Embryo Project Encyclopedia

"Induction and Patterning of the Primitive Streak, an Organizing Center of Gastrulation in the Amniote," (hereafter referred to as "Induction") examines the mechanisms underlying early amniote gastrulation and the formation of the primitive streak and midline axis. The review, authored by Takashi Mikawa and colleagues at Cornell University Medical College, was published in Developmental Dynamics in 2004. The article primarily discusses chick embryos as a model organism for nonrodent amniote gastrulation, although it intermittently touches on nonamniote gastrulation for comparative purposes. "Induction" attempts to explain the initiation of cell differentiation and embryo organization, one of the most intriguing processes of embryology.

Meiosis, the process by which sexually-reproducing organisms generate gametes (sex cells), is an essential precondition for the normal formation of the embryo. As sexually reproducing, diploid, multicellular eukaryotes, humans rely on meiosis to serve a number of important functions, including the promotion of genetic diversity and the creation of proper conditions for reproductive success. However, the primary function of meiosis is the reduction of the ploidy (number of chromosomes) of the gametes from diploid (2n, or two sets of 23 chromosomes) to haploid (1n or one set of 23 chromosomes). While parts of meiosis are similar to mitotic processes, the two systems of cellular division produce distinctly different outcomes. Problems during meiosis can stop embryonic development and sometimes cause spontaneous miscarriages, genetic errors, and birth defects such as Down syndrome.

Hans Peter Dietz and Judy Simpson published, “Levator Trauma is Associated with Pelvic Organ Prolapse,” in the journal BJOG: An International Journal of Obstetrics and Gynecology in 2008. In their article, Dietz and Simpson estimated the risk of pelvic organ prolapse in women who attained injuries to the pelvic levator muscles. The levator muscles, also known as the levator ani, are a major muscle group that comprise the pelvic floor. Along with other muscles, the pelvic floor supports organs in a woman’s pelvis, such as the bladder, uterus, and rectum. Vaginal childbirth can cause a weakening of the pelvic muscles. That can lead to pelvic organ prolapse, which results in the descent of the pelvic organs towards a woman’s vaginal opening. In, “Levator Trauma is Associated with Pelvic Organ Prolapse,” Dietz and Simpson found that women were more likely to have pelvic organ prolapse if they had levator trauma, and called for further research to understand the relationship between levator ani trauma and pelvic organ prolapse.

In 1997, physicians and researchers Ambre Olsen, Virginia Smith, John Bergstrom, Joyce Colling, and Amanda Clark published, “Epidemiology of Surgically Managed Pelvic Organ Prolapse and Urinary Incontinence,” in the journal Obstetrics and Gynecology. In their article, the authors retrospectively analyzed data from patients who underwent surgery for pelvic organ prolapse or urinary incontinence two years prior in 1995. Often due to a weakening of or damage to their pelvic muscles, women with pelvic organ prolapse can experience a descent of pelvic organs into the lower pelvis and vagina. People with urinary incontinence can experience bladder control issues and urinary leaks. According to the authors, an estimated fifty percent of women who have previously given birth have had a prolapse. In their article, Olsen and colleagues analyze factors such as race, age, and weight in women who had surgery to treat pelvic organ prolapse and ultimately advocate for a standard assessment for the severity of those conditions.

In 1996, a team of researchers associated with the International Continence Society published “The Standardization of Terminology of Female Pelvic Organ Prolapse and Pelvic Floor Dysfunction” in American Journal of Obstetrics and Gynecology. Pelvic organ prolapse is characterized by the descent of the pelvic organs into the lower portion of the pelvis and is often caused by a weakening of the muscles and ligaments that normally hold the organs in place. The authors concluded that physicians and researchers needed to develop a system of standardized terms to use to describe the anatomical position of pelvic organ prolapse in women. They propose using terms that emphasize the location of the prolapse rather than just the involved organ. They also suggest that the system utilizes a series of examinations and imaging to uniformly describe and quantify pelvic organ prolapse. The article by Bump and colleagues was one of the first to call for a standardized system using specific terms to communicate findings about pelvic organ prolapse systematically across clinical and academic research settings.

