SEROSAI, AND h l CJCOSAL DINENSIONS AT DIFFEREXT LEVELS O F THE DOG’S

SMALL INTESTINE

RICHARD WA4RREN Gustro Inteslwul Sectzon (E tnsey Thomas jroundat lon) of the Medam1 Clziazc of the

Hocpital and Department of Anutomy of the Medzcul Scltool, Unzverszty of Pennsijli anza, Plztladrlphm

THREE FIG71RES

Tlie irregularity of the mucosal surface of the small in- testine produced by the configuration of the villi and of the valvulae conniventes (folds of Iierkring) has an obvious functional significance. It makes available a large epithelial area for the rapid absorption of nutrient material from the intestinal lumen. The need f o r a numerical expression of the proportional amounts of sach areas a t different levels of the intestine makes itself felt t o the anatomist, who wishes to describe accurately the intestinal tract as a whole, to the surgeon, who wishes to know the amount of functional absorb- ing surface he removes when he resects a given length of bowel, and particularly to the physiologist, who, in his studies on the absorption velocities of various materials, wishes to linow the surface areas of his experimental loops.

A summary of the significant previous work on the subject is given in table 1. In reviewing this work several facts of interest stand out. -4s nearly as can be determined in each case, tlie calculations depended upon measurements of indi- vidual villi either in mounted specimens of fixed intestine or in the living animal by the use of the ocular micrometer. The areas of individual villi were calculated arbitrarily from their linear dimensions, assuming them to be cylindrical in

Fellow in Gastro-eiiterology and Assistant Iiistructor in Medicine, Medical Scliool of the University of Pennsylvania.

427

428 RICHARD WARREN

shape. The number of villi per unit area were then counted and the mucosal area thus approximated. There is considerable disagreement in results, most notably between those of Heiden- liain (1888) and of Krogh ( '29) on the dog. This is due to the fact that Spee (1885), from whose work Heidenhain made his calculations, procured average lengths for villi about double

TABLE 1

Literature on iiitestznal surface ni ea

AUTHOR

Heidenhain (1888) (from Spee, 1585)

Mall (1857)

Krause (1890)

Krogh ('22) (fromMal1, 1857)

(quoted by Krogh, '22)

Verzbr ( ' 3 G )

Vimt rump

Maxiinow and Bloom ( '38)

those obtained by

METHOD

P'ixeci specimens (osmic acid)

Fixed ~pecimens

Fixed specimens

Fixed specimens and calculations from Mall's dat

Fixed specimens

Direct mcasure- ments in the living

Not stated

LNTPESTINAL I A V E L

Sot specifiec

Sot speeifiec

Vhole small intestine

Jot specifiec

)uodcnum

hiall intestine

!inall intestine

iillus surface = 0.96 nim.z 23 em.' for each cm.2 surface hbmucosal surface 657 em? Tillus surface = 0.3 to 0.7 m.? 4,000,000 villi in sinall intestine = 1.6 sq. meters. Multiplica- tion of area is 5 X ' mm.2 for each 1 mm.2 surface

7.6 nini.' for each 1 nmi.* surface

rota1 surface 689 cm2. Ratio of mucosal to serosal area is 8/1, 3rd of it i n duodenum

\Iucosal surface = 4 to 5 sq. meters

Mall (1887) from whom Krogh got his data. Review of their work does not suggest that the dis- crepancy arose from using different and non-comparable levels of the intestine. None of the workers, except Vorzrir and MeDougall ( '36) has emphasized difference in mucosal area per unit of length a t different levels, and their work was on the pigeon.

