CARBOHYDRATES 2021-2022 PRINT BO PARSTARY.pptx

Digestion , absorption and metabolism
of
Carbohydrate &
protein
Nursing department – first year
2021-2022
Friday, October 28, 2022 1

Digestion and absorption of
carbohydrate
Digestion of carbohydrate :
1- digestion in the mouth:
Saliva contain salivary amylase (ptyalin),
an enzyme that catalyzes hydrolysis of
starch and glycogen to dextrin( short
chain of carbohydrate) and maltose.
2- digestion in the stomach:
There is no digestion of carbohydrate in
the stomach because there is no
carbohydrate splitting enzyme in gastric
juice .

3- digestion in small intestine:
A- pancreatic juice contain pancreatic amylase which
catalyze hydrolysis of starch and glycogen to glucose
and maltose .
B- The intestinal mucosa cells contain the enzymes
(maltase , sucrase , lactase , which catalyzes hydrolysis
of maltose, sucrose, and lactose.

Absorption of carbohydrate
The principle digestion of carbohydrate
takes place in small intestine ,
monosaccharides are transported through
the walls of the small intestine directly into
the blood stream.
1- glucose ,fructose, and galactose are
absorbed into the blood stream through
the small intestine .
2- fructose and galactose go to the liver .
3- Liver change these sugars into glucose .
4- all carbohydrates 100% become glucose.

Uses of Glucose
1- energy for the cells
2- exclusive energy for brain and nerve system.
3- converted to glycogen .
4- converted into adipose tissue .
5- facilitate the metabolism of fat into energy.

Metabolism of carbohydrate
1- Glycogenesis :
Is the process of glycogen synthesis from
glucose , it takes place in the liver and
muscle , and it activated by insulin in
response to high glucose level for
example after a carbohydrate
containing meal.

Glycogenesis
Glucose glycogen +
water
glycogenolysis

In this way , the glycogen chain can be extended by
one glucose unit at a time . In each extension 2ATP
molecules are expended :
One in phosphorylation of glucose to form
glucose-6- phosphate .
 another in regeneration of UTP .

2- Glycogenolysis :
Is the breakdown of glycogen to glucose This
process occur in the liver only because the
enzyme Glucose-6- phosphate found in the
liver only but is not found in the muscles,
therefore muscle glycogen can not serve as
glucose source for blood.
This process is occur by the enzyme
glycogen phosphorylase when blood
glucose level fall (hypoglycemia) , glycogen
stored in the liver is broken down .

Glycogen + phosphate group (pi)
debranching enzyme Glycogen
phosphorylase
Glucose -1- phosphate +glycogen(n-1)
Phosphoglucomutase
Mg+2
Glucose -6- phosphate
Glucose-6-phosphatase
Glucose + phosphate group(pi)

Muscle cells in human do not possess
glucose -6-phosphate , and therefore will
not release glucose , but instead use the
glucose -6- phosphate in glycolysis.

3- Glycolysis
In the process in which glucose is broken down
into molecules of pyruvate (pyruvic acid), it
occurs in the cytoplasm of the cell and is an
anaerobic process (with out oxygen)
 Glucose+ 2NAD+ +2Pi +2ADP
2Pyruvate+ 2NADH+ 2ATP+2H+ +2H20
NAD: nicotine amide adenine dinucleotide
NADP: nicotine amide adenine dinucleotide phosphate
Are coenzymes which are necessary for many metabolic
processes. Including tissue respiration, lipid
metabolism, and glycolysis. The reduction of the
coenzymes yields NADH OR NADPH

 Glycolysis is the source of ATP for
tissues that lack mitochondria as RBCs ,
lens, or tissues with few mitochondria as
kidney medulla ,testis ,leukocytes.
 Glycolysis for tissues that has
mitochondria is considered as a
preparatory step for complex oxidation via
citric acid cycle.
Aerobic respiration :
A chemical process in which oxygen is
used to make energy (ATP) from glucose
.

1- Glycolysis .
2- Formation of acetyl coenzyme A.
3- Citric acid cycle (Krebs cycle).
4- Electron transport chain .

