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Antenatal intestinal adaptation with experimental jejunoileal atresia
Antenatal Intestinal Adaptation With Experimental Jejunoileal Atresia By Robert J. Touloukian 9 Jejunoileal atresia w i t h o u t significant shortening of total intestinal length, was created in five date-bred Dorset e w e s by devascularizing a 15 cm segment of fetal intestine at 9 0 - 1 0 0 days gestation. Light microscopy showed mucosal hypertrophy distal to the atresia with almost total obliteration of the lumen by tall, feathery-shaped villi similar to those observed in newborns with jejunal atresia. Scanning electron microscopic views of the proximal mucosa showed the villi to be thicker, more segmented and tended to congregate compared to normal villi and those distal to the atresia. No evidence of microvillus, intracellular or capillary m e m b r a n e change or injury could be identified to explain the functional secretory state. I N D E X W O R D S : Experimental intestinal atresia.
ILLUS HYPERTROPHY is a wellknown, hut poorly understood, compensatory mechanism following a major intestinal resection in any age group. Fifty percent m i d e n t e r e c t o m y , a classic e x p e r i m e n t a l procedure utilized to study this phenomenon, has shown that the most marked villus enlargement occurs in the distal ileum.' Similarly, villus hypertrophy is found in newborn babies with jejunoileal atresia and is most marked in the intestine distal to a jejunal atresia. 2 The data question the role of intestinal obstruction in the pathogenesis of antenatal villus hyp e r t r o p h y both proximal and distal to the atresia. Experimental jejunoileal atresia without significant loss of intestinal mass was selected as a model to gain further information about the pathogenesis of antenatal intestinal adaptation.
V
METHODS A N D MATERIALS
Five date-bred, pregnant Dorset ewes were anesthetized at 90-100 days gestation with intravenous 4.5% suritol, intubated with a cuffed endotracheal tube and maintained with 0.5% 1.0% halothane using an Air-Shields ventilator. The
From the Department of Surgery, Section of Pediatric Surgery, Yale University School of Medicine, New Haven, Conn. 06510. Supported by National Foundation March of Dimes, Grant #1-380. Address reprint requests to Robert J. Touloukian, M.D., Department o f Surgery, Yale University School of Medicine, New Haven, Conn. 06510. 9 1978 by Grune & Stratton, Inc. 0022-3468/78/1306 0002501.00/0
468
gravid uterus was mobilized through a lower-midline incision and bony landmarks palpated to determine fetal orientation. A transverse hysterotomy was made over the fetal abdomen and the amniotic membranes bluntly dissected away from the overlying muscle. The amniotic cavity was drained through a #18 French catheter and one million units of aqueous crystalline penicillin added to the recovered amniotic fluid maintained at 37~ The fetal intestine was gently mobilized and a 15 cm segment stripped free of its mesentery. The devascularized gut was replaced and the fetal abdominal cavity closed with fine chromic catgut. The amniotic fluid was returned through a catheter after the amnion and uterine wall were nearly closed. The maternal abdominal wall was repaired with a running #1 Tevdek suture. The animals were delivered by cesarean section approximately 5 days before the due date and full thickness sections of intestine were obtained, both 15 cm proximal and distal to the atresia, for light, scanning, and ultramicroscopy. The height of the five tallest intact villi in the proximal and distal atretic segments was measured with a micrometer mounted in the lens of a light microscope and compared to normal controls. RESULTS
All o p e r a t e d f e t u s e s w e r e a l i v e w h e n d e l i v e r e d by c e s a r e a n s e c t i o n . T h e a b d o m e n o f t h e newborn lambs was distended and showed comp l e t e i n t e s t i n a l o b s t r u c t i o n w i t h a c l a s s i c a l app e a r a n c e o f j e j u n o i l e a l a t r e s i a 50 175 c m f r o m t h e l i g a m e n t o f T r e i t z (Fig. 1). T h e o b s t r u c t e d p r o x i m a l s e g m e n t w a s d i s t e n d e d a n d filled w i t h i n t e s t i n a l fluid w h i l e t h e d i s t a l s e g m e n t w a s uniformly tiny and collapsed. A 5-10 times d i f f e r e n c e in i n t e s t i n a l d i a m e t e r w a s o b s e r v e d . T o t a l i n t e s t i n a l l e n g t h v a r i e d f r o m 315 to 337 c m c o m p a r e d to a m e a n o f 347 • 10 c m , in normal controls.
