Table Of ContentAdvances in Anatomy
Embryology and Cell Biology
Vol. 138
Editors
F. Beck, Melbourne D. Brown, Charlestown
B. Christ, Freiburg W. Kriz, Heidelberg
E. Marani, Leiden R. Putz, Munchen
Y. Sano, Kyoto T.H. Schiebler, Wurzburg
K. Zilles, Dusseldorf
Springer
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Heidelberg
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Robert L. Snipes
Intestinal
Absorptive Surface
in Mammals
of Different Sizes
With 11 Figures and 21 Tables
Springer
Dr. Robert 1. Snipes
Institute of Anatomy and Cell Biology
Ju stus-Liebig-University
Aulweg 123
35385 Giessen
Germany
ISBN-13: 978-3-540-62986-3 e-ISBN -13: 978-3-642-60822-3
DOl: 10.1007/978-3-642-60822-3
Library of Congress-Catalog-Card Number
Snipes, Robert 1., 1948-Intestinal absorptive surface in mammals of different
sizes / Robert 1. Snipes. p. cm. - (Advances in anatomy, embryology, and cell
biology; vol. 138) Includes bibliographical references and index.
ISBN -13: 978-3-540-62986-3
(softcover: alk. paper) 1. Mammals-Digestive organs. 2. Intestinal absoprtion.
I. Title. II. Series: Advances in anatomy, embryology, and cell biology; v. 138
QL801.E67 vol. 138 [QL739] 571 s-dc21 [573.3'19]
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Acknowledgements
The process of accumulating and integrating data into a cumula
tive work that has spanned more than two decades brings to
mind the numerous colleagues and technical workers who have
been instrumental in aiding the author. Indeed, without their
help this work would never have been accomplished. It is indeed
a pleasure to acknowledge these colleagues and friends for their
support and encouragement.
For his ever supportive encouragement and unending reserve
of ideas' and suggestions, for his patience and endurance in
counseling, and his sensitivity about when to intervene and when
not to, I am deeply indebted to Prof. Dr. Dr. H. R. Duncker, who
accepted me into his research group and department. I am ex
ceedingly grateful to him for his understanding and insight,
especially into my personality and temperament which was and
is not native to this country. He was accepting of my ideas and
concepts and always showed fairness and temperance when ob
jective facts were offered. I am particularly grateful to him for
allowing me to develop my own area of research within his
conception of the comparative anatomical approach. As mentor
and counselor, both in private and institutional matters, his
constructive criticism and objective opinions proved continually
rewarding.
I want to acknowledge my colleague and friend Prof. Dr. Peter
Langer for years of collaboration and exchange of ideas in an area
of mutual interest; for his friendly and unselfish sharing of mate
rial and ideas, for including me in his international scientific
exchanges, and for the many hours of stimulating discussions
and often amusing and interesting conversations.
To Dr. Wieland StOckmann I owe a debt of gratitude not only
for his patience in explaining to me the mysteries of statistics and
for allowing me to draw from his enormous wealth of knowledge
in biology, but also for his support as a friend who has shared a
good portion of my institutional and private life (we are godfa
thers to each others children). His altruism and benevolence
have enriched my life and I am deeply indebted to him beyond
words for his support and generosity, both in time and thought,
and for his thoughtfulness and concern for my family.
My friend and colleague Dr. Sarwar Syed Ali has shared trials
and tribulations as well as pleasant times in the institute and in
private life. Being a kindred soul and of similar education and
upbringing he has shared with me many thoughts and feelings
that only we understood. I should like to thank him for this
understanding and for his steadfast friendship.
I am truly indebted to the technical staff of the Institute of
Anatomy and Cell Biology for their generous support and aid
during all portions of this investigation over a span of many
years; it has allowed friendship to develop in the realm of scien
tific work. I should like to acknowledge Ms. Andrea Klein, Ms.
Magdelena Gottwald, and Ms. Corinna Kabot for their ever
friendly willingness to be accommodating and devote their time
and efforts.
Two technical assistants worked directly on these projects for
numerous hours: Ms. Heidrun Sust, whose patience at the initial
phase of the measurements and whose perseverance were instru
mental in the development and optimization of the technique.
