Science Glossary

Science Glossary

Human Embryology Glossary

Click on a term to expand its definition and description.

Description:
Biological development does not cease at birth. There are biological “marker” events that occur throughout the continuum of human life, where the biological characteristics of a human being change and keep changing until death. Marker events are simply developmental milestones. Some examples of this are complete physiological brain integration, sentience (your capacity to feel pleasure and pain) and implantation. There are many of these “biomarkers” throughout the continuum of human life, and they do not imply any change in the nature or essence of an already existing human being who already has these capacities but who needs time for them to fully develop. Implantation is complete at about five to seven days after a new human being begins to exist. Physiological brain integration and sentience are not complete until your early twenties.

Description:
“Birth control” or “fertility control” used to refer only to “contraception”, i.e., preventing fertilization and thus preventing the reproduction of a new human being. However today it refers to any drug, device, practice or surgery that controls or prevents the birth of new human beings who may or may not already exist. Birth control includes many methods and some of these methods are “contraceptive”, while others are “abortifacient”. The key difference between contraception and abortifacients is WHEN the birth control method works — before or after a new human being has begun to exist. Since a new human being (a human embryo) begins to exist and pregnancy begins at the beginning of the process of fertilization (in a woman’s fallopian tube), birth control that works BEFORE FERTILIZATION occurs = CONTRACEPTION, and birth control that works AFTER FERTILIZATION occurs = ABORTIFACIENT.

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Description:
Human embryonic life starts with fertilization and the beginning of the process is when a new human being begins to exist. Carnegie Stage 1 represents the fertilization process. Stage 1 is divided into three substages (1a, 1b, 1c) and this Stage’s feature is the unicellular embryo that contains unique genetic material and is an individually specific single-cell human being who will develop into all of the subsequent stages of a human being. Carnegie Stage 1a is the beginning of embryonic life and ontogenetic development that starts when a sperm makes contact with an oocyte. This is the first event of fertilization. The human embryo, by the end of Stage 1, has a postfertilization age of approximately one day, is between 0.1 to 0.15 mm in diameter and weighs approximately 0.004 mg.
http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm
http://www.medicalmuseum.mil/assets/documents/collections/hdac/stage01.pdf

Description:
Stage 1a is the beginning of the process of fertilization (first contact and penetration of the sperm and the occyte), and when a new, whole and individual human being begins to exist. All of the genetic material necessary for the new individual is now within a single cell membrane. This Stage of human development is also called the Penetrated Oocyte, as the fertilizing sperm has passed through the zona pellucida and its plasmalemma has fused with that of the oocyte or “egg”.
http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm

Reference(s):
The Virtual Human Embryo (VHE) project – Digitally Reproduced Embryonic Morphology (DREM)

Description:
The single cell human being is now referred to as the Pronuclear Embryo or the Ootid. In the Pronuclear Embryo Stage, the male and female pronuclei move toward each other and eventually compress their envelopes where they lie adjacent to the center of the cell.
http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm

Reference(s):
The Virtual Human Embryo (VHE) project – Digitally Reproduced Embryonic Morphology (DREM)

Description:
The Syngamic Embryo or Zygote is the name of the embryo during the last phase of the fertilization process, and this phase exists for a relatively short period. The pronuclear envelopes disappear, and the parental chromosomes that were contained in separate pronuclei come together. Note that the Zygote is not when the new human embryo begins to exist. The new human being begins to exist in Stage 1a (Primitive Embryo).
http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm

Reference(s):
The Virtual Human Embryo (VHE) project – Digitally Reproduced Embryonic Morphology (DREM)

Description:
There is international agreement among embryologists that human development during the embryonic period be divided into 23 stages. These have come to be known as the Carnegie Stages of Early Human Embryonic Development. The Carnegie Stages were instituted in 1942 by the National Museum of Health and Medicine’s Human Developmental Anatomy Center. The Carnegie Stages are the most reliable sources for accurate scientific facts of sexually reproduced human beings – the gold standard. They are based on acclaimed research and are consistently updated by the international nomenclature committee (20-25 of the leading Ph.D’s in human embryology). The Carnegie Stages are internationally required to be used professionally in all textbooks written by human embryologists.
http://virtualhumanembryo.lsuhsc.edu/

Reference(s):
The Virtual Human Embryo (VHE) project,
The VHE Atlas of Human Embryology,
Ronan O’Rahilly and Fabiola Muller Developmental Stages in Human Embryos (Carnegie Institute of Washington, 1987)
and Dianne N. Irving, M.A., Ph.D.

