12 Postgraduate Medical Journal Postgrad Med J: first published as 10.1136/pgmj.44.507.12 on 1 January 1968. Downloaded from

return to the patient and determine to what DANES, B.S. & BEARN, A.G. (1967) The effect of retinol extent the findings derived from in vitro studies (vitamin A alcohol) on urinary excretion of mucopoly- saccharides in the Hurler syndrome. Lancet, i, 1029. are directly applicable to the human condition. HENDERSON, J.L. (1940) Gargoylism; review of principal features with report of five cases. Arch. Dis. Child. 15, 215. McKUSICK, V.A. Heritable Disorders of Connective Tissue. References Mosby, St Louis. DANES, B.S. & BEARN, A.G. (1966a) Hurler's syndrome. A SATO, A. (1955) Chediak and Higashi's disease. Probable genetic study in cell culture. J. exp. Med. 123, 1. identity of 'a new leucocytal anomaly (Chediak)' and DANES, B.S. & BEARN, A.G. (1966b) Hurler's syndrome. 'congenital gigantism of peroxidase granules (Higashi).' Effect of retinol (vitamin A alcohol) on cellular mucopoly- Tohoku J. exp. Med. 61, 201. saccharides in cultured human skin fibroblasts. J. exp. WHITE, J.G. (1966) The Chediak-Higashi syndrome: A Med. 124, 1181. possible lysosomal disease. Blood, 28, 143.

Enteropoiesis: structural and functional relationships of the enterocyte

C. C. BOOTH Royal Postgraduate Medical School, London Protected by copyright. THE REMARKABLE turnover of the cells of the layer of the small intestine is markedly increased, intestinal mucosa was first suspected by Bizzozero 'the situation is comparable with anaemia in as long ago as 1888 and has been firmly estab- which there is reduction of the peripheral red lished by modern techniques during the past 20 cells (villous cells) and compensatory hyper- years (Leblond & Stevens, 1948; Leblond & trophy of the red bone marrow (glandular Messier, 1958; Creamer, Shorter & Bamforth, mucosa)'. 1961). The absorbing cells of the small intestine This paper explores further the theoretical have, as Smyth has pointed out, a 'short life and possibilities raised by Doniach's haematological a merry one ... if merriment is the equivalent analogy and suggests a new nomenclature for in cellular terms of a remarkable range of acti- the intestinal mucosal cells. The functional im- vities possessed by few other cells in the body' plications of this classification are also discussed. (Smyth, 1967). Formed in the crypts of Lieber- kuhn, the intestinal cells are extruded on to the Nomenclature of the intestinal absorbing cells surface of an adjacent villus whose side they There are a variety of different cell types pre- http://pmj.bmj.com/ climb until they reach the villus tip, from where sent in the intestinal mucosa. Paneth cells, argen- they are shed into the intestinal lumen. The total taffin cells and goblet cells mingle with the turnover time for the cells of the jejunum is columnar cells which make up the major part known to be as rapid as 2 or 3 days in the of the absorptive epithelium and which are the mouse and perhaps 5 days in man (MacDonald, concern of this paper. These columnar cells have Trier & Everett, 1964; Shorter et al., 1964), so been given a variety of names such as villous that the body only uses the extraordinary bio- cells, absorptive cells, mucosal surface cells and on September 30, 2021 by guest. logical activities of these cells for a very brief adult epithelial cells, and the cells in the crypts period. of Lieberkuhn have been variously called the Doniach & Shiner (1960) were the first to draw glandular cells, germinative zone or production the analogy between the intestinal epithelial cells zone. The use of a haematological analogy sug- and the haemopoietic system. They compared gests a more satisfactory nomenclature which at the germinative or crypt zone, where the cells the same time links the formative cells of the are manufactured, with the erythroblasts of the crypts with their adult counterparts. If the ab- bone marrow and the adult absorbing cells of sorptive cell on the surface of the villus is given the villi with the erythrocytes of the peripheral the term 'enterocyte', then the germinative cell blood. Doniach & Shiner pointed out that in in the glandular mucosa should be called an coeliac disease, where the jejunal mucosa is 'enteroblast', the function of this cell being devoid of villi but the glandular or germinative 'enteropoiesis'. The further implications of this Festschrift for Sir John McMichael 13 Postgrad Med J: first published as 10.1136/pgmj.44.507.12 on 1 January 1968. Downloaded from nomenclature are shown schematically in Fig. 1. not hitherto been encountered in this situation. The enterocyte may be enlarged (a macroentero- cyte), normal, or reduced in size (a microentero- The normocytic enterocyte cyte). The numbers of the enterocytes may be As indicated in Fig. 1, the normocytic entero- increased (enterocytic hyperplasia), normal or re- cyte may be normoplastic, hyperplastic or hypo- duced (enterocytic hypoplasia). Furthermore, the plastic, and its function may be increased, function of the enterocyte is not static for under normal or decreased. certain circumstances there may be either in- creased or decreased function of this cell. Defin- (i) Normoplasia ing the intestinal cell in this way poses a num- Clearly the normal situation in the small in- ber of questions which can only be resolved testine is established when there are normocytic by future research, but recent studies have al- enterocytes which are present in 'normal' num- ready demonstrated many of the situations bers and which function 'normally'. As with all shown in Fig. 1. other biological phenomena, however, there is a considerable range of normality in the small The macrocytic enterocyte intestine. There are marked variations in the In pernicious anaemia it is well known that number of enterocytes which constitute norm- the cells of the buccal mucosa may be larger ality and these variations are reflected by differ- than normal. Similarly in the small intestine a ences in the appearance of the surface mucosa recent report has described macrocytic entero- in different individuals and in different popula- cytes and a megaloblastic enteroblast (Foroozan tions throughout the world. Under the dissecting & Trier, 1967). This appears to be associated microscope, the shapes of the villi of the small with enterocytic hypoplasia since there is also intestine vary widely, some individuals showing

