The document summarizes the process of blastulation in embryonic development. It describes how the zygote undergoes cleavage, forming blastomeres that arrange into a structure called a morula. The morula then develops into the blastula stage, where the cells form a blastoderm layer surrounding an interior cavity called the blastocoel. There are different types of blastulae depending on features like whether the blastocoel is present, the number of cell layers in the blastoderm, and how yolk is distributed. Key blastula types include coeloblastula, stereoblastula, periblastula, discoblastula, and blastocyst.

1. Blastulation
Asst Prof: Chetana Kanekar
Ashoka College Of Education

2. • The cleavage is the fractionating process which
splits zygote or fertilized egg into smaller cells
called blastomeres.
• These cells formed in typical doubling sequence
2,4,8,16,32,64 etc.
• The Geometrical regularity exist s only in early
developmental stages.

3. • Later on the process of cleavage becomes
entirely irregular.
• During early cleavage stages the blastomeres
form the structure of embryonic stage called
Morula.
• Later on Morula develops into the next
embryonic stage called Blastula.

4. Blastula
• As the cleavage proceeds ,the number of
blastomeres of the morula increases and
blastomeres undergo rearrangement.
• The cells adhere to each other and they arrange
themselves into true epithelium.
• This may be single cell thick (e.g.echinoderms)
or many cells thick (e.g.vertebrates)

5. • This epithelium is called blastoderm.
• The fluid filled space or cavity called blastocoel
appears in the centre of blastoderm.
• This hollow ,spherical, and unepithelial thick
embryonic stage is called blastula and the process
of its formation is called blastulation

6. Sea urchin blastula

7. Blastula of frog

8. A Dendraster blastula (micrograph
courtesy of George von Dassow,
Center for Cell Dynamics, Univ. of
Washington).

11. Types of Blastulae
• Coeloblastula
• Stereoblastula
• Periblastula or Superficial Blastula
• Discoblastula
• Blastocyst

12. Coeloblastula
• It is hollow sphere and blastocoel is filled with
mucopolysaccrides and blastoderm is of single
layer of cells.
• E.g. Echinoderms

14. Stereoblastula
• It is a Solid blastula because there is no
blastocoel cavity.
• This type is formed due to spiral cleavage.
• E.g. Molluscs.

16. Superficial Blastula
• It is also called periblastula.
• Periblastula is formed in insect eggs due to
superficial cleavge and there is no blastocoel in it.
• The nucei collect in the peripheral layer.
• Actually cavity is present but filled with yolk from
beginning of cleavage

18. Discoblastula
• This type of blastula is found in yolky eggs of
fishes,reptiles and birds.
• It is called discoblastula because it appears at
the animal in the form of small multilayered
flat disc separated from yolk by narrow
subgerminal cavity.

20. Blastocyst
• This type of blastula is formed in mammals by
regular cleavage
• The small cavity called blastcoel .
• The cluster of cells differentiates into two
distinct groups called trophoblast cells or
nutritive and formative cells

21. Human blastula

22. Thank you