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Homunculus

The term homunculus is Latin for "little man." It is used in neurology today to describe the map in the brain of sensory neurons in each part of the body (the somatosensory homunculus). An early use of the word was in the 1572 work by Paracelsus regarding forays into alchemy, De Natura Rerum, in which he gave instructions in how to create an infant human without fertilization or gestation in the womb. In the history of embryology, the homunculus was part of the Enlightenment-era theory of generation called preformationism.

Format: Articles

Subject: Processes

Morphogenesis

The term morphogenesis generally refers to the processes by which order is created in the developing organism. This order is achieved as differentiated cells carefully organize into tissues, organs, organ systems, and ultimately the organism as a whole. Questions centered on morphogenesis have aimed to uncover the mechanisms responsible for this organization, and developmental biology textbooks have identified morphogenesis as one of the main challenges in the field. The concept of morphogenesis is intertwined with those of differentiation, growth, and reproduction.

Format: Articles

Subject: Processes

Endoderm

Endoderm is one of the germ layers-- aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. All animals, with the exception of sponges, form either two or three germ layers through a process known as gastrulation. During gastrulation, a ball of cells transforms into a two-layered embryo made of an inner layer of endoderm and an outer layer of ectoderm. In more complex organisms, like vertebrates, these two primary germ layers interact to give rise to a third germ layer, called mesoderm.

Format: Articles

Subject: Processes

Ectoderm

Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.

Format: Articles

Subject: Processes

Regeneration

Regeneration is a fascinating phenomenon. The fact that many organisms have the capacity to regenerate lost parts and even remake complete copies of themselves is difficult to fathom; so difficult, in fact, that for a very long time people were reluctant to believe regeneration actually took place. It seemed unbelievable that some organisms could re-grow lost limbs, organs, and other body parts. If only we could do the same!

Format: Articles

Subject: Processes

Mesoderm

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers.

Format: Articles

Subject: Processes

“All-fours Maneuver for Reducing Shoulder Dystocia During Labor” (1999), by Joseph P. Bruner, Susan B. Drummond, Anna L. Meenan, and Ina May Gaskin

In 1999, Joseph Bruner, Susan B. Drummond, Anna L. Meenan, and Ina May Gaskin published, “All-fours Maneuver for Reducing Shoulder Dystocia During Labor,” in the medical journal, Obstetrical and Gynecological Survey. In the article, the authors described a birthing technique named the all-fours maneuver, or the Gaskin maneuver, and explained its effectiveness in treating fetal shoulder dystocia as compared to other maneuvers.

Format: Articles

Subject: Publications, Processes

Sex-determining Region Y in Mammals

The Sex-determining Region Y (Sry in mammals but SRY in humans) is a gene found on Y chromosomes that leads to the development of male phenotypes, such as testes. The Sry gene, located on the short branch of the Y chromosome, initiates male embryonic development in the XY sex determination system. The Sry gene follows the central dogma of molecular biology; the DNA encoding the gene is transcribed into messenger RNA, which then produces a single Sry protein.

Format: Articles

Subject: Processes

Biological Clocks and the Formation of Human Tooth Enamel

Tooth enamel contains relics of its formation process, in the form of microstructures, which indicate the incremental way in which it forms. These microstructures, called cross-striations and striae of Retzius, develop as enamel-forming cells called ameloblasts, whcih cyclically deposit enamel on developing teeth in accordance with two different biological clocks. Cross-striations result from a twenty-four hour cycle, called a Circadian rhythm, in the enamel deposition process, while striae of Retzius have a longer periodicity.

Format: Articles

Subject: Processes

Ectopic Pregnancy

Many difficulties can arise with a pregnancy even after the sperm successfully fertilizes the oocyte. A major problem occurs if the fertilized egg tries to implant before reaching its normal implantation site, the uterus. An ectopic pregnancy occurs when a fertilized egg implants anywhere other than in the uterus, most commonly in the fallopian tubes. Ectopic pregnancies cannot continue to term, so a physician must remove the developing embryo as early as possible.

Format: Articles

Subject: Disorders, Processes, Reproduction

Chemical Induction

Research in chemical induction seeks to identify the compound or compounds responsible for differentiation in a developing embryo. Soren Lovtrup compared the search for these compounds to the search for the philosopher's stone. It was based on the assumption that the differentiating agents have to be chemical substances either within cells or in the extracellular matrix.

Format: Articles

Subject: Processes

Hartsoeker's Homunculus Sketch from Essai de Dioptrique

This embryology image is a pencil sketch by Nicolaas Hartsoeker, published as part of his 1694 French-language paper entitled Essai de Dioptrique, a semi-speculative work describing the sorts of new scientific observations that could be done using magnifying lenses. Dioptrique was published in Paris by the publishing house of Jean Anisson. The image depicts a curled up infant-like human, now referred to as a homunculus, inside the head of a sperm cell.

Format: Articles

Subject: Theories, Processes

Golgi Staining Technique

The Golgi staining technique, also called the black reaction after the stain's color, was developed in the 1870s and 1880s in Italy to make brain cells (neurons) visible under the microscope. Camillo Golgi developed the technique while working with nervous tissue, which required Golgi to examine cell structure under the microscope. Golgi improved upon existing methods of staining, enabling scientists to view entire neurons for the first time and changing the way people discussed the development and composition of the brain's cells.

Format: Articles

Subject: Technologies, Processes

James G. Wilson's Six Principles of Teratology

James Graves Wilson's six principles of teratology, published in 1959, guide research on teratogenic agents and their effects on developing organisms. Wilson's six principles were inspired by Gabriel Madeleine Camille Dareste's five principles of experimental teratology published in 1877. Teratology is the study of birth defects, and a teratogen is something that either induces or amplifies abnormal embryonic or fetal development and causes birth defects.

