Part 1: BASIC FOUNDATIONS OF CARDIOLOGY Chapter 5:
MOLECULAR AND CELLULAR BIOLOGY OF THE NORMAL, HYPERTROPHIED, AND FAILING HEART
Author: Richard A. Walsh INTRODUCTION
Growth of the heart is a dynamic process that occurs during embryogenesis, postnatal development, maturity, and senescence and in response to changing environmental and pathologic conditions. Cardiac growth occurs at the cellular level as a consequence of the interplay between hyperplasia (increase in cell number) and hypertrophy (increase in cell size) or a combination of both processes. The relative importance of each of these two mechanisms depends upon the cell type, developmental stage, and the nature of the growth stimulus. These two forms of cell growth are variably modulated by apoptosis, or programmed cell death.!,2 This phenomenon is of importance in the determination of heart shape and chamber formation during cardiogenesis and may contribute to altered cardiac chamber geometry in response to pathologic stimuli. Physiologic and pathologic cardiovascular growth are generally mediated by developmental programs, mechanical deformation, and injury in various combinations. These processes stimulate a repertoire of biochemical signals that alter the cardiovascular phenotype. The application of molecular and cell biological approaches to this problem is rapidly defining the precise factors responsible for normal and pathologic growth of the heart and the mechanisms responsible for altered cardiac function.
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