Description:
The term “conception” is not scientifically accurate and has been formally rejected by the international nomenclature committee on human embryology (part of FIPAT, under the IFAA). The term may refer either to fertilization or to implantation and is best avoided. Also, in the United States many states legally mis-define “conception” as beginning at implantation (5-7 days post-fertilization).

Reference(s):
Fertilization and Implantation of the Early Human Embryo: Accurate Scientific Resources. Dianne N. Irving, M.A., Ph.D. May 8, 2013

Description:
Within the science of Human Embryology the continuum of human life is a critical point as a biological fact. The fact that development and developmental principles do not cease with birth is fully realized. The continuum of human life is a biological fact that states at any point in time from the very beginning of the process of human sexual reproduction (fertilization, the moment when the sperm makes first contact with the oocyte or “egg”) or of a-sexual reproduction (when the DNA in a mere cell is regulated back to that of an organism, as in identical “twinning”) until death, there exists the same, whole, individual and integrated human being. There is no moment along the entire continuum when there is just a “bunch of cells”, and then suddenly there is a whole human organism – a human being.

Quote

“At any point in time, during the continuum of life, there exists a whole, integrated human being. This is because over time from fertilization to a 100 year old senior, all of the characteristics of life change, albeit at different rates at different times: size, form, content, function, appearance, etc.” “From the moment when the sperm makes contact with the oocyte, under conditions we have come to understand and describe as normal, all subsequent development to birth of a living newborn is a fait accompli…Thus, the beginning of a new life is exacted by the beginning of fertilization, the reproductive event which is the essence of life.”

C. Ward Kischer Ph.D

Reference(s):
When Does Human Life Begin? The Final Answer A human embryologist speaks out about socio-legal issues involving the human embryo.C. Ward Kischer, Ph.D. 2003

Description:
As early as 12-24 hours after fertilization, pregnancy can be confirmed by detecting a protein called “early pregnancy factor” or EPF in the mother’s serum (blood plasma). Early pregnancy factor (EPF) is an immunosuppressive substance and is a pregnancy-specific protein. The detection of this protein indicates a viable human embryo/human being exists. EPF is necessary for embryonic survival as it prevents rejection of the “foreign” embryo by the mother (there are two bodies, each genetically distinct, and each “foreign” to the other). EPF acts as both an immunosuppressant and growth factor. There are companies developing over-the-counter EPF tests, so women will more easily be able to know if they are pregnant within 12 hours of fertilization.

Description:
The embryonic period is the first eight weeks of human development (in normal sexual reproduction it is from the beginning of fertilization through eight weeks). After eight weeks the embryo becomes a fetus. The fetal period is from the beginning of nine weeks through birth.

Quote

“After fertilization the single-cell human embryo doesn’t become another kind of thing. It simply divides and grows bigger and bigger, developing through several stages as an embryo over an 8-week period. Several of these developmental stages of the growing embryo are given special names, e.g., a morula (about 4 days), a blastocyst (5-7 days), a bilaminar (two layer) embryo (during the second week), and a trilaminar (3-layer) embryo (during the third week).”

Dianne N. Irving, M.A., Ph.D.

Reference(s):
When do human beings (normally) begin? “scientific” myths and scientific facts Dianne N. Irving, M.A., Ph.D. Copyright February 1999

Description:
Fertilization is a process. The procession of events that begins when a spermatozoon (“sperm”) makes contact with a secondary oocyte (“egg”) or its investments, and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote. Fertilization normally takes place in the fallopian tube. Also, the entire process of fertilization takes about one day (roughly 24 hours), however, a new human being/human embryo begins to exists at the beginning of the process (Carnegie Stage 1a).

Quote

“…the life of the new individual human being begins with fertilization. Virtually every human embryologist and every major textbook of Human Embryology states that fertilization marks the beginning of the life of the new individual human being.”

