Question

What cellular events lead to the formation of different germ layers during gastrulation in amphibians. Discuss the role and function of superficial and deep cells, bottle cells, the blastocoel, the blastopore lip, the IMZ, the NIMZ, the archenteron, mediolateral intercalation, convergent extension, the yolk plug, and epiboly.

Answer 1

ROLE AND FUNCTION

• superficial and deep cells :- The superficial layers are Ectoderm and Endoderm, while Mesoderm forms the inner core or deep cells. The ectoderm forms the outer layer of skin, part of Oesophagus and nerve tissues. The Endoderm develops to become the digestive tract of the organism as well as many assorted organs and the linings, like liver and lungs. Mesoderm develops into the skeletal muscle structure of the organism as well as it develops into become the bone, blood and sex organs
• bottle cells :- these are located in the dorsal marginal zone and are apically constricted inwards to start blastopore involution. Bottle cells form by the shrinking and thickening of the superficial layer within the late blastula and early gastrula. they're captive within, for the most part attributable to their attachment to the underlying deep cells, then they unfold and flatten within the latter 1/2 gastrulation to create an oversized space of the liner of the outer boundary of the archenteron.
• the blastocoel : a) permits cell migration during gastrulation

                                    b) prematurely prevents the interaction of the cells below with the cells above

                                         

• the blastopore lip :- The dorsal lip of the porta is seen as a finger like projection pointing toward the vegetal pole. the opening lip becomes composed of involuting cells that are precursors of the top germ layer. successive cells involuting over the dorsal lip of the opening are referred to as the chorda germ layer cells. These cells can form the backbone, a transient mesoblastic “back bone”
• the IMZ
• the NIMZ
• the archenteron :-  
• mediolateral intercalation : -- rows of cells move between one another, creating an array of cells that is longer but thinner.
• convergent extension :-   rows of cells intercalate, but the intercalation is highly directional.
• the yolk plug: yolk plug is the remaining patch of the endodermal cells that is created during the formation of dorsal lip of blastopore.
• epiboly :    a sheet of cells spreads by thinning.