University:
Kentucky State University
Course:
BIO 304 | Vertebrate Embryology
Academic year:

2022
Views:

98

Pages:

25
Author:

Kundulu8mbj

Derivatives of the mesodermal germ layer Paraxial mesoderm It develops into TWO PERIPHERAL MASSES and a constriction in the middle Called: 1-Medail mesoderm 2-Intermediate mesoderm 3-lateral mesoderm Medial mesoderm •The medial mesoderm enlarges pushing the ectoderm upwards to give the As the embryo develops the number of the somites Increases from one to reach about 44-45 somites  when the embryo is completely developed About 10 somites vanish when the tail of the embryo is lost somites The first pair of somites arises in the occipital region of the embryo at approximately the 20th day of development From here, new somites appear in craniocaudal sequence at a rate of approximately three pairs per day until the end of the fifth week, There are: four occipital eight cervical 12 thoracic five lumbar five sacral, and eight to 10 coccygeal pairs. The first occipital and the last five to seven coccygeal somites later disappear WHAT IS THE destiny OF EACH SOMITE? shatarat By the beginning of the fourth week cells forming the ventral and medial walls of the somite lose their compact organization, and shift their position to surround the notochord These cells, collectively known as THE SCLEROTOME They will surround the spinal cord and notochord to form the vertebral column Cells at the dorsolateral portion of the somite also migrate as precursors of the limb and body wall shatarat musculature (hypomeric) musculature After migration of these muscle cells and cells of the sclerotome, Cells at the dorsomedial portion of the somite proliferate and migrate to form a new layer THE MYOTOME myotome contributes to muscles of the back (epaxial musculature) or epimeric musculature the extensor muscles of the vertebral column shatarat The remaining dorsal epithelium forms the dermatome dermatomes form the dermis and subcutaneous tissue of the skin Derivatives of the intermediate mesoderm It gives off: 1- Urine performing tubule (Kidney and ureter) 2-internal genitalia in males and femals (part of it not all) shatarat WHY the embryo folds? 1- Extensive and rapid growth of the cranial end of the neural tube 2- The faster growth of the axial part of the embryonic disc than its periphery 3- Enlargement of the amnion Folding of the embryo Cephalocaudally and Laterally Head (cephalic) fold shatarat Tail (caudal) fold The embryonic disc begins to bulge into the amniotic cavity and to fold Cephalocaudally Folding of the embryo Cephalocaudally Folding of the embryo Laterally Derivatives of the lateral mesoderm The intraembryonic coelom (body cavity) first appears as small, isolated, coelomic spaces in the lateral intraembryonic mesoderm These spaces coalesce to form a single, horseshoe-shaped cavity— the intraembryonic coelom The coelom divides the lateral mesoderm into two layers: Lateral mesoderm splits into two layers: 1- Parietal (somatic) 2- Visceral (splanchnic) Mesoderm from the parietal layer, together with overlying ectoderm, forms the lateral body wall folds These folds, together with the head (cephalic) and tail (caudal) folds, close the ventral body wall The visceral layer of lateral mesoderm Surrounds the primitive gut and together with embryonic endoderm, forms THE WALL OF THE GUT TUBE DERIVATIVES OF THE ENDODERMAL GERM LAYER The gastrointestinal tract is the main organ system derived from the endodermal germ layer The tube is divided into three regions: FOREGUT MIDGUT HINDGUT The midgut remains in communication with the yolk sac. Initially, this connection is wide but as a result of body folding, it gradually becomes long and narrow to form the vitelline duct Only much later, when the vitelline duct is obliterated, does the midgut lose its connection with the original endoderm-lined cavity and obtain its free position in the abdominal cavity shatarat

Derivatives of the Mesodermal Germ Layer

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