Light Microscopy The normal jejunal villus of the newborn lamb had a slim and feathery appearance with a mean length of 403 i 22 uM. The ileal villus was shorter, but also feathery in shape and had a mean length of 257 ~: 18 uM. Mean villus length and shape depended upon where the section was obtained. Villi at the extreme tip of the proximal atretic segment were blunted and club-shaped and the muscularis layer was thickened (Fig. 2) compared to normal controls. Sections obtained 15 cm
Journal of Pediatric Surgery, Vol. 13, No. 6 (October), 1978
ANTENATAL INTESTINAL ADAPTATION
469
Fig. 1. Jejunal atresia w i t h a mesenteric d e f e c t in a newborn lamb. The proximal intestine is distended while the distal bowel is t i n y and collapsed.
proximal to the atresia showed taller, straighter villi having a mean length of 454 + 21 # M (Fig. 3). The villi distal to the atresia were feathery and significantly enlarged, often obliterating the lumen. These villi measured 643 • 57 # M from crypt to tip (Fig. 4).
Scanning Electron Microscopy One hundred-15,000 power magnification views obtained with the scanning electron mi-
croscope showed significant differences in the villi of the proximal and distal atretic segments compared to the control subjects. At 100, 200, and 500 power magnification, the proximal villi were more fixed and stiff compared with the more pliable and mobile villi observed in normal animals. The tips of the villi in the proximal segment were blunted and had a tendency to agglutinate or congregate. Shreds of mucin traversed villus tips. The villi of the distal seg-
Fig. 2. Villi at the tip of the proximal atretic segment are blunt and club-shaped. The muscularis layer is thicker than normal (H&E. • 40).
470
ROBERT J. TOULOUKIAN
Fig. 3. Villi 15 cm from the tip of the proximal atretic segment are taller and straighter but not significantly longer than normal controls (H&E. • 100),
ment were free-standing and more feathery than villi from normal controls. No difference in villus length was observed (Fig. 5). At 5000 power magnification, the cells from the normal villi were aligned in a regular, wellordered hexagonal network. Microvilli were clearly visible at this magnification and had a fine granular appearance. The hexagonal pattern of the cells in villi from proximal and distal atretic segments was distorted; some assumed a spheroidal while others had a angulated shape (Fig. 6). The cellular architecture was similar at 15,000 power magnification. These views showed the microvilli of the proximal and distal atretic segments to be indistinguishable from normal controls.
Ultrastructure Electron Microscopy The internal structure and microvilli of the intestinal epithelial cell in the animals with atresia were similar to normal control subjects. The junctional (Fig. 7A) complex in the cells membranes was normal and the endothelial membrane of the subcellular capillary bed was intact throughout its visible circumference (Fig. 7B). DISCUSSION
The light m i c r o s c o p y o b s e r v a t i o n s of proximal and distal intestinal segments from animals with intestinal atresia have a striking similarity to newborns with jejunal atresia. ~ Of
ANTENATAL INTESTINAL ADAPTATION
Fig. 4,
471
Villi distal to the atresia are tall and feathery, nearly obliterating the tiny lumen (H& E. • 40),
prime importance is the reversal of the normally diminishing aboral gradient in villus length and the nearly total obliteration of the tiny distal lumen with enlarged villi. Many villi, distal to the atresia in newborn babies, were
also tortuous and intertwined and some had a unique side-branching off the main stalk giving the appearance of pseudopodia, These "giant" deformed villi were not observed in our experimental subjects.
Fig, 5. Scanning electron microscopic appearance of villi in normal (A), proximal atretic (B) and distal atretiC (C) intestine, Villi in the proximal intestine are visibly thicker, segmented and tend to Congregate while villi distal to the atresia a r e tall and feathery (200 • magnification).
472
ROBERT J. TOULOUKIAN
Fig. 6. Scanning electron microscopic appearance of mucosal cell surface in normal (A), proximal atretic (B) and distal atretic (C) intestine. Distortion of cellular shape and alignment is obvious ( 5 0 0 0 • magnification).
