Embryology

• The formation of the neural tube through neurulation is a critical step in the development of the central nervous system.
• Germ layer – cells that give rise to all tissues and organs of the body. There are three primary germ layers
• The caudal end of the heart receives three sets of venous vessels: common cardinal, vitelline, and allantoic veins.
• ECTODERM is the outermost or upper layer of cells that gives rise to the epidermis, nervous tissue and some skeletal and connective tissue of the head.
• MESODERM is the middle layer of cells that forms most of the muscles and skeletal tissues, urogenital system and the heart and blood vessels.
• ENDODERM is the deepest or innermost layer of cells that lines the digestive, respiratory tract and those organs associated to digestion.
• MESENCHYME is the precursor of all connective and muscle tissues and is a component of all organs except the CNS.
• TERATOLOGY is a branch of embryology that deals with the causes and results of abnormal development or congenital malformation.
• Congenital malformation or congenital defect is an abnormality that arises during prenatal development due to hereditary or environmental factors.
• Anomaly is a congenital defect caused by disturbance of development of an organ or portion of an organ.
• Monstrosity is a congenital defect caused by disturbance of development of several organs and causes great distortion of the individual.
• Epithelium is a single layer or several layers of cells that rest on a basal lamina; cells are closely joined together at their lateral surface.
• Mesenchyme is a group of loosely and irregularly arranged cells separated by a large amount of extracellular matrix.
• Connective Tissue is a tissue which connects and supports other tissues of the body, such as adipose tissue, tendons, ligaments, cartilage and bone.
• Dorsal pertains to the back.
• Ventral is the belly.
• Cephalic pertains to the head.
• Caudal pertains to the tail.
• Medial pertains to the middle part.
• Lateral pertains to the side of the embryonic body.
• Rostral is used to refer to the extreme anterior portion of the head or the relative location of intracephalic structures such as the various parts of the brain.
• Adverbs of motion or direction: dorsad (toward the back); cephalad (toward the head).
• Body is covered by a layer of ectodermal epithelium which will become the epidermis of the skin.
• Neural tube is an elongated hollow structure derived from ectoderm and located beneath the ectodermal epithelium which runs along the dorsal midline of the body; during later stages of development rostral (anterior) portion of the neural tube presents enlargements called vesicles of the brain.
• Initially, there are 3 brain vesicles: prosencephalon or forebrain (most rostral), mesencephalon or midbrain and rhombencephalon or hindbrain (most caudal).
• Gut tube is another hollow tube that run the length of the embryo near the ventral midline and gives rise to the digestive tract.
• Gut tube is derived from the folding of the endoderm.
• The rostral end of the gut tube becomes the future pharynx and the caudal end is the future anus.
• The ventral aorta arises as a single arterial blood vessel from the rostral end of the heart.
• Heart is first seen as a slightly curved tube located in the ventral midline of the embryo beneath the caudal part of the pharynx.
• The yolk sac and allantois are extraembryonic membranes that connect with the embryo through the yolk stalk and allantoic (umbilical) stalk, respectively.
• Veins include the cranial and caudal cardinal veins, the common cardinal veins, vitelline veins and allantoic veins.
• Notochord is a longitudinal rod of mesodermal cells located beneath the neural tube that extends from the midbrain to the tail; it will not give rise to any adult structure in vertebrate embryos although in lower forms of fishes, it gives rise to the axial skeleton.
• The aortic arches are paired blood vessels which arise from the ventral aorta and pass in front of each pharyngeal pouch to connect with the dorsal aortae.
• The dorsal aortae are paired blood vessels that extend caudally from the ventral aorta and fuse into a single dorsal artery caudal to the heart.
• The caudal cardinal veins are also paired vessels that originate from the caudal region of the body and connect with the common cardinal veins at the level of the heart.
• The somatic layer of the lateral mesoderm is closely associated with the overlying ectoderm while the splanchnic mesoderm is closely related to the underlying endoderm.
• The lateral mesoderm separates throughout the embryo except in the head and tail regions where the coelom is absent.
• Intermediate mesoderm is a small cluster of mesodermal cells located lateral to the paraxial mesoderm; it gives rise to the embryonic kidneys (pronephros and mesonephros) and the gonads (testes and ovaries).
• The cranial cardinal veins are paired venous vessels that originate from the head region and connect with the common cardinal veins at the level of the heart.