gastrulation and neuralation (week 8)

Question 1

What (in its most simple form) is gastrulation?

Answer 1

when two layers become three

Question 2

what happens at the beginning of week 3 (after about 13 days) (beginning of gastrulation)?

Answer 2

There is already an anterior/posterior axis established. Along the posterior (tail) end the primitive groove begins to form in the epiblast layer with the primitive node at the head. the cilia in the primitive pit below the primitive node define left and right in the embryo.

Question 3

what is the name of the anterior region of the epiblast at 13 days?

Answer 3

the anterior visceral endoderm.

Question 4

what begins to happen at the primitive streak and node?

Answer 4

epiblast cells (endoderm) begin to stream into the embryo and pile up in between the epiblast and hypoblast cells as well as replacing the hypoblast cells. A middle mesoderm layer develops as well as the bottom endoderm layer. A special structure called the notochord also forms in front of the primitive node.

Question 5

which structure organises dorsal structures in the developing embryo?

Answer 5

the primitive node/notochord.

Question 6

how does the skin/ventral structure (belly) develop?

Answer 6

by using signals from bone morphogenic proteins (BMPs)

Question 7

how does the primitive node and notochord promote the development of the spinal and neural tissue?

Answer 7

by releasing BMP blocking factors: chordin, noggin and follistatin. The blockage of BMP results in the development of neural/back tissue instead.

Question 8

which structure induces neurulation (the folding of the neural plate to form a neural tube)

Answer 8

the notochord, deep to the neural epithelium

Question 9

what happens to the epithelial cells just before neurulation?

Answer 9

they become columnar

Question 10

at what point (how many days) does a midline groove become apparent?

Answer 10

19+

Question 11

at how many days do the cells on the plate edge thicken forming neural folds and a neural groove?

Answer 11

at 10-21 days (end of third week)

Question 12

What happens at around day 22?

Answer 12

the edges of the neurual folds roll over and a neural tube forms. This happens by the apical cells constricting at their apex by the actin fibres of the cytoskeleton constricting in a ring.

Question 13

where is the first region to fuse to form the neural tube?

Answer 13

the cervical region

Question 14

what is the rostral neuropore?

Answer 14

the opening of the neural tube which forms the head end

Question 15

what is the caudal neuropore?

Answer 15

the opening of the neural tube which forms the ‘tail’ end.

Question 16

how many vesicles develop into the brain?

Answer 16

3

Question 17

what is the condition called which results in the failure of the rostral neuropore to close?

Answer 17

anencephaly

Question 18

what is the resulting condition caused by the failure of the caudal neuropore to close?

Answer 18

some forms of spina bifida

Question 19

after how many days should the rostral neuropore close?

Answer 19

after 25 days

Question 20

after how many days should the caudal neuropore close?

Answer 20

after 27 days

Question 21

where do neural crest cells come from?

Answer 21

above the neural tube in the epithelium. They migrate away from the neural tube epithelium and give rise to a variety of cells.

Question 22

which ganglia cells do the neural crest cells produce?

Answer 22

cranial nerve ganglia, dorsal root ganglia and autonomic ganglia

Question 23

what other neural cells do the neural crest cells produce?

Answer 23

schwann cells and peripheral glial cells

Question 24

what are some of the cells in the face that the neural crest cells produce?

Answer 24

odontoblasts and craniofacial skeleton.

Question 25

what are some other cells that the neural crest cells give rise to?

Answer 25

adrenal medulla, thyroid parafollicular (C) cells and melanocytes and smooth muscle of cardiac outflow

Question 26

what are some symptoms of wwarddenburg's syndrome?

Answer 26

pigment abnormalities (even albinism), deafness, telecanthus (widely spaced eyes), heterochromia of eyes (different coloured eyes) some types shoe constipation

Question 27

what is treachercollins syndrome?

Answer 27

defective protein calles treacle (TCOF1 gene); failure of formation/apoptosis of neural crest cells; abnormal eye shape; micrognathia; conductive hearing loss; underdeveloped zygoma and malformed ears

Question 28

what is the mesoderm called closest to the notochord?

Answer 28

the paraxial mesoderm

Question 29

what is the next layer of mesoderm called closest to the paraxial mesoderm?

Answer 29

the intermediate mesoderm

Question 30

what is the new layer of mesoderm called after the intermediate mesoderm?

Answer 30

the lateral plate mesoderm

Question 31

where do somites begin to develop?

Answer 31

on either side of the neural tube on the paraxial mesoderm

Question 32

how do cells form somites along the paraxial mesoderm?

Answer 32

cells go through a 90 minute cycle signalled by the notch signalling clock. There is a wave of FGF signal which passes along the embryo during the 90 minute cycle and signals to the cells which part of the somite they should be (front, mid or tail) depending on when the FGF passes the cells during the cycle (early, mid or late). the somites form the different segments of the body (Sclerotome, myotome and dermatome)

Question 33

what are the different segments of the body which arise from the somites?

Answer 33

sclerotome, myotome and dermatome

Question 34

what does the intermediate mesoderm give rise to?

Answer 34

the kidney and gonads

Question 35

what does the lateral plate mesoderm give rise to?

Answer 35

Splanchnic (coverings, viscera and CVS) and somatic (body wall)

Question 36

what does the notochord become in the adult body?

Answer 36

the nucleus pulposus

Question 37

how does the gut tube form?

Answer 37

the surface ectoderm (epiblast cells) surround the yolk sac completely. The yolk sac then becomes the gut tube and an embryonic body cavity forms around the gut tube.

Question 38

what is the vitelline duct?

Answer 38

the remainder of the connection between the gut tube and yolk sac. Usually obliterated around 5-6 weeks. Can cause Mockers diverticulum in about 2% of population if it remains (2% of affected individuals experience symptoms e.g. bleeding)

Question 39

what are some derivatives of the ectoderm?

Answer 39

epidermis, lens and retina olfactory epithelium, oral cavity epithelium, sensory organs of ear, glands:salivary gland, sweat gland and mammary gland and adenohypophysis.