AN76.1-2 | Introduction to embryology — Glossary

The branch of biology that studies the prenatal development of organisms from fertilisation to birth

The developmental history of an individual organism from fertilisation through all stages of growth and differentiation to maturity

The evolutionary history and relationships of a species or group of organisms

The concept that an organism develops progressively from an undifferentiated egg through sequential stages of increasing complexity, not from a preformed miniature

One of three approximately equal periods dividing pregnancy: first (weeks 1-12), second (weeks 13-28), third (weeks 29-40 gestational age)

The ability of a foetus to survive outside the uterus, generally considered from 24 weeks gestational age with modern NICU support

Age of the pregnancy calculated from the first day of the last menstrual period (LMP), approximately 2 weeks more than the fertilisation age

Age of the embryo/foetus calculated from the date of fertilisation, approximately 2 weeks less than gestational age

The process of organ formation during the embryonic period (weeks 3-8), when all major organ systems are established

The specific time window during development when an organ or structure is most susceptible to teratogenic disruption

Any agent (drug, infection, chemical, physical factor) that can cause structural or functional abnormalities in the developing embryo or foetus

The process by which congenital malformations are produced by exposure to teratogenic agents during critical periods of development

The first two weeks of development when teratogenic exposure either kills the embryo or causes no malformation, because the pluripotent cells can compensate for damage

The first two weeks after fertilisation, encompassing cleavage, morula and blastocyst formation, and implantation

Weeks 3-8 of development (fertilisation age), the period of organogenesis when all major organ primordia are formed

From week 9 to birth, characterised by growth, maturation, and histological differentiation of the organ systems formed during the embryonic period

A structural or functional abnormality present at birth, which may be genetic, teratogenic, or multifactorial in origin

Bar-like mesodermal condensations in the developing pharyngeal region that give rise to structures of the face, jaw, ear, and neck

A group of congenital infections: Toxoplasma, Others (syphilis, varicella, parvovirus), Rubella, Cytomegalovirus, Herpes simplex

Principles stating that general embryonic features appear before specific ones, and early embryos resemble early stages of other species rather than their adult forms

Haeckel's principle that ontogeny recapitulates phylogeny; now modified to state that ontogeny reflects but does not literally repeat phylogenetic stages

A congenital malformation resulting from failure of neural tube closure, including anencephaly (cranial) and spina bifida (caudal)

The measurement from the top of the head to the bottom of the rump of an embryo or foetus, used to estimate gestational age especially in the first trimester