Mechanisms of Epiboly of ectoderm in the Xenopus Laevis embryo
Introduction
Epiboly is a movement of gastrulation in the amphibian embryo, whereby ectodermal precursors expand to cover the entire embryo. This process occurs in the surface and deep layer cells in the animal and marginal regions. Three rounds of cell division occur in the deep cells, while they also rearrange to form fewer layers. Superficial cells elongate by cell division while flattening, which gives them greater surface area and thinner depth. The ectoderm eventually covers the entire embryo, internalizing the endoderm. This process sets up the correct position for the three germ layers, with the ectoderm on the outside, mesoderm in the middle and endoderm on the inside.
Keller (1980) found that superficial cells spread, divide, and undergo rearrangements and a temporary change in shape, which produces an increase in area. The deep cells become thinner and decrease in the number of layers. They do this by a process called radial interdigitation. Radial interdigitation is when the deep cells elongate, extend protrusions between one another along radii of the embryo and interdigitate to form fewer layers with greater area. Once this process is complete, the deep region consists of one layer of columnar cells, which flatten and spread to further increase area. In the dorsal marginal zone the cells also undergo a shape change, which is not seen in the cells of the animal region. The difference may be due to the uniform spreading in the animal region contrasted with extension and convergence that occurs in the dorsal marginal zone.
In his work on time-lapse films of exogastrulae, Keller (1980) found that the ectoderm becomes corrugated by rapid constrictions of the apices of superficial cells and by the appearance of holes in the epithelium. From this, he suggested that shrinkage, rather than expansion aids in epiboly of the ectoderm. He presents a model (see Figure 1) in which the superficial layer is under tension and the force for expansion must come from the deep cells. The expansion of the deep region is resisted by the tension in the superficial layer resulting in an outward curling of the bilayer (deep and superficial layers).
An alternative model (see Figure 2) is also proposed, in which the superficial epithelium is stretched by tension at the margin of the blastopore, which initiates the superficial cells to spread passively (Keller, 1980). While the deep cells rearrange themselves to occupy the areas now available that were once occupied by the superficial cells.
...er with the plasma membrane all over the edges of the cell, thereby completing the division of both daughter cells. In the middle of both plasma membranes stretch out on the central lamella that bisects the daughter cells. Every daughter cell then leaves a primary wall just next to the central lamella. Additionally, each of the two daughter cells deposits another primary wall layer all over the whole protoplast. The new wall formed combines with the cell plate’s wall to form one complete wall. The original cell wall enlarges until it ruptures because of the growth and expansion of the two daughter cells (Starr et al, 2012).
Simple epithelia: Epithelia tissue can have cell shapes these are the Columnar, Cuboidal, and Squamous Cell Shapes. All this cells shapes are part of a type of an epithelia tissue which is the simple Epithelia. There are columnar cells, which means column-like cells and squamous cells, which are flattened and scale-like cells, simple squamous epithelia is found in walls of lung alveoli, blood capillaries and bowman’s
After careful consideration I relate more to Dr. Davis M. Buss, known for his evolutionary research on human sex differences in mate selection. Sex differences. Buss posits that men and women have faced different adaptive challenges throughout human history, which shape behavioral difference in males and females today. Example women have to carry the child for nine months and then make it though delivery. Men during pregnancy have thoughts of paternity and having as many children as possible. He also focused on short and long term mating strategies, male and female preference, deception, love, jealousy, and a host of other topics that deal hand and hand with relationships and relationship disputes. I Personally, relate to these theories because
There are many things one has learned from the experience, although the twelve versions of Cinderella are similar to each other but yet in some way they are different, which make it unique. Similar plot and similar circumstances however, different author with different minds. They are portraying with similar knowledge but the way the story may be told is different such as the characters names, locations, and the time it was created. No matter what it is I’ve learn that Cinderella will be Cinderella regardless of the different author, different time or different title. These creations of different versions is precisely similar to when one tells another person a story and is passed on to another person than the story will be shorten with less details and added with a few other exaggerations, in which will cause the stories to be different from each other.
