1 / 13

Embryonic Development

Embryonic Development. Variations in Embryonic Germ Layers and Body Cavity. Formation of the Digestive Cavity. At the Blastula stage, the embryo forms a fluid filled ball of cells

sugar
Download Presentation

Embryonic Development

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Embryonic Development Variations in Embryonic Germ Layers and Body Cavity

  2. Formation of the Digestive Cavity • At the Blastula stage, the embryo forms a fluid filled ball of cells • During Gastrulation, the blastula caves in on one end to form a Gastrula. The cavity formed by gastrulation will form a digestive cavity or digestive tract. • If gastrulation is incomplete, the gastric cavity will have only one opening. This arrangement is characteristic of Cnideria and Platyhelminthes • If gastrulation is complete, the digestive tract will have two openings. This arrangement has 2 variations, protostomes and deuterostomes

  3. Protostomes vs. Deuterostomes In Protostomes, the blastopore forms the mouth. In Deuterostomes, the blastopore forms the anus and the mouth is the second opening

  4. Embryonic Germ Layers • Organisms that undergo gastrulation fit into 2 categories: diploblasts and triploblasts • Diploblasts only have 2 embryonic germ layers • Gastrulation forms an inner layer of cells (endoderm) and an outer layer (ectoderm) • This diagram shows the endoderm in blue and the ectoderm in black

  5. Embryonic Germ Layers • Triploblasts develop a third germ layer in between the endoderm and the ectoderm • The middle layer is called mesoderm • In the diagram, mesoderm is represented in yellow • Variations in the presence, absence and arrangement of mesodermal tissue is one of the most important distinguishing features of animal phyla

  6. Phylogeny based on Mesodermal Arrangement • Phylum porifera lack a true digestive cavity • Cnideria are diploblastic. They have a digestive cavity but lack mesodermal tissue • The triploblastic phyla vary in regard to the arrangement of mesoderm and body cavity

  7. Development of Mesodermal Tissue • Mesoderm is formed by a migration of endodermal cells into the blastocoel. • Mesoderm forms by one of 2 possible mechanism • The diagram at the right shows mesoderm development in acoelomates and protostomes • The formation of mesoderm initiates near the blastopore. Dividing mesodermal cells migrate into the blastocoel

  8. Acoelomate phyla • Acoelomates do not form a body cavity • Flatworms (Platyhelminthes) are acoelomate • Mesodermal cells fill the entire blastocoel • Internal organs form, but are not separate and distinct

  9. Pseudocoelomate Phyla • Pseudocoelomates have a body cavity, but mesoderm is associated with the outer body wall (ectoderm). • Nematodes and rotifers are pseudocoelomate • All pseudocoelomates have a true digestive tract (2 openings) and are protostomes (blastopore = mouth) • The digestive tract lacks mesodermal tissue, thus is not muscular

  10. Cross Section of a Pseudocoelomate • The diagram shows a cross section through a nematode • Notice the space between organs (body cavity), but note that there is only mesoderm on the outer boundary, associated with the body wall. The Intestine is a simple layer of epithelium (no muscle) • The organs are separate and distinct, but the body cavity is “false” – not fully lined with mesoderm

  11. Coelomate Protostomes • A true body cavity is fully lined with mesodermal tissue. • In coelomate protostomes, the body cavity is “schizocoelous” (note the descriptive root word “schizo”) • The solid mass of mesoderm filling the blastocoel splits due to the programmed cell death (“apoptosis”) of some centrally located cells • The diagram shows the coelom in pink

  12. Coelomate Deuterostomes • All deuterostomes have a true body cavity • In deuterostomes, the blastopore forms the anus (so the “second opening” forms the mouth”) • In deuterostomes, the mesoderm forms from outpouching of the gut • Since it is “caving in” it is “enterocoelous” • Because the coelom is formed from pouches, it is completely surrounded by mesodermal tissue

  13. SchizocoelousvsEnterocoelous

More Related