Transcript IV. CARBOHYDRATES

IV. CARBOHYDRATES
A. Two Types
1. Simple Carbohydrate
a. Monosaccharides
i. Glucose-mild sweetness
blood sugar for the body
i. Fructose-intensely sweet
found in fruits and honey
iii. Galactose-hardly sweet
not found in many foods
b. Disaccharides
i. Maltose (glucose + glucose)
produced when starch breaks
down.
ii. Sucrose (glucose + fructose)
table sugar
iii. Lactose (glucose + galactose)
milk sugar
2. Complex Carbohydrate
a. Polysaccharides-chains of
monosaccharides
i. Glycogen- the human body
stores glucose as glycogen
ii. Starches- plant cells store
glucose as starches. All
starches come from plants.
Grains and legumes are the
richest food source.
iii. Fibers- structural parts of
plants derived from fruits
veg, whole grains and
legumes. The bands
cannot be broken down by
hydrolysis like starches so
fiber passes through the
body providing no calories.
There are two types of
fiber:
aa.Soluble-fiber that
dissolves in water and
is easily digested by
bacteria in the colon.
Food sources include
oats, legumes and
citrus fruits.
bb. Insoluble-fibers that do
not dissolve in water.
Found in whole grains,
and vegetables.
B. Digestion
1. Digestion occurs when the sugars and
starches are broken down into small
molecules (glucose) so the body can
absorb it and use it.
2. The initial breakdown occurs in the
mouth and the final in the sm. intestine
along with absorption.
3. The conversion to glucose takes place in
the liver.
4. Small Intestine- most carb. Digestion
occurs here.
a.Pancreatic amylase breaks down
the polysaccharides to shorter glucose chains
and maltose.
b. Disaccharides are broken down
by specific enzymes:
1. Maltase-breaks maltose into
two glucose molecules
2. Sucrase-breaks sucrose into
one glucose molecule and
one fructose molecule
3. Lactase-breaks lactose into one
glucose molecule and one
galactose molecule
5. Large Intestine – fibers attract
water which soften the stool for
passage. Bacteria ferments
some of the fibers producing
gas.
C. Carbohydrate Absorption
1. Glucose and Galactose – by way
of active transport enter the
cells lining the sm. intestine
2. Fructose – by way of facilitated
diffusion enters the cells of the
small intestine
3. Blood from the sm. intestine
circulate through the liver and
the liver cells take up fructose
and galactose and convert them
to glucose.
D. Carbohydrate Metabolism
1. The liver stores 1/3 of the body’s
total glycogen.
2. After a meal blood glucose levels
rise and liver cells link the excess
glucose molecules to form glycogen.
3. When blood glucose levels fall the
liver cells break glycogen by
hydrolysis into single molecules of
glucose and release them into the
bloodstream.
4. Muscle cells can also store glucose as
glycogen (the other 2/3), but they
take most of this supply using it for
themselves during exercise.
5. The brain maintains a small amount of
glycogen which is thought to provide
an emergency energy reserve during
times of glucose deprivation.
6. Glycogen holds water and the body can
only store enough glycogen to provide
energy for less than a day during rest
and a few hours during exercise.
7. Glucose fuels the body’s cells by being
broken down in half and then further
broken down completely to carbon
dioxide and water yielding energy
8. Glucose is the preferred energy source
for the brain, nerve cells and RBC
E. Blood Glucose Homeostasis
1. When a person eats blood glucose
rises.
2. High blood glucose stimulates
pancreas to release insulin.
3. Insulin stimulates the uptake of
glucose into cells and storage as
glycogen in the liver and muscles.
Insulin also stimulates the conversion of excess glucose into fat.
4. As the body’s cells use glucose, blood
levels decline.
5. Low blood glucose stimulates the pancreas to release glucagon into the
bloodstream.
6. Glucagon stimulates liver cells to break
down glycogen and release glucose
into the blood.
7. Blood glucose begins to rise.
***See p.114 Fig. 4-12 Illustrate***