Total intestinal length in animals with atresia was not significantly shorter than normal controls while babies born with jejunoileal atresia may have marked shortening of total intestinal length. We must conclude, therefore, that diminished intestinal length cannot be the only stimulus for villus hypertrophy. Tilson reached a similar conclusion by showing a 39% increase in villus height in rats having partial intestinal bypass. 3 Also eliminated as the only mechanism is the workload hypertrophy theory, ~,~ which holds that ingested nutrients stimulate villus growth. Intestinal villi in babies with the "shortg u t " s y n d r o m e h y p e r t r o p h y d u r i n g total parenteral nutrition '~ but do not in animals having normal intestinal length. '~ We believe that villus hypertrophy of the fetal intestine observed in babies born with jejunoileal atresia is achieved through placental nutrition by a mechanism similar to that which must occur with total intravenous nutrition. Shortening of fetal intestinal length may exert an additional influence on this intrauterine effect. Obstruction to the fetal intestinal lumen itself may have a vital role in explaining our observations. The distal segment collapses since it does not receive swallowed amniotic fluid and biliary, pancreatic and intestinal secretions. This loss of intraluminal pressure may conceivably enlarge villi by the reverse mechanical effect that high pressure blunts and clubs the villi at the tip of the proximal segment. Some degree of villus enlargement in the distal segment may also be more apparent than real because of the crowding effect in the tiny lumen. Supporting this con-
cept is that scanning electron microscopy showed no apparent difference in the height of villi in the proximal and distal segments compared to controls. Electron microscopy of intestinal villi from newborns with atresia is not yet available to compare with normal villi. However, no significant structural differences were found in cells from villi in the proximal and distal atretic segments of experimental subjects when compared to normal animals. Finding some specific anatomic change was anticipated, since previous studies, using this model, 7 and by other investigators ~ have shown that obstruction produces net secretion while net absorption is found beyond the obstructed segment and in normal i n t e s t i n e . U n d e r c e r t a i n conditions, nono b s t r u c t e d i n t e s t i n e may e i t h e r h y p e r secrete or develop an enhanced absorptive c a p a c i t y . E l e c t r o n m i c r o s c o p y studies o f h y p e r s e c r e t i n g j e j u n a l m u c o s a in c h o l e r a patients 9 has shown evidence of both cellular changes and marked irregular widening of the interepithelial spaces at the midvillus areas suggesting that fluid is transported from blood vessels to intestinal lumen through the interepithelial spaces and through damaged cells. The microvilli and lateral cell m e m b r a n e s hypertrophy in both ileal and jejunal cells after resection of the midintestine 1~ reflecting the known increased capacity for glucose and sodium transport. Cellular catabolism, ischemia, and membrane injury are known to play a vital role in the pathogenesis of the fluid and elect r o l y t e c o m p l i c a t i o n s of a c u t e intestinal
ANTENATAL INTESTINAL ADAPTATION
Fig. 7. within villi segment is membranes endothelial (B) (35,000
Cellular structure in proximal atretic normal (A). The cell and the subcel|ular membrane is intact magnification),
473
474
ROBERT J, TOULOUKIAN
obstruction. These observations suggested that some histologic evidence of either active secretion by t h e e p i t h e l i a l cell o r loss o f e x t r a c e l l u l a r fluid t h r o u g h d a m a g e d s u b c e l l u l a r l y m p h a t i c and c a p i l l a r y m e m b r a n e s w o u l d be f o u n d in o u r
l a m b s w i t h a t r e s i a . Failing to find such evidence, we conclude that chronic intestinal o b s t r u c t i o n in a f e t a l m o d e l m a y c a u s e functional c e l l u l a r c h a n g e s w i t h o u t a l t e r i n g histology.
