Diseases of the Small Intestine in Childhood

John A. Walker-Smith

• Editore: Butterworth-Heinemann
• Anno: 2013
• ISBN:
  9781483161129
• Edizione: 3
• Argomento: Medicine
• Categoria: Gynecology, Obstetrics & Midwifery

Diseases of the Small Intestine in Childhood, Third Edition, reviews diseases of the small intestine in children with emphasis upon a discussion of their causes, clinical manifestations, and the newer techniques used in diagnosis as well as modern methods of management. The book begins with a discussion of the development of pediatric gastroenterology and the function and physiology of the small intestine. This is followed by separate chapters on the importance of history taking and physical examination of children with small intestinal disease; and techniques to investigate the small intestine. Subsequent chapters are devoted to specific diseases such as celiac disease, food protein intolerance, acute gastroenteritis, defective digestion and absorption of sugars, parasitic infestation, Crohn's disease and abdominal tuberculosis, and chronic diarrhea. This book will be of value to the consultant pediatrician and pediatric surgeon as well as to the pediatric registrar and house officer as a practical guide to their understanding of these diseases. It is also intended for those adult physicians, gastroenterologists, and surgeons who wish to survey the clinical spectrum of disease of the small intestine in childhood.

1

General introduction

Publisher Summary

Gastroenteritis and cholera disorders that have their principal effects on the small intestine have through the ages had a high prevalence and mortality among infants and children. The small intestine is the principal organ of absorption in the human body and carries out a number of important functions, including the onward passage of the ingested food bolus, continued digestion of this bolus, a regulatory role in protein metabolism, and the secretion of hormones. The diseases of the small intestine manifest as a disruption of one or more of these functions and may also disrupt the normal process of fat absorption in a number of ways such as the deficiency of conjugated bile salts as occurs in the stagnant loop syndrome, the decreased uptake of fat as occurs with a reduction in the absorptive area, the deficiency of chylomicron formation, and the deficiency of transport of chylomicrons via the thoracic duct. The malabsorption of ingested nutrients such as fat or protein is a major consequence of small-intestinal disease. This may be accompanied by an abnormal secretion of fluid and electrolytes into the small-intestinal lumen. Small-intestinal secretion represents the balance between the influx of fluid and the efflux of fluid from small-intestinal mucosa.

Development of paediatric gastroenterology

Diseases of the small intestine have long afflicted children. Gastroenteritis and cholera, disorders that have their principal effect on the small intestine, have through the ages had a high prevalence and mortality among infants and children. They continue to do so today in the less fortunate parts of the world, but small intestinal disease is also an important health problem among children of all countries.

Many individuals over the past century have added to the knowledge of these diseases, but only in the last 40 years have certain centres become especially associated with the development of paediatric gastroenterology. Reviews of paediatric gastroenterology in the journal Gastroenterology, in 1967 (Morin and Davidson) and 1970 (Silverberg and Davidson), and the formation of the European Society for Paediatric Gastroenterology in 1968, drew attention to these developments and led to a wider recognition of the diversity and importance of paediatric gastroenterology and, in particular, small intestinal disease in children.

In recent years there has been a much wider understanding of the physiology and pathology of the small intestine in man. This has been due firstly to new laboratory techniques, notably those using preparations of animal small intestine; and secondly to the development of sophisticated methods of investigating small intestinal structure and function in man, such as small intestinal biopsy and small intestine perfusion.

A great deal of this new investigative work has been done in adults, but increasingly observations are being made in children. As a result, the body of knowledge of the small intestine, its structure and function both in health and in disease in childhood has increased enormously.

Of particular importance in the development of paediatric gastroenterology was the demonstration by Sakula and Shiner in 1957 of a flat, small intestinal mucosa on biopsy of the small bowel of a child with coeliac disease. The subsequent confirmation of this observation in large numbers of children with coeliac disease by many other investigators, and the development of a safe intestinal biopsy capsule as a diagnostic tool in paediatric practice, led to a great surge of interest in small intestine disease in children and played a major part in the development of paediatric gastroenterology as a legitimate speciality within paediatrics.

