• Which organ is the most important organ in the
body? Most people would say the heart or the
brain, completely overlooking the gastrointestinal
tract (GI tract).
• The GI tract is imperative for our well being and
our lifelong health.
• A non-functioning GI tract can be the source of
many chronic health problems that can interfere
with your quality of life and or even death.
• The old saying "you are what you eat"
perhaps would be more accurate if worded
"you are what you absorb and digest".
• we will be looking at the importance of these
two functions of the digestive system:
digestion and absorption.
• Digestion is the mechanical and chemical break down of
food into small organic fragments.
• Mechanical digestion refers to the physical breakdown of
large pieces of food into smaller.
• In chemical digestion, enzymes break down food into the
small molecules before they can be absorbed by the
digestive epithelial cells.
• The Human diet needs carbohydrates, protein, and fat, as
well as vitamins and inorganic components for nutritional
Enzyme Produced In Site of Release
Salivary amylase Salivary glands Mouth
Pancreatic amylase Pancreas Small intestine
Maltase Small intestine Small intestine
Pepsin Gastric glands Stomach
Trypsin Pancreas Small intestine
Peptidases Small intestine Small intestine
Lipase Pancreas Small intestine
• The digestion of carbohydrates begins in the
mouth. The salivary enzyme (amylase)
food starches into maltose, a disaccharide.
• In the duodenum. The chyme from the
stomach enters the duodenum and mixes with
the digestive secretions from the pancreas,
liver, and gallbladder.
• Pancreatic juices (amylase), breakdown of starch
and glycogen into maltose and other
• These disaccharides are then broken down into
monosaccharides by enzymes called maltases,
sucrases, and lactases.
• The monosaccharides are absorbed across the
intestinal epithelium into the bloodstream to be
transported to the different cells in the body .
• A large part of protein digestion takes place in the stomach.
• The enzyme pepsin digestion proteins by breaking them
down into peptides, short chains of four to nine amino
• In the duodenum, other enzymes (produced by the
pancreas) – trypsin, elastase, and chymotrypsin – act on
the peptides, reducing them to smaller peptides.
• Further breakdown of peptides to single amino acids is
aided by enzymes called peptidases (those that break
• The amino acids are absorbed into the bloodstream
through the small intestine.
• Lipid (fat) digestion begins in the stomach with
the aid of lingual lipase and gastric lipase.
• However, the bulk of lipid digestion occurs in the
small intestine due to pancreatic lipase.
• Bile aids in the digestion of lipids, primarily
triglycerides, through emulsification.
• Emulsification is a process in which large lipid
globules are broken down into several small lipid
• Lipases break down the lipids into fatty acids and
• The bile salts surround long-chain fatty acids and
monoglycerides, forming tiny spheres called micelles.
• The long-chain fatty acids and monoglycerides recombine
in the absorptive cells to form triglycerides, which
aggregate into globules, and are then coated with proteins.
• These large spheres are called chylomicrons.
• Chylomicrons contain triglycerides, cholesterol, and other
lipids; they have proteins on their surface.
• Chylomicrons leave the absorptive cells entering the
• From there, they enter the blood in the subclavian vein .
• Vitamins can be either water-soluble or lipid-
• Fat-soluble vitamins are absorbed in the same
manner as lipids.
• Water-soluble vitamins can be directly
absorbed into the bloodstream from the
• Malabsorption ; A defect in the absorption of
one or more nutrients.
• Malabsorption syndromes encompass
numerous clinical entities that result in
chronic diarrhea, abdominal distention, and
failure to thrive.
• Carbohydrate, fat, or protein malabsorption is
caused by a disorder in the intestinal
processes of digestion, transport, or both of
these nutrients across the intestinal mucosa
into the systemic circulation.
• Either a congenital abnormality in the
digestive or absorptive processes or, more
commonly, a secondarily acquired disorder of
such processes may result in malabsorption.
Disorders of Carbohydrate
• Disorders of Carbohydrate metabolism can be:
• cystic fibrosis and Shwachman-Diamond syndrome, which
may cause amylase deficiency;
• the extremely rare congenital lactase deficiency;
• sucrase-isomaltase deficiency;
• the most common being lactose intolerance, typically
secondary to a damage of the mucosa, such as a viral
• conditions that cause mucosal atrophy, such as celiac
Disorders of protein metabolism
Congenital: cystic fibrosis, Shwachman-Diamond
syndrome, and enterokinase deficiency, which
cause inadequate intraluminal digestion.
