Basic Organ Systems

• Neuralization is a process of formation of the neural plate and the neural folds.
• The closure of neural folds results in the formation of the neural tube.
• The ectoderm of the neural plate is called Neuroectoderm.
• Neuroectoderm gives rise to Brain and Spinal Cord.
• Notochord induces the overlying ectoderm to form Neural Plate.
• In the 18th day, neural plate invaginates to form Neural Groove.
• Neural folds appear on each side of neural groove.
• By the end of 3rd week, neural folds fuse and form the Neural Tube.
• Neural Tube is then separated from the surface ectoderm.
• Neural Groove and Neural Tube are present in the 3-4th week.
• Brain and Spinal Cord are present in the 3-4th week.
• Endocardial heart tubes develop during the 3rd week.
• By the end of the 3rd week, blood circulates and the heart begins to beat on the 21st or 22nd day.
• Blood formation does not begin in the embryo until the 5th week.
• Blood begins to circulate by the end of the 3rd week.
• The development of the cardiovascular system is the first system to function in the embryo.
• The primitive cardiovascular system consists of paired, endothelium-lined channels, known as endochardial heart tubes.
• Cardiogenic cords contribute to the formation of the heart.
• The cardiovascular system is formed from angioblastic tissue.
• The primordium of the heart refers to the earliest developmental structure or tissue that gives rise to the heart during embryogenesis. In vertebrate embryonic development, the heart originates from a specialized area known as the cardiogenic region or protocardiogenic mesoderm.
• The tubular heart joins with blood vessels in the embryo, connecting stalk, choiron and yolk sac to form a primordial cardiovascular system.
• Neuroepithelium is present in the 3-4th week.
• Neural Crest Cells are present in the 3-4th week.
• During the separation of Neural Tube from the surface ectoderm, some neuroectodermal cells lying along the crest of each neural fold, known as Neural Crest Cells, lose their epithelial affinities and form irregular masses on the ventrolateral side of neural tube.
• Malformation involving the spinal cord and vertebral arches are referred to as spina bifida.
• At the end of third week, neural folds are thickened.
• Folding in both median and horizontal planes is due to rapid growth of embryo.
• Somites are used as one of the criteria to determine embryo’s age.
• During longitudinal folding, part of the yolk sac is incorporated within embryo as Foregut.
• Most major congenital malformations of the brain result from defective closure of the neuropore during the 4th week and involve the spinal cord and vertebral arches. These malformations are referred to as spina bifida
• Oropharyngeal Membrane separates the foregut from Stomadeum.
• Tail region projects over Cloacal membrane ( Future site of anus ).
• Tail folding occurs later than that of cranial end and results from growth of developing spinal cord.
• Dermatome refers to the dermis, Sclerotome to cartilage and bone, and Myotome to muscles.
• 42 to 44 pairs of somites form during the Somite Period.
• Folding at cranial and caudal ends occurs at the same time.
• 38 pairs of somites form during the Somite Period ( between 20 to 30 days ).
• Somites are tissue blocks derived from paraxial mesoderm.
• Developing forebrain grows cranially and overhangs developing heart.
• Neural Crest Cells contain GANGLIONIC CELLS, SCHWANN CELLS, MELANOCYTES, ADRENAL MEDULLA, SKELETAL AND MUSCULAR COMPONENTS OF THE HEAD.