

+ Some types have Pax-3 deletion

+ Pigment abnormalities (even albinism)

+ Deafness

+ Heterochromia of eyes

+ Telecanthus (widely serparated eye "corners")

+ Other types show additional constipation (SOX10)


What are features of Treacher Collins Syndrome?

+ Defective protein called Treacle (TCOF1 gene)

+ Failure of formation/apoptosis of neural crest cells

+ Abnormal eye shape

+ Micrognathia

+ Conductive heating loss

Underdeveloped zygoma

+ Malformed ears


What are the different layers of mesoderm?

+ Paraxial
+ Intermediate
+ Lateral plate


What is formed when the paraxial mesoderm becomes segmented?



What are the features of somite formation?

+ Cells have a timer along paraxial mesoderm

+ Go through cycles every 90 mins defined by notch signalling clock

+ Wave of FGF signal that passes along the embryo

+ When wave passes cells they are programmed to change into part of a somite


What are the crucial timings of the somite formation cycle?

+ If the wave passes cells early in the cycle they become the front end of the segment

+ If the wave passes cells late in the cycle they become the tail end of the segment

The process is repeated over and over


What do homeobox genes do?

+ Direct formation of body structures e.g from body segments

+ Critical for forming body axes


What are derivates of the paraxial mesoderm?

+ Head

+ Somites (sclerotome, myotome, dermatome)


What are derivates of the intermediate mesoderm?

+ Kidneys
+ Gonads


What are derivates of the lateral plate mesoderm?

+ Splanchnic (coverings, viscera, CVS)

+ Somatic (parietal, body wall)


What are derivates of the midline mesoderm?

+ Prechordal plate

+ Notochord (nucleus pulposus)


What does the yolk sac become?

The gut tube (remnant of gut tube)


How does the gut tube form?

Amniotic cavity enwraps and surrounds the embryo, almost completely cutting off gut from the yolk sac


What does the urinary bladder have a connection with?

The cloaca


When does the vitelline duct usually obliterate?

Around 5-6 weeks


What is and what causes Meckels diverticulum?

+ A congenital abnormality of the small intestine

+ Due to remnant of vitalline duct (yolk sac/gut connection)


What are some derivatives of the ectoderm?

+ Epidermis
+ Lens and retina
+ Olfactory epithelium
+ Oral cavity epithelium
+ Sensory organs of ear
+ Glands: salivary, sweat, mammary
+ Adenohypophysis