Embryonic Development PDF

 Regarding the following structure: A – The starred structure gives rise to which B - What is the name of structure number (2)? structure of the followings in the future? a- Somatic extraembryonic mesoderm. a- Placenta. b- Visceral extraembryo...

 Regarding the following structure: A – The starred structure gives rise to which B - What is the name of structure number (2)? structure of the followings in the future? a- Somatic extraembryonic mesoderm. a- Placenta. b- Visceral extraembryonic mesoderm. b- Umbilical cord. c- Somatic intraembryonic mesoderm. c- Chorion. d- Visceral intraembryonic mesoderm. d- Notochord. e- Extraembryonic coelom. e- Cloacal membrane.  List the events that occurs during the first week after fertilization. A-………………………….. B-…………………………… C-…………………………… Justify the blood testing for detection of pregnancy during the second week of pregnancy. ……………………………………………………………………………………  ILOs Outline the development of the followings: 1.Prechordal plate 2.Notochord 3.Neural tube  Third week developmental changes 1- Development of midline structures in embryonic disc 2- Gastrulation (trilaminar embryonic disc) 3- Neurulation (neural tube formation)  Midline structures of embryonic disc 1- Prechordal plate ------- forms future mouth 2- Notochord……………….represents the body axis 3- Primitive node and streak----- gives rise to intraembryonic mesoderm 4- Cloacal membrane….. forms future anus A.The development of prechordal plate: ❑ Near the cranial end of the embryonic disc, the cubical hypoblastic cells in the middle line increase in height and fuse with the overlying epiblast forming a plate.  B. Development of primitive streak, node, groove and pit: ❑ Primitive streak and node: It results from the proliferation of cells of the epiblast in the median plane of embryonic disc. ❑ Primitive groove and pit : A depression in the middle of the primitive streak and node due to migration of the cells. A C BB c. Development of notochord: Some cells of primitive node grow cranially between the epiblast and hypoblast until reach prechordal plate forming notochord process which undergoes many changes to form definite notochord. ❑ Fate of Notochord: 1)Part of notochord in the center of bodies of vertebra: degenerates and disappear. 2)Part of notochord in the intervertebral disc undergoes mucoid degeneration and forms nucleus pulposus. Primitive  Gastrulation ❑ Definition: is the process by which the bilaminar embryonic disc is converted into a trilaminar embryonic disc. ❑ Time: During the 3rd week ❑ Origin of the three layers: 1) Some cells of the epiblast of the primitive streak displace the hypoblast, forming the intraembryonic endoderm (the hypoblastic layer disappears). 2) Cells remaining in the epiblast form the intraembryonic ectoderm. 3) Some cells from the sides of the primitive streak migrate laterally and cranially between the ectoderm and endoderm. This third layer of embryo is known as the intraembryonic mesoderm 4) By the middle of the 3rd week, intraembryonic mesoderm separates the ectoderm from endoderm every where except: A. At the oropharyngeal membrane (prechordal plate) cranially. B. In the median plane cranial to the primitive node where the notochordal process is located. C. At the cloacal membrane caudally.  Development of neural tube ❑ Time: it is formed at 3rd week. ❑ Stages: Increase height of ectoderm cells which form (neural plate) Elevation of the lateral margin of neural plate to form (neural folds) Depression of the median part of neural plate to form (neural groove) Fusion of neural folds converting neural plate into (neural tube) Neural tube separates from ectodermal surface. Some neuroectodermal cells separate and lie between neural tube and ectoderm (neural crest) At first cranial and caudal ends of neural tube are open then are closed ❑ Fate: Cranial end of tube dilates to form brain and the caudal end forms spinal cord.  A)Development and derivatives of neural crest ❑ Derivatives: Neuroblasts which gives:  Nerve cells of sensory ganglia (5th, 7th, 9th, 10th cranial nerve)  Nerve cells of dorsal root ganglia, sympathetic ganglia and parasympathetic ganglia of cranial nerves (3rd, 7th, 9th, 10th) Spongioblasts which gives:  pia and arachnoids mater  Schwan cells. Chromaffin cells which gives:  Suprarenal medulla.  Carotid and aortic bodies’ cells. Melanocytes: pigment cells of skin.