China
Africa
Explore chapters and articles related to this topic
Toxic Responses of the Female Reproductive System
Published in Stephen K. Hall, Joana Chakraborty, Randall J. Ruch, Chemical Exposure and Toxic Responses, 2020
Joana Chakraborty, Maureen McCorquodale
The sperm and egg must unite by a process called fertilization to produce an embryo. For successful fertilization, both the spermatozoon and the egg must undergo a series of changes. In order to penetrate through the corona radiata cells and the zona pellucida to fertilize the egg, the sperm cells must undergo a process called capacitation. In humans, it takes about seven hours for the sperm to complete capacitation. Morphologically it is impossible to distinguish the capacitated from the noncapacitated spermatozoa. The process of capacitation will allow the sperm cells to undergo the next process called activation. The spermatozoa, once capacitated, are still unable to fertilize the egg until they undergo a final change of activation. Three types of changes occur in spermatozoa during the activation process. First, as a result of membrane fusion the contents of the acrosome (a structure located in the anterior region of the spermatozoan head) become exposed to the exterior. This process is called acrosome reaction. Second, changes occur in the flagellar beat, leading to a single episodic “whiplash” type of beat replacing the undulating wavelike beat. Third, changes occur in the plasma membrane surrounding the post nuclear cap region, thus making it more specialized for membrane fusion.
Culture of Chinese Carp
Published in Karol Opuszynski, Jerome V. Shireman, HERBIVOROUS FISHES: Culture and Use for Weed Management, 2019
Karol Opuszynski, Jerome V. Shireman
The production of grass carp triploids has become the method of choice to obtain sterile grass carp and is widely used by many commercial producers in the U.S. The biological mechanism for triploid induction consists of inhibiting the second meiotic division of the egg. This division takes place when the matured egg is ovulated and the sperm enters the egg. Because one set of chromosomes is ejected from the egg together with the second polar body, the genetic material of the egg is reduced to In. The genetic material of the sperm (In) and the genetic material of the egg (In) then combine to form a diploid (2n) embryo. When the second meiotic division is inhibited, two sets of chromosomes are contributed by the egg and one by the sperm which results in a triploid embryo.
Fundamentals of biology and thermodynamics
Published in Mohammad E. Khosroshahi, Applications of Biophotonics and Nanobiomaterials in Biomedical Engineering, 2017
Another type of cell that has received considerable attention during recent years is the stem cell. Stem cells can be thought of as blank cells that have yet to become specialized (differentiated), giving them the characteristics of a particular type of cell, such as the ones described above. Stem cells thus have the ability to become any type of cell to form any type of tissue (bone, muscle, nerve, etc.). The three different types of stem cells are (i) embryonic stem cells, which come from embryos, (ii) embryonic germ cells, which come from testes, and (iii) adult stem cells, which come from bone marrow. Embryonic stem cells are classified as pluripotent because they can become any type of cell. Adult stem cells, on the other hand, are multipotent in that they are already somewhat specialized.
Untangling Twinning: What Science Tells Us about the Nature of Human Embryos
Published in The New Bioethics, 2021
Condic then considers the definition of an embryo, developing criteria for identifying an embryo, as distinct from other human cells — it has a human nuclear genome, and initiates a ‘globally organized and integrated developmental process’. Embryos arise from the fusion of a human oocyte and human sperm, or any other process that initiates this developmental process, and they have less than eight weeks of development. An important question is how to determine if this development process is underway, and Condic explains that the formation of the trophectoderm and the inner cell mass provide sufficient evidence for this — they are the first two committed cell types, and demonstrate the embryos has the ability to produce a variety of different cell types. This does not, however, mean the developing entity becomes a human embryo at this point — rather, this is the earliest point it can be determined. An embryo is present as soon as an entity capable of such an organised development process comes into existence.
Ordinary ethics. Examining ethical work in the Argentine fertility clinic
Published in Tapuya: Latin American Science, Technology and Society, 2020
This article offers preliminary results from a study regarding the use of pre-implantation genetic diagnosis and screening (PGD/PGS1) in the City of Buenos Aires, Argentina. PGD/PGS refer to a set of genetic testing techniques used to identify the chromosomic constitution of the embryo before its transfer to the uterus, during assisted reproduction cycles. Whereas pre-implantation genetic diagnosis (PGD) refers to the testing for specific and well-documented genetic anomalies (like trisomy 21, which causes Down’s syndrome), pre-implantation genetic screening (PGS) refers to a general, exhaustive screening of the embryo’s constitution in search for unknown genetic differences.2 The main force behind PGD/PGS is the birth of a “healthy baby” (Franklin and Roberts 2006); a result achieved by ruling out the presence of genetic anomalies in the fertilized, transferable egg. In the case of PGS, another relevant factor for its development is the need to provide further medical responses to patients who are unable to conceive after a number of ART attempts (see below). Between eight and ten cells are extracted from the embryo before its transfer to the uterus, usually on day five of development (blastocyst stage). Biopsied cells are then analyzed using complex biomolecular technologies with the purpose of establishing if they possess any genetic alteration that may cause a genetic illness or disability in the potentially resulting person.