REFERENCES
1. Dowling RH, Booth CC: Structural and functional changes following small intestinal resection in the rat. Clin Sci 32:139, 1967 2. Touloukian R J, Wright HK: Intrauterine villus hypertrophy with jejuno-ileal atresia. J Pediatr Surg 8:779, 1973 3. Tilson MD: Compensatory hypertrophy of the gut: testing of the tissue mass, intraluminal nutrition and functional demand hypothesis. Arch Surg 104:69, 1972 4. Gleeson MH, Cullen J, Dowling RH: Intestinal structure and function following small bowel bypass in the rat. Clin Sci 43:731, 1972 5. Wilmore DW, Dudrick S, Daly JM, et al: The role of nutrition in the adaptation of the small intestine after massive resection. Surg Gynecol Obstet 132:673, 1971
6. Koga Y, Ikeda K, Inokuchi K, et al: The digestive tract in total parenteral nutrition. Arch Surg 110:742, 1975 7. Touloukian R J: The composition of amniotic fluid with experimental jejuno-ileal atresia. J Pediatr Surg 12:397, 1977 8. Shields R: The absorption and secretion of fluid and electrolytes by the obstructed bowel. Am J Surg 52:774, 1965 9. Asakura H, Tsuckiya M, Watanake Y, et al: Electron microscopic study in the jejunal mucosa in human cholera. Gut 15:531, 1974 10. Tilson MD, Wright HK: The effect of resection of the small intestine upon the fine structure of the intestinal epithelium. Surg Gynecol Obstet 134:992, 1972
ILLUS HYPERTROPHY is a wellknown, hut poorly understood, compensatory mechanism following a major intestinal resection in any age group. Fifty percent m i d e n t e r e c t o m y , a classic e x p e r i m e n t a l procedure utilized to study this phenomenon, has shown that the most marked villus enlargement occurs in the distal ileum.' Similarly, villus hypertrophy is found in newborn babies with jejunoileal atresia and is most marked in the intestine distal to a jejunal atresia. 2 The data question the role of intestinal obstruction in the pathogenesis of antenatal villus hyp e r t r o p h y both proximal and distal to the atresia. Experimental jejunoileal atresia without significant loss of intestinal mass was selected as a model to gain further information about the pathogenesis of antenatal intestinal adaptation.
V
METHODS A N D MATERIALS
Five date-bred, pregnant Dorset ewes were anesthetized at 90-100 days gestation with intravenous 4.5% suritol, intubated with a cuffed endotracheal tube and maintained with 0.5% 1.0% halothane using an Air-Shields ventilator. The
From the Department of Surgery, Section of Pediatric Surgery, Yale University School of Medicine, New Haven, Conn. 06510. Supported by National Foundation March of Dimes, Grant #1-380. Address reprint requests to Robert J. Touloukian, M.D., Department o f Surgery, Yale University School of Medicine, New Haven, Conn. 06510. 9 1978 by Grune & Stratton, Inc. 0022-3468/78/1306 0002501.00/0
468
gravid uterus was mobilized through a lower-midline incision and bony landmarks palpated to determine fetal orientation. A transverse hysterotomy was made over the fetal abdomen and the amniotic membranes bluntly dissected away from the overlying muscle. The amniotic cavity was drained through a #18 French catheter and one million units of aqueous crystalline penicillin added to the recovered amniotic fluid maintained at 37~ The fetal intestine was gently mobilized and a 15 cm segment stripped free of its mesentery. The devascularized gut was replaced and the fetal abdominal cavity closed with fine chromic catgut. The amniotic fluid was returned through a catheter after the amnion and uterine wall were nearly closed. The maternal abdominal wall was repaired with a running #1 Tevdek suture. The animals were delivered by cesarean section approximately 5 days before the due date and full thickness sections of intestine were obtained, both 15 cm proximal and distal to the atresia, for light, scanning, and ultramicroscopy. The height of the five tallest intact villi in the proximal and distal atretic segments was measured with a micrometer mounted in the lens of a light microscope and compared to normal controls. RESULTS
All o p e r a t e d f e t u s e s w e r e a l i v e w h e n d e l i v e r e d by c e s a r e a n s e c t i o n . T h e a b d o m e n o f t h e newborn lambs was distended and showed comp l e t e i n t e s t i n a l o b s t r u c t i o n w i t h a c l a s s i c a l app e a r a n c e o f j e j u n o i l e a l a t r e s i a 50 175 c m f r o m t h e l i g a m e n t o f T r e i t z (Fig. 1). T h e o b s t r u c t e d p r o x i m a l s e g m e n t w a s d i s t e n d e d a n d filled w i t h i n t e s t i n a l fluid w h i l e t h e d i s t a l s e g m e n t w a s uniformly tiny and collapsed. A 5-10 times d i f f e r e n c e in i n t e s t i n a l d i a m e t e r w a s o b s e r v e d . T o t a l i n t e s t i n a l l e n g t h v a r i e d f r o m 315 to 337 c m c o m p a r e d to a m e a n o f 347 • 10 c m , in normal controls.