There is still a real danger that when specialists concentrate on one organ or on one restricted branch of medicine they may neglect the whole individual. As the function of the small intestine impinges so much on the function of so many other organs, those clinicians who interest themselves in this organ and its diseases should be particularly aware of the principles and practice of general paediatrics. It is equally true that the general paediatrician should have a real understanding of diseases of the small intestine and their management.

Function of the small intestine

The small intestine is the principal organ of absorption in the human body and complete resection of the small intestine is not compatible with life. It is thus a vital organ whose continuing healthy function is a major determinant for the continuing good health and normal development of the growing infant and child.

The small intestine has a number of important functions. These include:

• The onward passage of the ingested food bolus.

• Continued digestion of this bolus.

• Absorption of the digested nutrients into the blood and lymph vessels.

• A vital immunological function including the production of secretory immunoglobulins.

• A regulatory role in protein metabolism.

• Secretion of hormones.

Disease of the small intestine may manifest as a disruption of one or more of these functions. Interference with the first of these produces the various syndromes of complete or incomplete small intestinal obstruction. Interference with the remaining functions characteristically produces diarrhoea, usually with failure to thrive, but there may also be systemic abnormalities, i.e. there are associated disturbances of organs outside the alimentary tract secondarily affected by disease of the small intestine. Indeed, a child with primary small intestinal disease may present with systemic symptoms alone and with no symptoms of gastrointestinal disturbance, e.g. a child with coeliaac disease may present only with shortness of stature. There is inadequate space to review all these functions here, but it is appropriate to mention some aspects of particular clinical importance and discuss them briefly.

Site of absorption

Knowledge of the site of absorption of various nutrients from small intestine (Figure 1.1) is of importance in understanding the various disturbances of absorption that may occur when lesions of the small intestinal mucosa chiefly affect the proximal small intestine (e.g. coeliac disease), the distal small intestinal (e.g. Crohn’s disease), or the whole length of the small intestine (e.g. tropical sprue). Important differences in function between proximal and distal small intestinal function are listed in Table 1.1.

Table 1.1

Functional differences between jejunum and ileum

	Jejunum	Ileum
Absorption of:
Sugar	+ +	+
Protein	+ +	+
Fat	+ +	+
Bicarbonate	Absorb	Secrete
Vitamin B12	-	+
Bile salts	-	+
Water and electrolyte absorption	‘glucose dependent’	‘glucose independent’

Courtesy Dawson (1974).

Figure 1.1 Sites of absorption from the small intestine. (Reproduced from Booth (1968) by kind permission of author and publishers.)

Mechanisms of absorption

Knowledge of the mechanisms of absorption of nutrients may have important clinical relevance to the understanding of small intestinal disease, and to illustrate this point the mechanisms of fat and protein absorption will be briefly discussed here. Absorption of other nutrients is discussed in appropriate chapters.

Fat absorption

The fat in the diet of man includes triglycerides, cholesterol, and fat-soluble vitamins. Triglycerides, the major source of dietary lipid, are tri-esters of glycerol, i.e. they consist of three molecules of fatty acid esterified to glycerol. Fatty acids are described as long, medium or short, depending upon their chain length, and they may be saturated or unsaturated, depending upon the presence or absence of a double bond.

In man, most dietary triglycerides contain long-chain fatty acids (LCT), the most important of which are the mono-unsaturated fatty acid, known as oleic acid, containing 18 carbon atoms, and the saturated palmitic acid containing 16 carbon atoms. Medium-chain triglycerides (MCT) contain fatty acids of 6–12 carbon atoms in length and do not constitute more than a minor proportion of normal dietary lipids.

Three of the fatty acids are generally known as essential fatty acids (EFA). These are linoleic acid, linolenic acid and arachidonic acid. Linoleic acid usually accounts for most of the essential fatty acids in a normal diet. In fact, most foods contain small quantities of linoleic acid in the cell wall, e.g. cereals 0.5%. When an artificial diet is introduced consideration of dietary deficiency of essential fatty acids must be given, especially in babies where it has been suggested that 2–4% of dietary energy should be provided as linoleic acid. In breast milk, 7% of the fatty acids are linoleic acid. Medium-chain triglyceride preparatio...