CARBOHYDRATES
PREPARED BY MR. ABHIJIT DAS
Carbohydrates are a type of macronutrient found in
foods and beverages. They are one of the body's primary
sources of energy. Chemically, carbohydrates consist of carbon, hydrogen, and oxygen atoms.
DIGESTION OF CARBOHYDRATES
1.
Buccal Cavity (Mouth):
·
Approximately 30%
of carbohydrate digestion begins in the buccal cavity (mouth).
·
Salivary amylase,
an enzyme produced by the salivary glands, starts the breakdown of complex
carbohydrates (starches) into smaller molecules.
·
Starches are hydrolyzed into maltose, composed of two glucose molecules bonded
together.
2.
Small Intestine:
·
The majority of carbohydrate digestion
occurs in the small intestine.
·
When the partially digested food enters
the small intestine, pancreatic amylase,
secreted by the pancreas, continues the
breakdown of remaining starch (70%) molecules into maltose.
·
Maltase,
an enzyme secreted by the glands of the small intestine (Crypts of Lieberkühn), specifically breaks down
maltose into two molecules of glucose.
ABSORPTION
Carbohydrate absorption
primarily occurs in the small intestine, specifically in the jejunum and ileum,
which are the middle and end portions of the small intestine, respectively.
METABOLISM OF CARBOHYDRATES
GLYCOLYSIS
Glycolysis is the
metabolic pathway that breaks down glucose
into pyruvate, generating ATP and NADH in the process. It consists of ten enzymatic
reactions, taking place in the cytoplasm of
cells, and is the first step in cellular respiration, which ultimately
produces energy for the cell.
Pyruvate
is converted to acetyl CoA before entering the Krebs cycle.
The conversion of pyruvate to acetyl CoA takes place in the mitochondrial matrix, specifically in the pyruvate
dehydrogenase complex. This complex catalyze the conversion of pyruvate to acetyl
CoA and also produce NADH as a byproduct.
KREBS CYCLE/TCA
CYCLE/CITRIC ACID CYCLE
The cycle involves a
series of enzyme-catalyzed reactions that convert acetyl CoA to carbon dioxide,
generating ATP, NADH, and FADH2 in the process.
These energy-rich molecules then participate in oxidative phosphorylation to
produce ATP through the electron transport chain.
REGULATION OF BLOOD GLUCOSE
Blood glucose levels
are tightly regulated by a complex interplay of hormones, including incretins,
amylin, insulin, glucagon, epinephrine, and cortisol.
INCRETINS
Incretins, such as
GLP-1 (glucagon-like peptide-1) and GIP (gastric inhibitory polypeptide), are
hormones released from the gut in response to food intake. They stimulate insulin release from the pancreas, inhibit glucagon release, and slow down the rate at which the stomach empties its
contents into the small intestine. Incretins also activate the satiety center in the hypothalamus to
decrease appetite and food intake.
AMYLIN
Amylin is a hormone
co-secreted with insulin by beta cells in the pancreas. It slows down the rate at which food empties from the stomach,
which helps to regulate blood glucose levels by reducing the amount of glucose
entering the bloodstream after a meal. Amylin also promotes
satiety and reduces food intake. Additionally, it helps to regulate
blood glucose levels by inhibiting the secretion of
glucagon from the pancreas and promoting insulin release.
INSULIN
In the liver, Insulin
stimulates the conversion of glucose into glycogen,
a process called glycogenesis, thereby promoting the storage of glucose in the
liver.
In muscle
cells,
insulin promotes the uptake of glucose.
Insulin triggers the
translocation of GLUT4 from intracellular compartments to the plasma membrane,
allowing glucose to enter the cell and be used for energy or stored as
glycogen.
GLUCAGON
Glucagon is a hormone
secreted by the alpha cells of the pancreas,
and it plays a crucial role in raising blood glucose levels in the body. It acts in opposition to insulin, which lowers
blood glucose levels.
When blood glucose
levels are low, glucagon is released to stimulate the liver to convert stored glycogen into glucose and release
it into the bloodstream, a process known as glycogenolysis.