This legend is based on the Brothers Grimm parable which is one of their earliest works. In the Grimm story, the Queen is the princess’s real mother. When the queen finds out from the mirror that her daughter is more beautiful than herself, she becomes jealous and grows to hate her own daughter - who is “fairest of them all” (The Origins of Snow White, Cinderella, and Sleeping Beauty" 2) at only seven years old. The queen sends the huntsman to kill Snow White like in the original story, however she requests the lungs and liver of her daughter, not the heart. The huntsman lets her go mostly because he thinks the wild animals will kill her anyways. During her sojourn with the dwarfs, the queen knows she is there and makes three more attempts on her life. The dwarves manage to save her the first two times, but they conclude that she is deceased the third time, when she gets a piece poison apple caught in her throat. A prince comes along one day and falls in love with the unconscious beauty. He then proceeds to take the corpse everywhere he goes, referring to her body as “his dearest possession,” (The Origins of Snow White, Cinderella, and Sleeping Beauty" 3). The piece of apple is dislodged waking the princess, and she falls in love with the prince. At their wedding, the queen is forced to put on red-hot iron shoes and dance until she dies. Although this tale had a happy ending, it contains a few gory details that the Disney animation did not
The study of cells is not limited to describing structures. A central concept in modern cytology is that each structure has a function that may be understood as a series of biochemical reactions. The understanding of these functions has been greatly aided by the development of cell fractionation techniques, using an ultracentrifuge to separate specific intracellular structures from the rest of the cell. Another technique is tissue culture, by which specific kinds of cells can be isolated and grown for study.
Even though the time periods are very different (by 200 years) the formulas for their fairy tales seems to remain constant. Character development, which is very important in fairy tales is both well done and accurately portrays the living situation for a character in the time period of when it was written. Perrault's version seems to put Cinderella's family in a higher, well-off situation of the Grimm's because she is still abided to obey the rules that her dying mother had set for her. Something that you would see a women do in the late 1600's. Her higher class and the rules of her generation has set her to not have revenge on her step-sisters and helps them marry in the end, making a happy ending to the story for everyone. This also gives off the rules of the time to the young girls who would be listening or reading this story back then. They knew their place in society and tales like Perrault's reinforced it. The Grimm's version, titled Ashenputtle, has key elements in the story line that make it very different from Perrault's Cinderella. The theme becomes very different as the end of the tale results in revenge on the step-sisters from Ashenputtle. This variation in the story line represents the setting in which the Grimm's either lived in themselves, or the living situation of the people who related this tale to the Grimm's.
There are many fairy tales that have been discussed in this class. The most interesting stories to me are Snow White by Brother Grimm and Ever After: A Cinderella Story directed by Andy Tennant based on Cinderella by Charles Perrault. There are many different versions of Snow White and Cinderella from numerous cultures. In every version, both stories are known as children bed time stories. In addition, the purpose of both stories is to give a life lesson to the children about overcoming evil to attain happiness. At first, every fairy tale has to deal with evil that threatens the protagonist, but in the end, good must always win. In the same way, both of the fairy tales have a similar scenario of a character that is beautiful and has an equally sweet disposition, but is thwarted by an antagonist
When planning a new project, how the project will be managed is one of the most important factors. The importance of a managers will determine the success of the project. The success of the project will be determined by how well it is managed. Project management is referred to as the discipline that entails the processes of carefully planning, organizing, controlling, and motivating the organization resources so as to foster and facilitate the achievement of specific established and desired goals and meet the specific criteria of success required in the organization (Larson, 2014). Over the course of this paper I will be discussing and analyzing the importance of project management.
The cilia found in epithelial cells means that substances can pass easier and quicker. Squamous epithelial tissue is very thin and also very flat. It is usually one cell thick and is therefore in contact with the basement membrane. Because it is so thin, it is brilliant at diffusion and filtration, and it is also found in locations where these functions are essential. Squamous epithelial cells also have an egg-shaped nucleus. Columnar epithelial tissues are elongated and column-shaped. They occur in one or more layers. This type of epithelial tissue enables movement of molecules due to the simple thin structure and therefore allows easy exchange. The nucleus is also elongated and are normally located near the base of the cells. Columnar epithelium makes up the lining of the stomach and also the lining of the intestines. Some of which are specialised for sensory reception, for example the nose, ears and taste buds. Unicellular glands are found between the columnar epithelium and the duodenum. They secrete mucus, lubricating the surface of cells. Cuboidal epithelium tissues are a cuboidal shape, and each have a circular nucleus in the middle of them. This type of epithelium tissue is found in the
Lack of coordination between the project management team causes the project to work at a much slower rate than estimated.
Histopathological samples are examined in vivo where the relationship between the cells is maintained and observable. These can be cross sections of small organs or slices of larger ones. This results in a large number of cells being available and their cell-to-cell interactions apparent for examination.
Coleridge, like many other romantic writers of his time such as Wordsworth, demonstrated through his works a great interest in nature. Instead of following the philosophy of the eighteenth century which drew the line between man and nature, Coleridge developed a passionate view of the idea that there is just ''one''. He believed that nature was ""the eternal language which God utters"", therefore conecting men, nature and the spiritual together. In his poetry, Coleridge used his philosophy to to explore wider issues through the close observation of images and themes relating to the natural world.
Spiess, L. and Waring, P. 2005. Aesthetic labour, cost minimisation and the labour process in the Asia Pacific airline industry. Employee Relations, 27 (2), pp. 193--207.