AssLecRehamsKadhum Diyala University college of Medicine Department of Anatomy Histology and Embryology Second stage First semester Specific Objectives At the end of the lecture you should know about ID: 1047047
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1. The Embryonic Period presented by Ass.Lec.Reham.s.Kadhum Diyala University college of Medicine Department of Anatomy ,Histology and Embryology Second stage First semester
2. Specific Objectives At the end of the lecture you should know about:Define embryonic period. State derivatives of germ layers.Explain various events during embryonic period.
3. The Embryonic PeriodThe Embryonic Period or period of organogenesis, occurs from end 3rd to 8th weeks of development and is time when each of the three germ layers (ectoderm, mesoderm , and endoderm), give rise to a number of specific organs and tissues.
4. Derivatives of the ectoderm:Initially, the ectodermal germ layer has the shape of a disc that is broader in the cephalic than in the caudal region. Appearance of the notochord and prechordal mesoderm induces the overlying ectoderm to thicken and form the neural plate. Cells of the plate make up the neuroectoderm , and their induction represents the initial event in the process of neurulation .
5. Derivatives of the ectoderm:1.Surface Ectoderm: gives rise to oEpidermis includes (skin, hair, and nails) oEnamel of teeth. oSensory epithelium of the ear, nose, and eye. oExocrine glands: Sweat, sebaceous, mammary, salivary gland.oThe pituitary gland.
6. Derivatives of the ectoderm:2. Neuro-ectoderm: oCentral nervous system (CNS)oRetina and optic nerve oPineal gland oGlial cells of CNS like astrocytes, oligodendrocytes, ependymal cells.
7. NeurulationIs the process whereby the neural plate forms the neural tube. The developing neural plate as a thickening on the ectoderm will elongate and expand toward the primitive streak during the third week of development. This neural plate will be folded and the depressed mid-region form a neural groove, the neural folds approach each other in the midline, where they fuse to form the neural tube.
8. 3. Neurual crest As the neural folds elevate and fuse, cells at the lateral crest of the neuroectoderm begin to separate from their neighbors. this cell population leaves the neuroectoderm by active migration to enter the mesoderm. Crest cell from the trunk region leave the neuroectoderm after the closure of the neural tube and migrate along with one of two pathways:1.a dorsal pathway: it enters the ectoderm to form melanocytes 2.a ventral pathway: migrate through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla. 3.neural crest cells also form and migrate from the cranial neural fold, these cells contribute to the craniofacial skeleton, as well as neurons for cranial ganglia, glial cells, melanocytes, and other cells types.
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11. Generally, the derivatives of the ectoderm are:The ectodermal germ layer give rise to organs and structures that maintain contact with the outside world:The central nerves system;The peripheral nervous system;The sensory epithelium of the ear, nose, and eye; andThe epidermis, including the hair and nails.Subcutaneous glands,The mammary gland, The pituitary gland,And enamel of the teeth.
12. Derivatives of the mesoderm: The sheet of loose mesodermal tissue differentiate during the third week of development into three parts:•Midline form a thickened tissue known as paraxial mesoderm. •Laterally remain thin and called lateral plate; lateral plate divides into:Somatic or parietal mesoderm layer continuous with amnion The layer continuous with the yolk sac is the splanchnic or visceral mesoderm layer.Together, these line a newly formed cavity, the intraembryonic cavity, which continuous with the extraembryonic cavity on each side of the embryo.Intermediate mesodermconnected paraxial and lateral plate mesoderm
13. Mesoderm DerivativesA. Paraxial mesoderm That appears as a thickened plates on the side of the midline, by the beginning of the third week, paraxial mesoderm begins to be organized into segments.Segmental organization known as somitomeres, first appear in the cephalic of the embryo, and their formation proceeds cephalocaudally.In the head region, somitomeres form in association with segmentation of the neural tube into neuromeres and contribute to mesenchyme in the head. First pair arise from the occipital region at approximately 20thday of development then they appear at the rate of 3 pairs per day until week 5. 42 to 44 pairs are present, 4 occipital, 8 cervical, 12 thoracic, 5 lumber, 5 sacral and 8 to 10 coccygeal pairs. Age determination.Gives somitomeres which forms somites, each somite forms:Sclerotome: bones and cartilage Dermatome: dermis of back also it own segmentalMyotome: muscle nerve component.
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16. Mesoderm DerivativesB. Intermediate mesoderm : Which connects between paraxial with lateral plate mesoderm. Forms segmental cell clusters, future nephrotomes. More caudally it forms an unsegmented mass of tissue, the nephrogenic cord. Excretory units of the urinary system and gonads form develop from this partly segmented, partly unsegmented intermediate mesoderm.
17. Derivatives of mesoderm C. Lateral plate mesoderm: Located lateral to the intermediate mesoderm forms; this part forms two layers by the intraembryonic cavity appeared inside it. The intraembryonic cavity between these two layers connected with the extraembryonic cavity on the sides of the embryo.
18. a. Somatic mesoderm the layer adjacent to the ectoderm: I.Bones, ligaments II.Blood vessels and connective tissue of limbs. It also gives rise to pulmonary system components, lymphatic system, adipose tissue, etc.b. Splanchnic mesoderm the layer adjacent to the endoderm:I.Heart and visceral layer of serous pericardium and blood vessels.II.Smooth muscle and connective tissues of respiratory and digestive organs.
19. Generally, the derivatives of the mesoderm are:1. The supporting tissues as the bone, cartilage, and connective tissue.2. Muscles. 3. The cardiovascular system and the blood. 4. The lymph cells and vessels. 5. The kidneys and their ducts. 6. The gonads and their ducts. 7. The cortex of the suprarenal gland. 8. The spleen.
20. Derivatives of the endoderm:1.Formation of the epithelial lining of the gut tube;the embryonic disc is folded during the embryonic period results in the formation of the gut tube. There are two directions of folding of the embryonic disc:•Cephalocaudal folding caused by the rapidly elongated neural tube, •The lateral folding caused by the rapid growth of the paraxial mesoderm forms the somites. The gut tube formed by the folded embryo is formed of three parts; a foregut anteriorly, a hindgut posteriorly, and a midgut in the mid-part. The midgut connected with yolk sac by a transient duct called the vitelline duct.
21. Derivatives of the endoderm:2.Formation of the epithelial ling of the allantois; the allantois incorporated in the embryonic body as a result of the embryonic folding. By further development, the allantois epithelia will form the epithelia of the urinary bladder and the urethra.3.Formation epithelial lining of the respiratory tract; the primordium of the respiratory tract buds from the foregut tub.
22. Derivatives of the endoderm:4.The tissues of the thyroid and parathyroid glands that are formed as buds from the gut tube.5.The liver tissues;formed by budding from the gut.6. The thymus.7.The epithelia of the tympanic cavity of the middle ear and the Eustachian auditory tube.
23. Generally, the derivatives of the endoderm areEpithelial lining of: GI tractRespiratory tract Tympanic cavity & auditory tubeUrinary bladder and urethraParenchyma of: Thyroid, parathyroid Liver, Pancreas
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25. Major derivatives Trilaminar disc
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