Intestinal Absorptive Surface In Mammals Of Different Sizes (advances In Anatomy, Embryology And Cell Biology)

The present treatise is primarily concerned with the structural and morphometric parameters of the cecum and large intestine of mammals. Over the past century, numerous accounts have visually presented the variation and diversity of the large intestine of mammals. This includes above all comprehensive works on the macroscopic anatomy. More recently, the microscopic anatomy of various animals at the light, electron, and scanning electron microscopy levels has been covered, especially for rodents and primates. In the past two decades, progress has been made by adding a new dimension to the previous structural studies, namely, the morphometrical analysis of the intestine of various animals and subsequent employment of this data in an analysis based on principles of scaling. The present account follows essentially this outline, but presented in a slightly different order. First, in the introductory section, the scientific aims and general prologue to this field of study are presented. Included in this section is a short, concise literature survey that deals with the major literature available on the subject of the large intestine at the macroscopical and microscopical level, as well as the most recent morphometric analyses of the intestines. The main focus of the present work is on the methodological; a new method is described to measure the intestines of animals ranging in size from the harvest mouse to the horse. This technique may also be applicable to other hollow or tube-like organs. Heretofore, previous techniques have been based on obtaining the area of the surface mucosa by measuring lengths and widths and calculating the area by multiplying the two measurements. Alternatively, some methods have taken probes and made measurements at the light microscopy level and then extrapolated these results to determine the entire area. The former method is inadequate, while the latter possesses the inherent disadvantages of all sampling techniques. The present technique has two levels: (1) obtaining the basal surface area of the entire intestine and (2) accounting for any increase in the mucosal surface area that is due to microscopically visible folds, villi, or other such structures. The former is accomplished by flattening appropriately sized pieces of intestine between two glass plates and tracing the contours onto transparent paper. The entire intestine is processed in this manner, resulting in a basal surface area, the contours having been submitted to analysis on a semi-automatic image analyzer to determine the area in square millimeters. The second-level measurements determine a factor of surface enlargement by calculating a ratio of the distance along the surface contour of the mucosa on a histological section cut perpendicular to the width of the intestine to a second distance (reference line) drawn straight beneath the mucosa but not tracing the enlargements. The measurements obtained at both levels are multiplied to give a final surface area. In addition to a detailed description of the technique complete with a flow sheet and pictorial diagram, the various aspects of proper fixation, tissue embedding, shrinkage, and determination of sampling sites (for the second level of measurement) are discussed. A pilot experiment to determine the surface enlargement due to microvilli is presented from material taken from the giant pouched rat. This was performed by measuring video sequences of microvilli taken from electron microscopy images. Cecal microvilli increase the surface area 15-fold, while in the colon the increase is approximately 19- to 20-fold. In the discussion, the choice of using three animals per group is discussed, based on simple statistical tests. Section 3 is entitled "Morphology of the Mammalian Cecum." Chronologically, it marks the onset of the entire investigation. Before having developed the method described in Sect. 2, these morphological investigations at the light, electron and scanning electron microscopy 1. 1 Scientific Aims In recent years, there has been a definite trend away from the casuistic scientific thinking which has dominated the scientific world, at least in the field of medicobi­ ological research. Now, in the last decade of this century, scientists are returning to a conceptual way of thinking that characterized the beginning of this century, namely organismal thinking. The holistic concept is not a new one; it was rekindled by a small group of scientists who, in the previous two decades, have begun to warn against too great an emphasis being placed on a molecular casuistic approach as the final pursuit to science (see Duncker 1983). These thinkers were perhaps instrumental in helping to turn the tide, to instruct and encourage fellow researchers to extend their findings from the molecular and to the organismal (see Duncker 1983, 1992a,b; Duncker and Kreite 1987). Having observed the ceca of many different animals for many years and having described their morphology at different levels of study -from the macroscopic to the electron microscopy level - the need to compare and observe these morphological entities in a quantitiative way became increasingly imminent. Quantitative methodol­ ogy in morphology requires the use of morphometry, which in the most general terms can be described as the measurement of the forms of animals. As defined by Reith and Meyhew (1988), it is quantitative morphology, i. e., the measurement of structures by any method, including stereology. This treatise combines a detailed methodology that is simple to follow and reconstruct, and can be universally used to determine the surface area or tubular organs, in this special case development for the intestines. It is especially appropriate for large intestine, but can be used for small intestine also. The great advantage is the applicability at the macroscopic and microscopic levels, measuring the entire intestine for determination of a ground or basal area, and using a large encompassing sampling technique to obtain a factor of surface enlargment due to such structural entitities as folds and plicae. A technique to determine the factor of increase due to microvilli is also introduced. Various factors that may influence the measurements are discussed. Application of the technique is presented within the concept of scaling. Numerous regression curves are presented to represent how intestinal surface area correlates with body weight. A unifying and correlating concept between morphology and morphometry is developed. Over 20 species are included. This volume describes a comprehensive but simple technique for determination of the intestinal absorptive surface area in mammals of different sizes (from harvest mouse to horse). It is a treatise of research carried out by the author over 25 years in a much neglected area: morphology and morphometry of the large intestine - specifically the caecum of mammals. Over 20 species are considered, at the macroscopic and microscopic levels.

The book contains black-and-white illustrations.

Front Matter....Pages I-VIII Introduction....Pages 1-9 Methodology....Pages 11-38 Morphology of the Mammalian Cecum and Colon....Pages 39-50 Morphometry of the Mammalian Cecum and Colon....Pages 51-78 Summary....Pages 79-80 Back Matter....Pages 81-90