DIMENSIONS OF DOG'S SMALL INTESTINE 429

All authors engaged in this work, including the present one, have recognized that any value used to express the whole mucosal surface area of the intestine or the area per unit length can be only a crude approximation. This is so not only because in the living animal the intestine is continually changing length as the tonus of its longitudinal muscle varies (van der Reis and Schembra, 'as), but also because, even if the length were constant, the individual villi in most species are continually changing their shape by pumping movements (King and Arnold, '21; Verziir and MeDougall, '36; Spee, 1885) with resultant change in surface area (Maximow and Bloom, '38 ; Heidenhain, 1888). Estimated areas are used in this work to show tendencies and trends because of the unavailability of exact measurements. Because of the sources of error inherent in the method this work is presented not as a final solution to the problem, but as adding some interest- ing data to those already accumulated. The method, which makes use of total linear dimensions rather than measure- ments of individual villi, is different from any heretofore used. Especial attention is paid to variations in mucosal surface at different intestinal levels.

PROCIEDURE

After prolonged but fruitless attempts to procure a human intestinal tract early enough post mortem to secure fixation before autolysis of the epithelium had occurred, the small intestinc of a 12 kg. dog was chosen for study. The dog, which tlie day before had had a laparotomy performed for other purposes, was sacrificed by intracardiac injection of 20 cc. of choroform. The whole small intestine was immedi- ately removed, closely shorn of its mesentery, and glass can- iiiilas were tied into each end. Formalin, 10% solution, was injected into the cannula at the duodenal end under a pressure of 60 em. of water. A large part of the intestinal contents mere thus washed out of the lower cannula. After 5 minutes of washing the lower cannula was closed and the whole specimen allowed to distend under the 60 em. pressure of the

430 RICHARD WARREN

formalin. When the distention appeared to have reached its limit the injection was stopped and the upper cannula was closed leaving the contents of the specimen under pressure. The intestine was then laid in two 10 foot troughs full of f ormalin. After fixation, lengths, approximately 8 em. long, were cut from the duodenum, mid jejunum, upper, mid and lower ileum. Each of these lengths was in turn cut into three pieces (fig. l), a center length of 5 em., and two end lengths of about 1.5 em. each. After wasliiiig, hardening in alcohol, and embedding in celloidin, transverse sections were cut from each of the end pieces and longitudinal sections from the

'< _..___.-._.. $EROS,lL LENGTH ( S L )..._._...._... *

Fig. 1 Diagrammatic representation of the manlier in which the segments were cut up.

center pieces. These were placed on slides, stained with hematoxyliii and eosin, and mounted in balsam.

The slides were projected with a Bausch and Lomb project- ing drawing apparatus onto a screen where the image was magnified eighty times. The serosal and mucosal outlines as shown 0x1 the screen were measured in their circumferential dinlensions on the transverse sections, and in their longitudinal dimensions on the longitudinal sections with a rotometer, or measuring wheel. The average thickness of the tunica muscularis was recorded. By taking the average of circum- ferential values procured for the two end lengths and the average of the longitudinal values for the two sides of the

DIMENSIONS O F DOG’S SMALL INTESTINE 431

center length, ratios of niucosal to serosal circumference and of mucosal to serosal length were calculated for each segment.

No exact formula for computation of the area of an ir- regular surface of undefined shape in terms of two dimensions

Fig. 2 A, B, C, aid D, low power ( x 1.8) magnifications of tramverse and loiigitudinal sections froin the duodenum (A and B) and the ileum ( C and D). F o r high power magilification of €3 and D, see figure 3.

can be derived. The following analysis was kindly pre- pared for us, however, by Dr. J. H. Austin.

I f SC = Serosal circuiiifereiice MC = Mucosal circumference SL = Serosal length

ML = hfucosal length RA = Serosal area

MA = Nucosal are:i

Then in general for an irregular surface

432 I:IC H A R D WARBE N

Fig. 3 1.: slid F, liigh power ( X 50) iiiagiiificatio~is f rom the saiiie levels as shown, rcspeetively, a t B and 11, i n figure 2.

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434 RICHARD WARREN

Examination of various measurable geometric projections indicates that a serviceable approximation for MA is an estimated area, EA, calculated with the following formula

It is not possible to state the deviations in any surface of unknown shape between EA and MA. We have, however, calculated JGA from our data as a plausible approximation to the mucosal area.