Format: Articles

Subject: Processes, Reproduction

Intraspecies Chimeras Produced in Laboratory Settings (1960-1975)

When cells-but not DNA-from two or more genetically distinct individuals combine to form a new individual, the result is called a chimera. Though chimeras occasionally occur in nature, scientists have produced chimeras in a laboratory setting since the 1960s. During the creation of a chimera, the DNA molecules do not exchange genetic material (recombine), unlike in sexual reproduction or in hybrid organisms, which result from genetic material exchanged between two different species. A chimera instead contains discrete cell populations with two unique sets of parental genes.

Format: Articles

Subject: Organisms, Processes

The Development of Silicone Breast Implants for Use in Breast Augmentation Surgeries in the United States

In the 1960s, two plastic surgeons from the United States, Thomas Dillon Cronin and Frank Judson Gerow, collaborated with the Dow Corning Corporation, which specialized in silicone products, to create the first silicone breast implant. Surgeons used the implant, named the Cronin-Gerow implant, to improve the look of a woman’s breasts, by correcting for asymmetry, augmenting the size, or creating a more uplifted profile.

Format: Articles

Subject: Technologies, Processes

Umbilical Cord Blood Stem Cells (UCBSC)

Umbilical cord blood (UCB) stem cells are hematopoietic stem cells (HSC) that are recovered from the blood of the umbilical cord and placenta after birth. Umbilical cord blood is rich in cells that express the CD34 molecule, a surface protein that identifies cells as stem cells. Prior to the discovery of UCB stem cells, it was standard procedure to discard the umbilical cord and placenta; now much effort is devoted to raising public awareness and to encouraging people to store or donate cord blood.

Format: Articles

Subject: Processes, Reproduction

Amniocentesis Prior to 1980

The extraembryonic membranes that surround and originate from the embryos of vertebrates such as birds, reptiles, and mammals are crucial to their development. They are integral to increasing the surface area of the uterus, forming the chorion (which in turn produces the placenta) and the amnion, respectively. The amnion will ultimately surround the embryo in a fluid-filled amniotic cavity. This amniotic fluid, which cushions and protects the fetus and helps prevent the onset of labor, is sampled in amniocentesis to screen for genetic diseases.

Format: Articles

Subject: Processes, Reproduction

Tissue Engineering

Tissue engineering is a field of regenerative medicine that integrates the knowledge of scientists, physicians, and engineers into the construction or reconstruction of human tissue. Practitioners of tissue engineering seek to repair, replace, maintain, and enhance the abilities of a specific tissue or organ by means of living cells. More often than not stem cells are the form of living cells used in this technology. Tissue engineering is one of the disciplines involved in translating knowledge of developmental biology into the clinical setting.

Format: Articles

Subject: Processes

Hamburger-Hamilton Staging Series (1951)

In 1951 Viktor Hamburger and Howard Hamilton created an embryonic staging series from a combination of photographs and drawings from other researchers. The Hamburger-Hamilton stages are a sequence of images depicting 46 chronological stages in chick development. The images begin with a fertilized egg and end with a fully developed chick. The Hamburger-Hamilton staging series was produced in order to replace a previous chick staging series created in 1900. The earlier attempt lacked specific details and staged the chick embryo by using only morphological characteristics.

Format: Articles

Subject: Processes

Homeobox Genes and the Homeobox

Homeobox genes are a cluster of regulatory genes that are spatially and temporally expressed during early embryological development. They are interesting from both a developmental and evolutionary perspective since their sequences are highly conserved and shared across an enormously wide array of living taxa.

Format: Articles

Subject: Processes

Circulatory Changes at Birth

When placental mammals are born their circulatory systems undergo radical changes as the newborns are prepared for independent life. The lungs are engaged, becoming the primary source of fresh oxygen, replacing the placental barrier as a means for blood-gas exchange.

Format: Articles

Subject: Processes

Hematopoietic Stem Cells

The discovery of hematopoietic stem cells (HSCs) provided a pioneering step in stem cell research. HSCs are a type of multipotent adult stem cell, characterized by their ability to self-renew and differentiate into erythrocyte (red blood cell) and leukocyte (white blood cell) cell lineages. In terms of function, these cells are responsible for the continual renewal of the erythrocytes, leukocytes, and platelets in the body through a process called hematopoiesis. They also play an important role in the formation of vital organs such as the liver and spleen during fetal development.

Format: Articles

Subject: Processes

Somatic Cell Nuclear Transfer in Mammals (1938-2013)

In the second half of the
twentieth century, scientists learned how to clone organisms in some
species of mammals. Scientists have applied somatic cell nuclear transfer to clone human and
mammalian embryos as a means to produce stem cells for laboratory
and medical use. Somatic cell nuclear transfer (SCNT) is a technology applied in cloning, stem cell
research and regenerative medicine. Somatic cells are cells that
have gone through the differentiation process and are not germ
cells. Somatic cells donate their nuclei, which scientists

Format: Articles

Subject: Theories, Technologies, Processes

Breast Augmentation Techniques

Breast augmentation involves the use of implants or fat tissue to increase patient breast size. As of 2019, breast augmentation is the most popular surgical cosmetic procedure in the United States, with annual patient numbers increasing by 41 percent since the year 2000. Since the first documented breast augmentation by surgeon Vincenz Czerny in 1895, and later the invention of the silicone breast implant in 1963, surgeons have developed the procedure into its own specialized field of surgery, creating various operating techniques for different results.

Format: Articles

Subject: Technologies, Processes, Reproduction, Ethics