#embryo

• From the origin — A Latin phrase meaning 'from the origin' or 'from the very beginning'. In medical genetics and embryology, it is used to describe a chromosomal anomaly, congenital malformation, or metabolic disorder present in the organism's biological framework since the moment of conception (ab origine), as opposed to conditions acquired later in life.
• From the egg / From the very beginning — A Latin phrase derived from Horace's writings, meaning literally 'from the egg'. In embryology and developmental toxicology, it refers to analyzing a biological process, cellular mechanism, or the action of a teratogenic agent (malformation-inducing toxin) traced right from the egg-cell (zygote) stage or from the moment of fertilization to fully map fetal development disruptions.
• Abaxial — An anatomical and histological term describing a structure located away from the axis of the body or an organ, facing away from the central axis. In embryology and developmental anatomy, it refers to surfaces or tissues that develop remote from the median axis (e.g., the lower surface of a primitive formation or a foliar structure used in medical botany).
• Acardiac — Lacking a heart, or possessing a rudimentary, completely non-functional heart. In neonatology and fetal medicine, the term describes an 'acardiac fetus' (or acardiac twin), an extremely rare congenital anomaly occurring exclusively in monochorionic twin pregnancies due to Twin Reversed Arterial Perfusion (TRAP sequence). In this condition, the malformed fetus survives in utero only because it receives blood pumped by the heart of its healthy co-twin (the pump twin).
• Acardia — A congenital absence of the heart or a complete cessation in the ontogenetic development of the cardiac structure in a fetus. This severe structural anomaly is incompatible with independent extrauterine life and is documented almost exclusively within monochorionic multiple pregnancies with asymmetric development (TRAP sequence), where the affected fetus's blood circulation is maintained solely by its twin's heart through placental vascular anastomoses.
• Acrania — A highly severe congenital structural defect characterized by the partial or total absence of the cranial vault (calvaria), while the skull base and facial bones are partially developed.
• Acrocyst — An anatomical, external, and temporary vesicular formation observed in the development cycle of certain marine hydroid organisms (polyps, hydrozoans), serving as a protective chamber or external structural sac inside which the sexual cells (eggs) are retained and protected during the initial stages of embryonic development before their release as planula.
• Acrospire — The first embryonic shoot, germ, plumule, or rudimentary stem developing from the embryo of a cereal seed (especially barley) during the germination process. In the malting and brewing industry, monitoring the length and development of this anatomical structure beneath the grain husk (the malted grain) is an essential technical parameter for evaluating the degree of modification and solubilization of starch within the endosperm.
• Adactyly — A rare congenital malformation characterized by the total or partial absence of fingers or toes. This structural anomaly of embryonic development can occur in isolation or as part of a complex malformativ syndrome, determined by genetic mutational factors or external teratogenic insults suffered by the embryo during the first weeks of pregnancy.
• Adelphophagy — A specific form of embryonic cannibalism observed in the animal kingdom, particularly in certain sharks, amphibians, or insects, where the strongest embryo feeds on its own siblings or unfertilized eggs inside the uterus or nest before birth or hatching. This structural survival behavior ensures that only the most vigorous specimens reach maturity.
• Adenectopia — A congenital anomaly or abnormal, faulty positioning of a gland or a lymph node outside its usual anatomical site. This structural phenomenon occurs during defective embryonic development, when the glandular tissue migrates incorrectly, potentially functioning normally or generating complications due to compression on neighboring organs.
• Adenoblast — An immature, undifferentiated embryonic cell from which glandular structures and the secretory epithelium of the organism subsequently develop. This structural cellular element plays an essential role in organogenesis, undergoing a series of divisions and biochemical specializations to form the functional components of the endocrine and exocrine systems.
• Agamospermy — A form of apomixis in higher plants (spermatophytes) within which seeds form directly, without the fusion of male and female gametes. Structurally, the embryo originates from a diploid cell of the ovule (such as the nucellus or integument) or from an unfertilized egg cell, resulting in viable seeds that contain offspring genetically identical to the mother plant.
• Agenetic — Relating to agenesis; characterized by the congenital absence of an organ, tissue, or body part, caused by the failure of its development during embryonic life. In a clinical sense, it describes an organism, anatomical segment, or process affected by this severe structural development anomaly.
• Agenesis — The congenital absence of an organ, tissue, or body part, caused by the failure of its development during embryonic life. Unlike aplasia, where the embryonic bud exists but fails to fully mature, in this severe structural anomaly the initial blueprint of the organ is completely missing from the genetic profile.
• Agenosomia — A severe congenital malformation of a teratological nature, characterized by the incomplete development or partial to total absence of external genital organs and the lower abdominal wall, frequently associated with visceral eventration. This severe structural anomaly is clinically investigated within fetal pathology and is commonly considered incompatible with long-term extrauterine survival.
• Agenesis — A rare congenital malformation characterized by the complete absence, structural underdeveloped state, or congenital lack of an organ, tissue, or body part since the intrauterine development period. The phenomenon is caused by genetic errors or teratogenic factors manifesting during the early phases of organogenesis.
• Agonadism — A highly rare congenital medical condition characterized by the complete structural and functional absence of gonads (testes or ovaries), caused by an anomaly in early embryonic development; it results in a lack of sex hormones and requires life-long hormone replacement therapy.
• Allanto- — A combining form or structural prefixoid used in international medical and biological terminology to introduce references to the allantois (a sac-like embryonic membrane), to allantoic acid, or to anatomical structures shaped like a sausage or an elongated sac. This lexical element serves to construct complex neologisms within the disciplines of embryology, urology, and histology.
• Allantoid — Pertaining to the allantois, or having the shape of a sausage or an elongated sac; allantoidian. In structural medical and biological terminology, the term describes the morphological configuration of certain embryonic appendages, fetal membranes, or elongated cavitary structures that appear during the early development phases of amniote vertebrates.