RESULTS

I n table 2 the figures to tlie left of the double line are accurate measurements and calculations. It can be seen that the ratios MC/SC and ML/SL decrease as the lower parts of the intestine are reached with the notable exception of the lowest specimen of all. This shows an increase to figures lower only than the duodenal values. The explanation for this is obvions if one examines the values for circumference and thickiiess of muscle layers in this segment. They indicate, as was apparent on inspection of the specimen, that in the last 75 em. the ileum was in spasm not overcome by distentioii with the fixative. The values for this segment are, then, not comparable with those of other segments where distention was obtained with the fixative.

The figures to the right of the double line in table 2 repre- sent values calculated from tlie approximation formula. A progressive decrease in estimated mucosal area per centi- meter of serosal length is observed as one passes downward to the mid ileum. The estimated mucosal area for the duodeiium, or 0.12 m.2, comprises about 7% of that estimated for the whole small intestine.

UISCU8SION

Sources of error inherent in the technique itself have been examined. Numerous measurements before and after fixation were made and support tlie observations of Patten and Phil- pott on chick embryos that no shrinkage takes place in 10%

DIMENSIONS OF DOG'S SMALL INTESTINE 435

Ihodenum Loircr jejunum Upper ileum Upper ileum Upper ileum

formalin. Contrary to their results, however, no shrinkage in the serosal dimensions was found in this work between fixation and mounting. The villi were not susceptible of measurement from this point of view. Probably shrinkage occurred. Patten and Philpott ( '20) estimated that using paraffin embedding the maximum shrinkage with this technique was about 20%. The larger the specimens, the smaller the

em. % x 19 MC 31.9-35.3 10.1 x 80 ML 22.7-22.8 0.4 x 80 ML 21.9-23.4 6.6 X 80 ML 21.9-21.9 0.0 X 80 MC 19.3-19.7 2.1

TABLE 3

Duplicate nieaswcmen1.r o n same inucosal dimensions

LEVEL I 119CNIFICATION I DTXEXSION I FIGURES I DIFFERENCE

TABLE 4

Maasurements of two sections f rorn similar levels

LEVEL

Upper jejunum Upper jejunum Upper jejunum Upper jejunum Upper jejunum TJpper jejunum Upper ileum Upper ileum Mid ileum Xid ileum

MAGNIFI - C.4TIOB

DISTANCE AT'ART

100 p

100 p Opposite sides Opposite sides

100 p

100 p

Opposite sides Opposite sides Opposite sides Opposite sides

)IDIE8NSION& COlIPARED

XC SC ML RL ML SL ML S L ML SL

FIGURES

cm. 26.4-27.9

6.6- 6.5 26.6-27.5

5.1- 5.0 26.6-27.5 5.1- 5.0

18.0-17.7 5.0- 5.0

21.9-21.9 4.9- 5.0

~~

J IBPERENCE

% 5.5 1.5 3.3 2.0 3.3 2.0 1.7 0 0 2.0

percentile shrinkage. Since celloidin embedding was used here, it is probable that the amount of error from this source was less than 10%. Table 3 gives data on re-measurement of the same mucosal dimensions with the rotometer. Table 4 shows measurements of similar but not identical sections within 100 to 300 p of each other, or, in the case of the longi- tudinal sections, from the opposite wall, to determine how

436 RICHARD WARREN

representative is the measurement of a single section. The average difference was 3.370 for mucosal measurements and 1.5% for serosal.

These results are applicable only to the intestine of the dog. This animal has a much less abrupt change in diameter be- tween the duodenum and the rest of the small intestine than the human. It has, moreover, no valvulae conniventes that are evident in preparations of this sort, although functional traiis- verse folds are the rule in the living. The valvulae in the human intestine cannot be flattened out by distention of the lumen (Maximow and Bloom, '38). It is obvious that RIA/SA diminishes in man also, the lower the segment of intestine considered; it is probable, however, that the ratio of mucosal to serosal surface area is greater in man than in the dog.

