pattens foundations of embryology 6th edition librarydoc64 pdf - reviewed by file free pdf ebook. source: carlson, b.m. patten's foundations of. pattens foundations of embryology 6th edition librarydoc64 pdf - reviewed by pdf this our library source: carlson, b.m. patten's foundations of embryology. Patten's Foundations of embryology / Bruce M. Carlson, [Matching item] Patten's foundations of embryology / Bruce M. Carlson. - 6th ed. New York: McGraw-Hill.
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In: Chapter 10, Early development and axis formation in amphibians. In: Chapter 13, Neural crest cells and axonal specificity. In: Chapter 11, The early development of vertebrates: Fish, birds, and mammals. In: Chapter 18, Metamorphosis, regeneration, and aging. In: Chapter 8, Early development in selected invertebrates. In: Chapter 9, The genetics of axis specification in Drosophila. In: Chapter 21, Environmental regulation of animal development.
Here, gap genes in the fruit fly are switched on by genes such as bicoid , setting up stripes which create the body's segmental form. Further information: evolutionary developmental biology , transcription factor , and gene regulatory network Several types of molecules are important in morphogenesis. Morphogens are soluble molecules that can diffuse and carry signals that control cell differentiation via concentration gradients.
Morphogens typically act through binding to specific protein receptors. An important class of molecules involved in morphogenesis are transcription factor proteins that determine the fate of cells by interacting with DNA. These can be coded for by master regulatory genes , and either activate or deactivate the transcription of other genes; in turn, these secondary gene products can regulate the expression of still other genes in a regulatory cascade of gene regulatory networks.
At the end of this cascade are classes of molecules that control cellular behaviors such as cell migration , or, more generally, their properties, such as cell adhesion or cell contractility.
For example, during gastrulation , clumps of stem cells switch off their cell-to-cell adhesion, become migratory, and take up new positions within an embryo where they again activate specific cell adhesion proteins and form new tissues and organs. Developmental signaling pathways implicated in morphogenesis include Wnt, Hedgehog , and ephrins.
Live cells were stained with DiI red or DiO green. The red cells were genetically altered and express higher levels of E-cadherin than the green cells.
The mixed culture forms large multi-cellular aggregates. At a tissue level, ignoring the means of control, morphogenesis arises because of cellular proliferation and motility. These changes can result in tissue elongation, thinning, folding, invasion or separation of one tissue into distinct layers. An adequate depiction of evolution requires the more complex concept of a network or 'forest' of life.
There is no consistent tendency of evolution towards increased genomic complexity, and when complexity increases, this appears to be a non-adaptive consequence of evolution under weak purifying selection rather than an adaptation.
Several universals of genome evolution were discovered including the invariant distributions of evolutionary rates among orthologous genes from diverse genomes and of paralogous gene family sizes, and the negative correlation between gene expression level and sequence evolution rate.
Simple, non-adaptive models of evolution explain some of these universals, suggesting that a new synthesis of evolutionary biology might become feasible in a not so remote future. Byrnes WM. Just is best known for his discovery of the "wave of negativity" that sweeps of the sea urchin egg during fertilization, and his elucidation of what are known as the fast and slow blocks to polyspermy.
Just's contemporary Johannes Holtfreter is known for his pioneering work in amphibian morphogenesis, which helped to lay the foundation for modern vertebrate developmental biology.
This paper, after briefly describing the life and scientific contributions of Just, argues that his work and ideas strongly influenced two of the concepts for which Holtfreter is best known: tissue affinity and autoneuralization or autoinduction.
Specifically, this paper argues that, first, Just's experiments demonstrating developmental stage-specific changes in the adhesiveness of the blastomeres of cleavage embryos helped lay the foundation for Holtfreter's concept of tissue affinity and, second, Just's notion of the intrinsic irritability of the egg cell, which is evident in experimental parthenogenesis, strongly informed Holtfreter's concept of the nonspecific induction of neural tissue formation in amphibian gastrula ectoderm explants, a phenomenon known as autoinduction.
Acknowledgment of these contributions by Just in no way diminishes the importance of Holtfreter's groundbreaking work. Understanding fundamental mechanisms and processes in development. Beyond developmental anatomy, the next level in approaching a more complete understanding of embryonic development is a familiarity with the ways in which components of the embryo interact. Countless experiments on a variety of species have given every reason to expect that human development is guided by the same mechanisms that control the development of the common laboratory animals.
In a dynamic, rapidly growing system such as an embryo, cell proliferation and its control is a dominant overall theme, although specific details of the cell cycle are often not taught in embryology courses.
In many medical schools, this topic is covered in courses in cell or molecular biology. Similarly, programmed cell death is a prominent embryologic control mechanism, but specific details of apoptosis and its control are typically presented in relation to pathologic processes, whether in a cell biology or a pathology course. Of greatest importance to introductory medical embryology is not so much mechanisms of cell death, but rather the role of programmed cell death as a mechanism for shaping developing organs.