C. Ward Kischer, Ph.D

Reference(s):
Ronan O’Rahilly and Fabiola Müller, Human Embryology & Teratology (New York: Wiley-Liss, 1994) (p. 19)

Description:
The production of male and female sex cells [gametes], i.e., spermatozoa and oocytes.

Quote

“We begin our description of the developing human with the formation and differentiation of the male and female sex cells or gametes, which will unite at fertilization to initiate the embryonic development of a new individual.”

William J. Larsen Ph.D.

Reference(s):
William J. Larsen,
Human Embryology (New York: Churchill Livingstone, 1997) (p.1). Ronan O’Rahilly and Fabiola Müller,
Human Embryology & Teratology (New York: Wiley-Liss, 1994) (pp. 13-14).

Description:
Not all humans are reproduced by sexual reproduction (fertilization); many are reproduced by human asexual reproductive. In human asexual reproduction (i.e., without the immediate use of human sperm and human oocyte) – both inside the body (in vivo) and outside the body (in vitro) – the biological beginning of a new human being occurs when the status of the DNA in a mere human cell or cells is reversed back to that of a new human being. Examples include naturally occurring human identical (monozygotic) “twinning” within the woman’s fallopian tube and/or uterus, and artificial “twinning” (genetic engineering and regenerative medicine research techniques in IVF/ART, and other research laboratories and infertility clinics).

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
Any human organism, including the single-cell human embryo, who possesses a genome specific for and consistent with an individual member of the human species, regardless of age, race, sex, gender, capacity to function, condition of physical or mental dependency and/or disability, or method of sexual or asexual reproduction used, whether existing in vivo or in vitro.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
All human beings during the first 8 weeks of their biological development, including single-cell human embryos from the beginning of their biological development.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
The science of when human life begins and its early development.

Quote

“The Science of Human Embryology has been around for more than 100 years. It embodies profound principles: 1. when human life begins; 2. the continuum of human life; 3. the origin of stem cells; 4. how cells build tissues; 5. how tissues form the human body; 6. pregnancy, and 7. birth defects.”

C. Ward Kischer Ph.D.

Reference(s):
Have They Never Heard Of Human Embryology? C. Ward Kischer, Ph.D.

Description:
All human beings from the beginning of the fetal period of their biological development (the beginning of 9 weeks) through birth.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
The total amount of nuclear and extra-nuclear DNA genetic material in a cell that constitutes an organism as an individual member of the human species – including the single-cell human embryo.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
In human sexual reproduction — both in vivo (inside the body) and in vitro (outside the body) — the biological beginning of a new human being/organism occurs when a human sperm makes contact with the protective covering of and fuses with a human oocyte or “egg” (before the “zygote” is developed). Examples include normal natural sexual intercourse, and artificial sexual reproduction in IVF/ART research laboratories and infertility clinics.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
Outside the body, e.g., in IVF/ART, genetic engineering, regenerative medicine and other research laboratories and infertility clinics.

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
Within the body (including the fallopian tube and the uterus).

Reference(s):
Updated References for Accurate “Language” Re “Human Being”/”Human Person”/”Personhood” Dianne N. Irving, M.A., Ph.D. Copyright February 2, 2015

Description:
Considering artificial reproduction in IVF/ART clinics, a woman is “pregnant” at implantation, when the clinician implants the 5-7 day old human embryo at the blastocyst stage into her uterus. The embryo has been reproduced either sexually (fertilization) or asexually (in the clinic’s petri dish), allowed to grow and develop there for several days, and then implanted into the woman’s uterus by the technician, When the embryo that has already been existing for a week is implanted into the woman’s uterus, only then is she “pregnant”.

Reference(s):
FERTILIZATION and IMPLANTATION of the Early Human Embryo: Accurate Scientific Resources Dianne N. Irving, M.A., Ph.D. Copyright May 8, 2013.