Glucagon also promotes the production of glucose from non-carbohydrate
sources, such as amino acids and fatty acids, a process called gluconeogenesis.
EPINEPHRIN
Epinephrine, also known as adrenaline, is a hormone produced by
the adrenal glands.
In the liver, epinephrine stimulates the breakdown of glycogen into glucose, a process known as
glycogenolysis. This glucose is then released into the bloodstream,
raising blood glucose levels. Epinephrine also
stimulates the production of glucose from non-carbohydrate sources, such as
amino acids and fatty acids, a process known as gluconeogenesis.
In muscle tissue, epinephrine promotes the breakdown of glycogen into glucose, which is then used by
the muscles for energy. At the same time, epinephrine reduces glucose
uptake by peripheral tissues such as adipose tissue, helping to ensure that
glucose is available to the muscles where it is needed most.
CORTISOL
Cortisol is a hormone
produced by the adrenal glands in response to stress.
One of its primary functions is to increase blood glucose levels in the body,
particularly during periods of stress or fasting.
Cortisol acts on
several organs and tissues to promote the breakdown
of glycogen into glucose, increase gluconeogenesis, and decrease glucose
uptake by peripheral tissues.
In the liver, cortisol stimulates the breakdown of glycogen into glucose, a process
known as glycogenolysis. This glucose is then released into the bloodstream,
raising blood glucose levels. Cortisol also
stimulates the production of glucose from non-carbohydrate sources, such as
amino acids and fatty acids, a process known as gluconeogenesis.
Cortisol also reduces glucose uptake by peripheral tissues such as
muscle and adipose tissue, which allows glucose to be available for
other vital organs such as the brain, heart, and liver.
DIABETES MELLITUS
Diabetes mellitus, commonly referred to as diabetes,
is a chronic metabolic disorder characterized by high blood glucose levels
(hyperglycemia) resulting from the body's inability to produce enough insulin
or use it effectively. Insulin is a hormone produced by beta cells of pancreas
that regulates blood sugar levels by helping glucose enter cells to be used for
energy.
NORMAL PHYSIOLOGY
Here's a brief overview of the normal physiology in
the body when you eat carbohydrates:
1.
Carbohydrate intake: When you eat
carbohydrates, they are broken down into glucose (a type of sugar) in the
digestive system.
2.
Glucose absorption into the blood: The
glucose is then absorbed into the bloodstream and transported to various organs
and tissues in the body.
3.
Glucose goes to pancreas: Some of the
glucose also goes to the pancreas, an organ located behind the stomach, which
plays a crucial role in regulating blood sugar levels.
4.
Beta cells of pancreas release insulin:
In response to the increase in blood glucose levels, specialized cells in the
pancreas called beta cells release insulin into the bloodstream.
5.
Insulin reduces blood glucose level:
Insulin helps the body's cells to absorb glucose from the blood, which reduces
the concentration of glucose in the bloodstream. This process is important for
maintaining normal blood sugar levels and providing energy to the body's cells.
6.
Glycogen storage: Any excess glucose
that is not immediately used for energy is converted into glycogen and stored
in the liver and muscles for future use.
7.
Blood sugar regulation: Overall, the
release of insulin helps to regulate blood sugar levels and prevent
hyperglycemia (high blood sugar levels) or hypoglycemia (low blood sugar
levels).
TYPES OF DIABETES MELLITUS
TYPE I
In type 1 diabetes, the immune system mistakenly
attacks and destroys the insulin-producing beta cells in the pancreas, leading
to:
- Little
or no insulin production
- Elevated
blood glucose levels
- Cells
cannot take up glucose for energy
- Increased
hunger and thirst
- Frequent
urination
- Weight
loss despite increased appetite
- Fatigue
and weakness
- Blurred
vision
- Increased
risk of diabetic ketoacidosis (DKA) if left untreated.
TYPE II DIABETES
In type 2 diabetes, the body becomes resistant to
insulin and/or the pancreas fails to produce enough insulin to meet the body's
needs. The insulin receptor on cells may also become damaged, leading to
further insulin resistance and impaired glucose uptake by cells.
1.
Insulin resistance: Cells become less
responsive to insulin, leading to elevated blood glucose levels.