shortening of the villi. How such cells function villi which are entirely finger-shaped, whereas Protected by copyright. is not known. The cause of the intestinal ab- others have a pattern of leaf- and tongue- normality in pernicious anaemia is presumably a shaped villi. Creamer (1964) has estimated that similar 'maturation arrest', involving the entero- the number of enterocytes required to cover blast, to that seen in the bone marrow. leaf-shaped villi are only 25% of those necessary As might be expected an arrest of cell turn- when the villi are finger-shaped. The variation over in the small intestine also occurs after in the number of enterocytes in different normal X-irradiation. A recent study of jejunal biopsies individuals is not surprising in an organ where obtained from patients undergoing therapeutic cell turnover is extremely rapid and where the X-irradiation (Trier & Browning, 1966) has de- balance between enteropoiesis and cell loss must monstrated that the mitoses in the enteroblastic often be precarious. layer of the small intestine are reduced within Increased function of normocytic enterocytes 12 hr of starting X-ray therapy. Thereafter, there may occur in a variety of situations of stress. is enterocytic hypoplasia, causing marked short- The effects of bulk-feeding in the rat provide ening of the villi and at the same time megalo- an interesting example of hyperfunction (Dowl- http://pmj.bmj.com/ blastosis and megalocytosis of the epithelial cells ing et al., 1967a). When the diet of the animal develops. As in pernicious anaemia, this situation contains a large amount of unabsorbed bulk, is rapidly reversible. there is an increase in the absorptive capacity of The question must also be asked whether the the small intestine without any change in the enterocyte may become macrocytic when there macroscopic appearance of the bowel and with- is compensatory hypertrophy following partial out enterocytic hyperplasia. Using the everted resection of the small intestine. Although there sac technique Dowling et al. (1967a)

showed that on September 30, 2021 by guest. is clear evidence of enterocytic hyperplasia after glucose absorption by the jejunum of rats whose intestinal resection, macrocytic enterocytes have diets contained 60 % or 80 % by weight of

