2. Digestion of carbohydrates:
Carbohydrates are broken down into smaller
polysaccharides in the mouth by the action of salivary
amylase. Once in the small intestine, pancreatic amylase
further breaks the polysaccharide into disaccharides. The
three most common disaccharides are maltose, sucrose and
lactose. These disaccharide are broken down into
monosaccharide by the digestive enzymes found at the
brush border of the enterocytes.
3. Maltose is obtain via the digestion of starch by
amylase. It consists of two glucose monomers
attached via α-1-4 glycosidic bond, which is broken
down by the brush border enzyme called maltase.
Sucrose consists of glucose and fructose and is
broken down by sucrase while lactose consists of
glucose & galactose and is broken down by lactase.
4. Absorption of carbohydrates:
The principal monosaccharide's produced by the digestion
of carbohydrates are glucose, fructose and galactose
Glucose accounts for 80% of the total monosaccharide
The absorption occurs mostly in the duodenum & upper
jejunum of small intestine
Only monosaccharaides are absorbed by the intestine
5. Absorption Rates:
Cori study:
He studies the rate of absorption of different sugars from small
intestine in rate
Galactose:
absorption rate for galactose is maximum
Glucose:
absorption rate for glucose is moderate
Fructose:
absorption rate for fructose is minimum
6. Comparison:
Glucose absorption as 100, comparative absorption of other
sugars as
Galactose =110, glucose=100, fructose=43,
mannose=19, xylose=15
Galactose is absorbed more rapidly than glucose
Pentose are absorbed slowly
7. Mechanism of absorption
Different sugars posses different mechanisms for
their absorption
Examples:
Glucose is transported into the intestinal mucosal
cells by a carrier mediated and energy requiring
process
8. Active transport mechanism
Glucose and sodium share the same transport system
referred to as sodium dependent glucose transporter
The concentration of sodium is higher in the intestinal
lumen compared to mucosal cells
Sodium moves into the cells along its concentration
gradient & simultaneously glucose is transported into the
intestinal cells
Mediated by same carrier system
9. Sodium diffuses into the cell and it drags glucose along with it
The intestinal sodium gradient is the immediate energy source for
glucose transport
This energy is indirectly supplied by ATP
Since the re-entry of sodium (against the concentration gradient)
into the intestinal lumen is an energy requiring active process
The enzyme sodium potassium ATPase is involved in the
transport of sodium in exchange of potassium against the
concentration gradient
10. Intestinal absorption of glucose
At the intestinal lumen, absorption is by SGluT and at the
blood vessel sides absorption is by GLuT2
13. Absorption of Fructose:
Fructose absorption is simple
Does not require energy and Na+ ions
Transported by facilitated diffusion mediated by a carrier
Inside the epithelial cell, most of the fructose is converted
to glucose
The latter then enters the circulation
15. Factors effecting:
Mucus membrane:
Mucus membrane is not healthy, absorption will decrease
Thyroid hormones:
Increases absorption of hexoses & act on intestinal mucosa
Adrenal cortex:
Absorption decreases in adrenocortical deficiency, mainly due to
decreased concentration of sodium
Anterior pituitary:
It affects mainly through thyroid hormones