2.
Impaired insulin secretion: The pancreas
may not produce enough insulin to overcome insulin resistance, exacerbating
high blood glucose levels.
3.
Abnormal glucose production: The liver
may produce too much glucose, further contributing to elevated blood glucose
levels.
4.
Hormonal imbalances: Hormones involved
in glucose regulation, such as glucagon, amylin, and incretins, may be
disrupted in type 2 diabetes.
5.
Beta cell dysfunction: Over time, beta
cells in the pancreas may become damaged or exhausted, further reducing insulin
production.
TREATMENT OPTIONS
Treatment options for diabetes may include:
- Lifestyle
modifications such as healthy eating, physical activity, and weight loss
- Medications
such as metformin, sulfonylureas, and insulin
- Regular
monitoring of blood glucose levels
- Managing
other health conditions that can affect diabetes, such as high blood
pressure and high cholesterol
- Diabetes
education and support from healthcare professionals and support groups
LIFE THREATENING CONDITIONS IN DIABETES
DIABETIC KETOACIDOSIS
Diabetic ketoacidosis (DKA) is a serious
complication of uncontrolled diabetes, typically seen in people with type 1
diabetes, but it can also occur in people with type 2 diabetes.
In DKA, the body's insulin deficiency leads to a
state of starvation, causing the body to break down fats for energy. This
process produces acidic byproducts called ketones, which can accumulate in the
blood and lead to a life-threatening condition known as ketoacidosis.
The buildup of ketones can cause the blood to become
acidic, leading to symptoms such as nausea, vomiting, abdominal pain,
confusion, and eventually coma. DKA can also cause dehydration, electrolyte
imbalances, and damage to various organs, such as the brain, kidneys, and
heart.
OSMOLAR HYPERGLYCEMIC NONKETOTIC
SYNDROME
Osmolar Hyperglycemic Nonketotic Syndrome (OHNS) is
a rare but serious complication of diabetes that occurs most commonly in older
adults with type 2 diabetes. It is characterized by very high blood glucose
levels and a high concentration of osmotically active particles in the blood,
leading to dehydration and electrolyte imbalances.
Symptoms of OHNS may include extreme thirst, dry
mouth, confusion, seizures, and coma. Treatment typically involves
hospitalization and aggressive rehydration with fluids and electrolytes, along
with insulin therapy to bring down blood glucose levels.
OHNS is a medical emergency and requires prompt
diagnosis and treatment to prevent potentially life-threatening complications.
HYPOGLYCEMIA
Hypoglycemia is a medical condition characterized by an abnormally low level of glucose (sugar) in the bloodstream. This
typically occurs when blood sugar levels drop below normal levels, leading to
symptoms such as dizziness, confusion, weakness, and in severe cases, loss of
consciousness.
CAUSES OF HYPOGLYCEMIA
1.
Excessive insulin or certain diabetes
medications: Taking too much insulin or certain medications used to manage
diabetes can lower blood sugar levels excessively.
2.
Delayed or missed meals: Not eating on
time or skipping meals can lead to drops in blood sugar levels, especially in
individuals with diabetes or those prone to reactive hypoglycemia.
3.
Intense physical activity: Intense or
prolonged exercise can deplete glycogen stores and lower blood sugar levels.
4.
Certain medical conditions: Conditions
such as insulinoma (a tumor of the pancreas producing excess insulin), liver
disease, kidney disorders, and certain hormonal deficiencies can cause
hypoglycemia.
5.
Medications: Besides diabetes
medications, certain other medications like quinine, salicylates, and some
antibiotics can induce hypoglycemia as a side effect.
6.
Rare enzyme deficiencies: Rare genetic
disorders affecting enzymes involved in glucose metabolism can lead to
hypoglycemia, such as glycogen storage diseases.
7.
Bariatric surgery: Certain weight loss
surgeries, like gastric bypass surgery, can affect nutrient absorption and insulin
regulation, leading to hypoglycemia.
8.
Critical illness: Severe illness,
trauma, or sepsis can disrupt the body's normal metabolic processes and lead to
hypoglycemia.