Acquired: disorders of protein digestion and/or
absorption are nonspecific (ie, they also affect
the absorption of carbohydrates and lipids) and
are found in conditions that result in damage to
the absorptive intestinal surface, such as
extensive viral enteritis, milk protein allergy
enteropathy, and celiac disease.
Disorders of Lipid metabolism
• Congenital: cystic fibrosis and Shwachman-
Diamond syndrome, which cause lipase and
• congenital primary bile acid malabsorption.
• Acquired (secondary mostly to disorders of the
liver and the biliary tract or to chronic
• Clearly, any condition that results in the loss of
small intestinal absorptive surface also causes
Classification and etiology
Disorders of intraluminal digestion.
Disorders of transport in the intestinal
Disorders of transport in the intestinal
Disorders of transport from mucosal cell
Systemic diseases associated with
Drugs causing malabsorption.
Disorders of intraluminal digestion
-carcinoma of pancreas
• Bile salt insufficiency:
• Rapid transit of food
• Increased bile salt loss in
-terminal ileal disease-
-terminal ileal resection
• Lack of intrinsic factor
Disorders of transport
in the intestinal
• Defect in brush border
• Defect in epithelial
Disorders of transport
from mucosal cell
• Lymphatic obstruction
• Defect in epithelial
• Addison’s disease
• Diabetes mellitus
• Collagen vascular
• Colchicine &
of bile salts in
gut,inhibition of lactase
• Methotrexate-folic acid
Genetically determined syndromes
• Celiac disease is by far the most common inherited
• Cystic fibrosis is the second most common
• Cow's milk and soy milk protein allergies are common,
especially in infants and young children.
• A transient and common form of malabsorption in
infants results from acute-onset enteritis (mostly viral,
specifically rotaviral), which causes transient lactose
• Celiac disease is slightly more common in females.
• Autoimmune enteropathy is an X-linked disorder that
only affects males in familial cases.
• Symptoms of a congenital disease are usually apparent
shortly after birth or after a short hiatus once a
particular substance is ingested in substantial amounts.
• Protein sensitivity syndromes to milk or soy protein
usually present in infants younger than 3 months.
• Solid food protein sensitivity syndromes are known to
occur in older patients.
Diet history: Obtain a complete
history of the patient's diet,
including the amount and type of
fluids, solid foods, and formula
GI tract symptoms:
• abdominal gaseous distention
• abdominal pain
• nausea &vomiting, Dehydration
• Chronic or recurrent diarrhea
• Poor appetite,
• failure to thrive, poor weight gain
• skin irritation in the perianal area
due to acidic stools are
characteristic of carbohydrate
• Systemic symptoms, including
weakness, fatigue, and failure to
• Protein sensitivity may be
associated with an eczematous
• folate and B-12 malabsorption
result in macrocytic anemia.
• Patients with
retinitis pigmentosa and ataxia
because of chronic fat-soluble
vitamin malabsorption and
deficiency (vitamins A and E).
Pediatric Malabsorption Syndromes
The following laboratory studies are indicated in
• Stool analysis
• liver function tests
• Total serum protein and albumin
• Celiac screening
• Imaging Studies, Barium studies
• Substance tolerance test
• Biopsy of Small-Intestinal Mucosa.
• Reducing substances indicates
that carbohydrates have not been
• Acidic stool has a pH level of less
than 5.5. This indicates
even in the absence of reducing
• Normally, stool bile acids should
not be detected.
• The level of quantitative stool fat
and the amount of fat intake
should be measured and
monitored for 3 days.
• The presence of large serum
proteins in the stool, such as a1 -
antitrypsin, indicates leakage of
serum protein and serves as a
screening test for protein-losing
• Examination of the stool for ova
and parasites may reveal the
presence of Giardia species, a
known cause of acquired
• Testing for other chronic
intestinal infections that cause
as Clostridium difficile
or Cryptosporidium species may
A CBC :
• megaloblastic anemia in patients
with folate and vitamin B-12
• Neutropenia in patients with
(associated with pancreatic
• In patients with
smears may reveal
In patients with inflammatory
bowel disease, the erythrocyte
sedimentation rate, C-reactive
protein level, or both are
Total serum protein and albumin
levels may be lower than
reference range in syndromes in
which protein is lost or is not
absorbed, particularly in:
o protein-losing enteropathy and
o pancreatic insufficiency or
o enterokinase deficiency.
