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During pregnancy the embryo, consisting of a small number of identical cells, undergoes a series of changes which results in the production of a body consisting of specialized tissues and cells. Describe the changes which occur during this process

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During pregnancy the embryo, consisting of a small number of identical cells, undergoes a series of changes which results in the production of a body consisting of specialized tissues and cells. Describe the changes which occur during this process and briefly discuss how the process is controlled: In my essay I am going to discuss how the cells develop at different stages of change, cleavage, gastrulation and implantation then I am going to discuss the formation of a variety of organs and go into detail with one. Fertilization and Cleavage 24 hours post fertilization the zygote, formed by fusion of the two haploid gametes (sperm and ovum) undergoes mitotic division. After fertilization of the egg, cleavage gives rise to 2 cells, 4 cells, 8 cells, 16 cells and 32 cells. At this stage the embryo consists of similar cells. Then subdivision occurs into the inner cell mass and the trophoblast giving rise to cells destined to form the embryo and the extra-embryonic tissues. It takes around a week for these cleavages to occur and for the embryo to move down the Fallopian tube into the uterus, where it will implant in the wall of the uterus. At about the time of implantation the inner cell mass becomes subdivided into two tissue layers and the embryo forms a disc. ...read more.


This is where exchanges are made between the fetal and maternal blood before the fetal blood leaves through the umbilical vein and maternal blood is present through the maternal venules. The major organ systems start to develop during the embryonic period. This period is also called organogenesis. I am going to give detail of the face, male / female reproductive tract, heart. The development of face is by fusion of five masses of tissue. Each mass forms the forehead, nose and middle of the upper jaw and lip. Two of the masses form from the maxillae (upper lip and jaw) and two form the lower lip and jaw. The nose starts as two structures. When the face reaches maturity and the brain enlarges, the two sides of the nose come to each other in the midline and fuse. The two masses forming the upper jaw expand toward the midline and fuse with part of the nose to form the upper jaw and lip. The top of the mouth starts to form as ventricle shelves of tissue grow on the inner of the maxillary masses. These shelves swing to a horizontal position and start to fuse with each other at about 56 days of development. ...read more.


Congenital heart defects are a problem, but they can be controlled as there is treatment. As the heart is forming defects can occur: * Ventricular septal defect- there is a fail in the forming of superior part of the interventricular septum.So, the blood from two ventricles mixes. This defect occurs in about 1 in every 500 births. * transposition of the great vessels-the aorta comes from the right ventricle, and pulmonary trunk from the left. Results when the bulbus cordis doesn't divide in the proper way. The unoxygenated blood passes repeatedly around systemic circuit, where as oxygenated blood recycles around the pulmonary circuit. This defect occurs in about 1 in every 1000 births. * Coarctation of the aorta- there is narrowing in the part of the aorta, so the work load on the left ventricle increases. This defect occurs about 1 in every 1500 births. * tetralogy of fallot-has multiple defects; pulmonary trunk narrows and pulmonary valve stenosed; ventricular septal defect; there is opening of aorta from both ventricles; by the overwork wall of right ventricle thickens. This defect occurs about 1 in every 2000 births. * pulmonary stenosis- there is lessening in the flow of blood to the lungs, because the pulmonary semi- lunar valve is narrowed. This defect occurs about 1 in every 2800 births. Most of the surgical techniques can correct most of these heart defects. ...read more.

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