Diploblastic in Simpler animals such as cnidarian , possess two germ layers

Triploblastic is a condition of the blastula in which there are three primary germ layers

GASTRULATION OCCURS IN THE FOLLOWING SEQUENCE:

(1) The embryo becomes asymmetric

(2) The primitive streak forms

(3) Epithelial to Mesenchymal transition

(4)Ingress cells at the primitive streak

Formation of the primitive streak

Primitive Streak

Primitive Groove

Primitive Node

Primitive Pit

Fate Mape of The Epiblast

Prechordal Plateprechordal plate forms both:•mesodermal (part of head mesenchyme) •endodermal (part of oropharyngeal membrane) •it is often considered to be a mesendodermalstructure

Epithelial to mesenchymaltransition

Notchord Formation

The notochord is formed through the addition of cells to its caudal end as the primitive streak regresses

Sacrococcygeal Teratoma

Left and right assymetry

Nodalal Flow Model

1.The Mechanosensory Model

2.Nodal Vesicular Parcels (NVP)

Nodal cilia

1.The Mechanosensory Model

2.Nodal Vesicular Parcels (NVP)

(Kartagener syndrome)Dysfunctional ciliaRespiratory problemsMale fertility problems

Situs inversus

Formation Of Definitive Endoderm

Formation Of Definitive Mesoderm

Paraxial mesoderm in Head region The paraxial mesoderm in the head region forms bands of un-

segmented cells

• It loosely fills the developing head as head mesenchyme

• The head mesenchyme gives rise to striated muscles of face, jaw

Paraxial mesoderm in trunk region•The mesoderm in the trunk region forms bands of segmented cells the somites•Somites give rise to most of axial skeleton, voluntary muscles of neck, body wall, and limbs and the dermis

Clock and wavefront model

MOLECULAR MECHANISM OF SOMITOGENESIS

Intermediate Mesoderm •It forms in trunk regiononly•It develops lateral to somites•It give rise to urinary system and parts of genital system

Lateral plate Mesoderm It also forms in trunk region only

It develops lateral to intermediate mesoderm

It splits into two layers

ventral associated with endoderm called as splanchnic mesoderm. It forms mesothelial covering of viscera and parts of wall of viscera

Dorsal associated with ectoderm is called somatic mesoderm. It forms inner lining of the body wall and parts of limbs

Gastrulation Ends with Formationof Tail Bud

THE NEURULATION

Under the inducing effect of the developing notochord, the overlying ectodermal cells thickens to form the neural plate

Neural Tube Formation

On 18th day: the neural plate invaginates to form neural groove & neural folds

Neural fold

Some neuroectodermal cells along the crest of the neural fold differentiate as the neural crest cells.

Neural crest cells

Neural fold

By the end of 3rd week, the neural folds move to the midline and fuse to form the neural tube

The fusion begins in the future cervical region and then extends both in cranial and caudal direction

Neural tube is open at both ends, communicating freely with the amniotic cavity.

The cranial opening, the rostral neuropore closes at about 25th day & the caudal neuroporecloses at about the 27th day

Neural tube is open at both ends, communicating freely with the amniotic cavity.

The cranial opening, the rostral neuropore closes at about 25th day & the caudal neuroporecloses at about the 27th day