A major theme, or organizing principle, of this book is the analogy of the endothelial cell (EC) to an input–output device. Input arises from the extracellular environment and includes numerous biochemical and biomechanical forces. These environmental cues trigger signaling in ECs through receptor-dependent and receptor-independent mechanisms. Intracellular signaling then results in post-transcriptional and/or transcriptional changes, ultimately leading to an alteration in output, or phenotype. Other sections in this book cover topics related to input and signaling. The chapters in the current section focus on the output side of the equation. An important qualification when discussing output is the scale of investigation that is being considered. For example, at the level of the single cell, ECs may undergo a change in calcium flux, cell shape, protein or mRNA expression, migration, proliferation, and/or apoptosis. Monolayers of ECs express barrier properties and may be assayed for adhesion and transmigration of leukocytes. Other (emergent) properties of the endothelium are only appreciated at the level of the whole blood vessel, organ, or organism. These include endothelial regulation of vasomotor tone and formation of new blood vessels.

In this section, we begin with novel in vivo proteomic approaches that underscore the remarkable heterogeneity of EC phenotypes at the level of the cell surface (Chapters 99 and 100). The next series of chapters focus on the role of the endothelium in hemostasis, beginning with an overview of coagulation (Chapter 101), followed by detailed discussions of specific procoagulant and anticoagulant molecules (Chapters 102–109). Another important function of the endothelium is the regulation of vasomotor tone. We have not included an overview chapter related to this topic.