In 2007, physicians John Jelovsek, Christopher Maher, and Matthew Barber published, “Pelvic Organ Prolapse,” in The Lancet. In their article, Jelovsek and colleagues provided an overview of pelvic organ prolapse in women and described the epidemiology, risk factors, symptoms, and management of the condition. Pelvic organ prolapse occurs when a woman’s pelvic floor is weakened or damaged from stress or trauma such as vaginal childbirth. The pelvic floor is a group of muscles that provides support to organs within the lower abdominal region of the body, including the bladder, uterus, and rectum. Disorders of the pelvic floor disrupt its normal function, often causing a feeling of uncomfortable pressure or pain, and incontinence, which is involuntary leakage of urine or feces. In their article, Jelovsek and colleagues reviewed the known information about pelvic organ prolapse as of 2007 and research teams who further studied the causes and management of pelvic organ prolapse in women later used the article as a reference.

Pelvic organ prolapse is a common condition in women that causes the pelvic organs to descend, often resulting from a weakened pelvic floor. Pelvic organs supported by the pelvic floor, such as the bladder, bowel, or uterus, can descend to such a degree that they project out from a woman’s body typically via the vagina. Pelvic floor stress or trauma, like vaginal childbirth, can cause pelvic organ prolapse. Women with pelvic organ prolapse also often experience other conditions, such as incontinence or the involuntary leakage of urine or fecal matter. As a result, while many women experience pressure or fullness from the prolapse itself, other common symptoms of pelvic organ prolapse are those involving the bladder or the bowel. Treatments for prolapse depend on the woman’s symptoms, and include pessaries, surgery, and pelvic floor exercises. As of 2021, researchers and physicians continue to study pelvic organ prolapse to determine how different treatments can be tailored to specific causes or symptoms.

The Public Broadcasting Station (PBS) documentary Life's Greatest Miracle (abbreviated Miracle, available at http://www.pbs.org/wgbh/nova/miracle/program.html), is arguably one of the most vivid illustrations of the making of new human life. Presented as part of the PBS television series NOVA, Miracle is a little less than an hour long and was first aired 20 November 2001. The program was written and produced by Julia Cort and features images by renowned Swedish photographer Lennart Nilsson. It comes as a sequel to the award-winning 1983 NOVA production, The Miracle of Life, which exhibits Nilsson's photography as well. The program showcases a combination of graphic animation, endoscopic and microscopic footage, as well as the story of a couple who are expecting a child. It features a number of new technological and scientific developments not present in its prequel, providing additional relevant information. By depicting human development in a clear and fresh manner, Miracle helps shed light on this indispensible aspect of life. Following is a description of the documentary, highlighting the key points of the film and explaining images featured in it.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century. Gurdon's research built on the work of Thomas King and Robert Briggs in the United States, who in 1952 published findings that indicated that scientists could take a nucleus from an early embryonic cell and successfully transfer it into an unfertilized and enucleated egg cell. Briggs and King also concluded that a nucleus taken from an adult cell and similarly inserted into an unfertilized enucleated egg cell could not produce normal development. In 1962, however, Gurdon published results that indicated otherwise. While Briggs and King worked with Rana pipiens frogs, Gurdon used the faster-growing species Xenopus laevis to show that nuclei from specialized cells still held the potential to be any cell despite its specialization. In 2012, the Nobel Prize Committee awarded Gurdon and Shinya Yamanaka its prize in physiology and medicine for for their work on cloning and pluripotent stem cells.

All sexually reproducing, multicellular diploid eukaryotes begin life as embryos. Understanding the stages of embryonic development is vital to explaining how eukaryotes form and how they are related on the tree of life. This understanding can also help answer questions related to morphology, ethics, medicine, and other pertinent fields of study. In particular, the field of comparative embryology is concerned with documenting the stages of ontogeny. In the nineteenth century, embryologist Karl Ernst von Baer famously noted that embryos of different species generally start out with very similar structure and diverge as they progress through development. This similarity allows for the construction of a series of detailed stages exhibited by a range of different organisms (though in reality embryonic development is a continuous, not staggered, process) describing the progression of events that begin with conception.