Understanding cell—cell and cell—substrate affinities, the importance of the cell surface, and cell migrations is vital to a real knowledge of how gastrulation is accomplished, how the neural crest is dispersed, or how the nervous system becomes organized.
The level of detail with which these cellular functions are presented depends upon the time allotted for embryologic instruction.
The concept of embryonic regulation is not commonly taught in medical embryology courses, but it can considerably facilitate the student's understanding of twinning. It is very important in discussions of contemporary ways of experimentally manipulating embryos.
Ethical considerations of the acquisition of embryonic stem cells have often focused on whether or not a single stem cell can form an entire embryo.
Embryonic induction and tissue interactions are key to understanding how organs form. All students of contemporary embryology should become familiar with inductive processes and their significance for organ formation, especially since the mechanisms underlying inductions are becoming better understood see next section.
Most medical embryology courses are not allotted sufficient time for intensive or broad coverage of differentiation, but presenting a single example e. Pattern formation and morphogenesis are still relatively poorly understood even by embryologists, and it is not reasonable to subject medical students to what is often arcane experimental detail. Nevertheless, if time permits these topics can be introduced in discussions of limb or brain development.
An understanding of the molecular and genetic basis of development. Since the late s, technical advances in molecular biology and genetics have allowed experimental analysis of aspects of embryonic development that were until then little more than black boxes.
Two good examples are embryonic induction and the developing limb. For almost a century embryologists have been obsessed with trying to fathom how one embryonic tissue inductor affects the fate of its neighbor responding tissue. Only in the s did it become apparent that many classic inductions are mediated by individual or combinations of growth factors or recently discovered signaling molecules.
The realization that several inductive interactions involve inhibitory mechanisms proved to be startling to many. Upon initial examination, the limb bud appears to be a mass of homogeneous looking mesenchymal cells surrounded by a layer of ectoderm, but decades of exacting experimental analysis provided evidence for the existence of complex sets of finely tuned control mechanisms operating within the morphologically homogeneous limb bud.
Molecular and genetic analysis has validated most of the older experimental findings and has filled in many of the blanks by supplying the names of specific molecules that mediate the tissue interactions that guide limb development. New developmentally relevant molecules are being described at an astounding rate, and the complexity of molecular pathways and regulatory networks is far greater than most scientists would have imagined even 10 or 20 years ago.
A central challenge for teachers of medical embryology is how to convey to their students the essential picture of the molecular control of development without overwhelming them with details. Another issue is proportionality—what is the appropriate balance of structural, experimental, and molecular detail for obtaining a good contemporary working knowledge of normal human development in a limited period of exposure.
For medical courses, greater emphasis is often placed on what has been found than how the information was found. Many medical students come to an embryology course without an organized framework in which to place molecular information.
A good way to begin is to introduce broad categories of developmentally important molecules, such as transcription factors, signaling molecules, ligands and receptors, and signal transduction pathways. By putting specific molecular information into these broader categories, the student is less likely to have to resort to rote memory in grasping the detail.
Which individual molecules to stress and in which context can only be determined by the individual instructor. I have found it useful to stress a few important ones, e. Because almost all medical embryology courses follow the systems approach, molecular information is most efficiently imparted by showing where and when a particular molecule is important in the formation of a particular structure or organ. At this point, going beyond gels and relating gene expression to developing structure can be accomplished by using examples of in situ hybridization analysis.
Another powerful way of demonstrating the function of specific molecules is to introduce the results of specific gene knockout experiments as they relate to the development of specific structures.
By using certain examples, one can also acquaint the student with the concept of redundancy of control genes e. The point of the latter can be made by comparison with blood clotting.
Just because a disturbance of one of the many blood clotting factors inhibits clotting, it does not mean that the factor in question is the only one involved in blood clotting. Because of its importance as a tool in understanding the molecular genetic control of development, transgenic methodology should be introduced to the students in embryology courses that involve molecular aspects of development. It is instructive to point out examples of the use of genetically marked cells as lineage tracers, as well as the use of genetically altered cells to influence developmental processes.
Other technologies, such as beads that can be soaked in growth factors and that release them slowly, have been important in elucidating important developmental controls and can be easily introduced to students. The conservation of developmentally important molecules is one of the major messages that can be presented to medical students. The students should realize that the same types of molecules are used to regulate development throughout the animal kingdom. For medical students, one does not need to get into long discussions of molecular evolution to get this point across, but pointing out that, despite differences in appearance and function, there are fundamental similarities in how animals are put together can introduce a sense of perspective.
It can also be used to justify the extrapolation of results obtained on experimental animals to humans. Reutilization of molecules at different times and in different systems during development is another important unifying molecular theme. Although time constraints make it impractical to attempt anything but an overview approach to molecular aspects of development, students can gain considerable perspective by following a single molecule e. Similarly, it is important for students to understand that many of the molecules that are of vital importance to the development of embryos also play equally important roles in postnatal life.
The students should also be made aware that other developmentally active genes can also play significant roles in the genesis of tumors.