Moreover, a keen sense of humor allowed her to retain sanity
during hours of tedious work. I am truly grateful for this devo
tion. A second medical technical assistant has also devoted dili
gence and thoroughness in performing the majority of the meas
urements: Ms. Heidi Snipes. It was indeed my great fortune to
have support both at home and in the lab with this project and to
have the peace of mind to know that she was carrying out the
measurements with a precision and devotion that I could not
have found elsewhere. Despite the tedious and nerve-wracking
hours of work on this project she retained a professionalism and
objectivity that I not only honor and respect but greatly admire. I
am truly thankful for her devotion, perseverance, and support.
I would like to dedicate this treatise to a colleague and friend,
the late Ms. Brigitte Wildner. She was a paragon of strength and
patience both before and during her illness. We all shared many
hours of stimulating discussions and amusing anecdotes. She is
remembered with fondness by all her friends and colleagues in
our institute.
VI
Contents
1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
1.1 Scientific Aims ............................ '. . . . . . . .. 1
1.2 GeneralIntroduction ....... . . . . . . . . . . . . . . . . . . . . . . .. 2
1.3 Literature Survey. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
1.3.1 General Information - Alimentary Canal. . . . . . .. 4
1.3.2 Morphometry, Morphometric Techniques,
and Quantitative Surveys . . . . . . . . . . . . . . . . . . . .. 5
104 Primary Objectives ................................. 6
2 Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11
2.1 Introductory Word on Techniques. . . . . . . . . . . . . . . . . . .. 11
2.2 Methods .......................................... 12
2.2.1 Animals .................................... 12
2.2.2 Fixation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13
2.2.3 Determination of Ground Level
of Basal Surface Area. . . . . . . . . . . . . . . . . . . . . . . .. 13
2.2.3.1 Small Intestine .............................. 14
2.204 Determination of Second -Order Enlargement
of the Surface Area ........................... 14
2.204.1 Sampling and Further Fixation . . . . . . . . . . . . . . .. 14
2.2.5 Tissue Embedding ........................... 15
2.2.5.1 Vertical Sections. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
2.2.6 Determination of Sampling Sites ............... 15
2.2.6.1 Pilot Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16
2.2.6.2 Alternative Methods for Large Animals. . . . . . . .. 17
2.2.7 Measurements .............................. 17
2.2.7.1 Aim ........................................ 17
2.2.7.2 Calibration ................................. 18
2.2.8 Measuring Devices. . . . . . . . . . . . . . . . . . . . . . . . . .. 18
2.2.8.1 Advantages of the Semi-automatic
Videoplan Analyzing System .................. 19
2.2.9 Measurement of Microvilli: Pilot Experiment .... 22
2.2.10 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23
2.3 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 24
2.3.1 Statistical Confirmation
of Using Three Animals Per Group ............ 24
2.3.2 Fixation .................................... 27
2.3.2.1 Method of Choice:
Intracorporeal/Intraluminal Fixation .......... 27
2.3.2.2 Other Considerations of Fixed Material ......... 29
2.3.3 Morphometric Techniques ................... 30
2.3.3.1 Measurement of Surface Enlargement .......... 31
2.3.3.2 Changes in Measured Structures Dependent
on External Factors .......................... 35
2.3.3.3 Microvilli Considerations .................... 35
2.3.4 Scaling Considerations:
Relationship to Body Weight .................. 35
2.3.5 Conclusions ................................ 38
3 Morphology of the Mammalian Cecum and Colon. . . . .. 39
3.1 Introduction. ...................................... 39
3.2 General Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 43
3.3 Terminology ...................................... 46
3.4 Methodology...................................... 47
3.5 Observations...................................... 48
3.5.1 Gross Anatomical Aspects ...................... 48
3.5.2 Second-Order Enlargements. . . . . . . . . . . . . . . . . . .. 48
4 Morphometry of the Mammalian Cecum and Colon. . . .. 51
4.1 Application ....................................... 51
4.1.1 Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56
4.1.2 Volumes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 58
4.1.3 Coefficients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59
4.1.3.1 Areas (Coefficient of Gut Differentiation) ....... 59
4.1.3.2 Volumes (Coefficient of Vo lume) . . . . . . . . . . . . .. 62
4.1.4 Area to Unit Volume Relationships ............ 65
4.2 Concluding Discussion ............................. 66
4.2.1 Areas ...................................... 66
4.2.2 Volume. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70
4.2.3 Coefficients ................................. 71
4.2.3.1 Areas ...................................... 71
4.2.3.2 Volumes................................... 72
4.2.4 Area to Unit Volume Relationships . . . . . . . . . . .. 73
5 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 81
Subject Index. ......................................... 89
VIII
1 Introduction
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. However, stereology as defined by Mayhew (1979)
is concerned with the mathematical reconstruction of three-dimensional structures
based on the mensuration (length, area, volume) of (ideally) two-dimensional images.