Van der Iteis and Schembra ('26) measured the percentile increase in length along the mesenteric border of the dog's small intestine at various intervals after the death of the dog and also after removal of the mesenteric attachments. If one applies their results to this intestine an approximate increase in serosal length of from 60 to 90% above the living values may be assumed to have occurred. Rough estimations of the mucosal area per unit length in the living dog may be arrived a t by taking this into consideration.

Comparing our average value for EA/SA, 8.5, with the values reported for the dog in table 1 it can be seen that our value is much lower than that of Heidenhain (1888), and approximates that of Krogh ( '29).

It seems to the author that the technique here used would be of value applied to human intestine.

SUMMARY

1. The mucosal and serosal linear dimensions, both longi- tudinal and circumferential, a t five levels of the autopsied small intestine of a dog have been measured and the error of these measurements has been indicated.

2. A formula is suggested which from these dimensions permits a crude estimate of mucosal area.

DIiMESSIONS O F DOG’S SMALL INTESTINE 437

3. The estimate of the ratio of mucosal area to serosal area fo r the whole small intestine was 8.5/1.

4. The estimate of tlie total mucosal surface was 1.6 square meters of which 7% was in tlic duodenum.

5. Striking decrease in mucosal area per unit of serosal area o r of serosal length is observed as one descends the gut to the mid ileum.

6. The impropriety of applying these results directly to tlie human subject is emphasized.

In addition to the invaluable advice of Dr. J. H. Austin, I wish to express my appreciation of the assistance given me by Dr. Balduin Luck&, who helped to devise the method, and by Mi-. Basil B. Varian, who prepared the sections.

LITERATUIIE CTTED

HEIDENHAIN, R. 1888 BeitrHge zur Histologie 11. Physiologie der Dunndarin- Schleimhnut. Pfliiger ’s Arehiv. f . d. Gesamte Physiologie, Supple- mentheft, Vol. 43.

KIaG, c. E., AND L. ARNOLD 1921 The activities of the intestillal motor

KRAUSE, W. Specielle u. macroscopisehe Anatonlie in C. 3’. D. Krause’s Handb. d. menschlichen Anatomie, 3 Aufl., 2 Band, Hannover, p. 454.

KKOGH, A. 1929 The Anatomy and Physiology o f the Capillaries. Yale Univer- sity Press, New Haven.

MWKLIN, C. C., ~ N D M. T. MSCKIJN 1932 The Intestinal Epithelium, in E. V. Cowdry’s Special Cytology, Hoeber, N. P.

MALL, J. P. 1887 Die Blut und Lymphwege im Diinlldarm des Hundes. Abhand. der niathematisch-physischer Classe der Konigl. Sachisehen Gesellsehaft der Wissenschaften, Bd. xir, p. 153.

M~s~ivon- , A. A, , AND W. BLOOX 1938 Text Book of Histology. 3rd. ed., Saunders, p. 408.

I ’S~EPT, R. M., AND R. PHILPOTT 1920 The shrinkage of embryos in the processes preparatory to sectioning. Anat. Rec., vol. 20, p. 393.

SPEE, F. GRAF. 1885 Arrhiv. f . Anat. u. Physiol. (Anat. Abt.), p. 159. VAN DER RELS, V., AND F. W. SCHEMBRA

mechanism. Am. J. Physiol., vol. 59, p. 97. 1879

1926 Weitere Studien iiber die funk- tionelle D ~ I mlange; Operative Ergebiiisse u. Beobaclitungen am Bauch- fenster. Zeit. f . d. ges. Exp. Ned., wl. 52 , p. 74.

V E R Z ~ R , F., AND E. J . MCDOUGALL 1936 Absorption from the Intestine. Long- mans, Grern and Co., Lonclon, p. 9.