Macrocytic Hyperplastic Hyperfunction Enteroblast-----)' Enterocyte Normocytic \--- Normoplastic Normofunction Microcytic Hypoplastic Hypofunction Enteropoiesis FIG. 1 14 Postgraduate Medical Journal Postgrad Med J: first published as 10.1136/pgmj.44.507.12 on 1 January 1968. Downloaded from powdered kaolin was 4-81 (± 0-99 SEM) mg and in control subjects and in patients with intestinal 9-96 (+053 SEM) mg respectively per 100 mg resection. Eight of the patients in whom resec- dried intestinal tissue per hour, compared with tion had been performed absorbed 60-9 (±2.20 2-52 (+0-66 SEM) mg in control rats. Detailed SEM) mg of glucose per 25 cm of intestine per anatomical and histological studies showed that minute, as compared with 48.3 (± 2-07 SEM) this functional response was not due to any in- mg in the control subjects (Dowling & Booth, crease in absorptive surface area. However, 1966). there was an increased activity of certain enzymes More direct observations on the relationship in the enterocytes (Riecken et al., 1965) suggest- between enterocytic hyperplasia and increased ing that the enhanced absorption may be intestinal function have been made in the rat related to increased activity of the individual (Dowling & Booth, 1967). In this animal, there mucosal cells. This contrasts with the situation is a different response to proximal and distal following intestinal resection, when, as described small bowel resection. When the jejunum is re- below, enterocytic hyperplasia alone appears to moved, the residual ileum shows marked entero- be the adaptative response. cytic hyperplasia and the height of the villi Decreased function of normocytic enterocytes increases by more than 50%. After ileal resec- may be either congenital or, less frequently, tion, however, the enterocytes of the jejunal acquired. The hereditary abnormalities of intes- remnant are less markedly hyperplastic and the tinal absorption (Milne, 1967), such as the rare villus height only increases by 10-15%. The condition of glucose/galactose malabsorption, functional response is directly related to the the much more common hereditary deficiency degree of enterocytic hyperplasia, for studies of of disaccharidases (alactasia for example), the glucose absorption in animals subjected to such absorption defect for aminoacids in cystinuria resections demonstrate that there is an increase or the hereditary defect of vitamin B12 absorp- in intestinal function per unit length of intestine Protected by copyright. tion described by Imerslund (1960) and Gras- which shows a highly significant correlation with beck et al. (1960) are all examples of congenital the amount of increase in villus height (Dowling decrease of the function of normocytic entero- & Booth, 1967). In other words, when there is cytes. enterocytic hyperplasia following partial resec- Acquired and transient defects in enterocytic tion of the small intestine, the increase in function have been described in acute gastro- intestinal function is a result of an increase in enteritis (King & Joske, 1960) or after neomycin the number of enterocytes and not of any in- administration (Reiner & Patterson, 1966). crease in the function of the individual intestinal mucosal cells. The absence of any functional (ii) Hyperplasia change in the individual enterocyte is supported After partial resection of the small intestine by the observation that the mucosal cell enzymes there is an increase in enteropoiesis (Loran & do not increase in this situation (Dowling, Althausen, 1960) and this results in enterocytic Riecken & Booth, 1967b), in striking contrast to hyperplasia. In man, for example, Porus (1965) the increase in enzymes demonstrated in animals http://pmj.bmj.com/ found an increase in the number of enterocytes after high-bulk feeding which has already been in the midzone of the villus in two out of four described. patients who had undergone resection of part of the small intestine, although the villi appeared to (iii) Hypoplasia be normal in height in these two individuals. Hypoplastic normocytic enterocytes have been Dowling & Booth (unpublished data) have also demonstrated in the small intestine where there demonstrated enterocytic hyperplasia after small is malnutrition. In monkeys with experimental on September 30, 2021 by guest. intestinal resection in man and have found en- kwashiorkor, for example, there is an overall largement of the villi. In jejunal biopsies obtained reduction in enteropoiesis. The enteroblastic from twelve patients who had been subjected to layer is reduced in thickness and the villi are partial resection of the small intestine, the mean shorter than normal (Deo & Ramalingaswami, villus height was 440 ,u (± 16 SEM) compared to 1965). This has been shown by 3H-thymidine a mean of 382 ,u (+ 20 SEM) in eleven matched labelling to be associated with a decreased turn- control subjects, the difference being statistically over of the intestinal mucosal cells. Similar ob- significant (P < 0 05). This enterocytic hyper- servations had been made in rats subjected to plasia was associated with an increase in the starvation (Stevens Hooper & Blair, 1958). functional capacity of the small intestine. Using a 21 mM glucose solution, absorption of glucose The microcytic enterocyte was compared in a 25 cm segment of jejunum Microcytic enterocytes are found either when Festschrift for Sir John McMichael 15 Postgrad Med J: first published as 10.1136/pgmj.44.507.12 on 1 January 1968. Downloaded from there is some factor damaging and destroying of the small intestine by feeding measured the enterocyte, a condition analagous to haemo- amounts of various substances and then estimat- lysis, or occasionally when there is inhibition of ing how much is excreted. Such balance experi- enteropoiesis. Microcytic enterocytes are invari- ments measure the overall function of a highly ably associated with hypoplasia and hypofunc- complex organ and have provided a great deal tion. of valuable information in the past. It is now (i) Factors damaging the enterocyte possible, however, to study intestinal function at The most striking example of the microcytic a cellular level so that the overall function of enterocyte is seen in coeliac disease. In this con- the organ may be expressed in cellular terms. dition, the enterocytes are markedly reduced in By the use of haematological, analogy, a new height and electron microscopy reveals intra- terminology has been developed to describe the cellular disorganization and severe disruption of relationship between structure and function in the microvillous border of the cell. There is a the small intestine which may be of value to gross reduction in the number of enterocytes so future research. that the villi disappear and the mucosa is fre- quently flat and Acknowledgments featureless. At the same time, I wish to thank my colleagues in the gastroenterology overall enteropoiesis appears to be increased, for group at Hammersmith for many interesting and instructive in contrast to the situation following X-ray discussions, and Professor Sir John McMichael for his therapy or in malnutrition, the enteroblastic constant support and encouragement. layer is markedly thickened and there is an in- crease in mitotic References activity within the crypts. The CREAMER, B. (1964) Variations in small intestinal villous shape available evidence suggests that the dietary con- and mucosal dynamics. Brit. med. J. ii, 1371. stituent, gluten, is toxic to the enterocyte, CREAMER, B., SHORTER, R.G. & BAMFORTH, J. (1961) The damaging and destroying it, and enteropoiesis is turnover and shedding of epithelial cells. 1. The turnover Protected by copyright. therefore in an of the gastrointestinal tract. Gut, 2, 110. accelerated attempt to keep pace DEO, M.G. & RAMALINGASWAMI, V. (1965) Reactions of the with the greatly increased loss of enterocytes. small intestine to induced protein malnutrition in Rhesus The reason why the enterocyte should be so monkeys-a study ofcell population kinetics in thejejunum. susceptible to damage by gluten is not yet known, Gastroenterology, 49, 150. but to pursue the DONIACH, I. & SHINER, M. (1960) Histopathology of the haematological analogy fur- stomach in pernicious anaemia and jejunum in steator- ther, the situation is not unlike the haemolysis rhoea. Brit. J. Radiol. 33, 238. caused by the dietary toxin, fava beans, when DOWLING, R.H. & BOOTH, C.C. (1966) Functional compensa- an individual is deficient in glucose-6-phosphate tion after small bowel resection in man. Lancet, ii, 146. dehydrogenase. It has DOWLING, R.H. & BOOTH, C.C. (1967) Structural and therefore been postulated functional changes following small intestinal resection in that coeliac disease may be due to a hitherto the rat. Clin. Sci. 32, 139. unknown enzyme defect in the enterocyte, a DOWLING, H., RIECKEN, E.O., LAWS, J.W. & BOOTH, C.C. hypothesis which is supported by the observation (1967a) The intestinal response to high bulk feeding. that the disease may be genetically determined Clin. Sci. 32, 1.

