Processes

Displaying 51 - 60 of 99 items.

Epithelium

By Kate MacCord

Frederik Ruysch, working in the Netherlands, introduced the term epithelia in the third volume of his Thesaurus Anatomicus in 1703. Ruysch created the term from the Greek epi, which means on top of, and thele, which means nipple, to describe the type of tissue he found when dissecting the lip of a cadaver. In the mid nineteenth century, anatomist Albrecht von Haller adopted the word epithelium, designating Ruysch's original terminology as the plural version. In modern science, epithelium is a type of animal tissue in which cells are packed into neatly arranged sheets.

Format: Articles

Subject: Theories, Processes

Gastrulation in Mus musculus (common house mouse)

By Justin M. Wolter

As mice embryos develop, they undergo a stage of development called gastrulation. The hallmark of vertebrate gastrulation is the reorganization of the inner cell mass (ICM) into the three germ layers: ectoderm, mesoderm, and endoderm. Mammalian embryogenesis occurs within organisms; therefore, gastrulation was originally described in species with easily observable embryos. For example, the African clawed frog (Xenopus laevis) is the most widely used organism to study gastrulation because the large embryos develop inside a translucent membrane.

Format: Articles

Subject: Processes, Experiments

Mesenchyme

By Kate MacCord

Mesenchyme is a type of animal tissue comprised of loose cells embedded in a mesh of proteins and fluid, called the extracellular matrix. The loose, fluid nature of mesenchyme allows its cells to migrate easily and play a crucial role in the origin and development of morphological structures during the embryonic and fetal stages of animal life. Mesenchyme directly gives rise to most of the body's connective tissues, from bones and cartilage to the lymphatic and circulatory systems.

Format: Articles

Subject: Processes

Bicoid

By Jack Resnik

Bicoid is the protein product of a maternal-effect gene unique to flies of the genus Drosophila . In 1988 Christiane Nüsslein-Volhard identified bicoid as the first known morphogen . A morphogen is a molecule that determines the fate and phenotype of a group of cells through a concentration gradient across that developing region. The bicoid gradient, which extends across the anterior-posterior axis of Drosophila embryos, organizes the head and thorax.

Format: Articles

Subject: Processes

Spemann-Mangold Organizer

By Samuel Philbrick, Erica O'Neil

The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. Hilde Mangold was a PhD candidate who conducted the organizer experiment in 1921 under the direction of her graduate advisor, Hans Spemann, at the University of Freiburg in Freiburg, German. The discovery of the Spemann-Mangold organizer introduced the concept of induction in embryonic development.

Format: Articles

Subject: Processes

The Carapacial Ridge of Turtles

By Guido Caniglia

Two main elements characterize the skeletal morphology of turtles: the carapace and the plastron. For a turtle, the carapacial ridge begins in the embryo as a bulge posterior to the limbs but on both sides of the body. Such outgrowths are the first indication of shell development in turtle embryos. While the exact mechanisms underpinning the formation of the carapacial ridge are still not entirely known, some biologists argue that understanding these embryonic mechanisms is pivotal to explaining both the development of turtles and their evolutionary history.

Format: Articles

Subject: Processes

Multi-Fetal Pregnancy

By Corinne DeRuiter

In humans, multi-fetal pregnancy occurs when a mother carries more than one fetus during the pregnancy. The most common multi-fetal pregnancy is twins, but mothers have given birth to up to eight children (octuplets) from a single pregnancy. Multiple fetusus can result from the release of multiple eggs or multiple ovulations, the splitting of a single fertilized egg, and fertility treatments such as in vitro fertilization (IVF) which involves the insertion of many fertilized eggs into the mother's uterus.

Format: Articles

Subject: Processes, Reproduction

Essay: Homology

By Ingo Brigandt

Homology is a central concept of comparative and evolutionary biology, referring to the presence of the same bodily parts (e.g., morphological structures) in different species. The existence of homologies is explained by common ancestry, and according to modern definitions of homology, two structures in different species are homologous if they are derived from the same structure in the common ancestor.

Format: Essays and Theses

Subject: Processes

Mechanistic Realization of the Turtle Shell

By Guido Caniglia

Turtle morphology is unlike that of any other vertebrate. The uniqueness of the turtle's bodyplan is attributed to the manner in which the turtle's ribs are ensnared within its hard upper shell. The exact embryological and genetic mechanisms underpinning this peculiar anatomical structure are still a matter of debate, but biologists agree that the evolution of the turtle shell lies in the embryonic development of the turtle.

Format: Articles

Subject: Processes

Gastrulation in Gallus gallus (Domestic Chicken)

By Corinne DeRuiter, Maria Doty

Gastrulation is an early stage in embryo development in which the blastula reorganizes into three germ layers: the ectoderm, the mesoderm, and the endoderm. Gastrulation occurs after cleavage but before neurulation and organogenesis. Ernst Haeckel coined the term; gaster, meaning stomach in Latin, is the root for gastrulation, as the gut is one of the most unique creations of the gastrula.

Format: Articles

Subject: Processes