Processes

Displaying 71 - 80 of 86 items.

Reassessment of Carrel's Immortal Tissue Culture Experiments

By Lijing Jiang

In the 1910s, Alexis Carrel, a French surgeon and biologist, concluded that cells are intrinsically immortal. His claim was based on chick-heart tissue cultures in his laboratory that seemed to be able to proliferate forever. Carrel's ideas about cellular immortality convinced his many contemporaries that cells could be maintained indefinitely. In the 1960s, however, Carrel's thesis about cell immortality was put into question by the discovery that human diploid cells can only proliferate for a finite period.

Format: Articles

Subject: Processes, Theories

Inducing Fertilization and Development in Sand Dollars

By Karen Wellner

Sand dollars are common marine invertebrates in the phylum Echinodermata and share the same class (Echinoidea) as sea urchins. They have served as model laboratory organisms for such embryologists as Frank Rattray Lillie and Ernest Everett Just. Both Lillie and Just used Echinarachnius parma for their studies of egg cell membranes and embryo development at the Marine Biological Laboratory (MBL) at Woods Hole, Massachusetts, in the early 1900s.

Format: Articles

Subject: Processes

Abortion

By Christina Raup

Abortion is the removal of the embryo or fetus from the womb, before birth can occur-either naturally or by induced labor. Prenatal development occurs in three stages: the zygote, or fertilized egg; the embryo, from post-conception to eight weeks; and the fetus, from eight weeks after conception until the baby is born. After abortion, the infant does not and cannot live. Spontaneous abortion is the loss of the infant naturally or accidentally, without the will of the mother. It is more commonly referred to as miscarriage.

Format: Articles

Subject: Processes, Ethics, Reproduction

Ectopic Pregnancy

By Tian Zhu

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

Sperm Capacitation

By Stephen Ruffenach

Sperm capacitation refers to the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg. This term was first coined in 1952 by Colin Russell Austin based on independent studies conducted by both Austin himself as well as Min Chueh Chang in 1951. Since the initial reports and emergence of the term, the details of the process have been more clearly elucidated due to technological advancements.

Format: Articles

Subject: Processes

Regeneration

By Mary E. Sunderland

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

Test-Tube Baby

By Stephen C. Ruffenach

A test-tube baby is the product of a successful human reproduction that results from methods beyond sexual intercourse between a man and a woman and instead utilizes medical intervention that manipulates both the egg and sperm cells for successful fertilization. The term was originally used to refer to the babies born from the earliest applications of artificial insemination and has now been expanded to refer to children born through the use of in vitro fertilization, the practice of fertilizing an embryo outside of a woman's body.

Format: Articles

Subject: Processes, Ethics, Reproduction

Leonardo da Vinci's Embryological Drawings of the Fetus

By Hilary Gilson

Leonardo da Vinci's embryological drawings of the fetus in the womb and his accompanying observational annotations are found in the third volume of his private notebooks. The drawings of Leonardo's embryological studies were conducted between the years 1510-1512 and were drawn with black and red chalk with some pen and ink wash on paper. These groundbreaking illustrations of the fetus reveal his advanced understanding of human development and demonstrate his role in the vanguard of embryology during the Renaissance.

Format: Articles

Subject: Processes

Hartsoeker's Homunculus Sketch from Essai de Dioptrique

By Cera R. Lawrence

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

Homunculus

By Cera R. Lawrence

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