1- Glycolysis: the first step of aerobic
respiration. This step takes place within the
cytosol of the cell and is actually anaerobic,
glucose is separated into two ATP and two
NADH molecules, which will be used later in
the process of aerobic respiration.
2- formation of Acetyl Coenzyme A:
(Coenzyme :an organic molecule, usually containing
phosphorus and some vitamins, sometimes separable
from the enzyme protein; a coenzyme and an
apoenzyme must unite in order to function (as a
holoenzyme).
coenzyme A : a coenzyme essential for carbohydrate
and fat metabolism; among its constituents are
pantothenic acid and a terminal SH group, which forms
linkages with various acids, e.g., acetic acid (acetyl
CoA) and fatty acids (acyl CoA); abbreviated CoA.)

Pyruvate is transported inside
mitochondria and oxidized to a compound
called Acetyl coenzyme A (abbreviated to
“acetyl CoA” )
This is an oxidation reaction and uses
NAD as an electron acceptor .
3- Citric acid cycle (Krebs cycle):
A series of enzymatic reactions in
mitochondria involving oxidative
metabolism of acetyl compounds to
produce high energy phosphate
compounds that are the source of cellular
energy. Friday, October 28, 2022 17

4- Electron Transport chain:
The final step in aerobic respiration the NADH and
FADH donate their electrons to make large amounts of
ATP . One molecule of glucose creates a total of 34
ATP molecules.
The krebs cycle occurs in the mitochondria and
generate a chemical energy (ATP , NADH, and FADH2
) from oxidation of pyruvic acid.
Net energy production from aerobic respiration :
Glycolysis : 2 ATP
Krebs cycle : 2 ATP
Electron transport chain: 34 ATP
38 ATP
1 NADH = 3 ATP , 10*3 = 30 ATP
1 FADH2 = 2 ATP , 2*2 = 4 ATP

4-Pentose –phosphate pathway
Hexose monophosphate
pathway
A biochemical pathway which provides
an alternative system to glycolysis.
This reaction is important because it:
1- provide the five- Carbone sugar(
ribose, deoxyribose) needed for the
synthesis of nucleic acids and
nucleotides.
2- produce NADPH (the reduced form
of nicotinamide adenine dinucletide
phosphate NADP+ a coenzyme
necessary for the synthesis of fatty

5- Gluconeogenesis :
Is the formation of glucose from non
carbohydrate substances such as amino acids
and glycerol .
This process is takes place primarily in the liver
and in small extent in the cortex of kidneys.
Gluconeogenesis is increased by protein diets
and decreased by carbohydrate diets. During
starvation, gluconeogenesis supplies glucose
form amino acids of the tissue proteins.

Anaerobic respiration:
Is the process of producing cellular
energy without oxygen , it is occurs in
the cytoplasm
There are two common forms of
anaerobic respiration .
1- alcoholic fermentation(in
plants,fungi,bacteria)
Pyruvate+ NADH ethyl alcohol + NAD+
+CO2
2- lactate fermentation (in animals)
Pyruvate + NADH lactic acid + NAD+

Hormones that effect on blood
glucose level:
1- insulin:
Is secreted by beta cells (ß-cells) of pancreas.
It decreases blood glucose level by :
A- glycogenesis(increased formation of glycogen
from glucose) .
B- decreased glycogenolysis (formation of glucose
from glycogen) .
C- promote formation of lipids from glucose
(lipogenesis) .
D- increased transportation of glucose across cell
membranes.
E- increased oxidation of glucose in the cells.

2- Glucagon:
Is secreted by alpha cells(œ-cells) of pancreas.It
increase blood glucose level by glycogenolysis
and gluconeogenesis .

3- Epinephrine : (adrenalin )
Is secreted by adrenal medulla , it
increased blood glucose level by
glycogen breakdown (glycogenolysis)
, and by release fatty acids from
adipose tissues .
4- Thyroxine :
Is secreted by thyroid gland, it increase
blood glucose level by increasing
absorption of glucose in small
intestine and by increasing

Epinephrine

Cortisol

Adrenocorticotropic hormone

5- Growth hormone:
Is secreted by anterior pituitary gland, it
increase blood glucose level by
gluconeogenesis .
6- Hydrocortisone (cortisol) :
Is secreted by adrenal cortex and increase
blood glucose level by increasing
glycogenolysis.
7- Adrenocorticotropic hormone (ACTH):
Is secreted by anterior pituitary gland, is
increase blood glucose level by
gluconeogenesis and increases the

8- somatostatin :
Is secreted by the gamma cells(ɣ) of
pancreas ,it increase blood glucose level
by inhibition of insulin.
Blood glucose level:
Normal value :
Fasting blood sugar (FBS) : 70-105
mg/100ml.
Random blood sugar (RBS) : 80-120
mg/100ml.

