The major hemodynamic abnormality underlying the elevated blood pressure in hypertension is an increase in vascular resistance. The microcirculation is a key site of increased vascular resistance in hypertension. A lesser density of arterioles and capillaries is an important common characteristic of various microvascular beds in many forms of hypertension. This microvascular rarefaction has been observed even in very early stages of hypertension development. A hypothesis is discussed to explain early microvascular rarefaction as the result of genetic and fetal mechanisms of decreased small blood vessel growth...