Derived from the Greek word meaning ‘a flower losing its petals’, it refers to programmed cell death and replacement. It is a normal biological process in metazoan development that allows the elimination of unwanted cells through activation of the cell death program. The products of apoptosis are absorbed by neighboring cells and by white blood …
Category Archives: Uncategorized
Appearance-reality distinction
The ability to distinguish the appearance of an object or situation (e.g., ‘looks like …’) from its underlying reality (‘really truly is’). For example, a white lamb seen through a red filter appears to be red, but is really white. This ability has been hypothesized to be maturationally constrained as it appears universally between 3 …
Aponeuroses
A wide flat, ribbon-shaped, sheet of dense fibrous tissue thatacts as a tendon for flat muscles containing fibroblasts that secrete collagen. Forexample, the sheet-like ventral abdominal musclesare united in the body midline by anaponeurosis. An aponeurosis can also exist without amuscle, where it is a fibroussheet of connective tissue (e.g., plantar aponeurosis found on theplantar …
Apical ectodermal ridge (AER)
The layer of transient surfaceectodermal cells at the apex of the embryonic limb bud (see figure below). Considered to exert an inductive influence on the condensation of underlying mesenchyme, and thereby to stimulate elongation of the limb along the proximal-distal axis and maintain signals required for patterning the limb. The majority of cell division (mitosis) …
Apnea
A pause between breaths in a respiratory cycle, usually lasting between 3 and 40 seconds, and due to obstructions to nasal, oral or tracheal passageways, or by malfunctioning of the brain stem itself. Thus, there are three types of apnea: central apnea (the cessation of both airflow and respiratory effort), obstructive apnea (the cessation of …
Aphasia
A communication disorder, acquired as consequence of damage to the left frontal lobe, left temporal lobe, or both, that affects comprehension, reading and writing, and speech. There are three major forms. In Broca’s aphasia, sometimes referred to as ataxic, expressive or non-fluent aphasia, speech consists of short, staccato-like sentences of a few words in which …
Aortic hypoplasia
Decreased growth of the aorta, the blood vessel that delivers oxygen-rich blood from the left ventricle to the body. It can involve congenital (or birth defect) coarctation (i.e., a discrete narrowing or constriction the distal segment of the aorta). Found in individuals with Williams syndrome, it is a consequence of supravalvular aortic stenosis, which involves …
Apgar score
An evaluation of a newborn’s physical status by assigning numerical values (0-2) to each of 5 criteria: heart rate respiratory effort muscle tone response stimulation, and skin colour (see table below). A score of 8-10 indicates the best possible condition (a score of 10, however, is very unusual as most newborns lose one point for …
Anthropology
The study of human beings worldwide in relation to distribution, origin, classification, and the relationships between variations in environmental and social influences as well physical characteristics and dietary intake relative to culture. The concept of culture is central to the work of anthropologists and the variations it creates (e.g., in beliefs and many other psychological …
Anthropological veto
The phrase coined by Margaret Mead (1901-1978) to refer to an anthropologist’s ability to disprove universal theories by finding one negative instance. See Cross-cultural psychology, Evolutionary psychology, Psychic unity of mankind, Relativism (or cultural relativism), Universalism