Fate of embryonic layers and structures develope from them

Fate of embryonic layers and structures develope from it. Embryonic layers ectoderm mesoderm and endoderm form different structures during embryonic development.

1. Fate of embryonic layers and structures developed from it Nizad sultana ch Department of zoology Faculty of science University of Gujrat

2. Establishing the neural cell Neural cell becomes specified through their interaction with other cells there are four stages through which pluripotent cells of blastula become neuroblasts. Competence where multipotent cell become neuroblasts if they are exposed to appropriate signals. Specification where cell have received appropriate signal to become neuroblasts but neural differentiation pathway can still be repressed. Commitment where in neuroblasts enter neural differentiation pathway and will become neurons even in presence of inhibitory signal. Differenciation wherein neuroblasts leave mitotic cycle and express gene characters of neurons.

3. Formation of neural tube There are two major of converting neural plate into neural tube. Primary neurulation Neural plate cell proliferate invaginate and pinch off from surface to form hollow tube. Secondary neurulation Neural tube arise from coalescence of mesenchyme cells into solid cord that form cavity that coalescence to create a hollow tube.

4. Primary neurulation Primary neurulation divide original ectoderm into three sets of cell Neural tube which will form brain and spinal cord. Externally positioned epidermis of skin. Neural crest cell form in region that connects neural tube and epidermis but they will migrate into new place where they will form neuron and ganglia pigment cell of skin.

5. Neurulation in amphibian Shortly after neural plate formed it’s edges thickens and move upward to form neural fold. U-shaped neural groove apears in center of plate dividing future right and lest side of embryo. Neural fold migrate towards midline fuses to form neural tube beneath ectoderm. Cells at dorsal most portion of neural tube.

6. Four steps in primary neurulation Formation and folding of neural plate Shaping and elevation of neural plate Convergence of neural folds creating a neural groove Closure of neural groove to form neural tube

7. Differentiation of Neural tube 4-5 weak Neural tube and it’s lumen bulge and constrict to form chambers of brain and spinal cord. Neuroepethelial cell differenciate to form to numerous type of cell nerve cells. Anterior portion of tube undergo drastic changes balloons to form forebrain midbrain and hindbrain Posterior of neural tube closes secondary bulge the optic vesicle which will become rating extended laterally from each side of developing forebrain.

8. Telencephlon will eventually form cerebral hemisphere. Diencephalon will form optic vesicles as well thalamus and hypothalamus Mesencephalon does not become subdivided it’s lumen become cerebral aqueduct Hindbrain(rhombencephalon) become subdivided into posterior myelencephalan that become medula oblongata. And metencephalon give rise to cerebellum part that is associated with coordinating movements posture and balance.

9. Differenciation of neurons in brain Human brain consists of 36 billion neurons Associated with gangalin cells. Neuroepethelial cell give rise to three type of cells. First Ventricular cells release cerebrospinal fluid. Second Precursors of neurons conduct electrical signal and coordinate our body functions Our sensation of world. Third they give rise to precursors of glial cell that add in construction of nervous system.

10. Spinal cord organization Cell adjacent to lumen continue to divide. Migrating cells form second layer around original tube. This layer become thicker to form mental zone. Germinal epithelium is now called as ventricular zone . Three zone pattern of spinal cord is as follows Gray matter (mantle) gradually become butterfly shape structure surrounded by white matter both encased in connective tissue. Logitudinal groove form dorsal and ventral half.

11. Development of vertebrate eye 4- Major sensory organs of head developed by interaction of neural tube with with cranial ectoderm placoid. Two placoid form form olfactory placoid. Two form otic placoid that invaginate to form inner ear labriyanth which cells form acoustic ganglia that unable us to hear. Lens placoid form transparent lens that allow light to impringe on rating. Interaction between lens placoid and ratina structure form complex organ.

12. Origin of epidermis Epidermis originate from ectodermal cells. Ectoderm is induce to form epidermis by action of BMPs. Epidermis is only one cell layer thick but in some animals it becomes two layered structure. Outer layer give rise to periderm it then differenciate to form true epidermis. Inner layer called basal layer or stratum germinativum. Cell division form younger cells and pushes older cell to border of skin.

13. Mesoderm Central tissue in region of trunk mesoderm will form Notochord. Flaking Notochord on both side is somite mesoderm. cells from somitic mesoderm will form Muscle and connective tissue. Intermediate region form urogenetial system kidney, gonads and associated organs. Lateral plate mesoderm give rise to heart blood vessels blood cells of circulatory system.

14. Roll of proteins Two proteins have critical role for formation of somite and it’s separation from mesoderm. Eph A4 and Eph tyrosine kinase proteins. Somite form cervical vertebrae of neck and lumber vertebrae of abdomen. Somite forming thoracis vertebrae form ribs. Myf5 and MyoD proteins involves in formation of muscles. Runx2 transcription factor involve in ossification. Glial derived Neuro trophic factor in formation of metanephric kidney.

15. Progression of kidney type Mamalian kidney developer through three major steps. Pronephric duct arises in intermediate mesoderm Cell of duct migrate caudally. Anterior region of duct induce mesenchyme cells to form pronephrous of kidney. Metanephric kidney of mamals is by interaction of intermediate mesodermal tissues. Ureteric bud (secrete WNT9 and WNT6) Metanephric mesenchyme

16. Lateral plate mesoderm and endoderm

17. Heart development Heart progenitor cells are located in two small patches on epiblast close to primitive streak. These cells migrate two type of cells formed:- Conus arteriosus truncus arteriosus That will form base of aorta and pulmonary artery and right ventricle these cells present medially close to primitive streak. These cells are specified but not determined.

18. Heart development  (also known as  cardiogenesis ) refers to the  prenatal development  of the  heart . This begins with the formation of two  endocardial tubes  which merge to form the  tubular heart , also called the  primitive heart tube . The heart is the first functional organ in  vertebrate  embryos, and in the human, beats spontaneously by week 4 of  development

19. Formation of gut from endoderm Mamalian Embryo form pharyngeal pouches. first pair of pharyngeal pouch will form auditary cavity. second pair will form tonsils Third pair will form thymus and parathyroid gland. Fourth Other pair of parathyroid gland. Pocket of endoderm mesenchyme Bud off and migrate into neck to form thyroid gland Respiratory tube sprouts to from pharyngeal Floor to form lungs.

20. Development of lungs

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