Description:
While the embryo begins as a “developmental individual” at the beginning of the process of fertilization, monozygotic (identical) “twinning” can take place. Monozygotic twins and some triplets are created by the subdivision and splitting of a single embryo. The separation of the cells of the early human embryo occurs naturally in .22% of all live births and results in identical twins. Two-thirds of naturally occurring human identical twins (in the woman’s body) takes place at the blastocyst stage – almost a week after fertilization, however, “twinning” can take place more than 14 days after fertilization. The first twin would be the original human embryo produced sexually (in vivo or in vitro) and would begin to exist as an individual at the beginning of fertilization (penetration of the oocyte by the sperm). The second twin is the new human embryo produced asexually (in vivo or in vitro) from totipotent cells that have separated from the original embryo, and this twin begins to exist as an individual when regulation is successfully completed and the DNA of the separated cells has been reprogrammed back to that of a new single- or multiple-cell embryo.

Reference(s):
FERTILIZATION and IMPLANTATION of the Early Human Embryo: Accurate Scientific Resources Dianne N. Irving, M.A., Ph.D. Copyright May 8, 2013. Also, When Does Human Life Begin? The Final Answer A human embryologist speaks out about socio-legal issues involving the human embryo. C. Ward Kischer, Ph.D. 2003

Description:
The production and maturation of oocytes, i.e.; the female sex cells or gametes derived from oogonia. The term “ovum” implies that polar body 2 has been given off, which event is usually delayed until the oocyte has been penetrated by a spermatozoon (i.e., has been fertilized). Hence a human ovum does not [really] exist (as once the sperm makes first contact with the oocyte, the proper term is embryo).

Reference(s):
Ronan O’Rahilly and Fabiola Müller,
Human Embryology & Teratology (New York: Wiley-Liss, 1994) (p. 16). William J. Larsen,
Human Embryology (New York: Churchill Livingstone, 1997) (pp. 3-11).

Description:
The term “preembryo” has been totally discredited, not only by all human embryologists, but has also been rejected by the Nomenclature Committee of the American Association of Anatomists for inclusion in the official lexicon of anatomical terminology, Terminologia Embryologica. This term is not used in any official textbook of Human Embryology. Since the term “pre-embryo” has been formally scientifically rejected, any similar attempt to falsify the science with a similar “pre-embryo substitute” is likewise scientifically false.

Reference(s):
When Does Human Life Begin? The Final Answer A human embryologist speaks out about socio-legal issues involving the human embryo. C. Ward Kischer, Ph.D. 2003. Also, Quick Scientific References: Human Cloning, Human Embryonic Stem Cell Research Dianne N. Irving, M.A., Ph.D. August 31, 2004

Description:
Considering normal sexual intercourse between a man and a woman, scientifically a woman is “pregnant” and “pregnancy” begins as soon as fertilization begins in her fallopian tube – when the sperm makes first contact and penetrates the oocyte or “egg”. This is when the new human being begins to exist.  The new human embryo then continues to grow and develop, and takes about a week to move through her fallopian tube towards her uterus to implant.

Reference(s):
FERTILIZATION and IMPLANTATION of the Early Human Embryo: Accurate Scientific Resources Dianne N. Irving, M.A., Ph.D. Copyright May 8, 2013.

Description:
Regulation is operative in both “zipping up” and “zipping down”. In “zipping up”, as in sexual reproduction (fertilization), regulation concerns various processes of differentiation; but it also becomes involved when an injury has occurred to the organism. Here, regulation is the ability of an embryo or an organ primordium to “heal” a normal structure if parts have been removed or added. In “zipping down”, as in a-sexual reproduction such as twinning, regulation could possibly revert separated totipotent embryonic cells back to new living human embryos, i.e., new living human beings. Indeed, this is what happens with human monozygotic twinning in vivo. The human embryo grows developmentally in total continuity with itself, and is composed initially of totipotent cells. If these totipotent cells of the embryo are damaged, the embryo could die, or regulation could set in to “heal” the embryo and restore it to wholeness. On the other hand, if these totipotent cells are actually separated from the whole embryo, then these separated cells too could just die, or regulation could possibly set in and revert these totipotent cells to new human embryos.

Reference(s):
Playing God by Manipulating Man: The Facts and Frauds of Human Cloning. Dianne N. Irving, M.A., Ph.D. 2003

Description:
The production of spermatozoa, continues from immediately after puberty until old age.

Reference(s):
William J. Larsen, Human Embryology (New York: Churchill Livingstone, 1997) (p.1).
Ronan O’Rahilly and Fabiola Müller, Human Embryology & Teratology (New York: Wiley-Liss, 1994) (pp. 13-14).