Light Microscopy The normal jejunal villus of the newborn lamb had a slim and feathery appearance with a mean length of 403 i 22 uM. The ileal villus was shorter, but also feathery in shape and had a mean length of 257 ~: 18 uM. Mean villus length and shape depended upon where the section was obtained. Villi at the extreme tip of the proximal atretic segment were blunted and club-shaped and the muscularis layer was thickened (Fig. 2) compared to normal controls. Sections obtained 15 cm
Journal of Pediatric Surgery, Vol. 13, No. 6 (October), 1978
ANTENATAL INTESTINAL ADAPTATION
469
Fig. 1. Jejunal atresia w i t h a mesenteric d e f e c t in a newborn lamb. The proximal intestine is distended while the distal bowel is t i n y and collapsed.
proximal to the atresia showed taller, straighter villi having a mean length of 454 + 21 # M (Fig. 3). The villi distal to the atresia were feathery and significantly enlarged, often obliterating the lumen. These villi measured 643 • 57 # M from crypt to tip (Fig. 4).
Scanning Electron Microscopy One hundred-15,000 power magnification views obtained with the scanning electron mi-
croscope showed significant differences in the villi of the proximal and distal atretic segments compared to the control subjects. At 100, 200, and 500 power magnification, the proximal villi were more fixed and stiff compared with the more pliable and mobile villi observed in normal animals. The tips of the villi in the proximal segment were blunted and had a tendency to agglutinate or congregate. Shreds of mucin traversed villus tips. The villi of the distal seg-
Fig. 2. Villi at the tip of the proximal atretic segment are blunt and club-shaped. The muscularis layer is thicker than normal (H&E. • 40).
470
ROBERT J. TOULOUKIAN
Fig. 3. Villi 15 cm from the tip of the proximal atretic segment are taller and straighter but not significantly longer than normal controls (H&E. • 100),
ment were free-standing and more feathery than villi from normal controls. No difference in villus length was observed (Fig. 5). At 5000 power magnification, the cells from the normal villi were aligned in a regular, wellordered hexagonal network. Microvilli were clearly visible at this magnification and had a fine granular appearance. The hexagonal pattern of the cells in villi from proximal and distal atretic segments was distorted; some assumed a spheroidal while others had a angulated shape (Fig. 6). The cellular architecture was similar at 15,000 power magnification. These views showed the microvilli of the proximal and distal atretic segments to be indistinguishable from normal controls.
Ultrastructure Electron Microscopy The internal structure and microvilli of the intestinal epithelial cell in the animals with atresia were similar to normal control subjects. The junctional (Fig. 7A) complex in the cells membranes was normal and the endothelial membrane of the subcellular capillary bed was intact throughout its visible circumference (Fig. 7B). DISCUSSION
The light m i c r o s c o p y o b s e r v a t i o n s of proximal and distal intestinal segments from animals with intestinal atresia have a striking similarity to newborns with jejunal atresia. ~ Of
ANTENATAL INTESTINAL ADAPTATION
Fig. 4,
471
Villi distal to the atresia are tall and feathery, nearly obliterating the tiny lumen (H& E. • 40),
prime importance is the reversal of the normally diminishing aboral gradient in villus length and the nearly total obliteration of the tiny distal lumen with enlarged villi. Many villi, distal to the atresia in newborn babies, were
also tortuous and intertwined and some had a unique side-branching off the main stalk giving the appearance of pseudopodia, These "giant" deformed villi were not observed in our experimental subjects.
Fig, 5. Scanning electron microscopic appearance of villi in normal (A), proximal atretic (B) and distal atretiC (C) intestine, Villi in the proximal intestine are visibly thicker, segmented and tend to Congregate while villi distal to the atresia a r e tall and feathery (200 • magnification).
472
ROBERT J. TOULOUKIAN
Fig. 6. Scanning electron microscopic appearance of mucosal cell surface in normal (A), proximal atretic (B) and distal atretic (C) intestine. Distortion of cellular shape and alignment is obvious ( 5 0 0 0 • magnification).
