Start learning
Anatomy
Embriology I: General Embriology
Embryology is a branch of biological sciences that focuses on the development of living organisms, from the formation of sex cells to birth. It is divided into different stages of development, including gametogenesis, zygote formation, gastrulation and neurulation, and organogenesis.
Teratology is another branch that investigates the impacts of environmental factors on the development of the human embryo, particularly congenital malformations.
The fundamental laws of embryology include the law of polarization, which leads to the development of distinct head and tail extremities, and the law of bilateral symmetry, which results in the formation of symmetrical halves in the embryo.
The 4 major stages of development in embryology are:
Introduction: Embryology is a branch of biological sciences that focuses on the development of living organisms, from the formation of sex cells to birth. It has become one of the most fascinating areas of research in biology since its establishment as a separate science in the early 19th century.
The first three stages of development (gametogenesis, zygote formation, gastrulation and neurulation in the embryonic stage) are covered by general embryology. The last stage (organogenesis) is covered by special embryology. We will divide our lessons in the same manner.
Besides these, Teratology, another branch of study, focuses on investigating the impacts of both internal and external environmental factors on the development of the human embryo. Its main objective is to understand the causes behind the occurrence of congenital malformations.
1. Pre-embryonic stage (gametogenesis): This stage involves the formation and maturation of specialized sex cells, known as gametes, within the parents' bodies.
2. Premorphogenetic stage (zygote formation): During this stage, the zygote, or fertilized egg, is formed through insemination, fertilization, and segmentation. The zygote contains equal amounts of maternal and paternal genetic material. Segmentation leads to the division of the fertilized egg into blastomeres, resulting in a spherical germ called a morula. The formation of a cavity inside the morula transforms it into a blastocyst, consisting of embryoblast and trophoblast. This stage does not significantly alter the shape and external dimensions of the germ, hence its name.
3. Morphogenetic stage (embryonic stage) (weeks III - VIII): This stage encompasses primordial morphogenesis (gastrulation) and secondary morphogenesis (neurulation). Gastrulation leads to the formation of the three embryonic layers (ectoblast, endoblast, and mesoblast) and the delimitation of the embryonic body. Neurulation follows gastrulation and is characterized by the development of the first axial organs in a nearly definitive topography.
4. Fetal stage (definitive morphogenesis, organogenesis): This stage involves the formation of tissues and organs from the three embryonic layers, integrating them into a unified whole. Humanization of the embryo begins during this stage. From the second month until the sixth month, it is referred to as the non-viable fetus stage. From the sixth month until birth, it is the viable fetus stage. After birth, it is the newborn stage. Human gestation lasts for nine months (273 days). Development continues after birth until adulthood, when the human body reaches its maximum morpho-functional development.
The fundamental laws of embryology can be categorized into two main principles: the law of polarization and the law of bilateral symmetry.
The law of polarization is responsible for the development of two extremities with distinct structures and functions: the cephalic extremity (head) and the caudal extremity (tail).
On the other hand, the law of bilateral symmetry states that from the zygote stage, even from the first two cells (blastomeres) resulting from the first cleavage division in the meridian plane, a separation occurs in the medio-sagittal plane, forming two symmetrical halves called antimeres. While symmetry gradually diminishes in the case of internal organs, it remains relatively constant in somatic structures.
Embryology is a branch of biological sciences that focuses on the development of living organisms, from the formation of sex cells to birth. It is divided into different stages of development, including gametogenesis, zygote formation, gastrulation and neurulation, and organogenesis.
Teratology is another branch that investigates the impacts of environmental factors on the development of the human embryo, particularly congenital malformations.
The fundamental laws of embryology include the law of polarization, which leads to the development of distinct head and tail extremities, and the law of bilateral symmetry, which results in the formation of symmetrical halves in the embryo.
The 4 major stages of development in embryology are:
