principles of embryology Flashcards
What is the pre-embryonic period of human development?
The pre-embryonic period begins at conception and lasts until the end of the second week of development. It includes processes such as fertilization, formation of the morula and blastocyst, and implantation of the blastocyst.
What is the embryonic period of human development?
The embryonic period spans from the end of the second week to the eighth week of development. During this time, germ layers develop, the placenta forms, and body systems start to develop from the trilaminar germ layers.
What is the foetal period of human development?
The foetal period begins at the eighth week of development and continues until birth (full term at 38 weeks). It is characterized by rapid growth and further development of visceral organs. The musculoskeletal system also becomes functional during this period.
What is the development of a morula?
After fertilization, the zygote undergoes mitotic divisions and splits into two cells, called blastomeres. The blastomeres continue to divide, resulting in a group of cells called a morula, which consists of around 16 cells.
What is the development of a blastocyst?
The morula undergoes further reorganization and forms a central cavity called the blastocyst cavity or blastocoel. At this stage, the structure is called a blastocyst. It consists of two main parts: the outer cell mass, known as the trophoblast, which contacts the endometrium for implantation and placenta formation, and the inner cell mass, known as the embryoblast, which is responsible for the development of the embryo itself.
What is the bilaminar disc?
During week 2 of development, the embryoblast divides into two layers: the epiblast and hypoblast, forming a two-layered structure called the bilaminar disc.
What are the two layers of the bilaminar disc?
The bilaminar disc consists of two layers: the upper layer called the epiblast and the lower layer called the hypoblast.
What forms within the epiblast of the bilaminar disc?
The amniotic cavity forms within the epiblast layer of the bilaminar disc.
What is gastrulation?
Gastrulation is the process during embryonic development where the two cell layers of the bilaminar disc (epiblast and hypoblast) transform into three germ cell layers: endoderm, mesoderm, and ectoderm.
What is the primitive streak?
The primitive streak is a groove that appears in the midline of the epiblast during the third week of development. It plays a crucial role in orchestrating gastrulation.
What are the three germ cell layers formed during gastrulation?
Endoderm: Formed by epiblast cells that migrate through the primitive pit and displace the hypoblast cells.
Mesoderm: Formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.
Ectoderm: Formed by the epiblast cells that remain in position.
What happens to the neural plate during embryonic development?
The lateral edges of the neural plate rise to form neural folds.
What is the result of the neural folds coming together?
The neural folds move towards each other and meet in the midline, forming the neural tube.
What is the role of the mesoderm in neuralation?
The mesoderm differentiates into the notochord, which stimulates neuralation.
What does neuralation cause in the ectoderm?
Neuralation causes the ectoderm to thicken.
