Intra uterine development

INTRA UTERINE DEVELOPMENT OF FETUS

1. Intra uterine Development of fetus PRIYANKA.PARATE NEURO MPT

2. 1. Fertilization

3. The division begins…

4. Rapid Mitotic divisions… Cleavage is a series of rapid mitotic divisions (without cell growth) 2-celled zygote divides repeatedly until a ball of 32 cells is formed This is the morula - 32 cells

5. Morula , on entering the uterine cavity, floats freely. Morula begins to accumulate fluid and forms a cavity between its cells. Once the cavity appears, it is now called a blastocyst .

6. Week 2 Inner cell mass divides into epiblast and hypoblast 2 fluid filled sacs Amniotic sac from epiblast Yolk sac from hypoblast Bilaminar embryonic disc : area of contact (gives rise to the whole body)

7. Bilaminar to trilaminar disc Three primary “germ” layers: all body tissues develop from these Ectoderm Endoderm Mesoderm Week 3

8. Formation of the 3 “germ” layers Primitive streak (groove) on dorsal surface of epiblast Gastrulation : invagination of epiblast cells Days 14-15: they replace hypoblast becoming endoderm Day 16: mesoderm (a new third layer) formed in between Epiblast cells remaining on surface: ectoderm

9. The three “germ” tissues “Germ” as in germinate, not germs Early specialization of cells Are precursors Ectoderm and endoderm are epithelial tissue (form sheets of tissue) Mesoderm is a mesenchyme tissue Mesenchyme cells are star shaped and do not attach to one another, therefore migrate freely

10. Notochord Days 16-18 Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells Rod defining the body axis is formed Future site of the vertebral column

11. Neurulation Notochord signals overlying ectoderm Formation begins of spinal cord and brain (neurulation) Neural plate to neural groove to neural tube: pinched off into body

12. Mesoderm begins to differentiate Lateral to notochord, week 3 Extends cranially and caudally (from head to tail or crown to rump) Division of mesoderm into three regions Somites: 40 pairs of body segments (repeating units, like building blocks) by end week 4 Intermediate mesoderm: just lateral to somites Lateral plate: splits to form coelom (“cavity”)

13. Closure of neural tube: begins at end of week 3; complete by end of week 4 (folic acid important for this step) Extends cranially (eventually brain) and caudally (spinal cord) Neural crest, lateral ectodermal cells, pulled along and form sensory nerve cells and other structures Central Nervous System Development

14. Divisions of the mesodermal lateral plate Somatic mesoderm: apposed to the ectoderm Splanchnic mesoderm: apposed to the endoderm Coelom in between will become the serous cavities of the ventral body cavity: Peritoneal Pericardial Pleural

15. Dorsal view of the tri laminar embryo A B C 1 2 3 4 Paraxial mesoderm ( Out of it develops the musculature, among other things) Intermediary mesoderm Lateral plate mesoderm Ectoderm Somite Somitocoel Neural tube

16. Musculature development… The musculature of the human body stems from the middle germinal layer , the mesoderm . One distinguishes three varieties of muscles: skeletal musculature cardiac musculature smooth musculature The mesoderm on both sides of the neural tube is called paraxial mesoderm . Out of it develops the musculature

17. Cardiac development… Cranial section of the embryo, in front of the prechordal plate, an accumulation of mesodermal cells form the cardiogenic plate , out of which the cardiac musculature derives. The flexion of the embryo causes the tissue of the original cardiogenic plate, which is enveloped by the pericardial cavity, to move into a ventral position . It consists of epicardium , myocardium and endocardium . A gelatinous mass, the cardiac jelly , temporarily forms between the myo - and endocardium and this is of decisive importance for the subsequent tube formation.

18. Respiratory development.. In contrast with the other organ systems the lungs begin their function as a gas exchange apparatus only at birth . During the pregnancy, however, they have an important function as an amniotic fluid-producing organ . Prenatally, the air spaces are thus filled with amniotic fluid that, with the first breath, must abruptly be replaced by air .

19. Gastrointestinal development.. The intestines arise from a tube that forms from the endoderm . Cranially this tube ends at the oropharyngeal membrane and caudally at the cloacal membrane . It is subdivided into a foregut , midgut and hindgut . The midgut is connected with the umbilical vesicle . The differing development of the various intestinal sections is based on the local interactions with the surrounding mesenchyma ( epithelio-mesenchymal interactions ).

20. Major derivatives of the embryonic germ layers

21. Human Development