DOWLING, R.H., RIECKEN, E.O. & BOOTH, C.C. (1967b) The http://pmj.bmj.com/ (MacDonald, Dobbins & Rubin, 1965). morphological and histochemical response to small bowel resection in the rat. (In preparation). (ii) Factors inhibiting enteropoiesis FOROOZAN, P. & TRIER, J.S. (1967) The small intestinal When enteropoiesis is inhibited by X-irradi- lesions in pernicious anaemia. Gasteroenterology, 52, 1085. ation, or in pernicious anaemia, the enterocytes GRASBECK, R., GORDIN, R., KANTERO, I. & KUHLBACK, B. develop macrocytosis. There are, however, other (1960) Selective vitamin B,, malabsorption and proteinuria in young people. Acta med. scand. 168, 289. situations in which ineffective enteropoiesis re- IMERSLUND, 0. (1960) Idiopathic chronic megaloblastic sults in the development of small and ineffective anaemia in children. Acta paediat., Stockh. 49, Suppl. 119. enterocytes. Folic acid antagonists such as KING, M.J. & JOSKE, R.A. (1960) Acute enteritis with on September 30, 2021 by guest. aminopterin are effective inhibitors of entero- temporary intestinal malabsorption. Brit. med. J. i, 1324. LEBLOND, C.P. & MESSIER, B. (1958) Renewal of chief cells poiesis and cause marked enteroblastic and and goblet cells in the small intestine as shown by radio- enterocytic hypoplasia in experimental animals. autography after injection of thymidine-3H into mice. Providing that the dose of aminopterin is suffi- Anat. Rec. 132, 247. ciently low to permit recovery, the enterocytes LEBLOND, C.P. & STEVENS, C.E. (1948) Constant renewal of intestinal epithelium in albino rats. Anat. Rec. 100, 357. may demonstrate marked microcytosis during LORAN, M.R. & ALTHAUSEN, T.L. (1960) Cellular prolifera- the recovery phase (see Fig. lIA and B, Zam- tion of intestinal epithelia in the rat two months after chek, 1960). partial resection of the ileum. J. biophys. biochem. Cytol. 7, 667. MACDONALD, W.C., DOBBINS, W.O. & RUBIN, C.E. (1965) Conclusion Studies of the familial nature of celiac spure using biopsy Enterologists usually approach the problems of the small intestine. New Engl. J. Med. 272, 448. 16 Postgraduate Medical Journal Postgrad Med J: first published as 10.1136/pgmj.44.507.12 on 1 January 1968. Downloaded from

