الفهرس 
Chapter 1: DefinitionOnly 14 pages are availabe for public view
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Abstract
Lactose is actually two sugar molecules joined together: it is known as a disaccharide (di = two saccharide = sugar). The digestive enzyme called lactase splits lactose into its two constituent sugars: glucose and galactose. These are single sugars, called monosaccharides (mono = one; saccharide = sugar). Monosaccharides are small enough to be transported across the cells that line the digestive tract and into circulation, where they are an important source of energy for many body functions. Lactose, being a disaccharide, cannot pass across the lining of the digestive tract.Human milk has more lactose but less protein than cow or goat milk.The composition of milk varies from differs various breeds. However, commercial milks are a blend of many animals of many breeds and have the average compositions. Human milk has the highest lactose percentage at around7%. Unprocessed cow milk has 4.7% lactose. Unprocessed milk from other bovids contains similar lactose percentages (goat milk 4.7%, buffalo 4.86%, and sheep milk 4.6%).Lactose intolerance has been recognized for many years as common problem in many children and most adults throughout the world. Lactose intolerance is a clinical syndrome of one or more of the following: abdominal pain, diarrhea, nausea, flatulence, and/or bloating after the ingestion of lactose or lactose-containing food substances.A deficiency of intestinal lactase prevents hydrolysis of ingested lactose. The osmotic load of the unabsorbed lactose causes secretion of fluid and electrolytes until osmotic equilibrium is reached. Dilation of the intestine caused by the osmosis induces an acceleration of small intestinal transit, which increases the degree of maldigestion. Within the large intestine, free lactose is fermented by colonic bacteria to yield short-chain fatty acids and hydrogen gas. The combined increase in fecal water, intestinal transit, and generated hydrogen gas accounts for the wide range of gastrointestinal symptoms.Primary disease is the most common form. The percentage varies according to ethnicity and is related to the use of dairy products in the diet, resulting in genetic selection of individuals with the ability to digest lactose. In populations with a predominance of dairy foods in the diet, particularly northern European people, as few as 2% of the population has primary lactase deficiency.Congenital lactase deficiency is an extremely rare autosomal recessive disorder associated with a complete absence of lactase expression. teleologically, infants with congenital lactase deficiency would not be expected to survive before the 20th century, when no readily accessible and nutritionally adequate lactose-free human milk substitute was available.Developmental lactase deficiency is now defined as the relative lactase deficiency observed among preterm infants of less than 34 weeks’ gestation.Secondary lactase deficiency implies that an underlying pathophysiologic condition is responsible for the lactase deficiency and subsequent lactose malabsorption. Etiologies include acute infection (eg, rotavirus) causing small intestinal injury with loss of the lactase-containing epithelial cells from the tips of the villi. The immature epithelial cells that replace these are often lactase deficient, leading to secondary lactose deficiency and lactose malabsorption.Symptoms of lactose intolerance, including abdominal distention, flatulence, abdominal cramping, and (ultimately) diarrhea, are independent of the cause of lactose malabsorption and are directly related to the quantity of ingested lactose.Diagnosis of lactase deficiency manifesting as lactose intolerance is based on a characteristic clinical history of precipitation of gastrointestinal and/or systemic symptoms within minutes to a few hours after consumption of products containing lactose (dairy and non-dairy).Resolution of symptoms with elimination of lactose-containing food products and resumption of symptoms with the reintroduction are findings suggestive of lactose intolerance.Diagnostic tools for lactose intolerance is Breath hydrogen test This is the diagnostic test of choice.There is no known way to prevent lactose intolerance. Prevention of the symptoms of lactose intolerance is primarily focused on avoidance of dietary milk and milk containing products. Some aspects of lactose intolerance may be genetically determined and not modifiable.Treatment is indicated only when lactase deficiency manifests as a clinical syndrome of lactose intolerance. Asymptomatic patients are not treated.When children are diagnosed with lactose intolerance, avoidance of milk and other dairy products will relieve symptoms. However, those with primary lactose intolerance have varying degrees of lactase deficiency and, correspondingly, often tolerate varying amounts of dietary lactose.Treatment consists of limitation of lactose-containing foods, use of lactase-treated dairy products, oral lactase supplementation, or elimination of dairy and non-dairy lactose.Treatment of secondary lactase deficiency and lactose malabsorption attributable to an underlying condition involves treatment of underlying causes, (e.g., small bowel injury, acute gastroenteritis, small bowel bacterial overgrowth, coeliac sprue, cancer chemotherapy, or other causes of injury to the small intestinal mucosa). Generally, these patients do not require dietary lactose restriction, although some patients with significant symptoms may need to temporarily restrict their intake of dairy products for symptomatic improvement. These patients may also require lactase, calcium, and vitamin D supplements as well as nutritionist consultation.Congenital lactase deficiency Without early recognition and prompt treatment, congenital lactase deficiency is potentially life threatening. Initial management of diarrhea includes intravenous rehydration and replacement of electrolytes. The only treatment is complete avoidance of lactose from birth. Treatment is life long and consists of simple removal of lactose frfrom the diet and substitution with a commercial lactose-free formula.Prognosis for patients with lactase deficiency with a clinical syndrome of lactose intolerance is excellent with lactose reduction. Persistent symptoms in a small number of patients are either due to ongoing inadvertent lactose exposure (especially from hidden lactose), irritable bowel syndrome, or poorly controlled underlying disorders of secondary lactase deficiency. Obviously treatment is life long and compliance may be a problem, especially in children.