GASTRULATION final.pptx

Gastrulation, biological processes , how gastrulation occurs

1. GASTRULATION Dr. SHOEBA BINTE ANIS

2. gastrulation Gastrulation is the first stage in forming the body plan. The single layered blastoderm give rise to 3 germ layers : ECTODERM ENDODERM MESODERM During the process of gastrulation the presumptive organ forming areas of blastula undergo axiation in terms of the body origination of the species.

3. THE PROCESS OF GASTRULATION Gastrulation usually involves some combination of several types of movements. These movements involve the entire embryo, and cell migration in one part of the gastrulating embryo must be intimately coordinated with other movements that are taking place simultaneously. Although pattern of gastrulation vary enormously throughout the animal kingdom.

4. There are only a few basic types of cell movementsare called Morphogenetic movements. Invagination : The infolding of a region of cells, much like the indenting of a soft rubber ball when it is poked. Involution: the inturning or inward movements of an expanding outer layer so that it spreads over the internal surface of the remaining external cells.

5. Ingression : The migration of individual cells from the surface layer into the interior of the embryo . The cells become mesenchymal ( i . e . , they separate from one another ) and migrate independently . Delamination : The splitting of one cellular sheet into two more or less parallel sheets . While on a cellular basisit resembles ingression, the result is the formation of a new sheet of cells .

6. Epiboly : The movements of epithelial sheets ( usually of ectodermal cells ) that spread as a unit ( rather than individually ) to enclose the deeper layers of the embryo . Epiboly can occur by the cells dividing by the cells changing their shape, or by several layers of cells intercalating into fewer layers . Often, all three mechanisms are used .

7. Amphioxus gastrulation and adult

8. Tubulation The process of formation of primary organ rudiments called tubulation . The 3 germinal layers represents variousparts of the future animal subdivided into groups of cells called Primary organ rudiments. Primary organ rudiments further differentiated into secondary organ rudiments. Includes:- A) Neurogenesis B) Notogenesis C) Mesogenesis

9. A) Neurogenesis Formation of neural tube which is differentiated into : Brain Spinal cord Sensory organs Olfactory= Nose Optic = Eye Auditory= Ear

10. Neural tube derived from the ectoderm along the mid dorsal axis of the vertebrate gastrula. The thickening of the ectoderm of the mid dorsal axis occur which is called neural plate. In different animals the neural plate differentiate into neural tube by 2 methods: 1. Thickened Keel Method 2. Neural Fold Method

11. 1. Thickened Keel Method Eg . In Teleost , ganoids and cyclostomes. Fishes, here neural plate material becomes aggregate in the form of thickened ridges or keel along the mid dorsal axis of embryo, the keel sinks below the overlapping ectoderm and transformed into hallow neural tube.

12. 2. NEURAL FOLD METHOD Eg . Amphibians, reptiles, birds & mammals here the centre of the neural plate deepens and the margin of the plate elevated, the depressed part from the groove along the length of the body called neural groove . Later margin of the neural groove meet dorsally forming a tube called neural tube. Which differentiate into anterior brain and posterior part into spinal cord. Neural creast cells are also created during neurulation . Neural crest cells migrate away from the neural tube and give rise to a variety of cell types, including pigment cells and neurons as well as mesoderm of the head etc.

13. Notogenesis and mesogenesis The cord mesoderm lies between the gut and the ectoderm, the median strip of the chorda mesoderm round up forming the notochord between the gut and developing neural tube above. When the lateral part of the chorda mesoderma continues to spread, and meet in the ventral mid-line and splits up into splancnic mesoderm and somatic mesoderm. By tubulation , the embryo becomes elongated and organ rudiments are formed.

14. Amphioxus : nerulation

15. SIGNIFICANCE OF GASTRULATION It brings the presumptive structures into their normal position in the embryo. Necessary for the formation of the nervous system.