Hyperglycemia :
Hyper : too much ,glycemia: glucose in the
blood. Increased blood glucose level more
than normal range.
The diseases and conditions that result in
elevated glucose level include:
1- diabetes
2- hyperthyroidism
3- hyperpituitarism
4- nephritis
5- infections
6-pregnancy

Symptoms of hyperglycemia :
1- Polyphagia ( frequently hungry )
2- Polyuria (frequently urination)
3- Polydepsia (frequently thirsty)
4- Blurred vision
5- Fatigue
6- Slow healing infections

Hypoglycemia :
Decreased blood glucose level ,less than
normal range , it is found in :
1- Hyperinsulinism .
2- Hypothyroidism .
3- Hypopituitarism .
4- Addison disease . (Addison's disease is characterized by
bronzing of the skin, anemia, weakness, and low blood pressure. is a
disorder that occurs when your body produces insufficient amounts of
certain hormones produced by your adrenal glands, your adrenal glands
produce too little cortisol and often insufficient levels of aldosterone as
well.)
5- Starvation .

Symptoms of hypoglycemia :
1- Sweating .
2- Hunger .
3- Trembling.
4- Anxiety.
5- Confusion.
6- Blurred vision. (double vision)

Diabetes mellitus :
A group of metabolic disease that lead to high
glucose level to detect in insulin secretion ,
insulin action or both.
Types of diabetes :
1- Type 1
(formerly called insulin dependent diabetes
mellitus, IDDM).
Hyperglycemia result from damage of beta
cells of pancreas (by viral infection or
genetic mutation ) and absolute insulin
deficiency.
Type 1 occurs before 30 years old of age, and
it constitutes only 5% - 10% of all diabetes .

The symptoms may occur suddenly (within
weeks or months) People with Type I
depend on insulin injection with restricted
diet to sustain life.

2- Type II
(formerly called non-insulin –dependent
diabetes mellitus, NIDDM)
Result from insulin resistant(If you have type
2 diabetes your body does not use insulin
properly. This is called insulin resistance.)
About 90% - 95% of people have type II
diabetes .
Type II affects individuals older than 40 years
.
Type II has as a slow onset ( take years for
the symptoms to appear) .
Treatment may include proper diet,
activity/exercise , and pill but sometimes
insulin is necessary .

3- Gestational diabetes :
It is a type of diabetes that occur during
pregnancy , it occurs in about 5% - 8%
of pregnancies each year, usually in the
second trimester.
During pregnancy placenta produce
various types of hormones that are
essential for baby growth , these
hormones causing the body to increase
its resistance to insulin .

Glycosuria :
Is the presence of glucose in the urine .
Glucose does not normally appear in the
urine except in amount to small to be
detected by benedicts solution.
In uncontrolled diabetes, when the blood
sugar level rises above (170-180
mg/100.ml) of blood , the sugar spills
over into the urine, the point at which the
sugar spill over into the urine is called
“Renal threshold” .

Glucose may be found in the urine
in the following cases :
1- Diabetes mellitus .
2- After a meal high in carbohydrate .
3- Pregnancy .
4- Liver damage.
5- Sever muscle exercises.
6- Emotional disturbances.

Oral glucose tolerance test (OGTT)
Is a laboratory test measure the body's ability to
use glucose.
OGTT can be used to diagnosis:
1- diabetes mellitus.
2- gestational diabetes( diabetes that occur with
pregnancy) .
The test is done in a fasting case (the patient
cannot eat or drink anything except water for 12
hours ) .
The patient is given a standard glucose solution
and the test is done again 30 minutes, 1 hours ,
2 hours, and 3 hours after drinking glucose
solution . Friday, October 28, 2022 45

In non diabetic:
The blood glucose level rise , but then fail
quickly back to normal ( because insulin is
produced in response to the glucose and
insulin has a normal effect of lowering
blood glucose level.
In a diabetic :
Glucose level rise higher than normal after
drinking the glucose solution and come
down to normal levels much slower (insulin
is either not produce , or it is produced but
the cells of the body do not response to it .