With bile acid malabsorption,
levels of the low-density
lipoprotein (LDL) cholesterol may
In patients with liver or biliary
disease, the results of liver
function tests may be higher
immunoglobulin A (IgA)
antigliadin and IgA
antibodies, or especially
antibodies, are useful in
the diagnosis of gluten-
Recently, a 13C-Sucrose
breath test has been
proposed as a
use, integrated marker
of the absorptive
capacity and integrity
of the small intestine.
• Substance tolerance test
• Attempt to isolate the substance that is causing
• Resolution of diarrhea after the suspected
substance is removed from the diet and
resumption of the diarrhea when the substance
is reintroduced are specific signs that the
particular substance is not adequately absorbed.
• Challenging the patient with the suspected
malabsorbed substance once the diarrhea has
resolved provides a more sensitive test.
Carbohydrate malabsorption tolerance test
• Carbohydrate malabsorption results in bacterial
fermentation. This biochemical process releases
hydrogen gas that is absorbed into the blood and
excreted by the lungs.
• The amount of carbohydrate administered is
typically 2 g/kg, with a maximum dose of 50 g.
• An increase in the exhaled hydrogen
concentration following ingestion of an oral
carbohydrate load (>20 ppm) indicates
Biopsy of Small-Intestinal Mucosa
• primary indications
(1) evaluation of a patient either with
documented or suspected steatorrhea or with
(2) diffuse or focal abnormalities of the small
intestine defined on a small-intestinal series
Lesions seen – classified into three
2. Patchy, specific
– Crohn’s disease,
– Intestinal lymphoma.
– celiac sprue,
– Tropical sprue
– Bacterial overgrowth
• evaluation of the patient with presumed or
• small-bowel series -a useful examination to
look for anatomical abnormalities, such as
strictures and fistulas (as in Crohn's disease)
or blind loop syndrome (e.g., multiple jejunal
diverticula), and to define the extent of a
previous surgical resection
• Replacement of nutrients, electrolytes and fluid may be necessary.
• In severe deficiency, hospital admission may be required for
• Pancreatic enzymes are supplemented orally in pancreatic
• Dietary modification is important in some conditions:
– Gluten-free diet in coeliac disease.
– Lactose avoidance in lactose intolerance.
– Food allergic enteropathy need to be on an elimination diet,
avoiding offending food antigens.
• Antibiotic therapy will treat Small Bowel Bacterial overgrowth (eg,
metronidazole , rifaximin).
• cholestyramine :In children with chronic diarrhea secondary to bile
acid malabsorption, the use of cholestyramine.
• Immunosuppressive medications can be used to control
autoimmune enteropathy .
• Carbohydrate intolerance
• Initiate treatment in patients with severe
acquired carbohydrate intolerance by eliminating
all dietary carbohydrates until the diarrhea is
resolved. Then, slowly reintroduce carbohydrates.
• In infants, use a glucose polymer (Polycose)–
based formula (eg, Pregestimil).
• In patients with the most severe carbohydrate
intolerance, a casein-based formula that contains
essential amino acids and medium-chain
triglyceride (MCT) oil and no carbohydrates.
• MCT oil is used to treat patients with poor weight
gain that results from fat malabsorption.
• MCT oil does not require traditional fat
metabolism and, thus, is more easily absorbed
directly into the enterocyte and is transported
through the portal vein to the liver.
• Fat-soluble vitamin supplements are required.
• Supplements in patients with fat malabsorption
should also include linoleic and linolenic fatty
Alternative formulas (protein intolerance)
• Currently, soy formulas are not considered effective for
the prevention or treatment of nutritional allergies.
Instead, use hydrolyzed protein formulas.
• High-degree protein hydrolysate formulas are used to
treat infants with a cow's milk allergy, but these
formulas may contain residual epitopes capable of
provoking a severe allergic reaction.
• In these infants, use formulas with crystalline amino
acids (eg, Neocate, EleCare) as the protein source.
• Mucosal atrophy caused by infectious
gastroenteritis, food-sensitivity enteropathies, or
malnutrition can result in an 80% reduction of
intestinal surface area.
• Once the causative agent is removed, the repair
of the small bowel is usually rapid (4-6 days).
• Some malabsorption syndromes are transient,
whereas others simply require a change in diet.
• Bacterial overgrowth compromises intestinal
adaptation and increases the risk of liver