Historically, these methods were developed for dealing with microscopic entities
(mostly at the electron microscopy level), the inherent drawback of these techniques
being the sampling problem and the resulting necessity of developing complicated
formulas to deal with the deficits of small sample sizes.
Confronted with a pictorial collection of micrographs from over 20 species and the
impending need to compare and contrast the morphological entities illustrated in
these micrographs on the one hand, and the desire to retain the organismal concept of
the material on the other, it became apparent that new morphometric techniques were
needed. Conventional stereologic methodology remains the gold standard for electron
microscopy and other microscopic investigations. However, these did not appear
appropriate for use in an organismal approach.
Obtaining numerical values for morphological entities makes it possible to make
interspecific comparisons more readily and indeed to discover many hidden factors
that cannot be deciphered from a picture. Ratios and graphic representations aid in
visualizing the relationships of many different factors which can only be handled with
1
quantitative data. Quantitative data also lends itself to use in scaling studies concern
ing the consequences of a change in size of animals (Schmidt-Nielsen 1975). Accord
ing to Kleiber's law, metabolic rate in mammals is scaled relative to body mass to the
power of 0.75. Scaling of intestinal parameters is directly related in some way to
metabolic requirements. Any organ directly concerned with metabolic turnover can
be expected to scale to body size in accordance with this law (Martin et al. 1985). Using
the concepts of isometry and allometry, it is possible to plot two variables on logarith
mic coordinates resulting in a straight line. Isometry infers that a change in anyone
characteristic linear dimension is accompanied by a change in all other linear dimen
sions in exactly the same proportions. Allometry describes the situation in which they
do not change in the same proportions. Using these concepts and regression lines,
overall trends can be obtained reflecting general systematic scaling principles, w4ile
positions of specific points above or below the best-fit line reflect the special adapta
tions of individual species ("graded differences"; Martin et al. 1985). In any biological
comparison, the departure of individual points from the best- fit line is just as interest
ing (if not more interesting) as the parameters on the line itself.
The expectation of being able to employ these comparative quantitative tools
prompted the search for a simple methodology for use !p. trend analysis, as can be
derived from combining morphometry with simplified scaling analysis. These were
the aims of the present investigation.
1.2
General Introduction
Over the years, the multiplicity in the form of the hindgut of different animals has
fascinated numerous researchers. Early' works in the previous century and at the
beginning of the present century are rich in descriptive passages of the macroscopic
anatomy of this portion of the intestine (see Sect.I.3).
Thus there is a wealth of literature on purely anatomical morphology of the intesti
nal systems from anuran to mammals giving a broad and well-founded basis upon
which to build. There has been only little conjecture about the functional significance
of the differences in the hindgut of animals - primarily attempting to correlate the
structural differences with the nutritional strategy of the animal. From these supposi
tions, some tendencies have become clear: animals, regardless of their taxonomic
grouping, which possess a large and voluminous cecum/colon are generally herbivo
rous, whereas animals with very short and undifferentiated large intestines are mostly
strict carnivores (e.g., Canis). It should be noted here that an enormous span exists
between these two extremes, including a wide variability in form of hindg uts coupled
with various intermediary nutritional strategies.
Sufficient exceptions to these tendencies (e.g., the berry-eating panda has no ce
cum, as is the case in most Cteroptera) gave rise to more investigations concerning
structure-function relationships in this major organ system.
Over the last 20 years, many structural researchers have attempted to add to these
early macroscopic investigations, using the existing modern tools of structural inves
tigation, i.e., various levels of submicroscopic analysis (light, scanning, and transmis
sion electron microscopy). From these studies, a certain scheme has arisen which
tends to substantiate the macroscopic investigations of the earlier part of this century.
2