Distinguish between Diabetes mellitus
and Diabetes insipidus:

Digestion and Absorption of
Protein
Stomach acid and enzymes
facilitate the digestion of protein.
It is first denatured, then broken
down to polypeptides. The small
intestine continues to break
down protein into smaller
peptides and amino acids so it
can be absorbed.

A-Protein Digestion
1. In the Stomach:
a. Protein is denatured by
hydrochloric acid.
b. Pepsinogen (a proenzyme) is
converted into its active form
pepsin in the presence of
hydrochloric acid.
c. Pepsin cleaves proteins into
smaller polypeptides.

2. In the Small Intestine:
a. Proteases hydrolyze protein into
short peptide chains called oligo
peptides, which contain four to
nine amino acids.
b. Peptidases split proteins into
amino acids.

B. Protein Absorption
1. Used by intestinal cells for
energy or synthesis of
necessary compounds
2. Transported to the liver
3. Taking enzyme
supplements or consuming
predigested proteins is
unnecessary

Amino acid metabolism
Metabolism of amino acids differs, but
3 common reactions:
◦ Transamination.
◦ Deamination.
◦ Formation of urea.

1- Transamination
Is a reaction between a –
amino acid and a-keto acid
which produce a new a-
amino acid and a new a-
keto acid .
In this way the body can
produce the amino acids it
needs.

Example of a Transaminase reaction:
1-Aspartate donates its amino group,
becoming the a-keto acid oxaloacetate.
2-a-Ketoglutarate accepts the amino
group, becoming the amino acid
glutamate.
aspartate a-ketoglutarate oxaloacetate glutamate
Aminotransferase (Transaminase)
COO
CH2
CH2
C
COO
O
COO
CH2
HC
COO
NH3
+
COO
CH2
CH2
HC
COO
NH3
+
COO
CH2
C
COO
O
+ +

In another example
alanine becomes pyruvate as the
amino group is transferred to a-
ketoglutarate.
alanine a-ketoglutarate pyruvate glutamate
Aminotransferase (Transaminase)
COO
CH2
CH2
C
COO
O
CH3
HC
COO
NH3
+
COO
CH2
CH2
HC
COO
NH3
+
CH3
C
COO
O
+ +

Transamination is catalyzed by a group of
enzymes called (transaminases)
(aminotransferases)such as :
GOT ( glutamic oxalo acetic
transaminase)
AST (aspartate transaminase)
GPT ( glutamic pyruvic transaminase)
ALT ( alanine transaminase)
Transaminases are used in the diagnosis of a
variety of disorders:
Test for S.GOT and S.GPT are used for
diagnosis of liver damage or liver disease.

Catabolism of amino acids
Degradation of an amino acid often
involves deamination by moving its
amino group to alpha-ketoglutarate,
forming glutamate. This process involves
transaminases, often the same as those
used in amination during synthesis.

2-Deamination
Is an oxidative deamination where the a-amino
group of an amino acid is removed forming
an a-keto acid and ammonia. Deamination
occurs in the liver and kidneys under the
catalysis of the enzyme amino acid oxidase.
amino acid
CH3—CH—COOH CH3—C—COOH+NH3
oxidase
NH2 O
NH2
Alanine pyruvic acid
a- amino acid a- keto acid

The a- keto acid that produce undergo
several types of reactions , it may be
Catalyzed to CO2 , H2O and energy in
Krebs cycle .
it can be converted to carbohydrate or
to fat.
It converted to a new a- amino acid by
transamination.

3-Formation of urea
Urea is waste product of protein
catabolism ,it is synthesized in the liver
from ammonia , which is produced as a
result of deamination of the amino acids .
ENZYMES
2NH3 + CO2 NH2—CO—NH2 + CO2
Urea is secreted by the kidneys .
Normally , urea in the blood form only
about 45% of the non protein nitrogen
compounds.

The importance of determination of blood
urea is as indicator of liver and kidney
functions.
Normal range : 14-40 mg/dl
Increased in blood urea more than normal
range (hyper uremia) is found in :
1- acute and chronic nephritis .
2- urinary tract disease .
3- acute myocardial infarction . (heart attack)
4- increased protein catabolism .
5- burns .

Decrease in blood urea (hypo uremia) is
found in:
1- acute liver dysfunction .
2- low protein diet .
3- drug poisoning .
4- pregnancy.

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CARBOHYDRATES 2021-2022 PRINT BO PARSTARY.pptx