zygote to embryo 3

Question 1

establishment of symmetry and asymmetry

Answer 1

expression of specific sets of genes establish cranial caudal and dorsal ventral axes of the embryo. Bilateral symmetry right and left sidedness is established by presence of midline structures like the notochord

Asymmetry is established by specific gene expression involving the primitive node

Question 2

inductive cell

Answer 2

induction requires:
Inducing tissue- gives the signal
transfer signal- usually diffusion
competent response- respondent tissue must be competent to respond to signal

Question 3

Neuroectoderm

Answer 3

rises from ectoderm: signaling molecules originating from the notochord and prechordal mesoderm cause changes in overlying ectoderm

ectoderm on either side of midline thickens (ectoderm cells get tallercalled neuroectoder/neural plate- precursor to the CNS

The neural plate elongates, expands cranially and narrows caudally, due to changes in cell shape and number and cycle length. Primary neurulation- when the neural plate becomes the neural tube occurs between day 18 and 28

bending and folding also occurs due to shape and cycle lengths, the basal midline or floor plate acts as a median hinge point, mesoderm proliferation helps rais folds

closure of neural tube happens at day 22

Question 4

Neural tube

Answer 4

cranial part becomes the brain, with a ventral flexture
Prodrncephalon, mesencephalon, rhombencephalon

By the mesencephalon- ectoderm thickens- inner ear
by the prsencephalon- eyeball

Question 5

Neural crest

Answer 5

cells that leave the neural tube, undergoes a epithelial->mesenchym transformation- becomes sensory neurons, PNS sheath, ANS and pigment cells

Question 6

Intraembryonic mesoderm is organized into 3 regions

Answer 6

paraxial, intermediate, and lateral

Question 7

paraxial mesoderm

Answer 7

in the head paraxial mesoderm remains unsegmented, in the trunk becomes segmented into somites, all somites are not present at once, somite formation goes cranially to caudally:
Fissure formation: mesenchy aggregates and makes presomites
Periodicity: segmentation clock and wave
Epithelialization: M->E !
Specification: regional patterns
Differentiations: form into specifc cells

Question 8

intermediate mesoderm

Answer 8

solid cell cord, nephrogenic ridge

Question 9

lateral mesoderm

Answer 9

intercellular spaces coalesce forming intraembryonic ceolom. Ceolon slits the lateral mesoderm, one layer associates with the ectoderm- this becomes the somatic mesoderm, the other layer associates with the endoderm- splanchnic mesoderm

ectoderm+ lateral mesoderm= somatopleure
endoderm + lateral plate mesoderm= splanchnopleure

Question 10

Early formation of cardiovascular system

Answer 10

precursors=hemeangioblasts, begins in wall of UV
vasculogenesis- denovo, angiogensis- branching
heart formation from splanchnic mesoderm in anteriolateral area of embryo

Question 11

folding of the embryo in the sagittal and transverse planes of the tube within the tube body plan of embryo

Answer 11

in the sagittal plane- becomes a C
neural tube elongation is the major driving force for folding
embryo lifted up into amniotic cavity

folding in transverse plane- becomes a tubular embryo- outer tube- ectoderm, inner tube- endoderm

Question 12

clsure of ventral body wall

Answer 12

4 folds- head and tail fold
2 lateral folds
draw together around the umbilical ring

heart starts beating