Total intestinal length in animals with atresia was not significantly shorter than normal controls while babies born with jejunoileal atresia may have marked shortening of total intestinal length. We must conclude, therefore, that diminished intestinal length cannot be the only stimulus for villus hypertrophy. Tilson reached a similar conclusion by showing a 39% increase in villus height in rats having partial intestinal bypass. 3 Also eliminated as the only mechanism is the workload hypertrophy theory, ~,~ which holds that ingested nutrients stimulate villus growth. Intestinal villi in babies with the "shortg u t " s y n d r o m e h y p e r t r o p h y d u r i n g total parenteral nutrition '~ but do not in animals having normal intestinal length. '~ We believe that villus hypertrophy of the fetal intestine observed in babies born with jejunoileal atresia is achieved through placental nutrition by a mechanism similar to that which must occur with total intravenous nutrition. Shortening of fetal intestinal length may exert an additional influence on this intrauterine effect. Obstruction to the fetal intestinal lumen itself may have a vital role in explaining our observations. The distal segment collapses since it does not receive swallowed amniotic fluid and biliary, pancreatic and intestinal secretions. This loss of intraluminal pressure may conceivably enlarge villi by the reverse mechanical effect that high pressure blunts and clubs the villi at the tip of the proximal segment. Some degree of villus enlargement in the distal segment may also be more apparent than real because of the crowding effect in the tiny lumen. Supporting this con-
cept is that scanning electron microscopy showed no apparent difference in the height of villi in the proximal and distal segments compared to controls. Electron microscopy of intestinal villi from newborns with atresia is not yet available to compare with normal villi. However, no significant structural differences were found in cells from villi in the proximal and distal atretic segments of experimental subjects when compared to normal animals. Finding some specific anatomic change was anticipated, since previous studies, using this model, 7 and by other investigators ~ have shown that obstruction produces net secretion while net absorption is found beyond the obstructed segment and in normal i n t e s t i n e . U n d e r c e r t a i n conditions, nono b s t r u c t e d i n t e s t i n e may e i t h e r h y p e r secrete or develop an enhanced absorptive c a p a c i t y . E l e c t r o n m i c r o s c o p y studies o f h y p e r s e c r e t i n g j e j u n a l m u c o s a in c h o l e r a patients 9 has shown evidence of both cellular changes and marked irregular widening of the interepithelial spaces at the midvillus areas suggesting that fluid is transported from blood vessels to intestinal lumen through the interepithelial spaces and through damaged cells. The microvilli and lateral cell m e m b r a n e s hypertrophy in both ileal and jejunal cells after resection of the midintestine 1~ reflecting the known increased capacity for glucose and sodium transport. Cellular catabolism, ischemia, and membrane injury are known to play a vital role in the pathogenesis of the fluid and elect r o l y t e c o m p l i c a t i o n s of a c u t e intestinal
ANTENATAL INTESTINAL ADAPTATION
Fig. 7. within villi segment is membranes endothelial (B) (35,000
Cellular structure in proximal atretic normal (A). The cell and the subcel|ular membrane is intact magnification),
473
474
ROBERT J, TOULOUKIAN
obstruction. These observations suggested that some histologic evidence of either active secretion by t h e e p i t h e l i a l cell o r loss o f e x t r a c e l l u l a r fluid t h r o u g h d a m a g e d s u b c e l l u l a r l y m p h a t i c and c a p i l l a r y m e m b r a n e s w o u l d be f o u n d in o u r
l a m b s w i t h a t r e s i a . Failing to find such evidence, we conclude that chronic intestinal o b s t r u c t i o n in a f e t a l m o d e l m a y c a u s e functional c e l l u l a r c h a n g e s w i t h o u t a l t e r i n g histology.
REFERENCES
1. Dowling RH, Booth CC: Structural and functional changes following small intestinal resection in the rat. Clin Sci 32:139, 1967 2. Touloukian R J, Wright HK: Intrauterine villus hypertrophy with jejuno-ileal atresia. J Pediatr Surg 8:779, 1973 3. Tilson MD: Compensatory hypertrophy of the gut: testing of the tissue mass, intraluminal nutrition and functional demand hypothesis. Arch Surg 104:69, 1972 4. Gleeson MH, Cullen J, Dowling RH: Intestinal structure and function following small bowel bypass in the rat. Clin Sci 43:731, 1972 5. Wilmore DW, Dudrick S, Daly JM, et al: The role of nutrition in the adaptation of the small intestine after massive resection. Surg Gynecol Obstet 132:673, 1971
6. Koga Y, Ikeda K, Inokuchi K, et al: The digestive tract in total parenteral nutrition. Arch Surg 110:742, 1975 7. Touloukian R J: The composition of amniotic fluid with experimental jejuno-ileal atresia. J Pediatr Surg 12:397, 1977 8. Shields R: The absorption and secretion of fluid and electrolytes by the obstructed bowel. Am J Surg 52:774, 1965 9. Asakura H, Tsuckiya M, Watanake Y, et al: Electron microscopic study in the jejunal mucosa in human cholera. Gut 15:531, 1974 10. Tilson MD, Wright HK: The effect of resection of the small intestine upon the fine structure of the intestinal epithelium. Surg Gynecol Obstet 134:992, 1972