MACDONALD, W.C., TRIER, J.S. & EVERETr, N.B. (1964) Cell SHORTER, R.G., MOERTEL, C.B., TITUS, J.L. & REITEMEIER, proliferation and migration in the stomach, duodenum R.J. (1964) Cell kinetics in the jejunum and rectum of man. and rectum of man: radioautographic studies. Gastro- Amer. J. digest. Dis. 9, 760. enterology, 46, 405. SMYTH, D.H. (1967) Intestinal absorption. Brit. med. Bull. MILNE, M.D. (1967) Hereditary abnormalities of intestinal 23, 207. absorption. Brit. med. Bull. 23, 279. PORus, R.L. (1965) Epithelial hypoplasia following massive STEVENS HOOPER, C. & BLAIR, M. (1958) The effect of starva- small bowel resection in man. Gastroenterology, 48, 753. tion on epithelial renewal in the rat duodenum. Exp. Cell REINER, E. & PATTERSON, H. (1966) The effects of neomycin Res. 14, 175. on disaccharidase activity of the small bowel. Clin. Res. TRIER, J.S. & BROWNING, T.H. (1966) Morphological re- 14, 499. sponse of the mucosa of human small intestine to X-ray RIECKEN, E.O., DOWLING, H., BOOTH, C.C. & PEARSE, exposure. J. clin. Invest. 45, 194. A.G.E. (1965) Histochemical changes in the rat small ZAMCHEK, N. (1960) Dynamic interaction among body intestine associated with enhanced absorption after high nutrition, gut mucosal metabolism and morphology and bulk feeding. Enzymol. biol. clin. 5, 231. transport across the mucosa. Fed. Proc. 19, 855.

Distribution of diffusing capacity in obstructive lung disease WILLIAM A. BRISCOE Columbia Medical Division ofBellevue Hospital; Department ofMedicine, College ofPhysicians and Surgeons, Columbia University, New York City Protected by copyright. WHILE I was a registrar at Hammersmith, Pro- that in some patients, the mixing of inert gases fessor McMichael remarked one day, 'Why between lungs and spirometer took much longer don't you do something about emphysema?' This than normal. This had been a technical bugaboo led to my introduction to McMichael's method. in previous methods of lung volume measure- ment. It now seemed worth while to study this McMichaers method source of technical error as an interesting and It is sometimes forgotten that McMichael was perhaps important aspect of pathophysiology. initially best known in the field of respiration The conclusions from this Hammersmith work rather than circulation. In 1939, he described his were: normal lungs mixed helium from the new closed-circuit spirometer for measuring the McMichael spirometer as if they were nearly functional residual capacity of the lungs evenly ventilated. In patients incapacitated by (McMichael, 1939). The four novel features he bronchitis and emphysema, the behaviour of the

introduced, partly in collaboration with Herrald lung could be almost exactly simulated by a http://pmj.bmj.com/ (Herrald & McMichael, 1939), were: (1) the main- simple two-chamber model, composed of two tenance of constant volume in the spirometer, differently ventilated bellows or balloons in from which a patient breathed for many minutes parallel. The well-ventilated bellows was small by adding oxygen at a rate equal to its meta- with a volume of about 1 litre, and ventilated bolic consumption; (2) a pump was used to cir- by about 450 ml breath. The poorly ventilated culate and mix the gases rapidly in the bellows was large with a volume of 3-5 litres, spirometer; (3) the re-breathing period was pro- and ventilated by only 50 ml breath (Briscoe, longed beyond the usual 7 min, when the Becklake & Rose, 1951; Briscoe, 1952; Briscoe on September 30, 2021 by guest. patient's lungs mixed slowly with the gas in the & McLemore, 1952). A lung of this type, with a spirometer; and (4) an insoluble inert gas, hydro- normal volume of conducting airways, behaves gen or helium, was used as the indicator, and as if it had a large physiological dead space- estimated by its thermal conductivity. These in- a simpler but less complete description of the novations resulted in what is still, 28 years later, real state of affairs. the best and most widely used method; it should We were not the only ones to recognize that perhaps be more widely referred to as uneven ventilation was the key to understanding McMichael's Method (Briscoe, 1965). the disturbance of function in obstructive lung disease: in the United States, Robertson, Siri & Bad nixing Jones (1950) and Fowler, Cornish & Kety (1952) Herrald & McMichael (1939) had emphasized published their classic studies of the distribution