Academic literature on the topic 'Rats – Embryologie'

Embryology is a fascinating subject and is the foundation of the development, growth, and maturation of all the cells, organs, and tissues of the body. Strictly, embryology is the study of the early processes of development beginning at fertilization and following the processes that turn a single cell into a multicellular organism. It is all about generation of the building blocks required to make a human body. Developmental anatomy is the study of how these building blocks are turned into specific cells, tissues, and organs as well as the general growth of the body. As you will soon appreciate in the following paragraphs, all organs and systems do not develop at the same rate so there is a degree of overlap between embryology and developmental anatomy. For example, the heart and circulatory system must develop and be functioning very early in development to ensure adequate supplies of nutrients to the developing fetal tissues. Teeth, on the other hand, are not going to be used until about six months after birth at the earliest; while the heart is already beating away, each developing tooth is merely a tiny group of cells bearing little resemblance to a fully formed tooth. Human gestation is considered to take nine months; more accurately, it usually lasts for 38 to 39 weeks from fertilization to birth. Clinically, it is divided into three trimesters of three months each. In this chapter, we will focus on events in the first few weeks. During the first two and a half weeks after fertilization, the very basic building blocks are formed from the single fertilized cell; this is the pre-embryonic period. The embryonic period covers the next five and half weeks during which these basic building blocks develop into the cells, tissues, and organs. As already indicated, some of these may be in a very rudimentary state at the end of the embryonic period. The remaining 30 or so weeks is the fetal period when the tissues and organs of the body grow and develop and the fetus grows considerably. We are not fully mature organisms at birth and have another 20 years a-growing.

Human anatomy concerns the structure of the human body. Anatomy is often interpreted as the study of only those structures that can be seen with the naked eye (gross anatomy). Anatomy also covers the study of structure at the cellular (histology) and subcellular level (ultrastructure). The formation (embryology) and growth of anatomical structures (developmental anatomy) influence their organization, appearance, and their relationship to other structures and often explain gross anatomical arrangement. Historically, physiology (the study of the function of the body) was regarded as a separate subject from anatomy but the relationships between structure and function (functional anatomy) is critical to understanding how the body works at all levels. Most modern dental curricula now have some degree of integration between anatomy and physiology to emphasize their interrelationship in the study of the human body. It is impossible to recognize changes in structure brought about by disease and their clinical manifestations and effects on function without an understanding of healthy structure and function. It is impossible to use any surgical procedures effectively and safely without a good working knowledge of the anatomy of the relevant part of the body. In clinical work, internal structures often need to be located accurately even when they cannot be visualized directly. A good example of this is the need to be able to locate the nerves supplying the teeth in order to deliver local anaesthetic accurately prior to carrying out a restoration or extraction. Fortunately, most structures have a fairly constant relationship to surface features (surface anatomy) to allow their position to be determined with considerable accuracy. Information about deep structures can also be obtained by the use of imaging techniques such as X-rays or scanning technology. Interpretation of radiographs and scans requires knowledge of the radiographic appearance of normal body structures (radiological anatomy). Surface and radiological anatomy are obviously of great practical importance and are covered in the relevant sections of the book. The principal aim of this book is to provide you with sufficient practical information about the anatomy of the human body to form a basis on which to build your clinical skills and practice.

During the prenatal period a state of physiologic pulmonary hypertension exists due to the equalization of pressures by the patent ductus arteriosus, resulting in similar wall thickness of the ascending aorta (AA) and main pulmonary artery (MPA). After birth, as the ductus arteriosus closes and pulmonary arterial pressure decreases, attenuation of medial smooth muscle occurs such that the ratio of medial thickness to external diameter decreases from about 25% in fetuses to less than 10% in infants 3 to 6 months of age. After the first year of life, thickness of the MPA is normally less than ha