Apical

Apical is an adjective meaning relating to or situated at the apex, or tip, of a structure. The term is used across biology and medicine to denote position, growth sites, or surface orientation.

In botany, apical refers to structures at the growing tips of plants. The apical meristem comprises undifferentiated cells at shoot and root tips and drives primary growth, increasing length. At shoots the apical meristem produces new tissues that form leaves, stems, and reproductive organs. Apical dominance is a phenomenon whereby the primary shoot apex suppresses growth of lateral buds, often via plant hormones such as auxin, shaping plant architecture. The term is also used for the apex of roots and for specialized cells at these tips.

In anatomy and histology, apical describes surfaces facing the lumen or external environment. Epithelial cells are polarized into apical and basolateral domains. The apical surface frequently features microvilli or cilia and is bounded by tight junctions and other specialized junctions that help regulate absorption and barrier function. The apical membrane contains proteins and transporters that differ from the basolateral membrane, reflecting functional polarity.

In cardiology, apical refers to the heart’s apex, used in clinical descriptions such as the apical impulse, the point of maximal impulse felt on palpation over the left chest.

The word derives from Latin apex, top, tip, and its use as a label of position spans many biological disciplines.