Understanding Embryogenesis and Development - AP Biology

The mesoderm is a primary germ layer that forms during gastrulation. The mesoderm develops into most of the organ systems of the human body, including the muscular system, circulatory system, and excretory system.

The neural plate is a cell layer opposite of the primitive streak in the developing embryo. It forms from a thickening and flattening of the ectoderm layer. These cells then take a columnar shape. The neural plate develops into the neural tube during primary neurulation.

The neural tube develops into the central nervous system, which is composed of the brain and spinal cord. The neural tube develops during primary neurulation from the neural plate.

Neurulation is the process of neural system development in vertebrates. This process can be divided into two stages: primary neurulation and secondary neurulation. The process of primary neurulation is the formation of the neural tube from the neural plate. The neural plate develops from the ectoderm is a structure that becomes the neural tube. This development occurs through the invagination of the neural plate and convergence of neural fold cells, pushing down neural plate cells. The neural folds eventually touch and separate from the neural plate to complete neural tube formation.

Neurulation, or the formation and development of the neural tube, can be divided into primary and secondary neurulation. During primary neurulation, the neural tube forms from the neural plate. During secondary neurulation, the neural tube develops from the caudal end of the embryo. Eventually both neural tubes connect.

Neurulation is induced in embryos through secreted growth factors and inhibitory factors from the notochord. The notochord is a rod-shaped structure located below the neural tube of chordate embryos. Notochords are important in signaling neurulation and organogenesis in embryos. The notochord secretes both growth and inhibitory factors in the regulation of neurulation.

Neural crest cells are a group of multipotent migratory cells. Prior to neurulation, neural crest cells are located between the neural plate and the ectoderm. During neurulation and the infolding of the neural plate, neural crest cells are located on the top of the neural tube. Afterwards, the cells migrate to the area between the neural tube and the ectoderm, where they differentiate into various cell types.

Miscarriage is the death and subsequent abortion of an embryo before it is able to survive outside of the mother. Miscarriage is more common early in pregnancy and common symptoms include vaginal bleeding and cramping. There are many risk factors associated with miscarriage including advanced maternal age, tobacco use, and obesity. In order to prevent miscarriage, expecting mothers are advised to avoid risk factors and practice good prenatal care.

Hemolytic disease of the newborn is a condition during pregnancy in which maternal antibodies pass to the fetus through the placenta. These antibodies attack fetal cells, specifically red blood cells, causing developmental and structural problems in the fetus. Treatment includes blood transfusion into the fetus or early induction of labor.

Hox genes are a class of genes that control body plan development during embryogenesis. The Hox gene DNA sequence is called a “homeobox” and codes for transcription factors.

Fetal alcohol syndrome (FAS) is a disease that occurs when the individual’s mother drank alcohol during the pregnancy in which they were conceived. There are many symptoms including brain damage, intellectual disabilities, and heart disease. These symptoms come from the passage of ethanol to the fetus from the placenta. The ethanol impairs nervous system development and negative impacts on other organ and developmental systems.

During the 1950’s, thalidomide was an over-the-counter drug advertised and used to treat morning sickness in pregnant women. Thalidomide was later found to cause limb and skeletal deformities in resulting fetuses. Subsequently, the sale and use of the drug has ended.

The primitive streak is an arrangement of cells that forms during gastrula development. The location of the primitive streak establishes the left/right axes, cranial/caudal axes, and bilateral symmetry of the developing embryo.

In gastrulation, the process of ingression forms the mesoderm. In this process, the epiblast ingresses at the primary streak into the area between the epiblast and hypoblast cell layers.

Invagination is the infolding of the epiblast cell layer to form the endoderm germ layer. This process takes place during gastrulation.

The “blastocoel” is a fluid-filled cavity in the blastocyst. It is enclosed by trophoblast cells.

Germ layers are primary layers of cells that form during embryogenesis. In mammals, they are the endoderm, ectoderm, and mesoderm. In embryo development, the germ layers differentiate during gastrulation.

The trophoblast is the outer layer of cells that make up the blastocyst. These cells provide nutrients to the developing embryo, and eventually develop into the placenta. During the later stages of cleavage, the trophoblast becomes distinguished from the inner layer of cells, which will develop into the embryo. There is a layer of fluid between the trophoblast and inner cell mass.

Developing mammalian embryos exhibit rotational cleavage. In this type of cleavage, the first cell division occurs on meridionally. The next cell division in the two resulting daughter cells occurs meridionally in one and equatorially in the other.