Over the past few decades an exceedingly large number of experimental and clinical investigations have been performed in an attempt to analyze the way in which the kidney functions. The basis for all this work was established during the nineteenth and the early twentieth century by morphologists (Bowman 1842; Hyrtl1863, 1872; Heidenhain 1874; Peter 1909; von Mollendorf 1930). All these investigators clearly outlined the extremely heterogeneous assembly of renal tissue and also defined the nephron as the smallest morphological unit. It was further the merit of these anato mists and histologists to preclude quite a number of nephron functions based merely on their careful observations. Contemporary histologists have been able to add little to these observations. Unfortunately with the introduction of physiologic in vivo et situ studies on kidneys the interest in heterogeneity waned. This lack of attention was aggravated by the introduction of the clearance techniques which cannot account for regional differences in the function of the smallest unit, the nephron. That ana tomic heterogeneity has a functional correlate was strongly suggested by Trueta et al. (1947) and vigorously stimulated a number of studies. The development of physiologic microtechniques, like micropuncture and microperfusion of single nephrons, or the perfusion of isolated nephron portions and electrophysiologic studies, enormously expanded our knowledge concerning details regarding nephron and total renal func tion.

1 Introduction

2 Organization of the Rat Kidney
2.1 Cortex
2.2 Outer Zone of Renal Medulla
2.3 Inner Zone of Renal Medulla
2.4 Nephron Structure
3 Basic Principles of Stereology
3.1 Structural Parameters and Profiles on Sections
3.2 Methods of Estimating Volume Densities
3.3 Estimation of Surfaces
3.4 Estimation of Length
4 Material and Methods
4.1 Stereological Analysis
4.2 Determination of Size of Reference Volumes
4.3 Biochemical Investigations
4.4 Physiologic Parameters
5 Results
5.1 Quantitative Morphology of the Normal Rat Kidney
5.2 Quantitative Morphology of the Acutely Injured Kidney Cortex
5.3 Functional Changes of the Acutely Injured Kidney Cortex
6 Discussion
6.1 The Normal Kidney
6.2 The Acutely Injured Kidney Cortex
7 Summary
References.