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PATHOPHYSIOLOGY
OF CARBOHYDRATEMETABOLISM
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Lactase intolerance
lactase = enzyme which splits disaccharide lactose(to glucose and galactose)
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Pathomechanisms
a) Activity of lactase is decreaseddecreased hydrolysis of
disaccharidedecreased resorbtion of substrateincreasedconcentration of disaccharide in small intestine lumenincreased osmotic activity of the lumen fluiddiarrhea
b)Activity of lactase is decreasedincreased concentration ofdisaccharide in small intestine lumen increased concentrationof disaccharide in large intestinedisaccharide fermentationby bacteriaincreased concentration of lactic acid and fattyacids stimulation of intestine wall abdominal cramps,
bloating, diarrhea, acidic stools, explosive diarrhea
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Lactase deficiency syndrome
Causes of lactase deficiency:- genetic defect (primary)
- secondary to a wide variety of gastrointestinal diseases
that damage the mucosa of the small intestine (secondary)
- Milk intolerance may not become clinically apparent until
adolescence
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Causes of secondary lactase deficiency:- nontropical (celiac disease)/ tropical sprue,
- regional enteritis,
- viral and bacterial infections of the intestinal tract,- giardiasis, cystic fibrosis, ulcerative colitis
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Glycogenosis (glycogen storage disease)
Autosomal recessive disease (inborn errors of metabolism,enzymopathy)
There are defects in degradation of glycogen.
The disturbances result in storage of abnormal glycogen,or storage of abnormal amount of glycogen in variousorgans of the body
Example: Hepatorenal glycogenosis (Morbus von Gierke)
Cause: Deficit of glucose-6-phosphatase in liver and kidneyResults: Hypoglycemia in fasting individuals
There are 9 other types of glycogenosis
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Glycogen Storage
Diseases are genetic
enzyme deficiencies
associated with excessive
glycogen accumulation
within cells.Some enzymes whose
deficiency leads to
glycogen accumulation
are part of the inter-connected pathways
shown here.
glycogen
glucose-1-P
Glucose-6-Phosphatase
glucose-6-P glucose + Pi
fructose-6-P
Phosphofructokinase
fructose-1,6-bisP
Glycolysis continued
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Symptoms in addition to excess glycogen storage:
When a genetic defect affects mainly an isoform of an
enzyme expressed in liver, a common symptom is
hypoglycemia, relating to impaired mobilization of
glucose for release to the blood during fasting.
When the defect is in muscle tissue, weakness &
difficulty with exercise result from inability to
increase glucose entry into Glycolysis during exercise.
Additional symptoms depend on the particular
enzyme that is deficient.
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Glycogen Storage DiseaseSymptoms, in addition to
glycogen accumulation
Type I, liver deficiency of
Glucose-6-phosphatase (von
Gierke's disease)
hypoglycemia (low blood
glucose) when fasting, liver
enlargement.
Type IV, deficiency of
branching enzyme in variousorgans, including liver
(Andersen's disease)
liver dysfunction and early
death.
Type V, muscle deficiency of
Glycogen Phosphorylase(McArdle's disease)
muscle cramps with exercise.
Type VII, muscle deficiency of
Phosphofructokinase.
inability to exercise.
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Galactosemia
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Galactosemia
* characteristics galactosemiaaffects thebodys ability toprocessgalactose (a
sugar found indairy products)
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Activation of Galactose
O
CH2OH
HOH
H OH
H
H
OH
H
OPO3=
O
CH2OH
HH
OHOH
H
H
OH
H
O P O
O
O
P O
O
O
Uridine
O
CH2OH
HOH
HOH
H
H
OH
H
O P O
O
O
P O
O
O
Uridine
UMP
Galactose-1-P
Galactose-1-PUridylyl Transferase
UDP-Glucose
Glucose-1-P
UDP-Galactose
Glucose-6-P
Phosphoglucomutase
Glycolysis
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Mode of Inheritance
* galactosemia autosomalrecessive (a child
has to inherit onegene from eachparent that is
defective)* Galt gene is on
chromosome 9
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Symptoms of Galactosemia
* symptoms: kidneyfailure, fine and
gross motor skilldelays, poorgrowth, and mentalretardation (all as
a result of thegalactose build-up)
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Detection of Galactosemia
* galactosemia appears in approximately
1 in every 30,000 live births and can
be detected by a blood test
* galactosemia is a universal genetic
disorder everyone has equal chancesof getting it
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Prognosis
if untreated, 75% of all infants withgalactosemia may die
galactosemia is treatable
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Additional Health Problems
galactosemia isn't usually lifethreatening
the common health problems include:hypoglycemia, cataracts, learningdisabilities, poor growth, and speechdisorders
Cataract development due to galactitol(dulcitol)
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Treatment
the only way to treat galactosemia isby changing one's diet
people with galactosemia need to stayaway from all foods and drinks thathave galactose (ex: milk, cheese,legumes, which are pods like peas or
beans)
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