LIPIDS
PREPARED BY MR. ABHIJIT DAS
Lipids are organic compounds that are hydrophobic, meaning they are insoluble in water.
They consist mainly of fatty acids and alcohols.
Lipids can be classified
into three main categories based on
their structure and composition: simple lipids, compound lipids, and derived
lipids.
1.
Simple Lipids:
·
These are the basic forms of lipids and
include triglycerides (fats and oils).
·
Triglycerides consist of three fatty acid molecules bonded to a glycerol molecule.
2.
Compound Lipids:
·
Compound lipids are lipids that contain other elements in addition to fatty acids
and glycerol.
·
Examples include phospholipids and glycolipids.
3.
Derived Lipids:
·
Derived lipids are formed from simple
and compound lipids through chemical or enzymatic processes.
·
Examples include steroids, like
cholesterol, and some vitamins.
FATTY ACIDS:
Fatty acids are long-chain hydrocarbon
molecules with a carboxylic acid group at
one end.
CLASSIFICATION:
Saturated fatty
acids have only single bonds between carbon atoms, making them solid at room
temperature.
Unsaturated fatty
acids have one or more double bonds, making them liquid at room temperature.
Unsaturated fatty acids can be further classified
into monounsaturated and polyunsaturated fatty acids. They are usually liquid
at room temperature.
Polyunsaturated fatty acids (PUFA) have two or more
double bonds in their hydrocarbon chain, while monounsaturated fatty acids
(MUFA) have a only one double bond.
Cis fatty acids have hydrogen atoms on the same side of the double bond,
creating a bent shape.
Trans fatty acids
have hydrogen atoms on opposite sides of the double bond, resulting in a
straighter shape.
Essential fatty acids:
Essential fatty acids are fats that our bodies cannot produce on their own.
An
example of an essential fatty acid is omega-3 fatty acid.
DIGESTION OF LIPIDS:
1.
Stomach:
·
Gastric Lipase
begins the process by breaking down some triglycerides into diglycerides.
2.
Small Intestine (with Pancreatic
Juice):
·
Pancreatic Lipase
further breaks down triglycerides into diglycerides.
·
Some diglycerides are then broken down
into monoglycerides.
3.
Small Intestine (with Lipase from
Small Intestine):
·
Lipase from the Small Intestine
breaks down monoglycerides into glycerol and fatty acids.
ABSORPTION OF LIPIDS:
1.
Absorption into Intestinal Cells:
·
Fatty acids, monoglycerides, and other
breakdown products are taken up by the intestinal cells (enterocytes).
2.
Formation of Chylomicrons:
·
Inside the intestinal cells, these
lipids are reassembled into triglycerides and packaged with proteins to form
chylomicrons.
3.
Transport into Lymphatic System:
·
Chylomicrons are released from the
intestinal cells into the lymphatic system because they are too large to enter
the blood directly.
4.
Delivery to Bloodstream:
·
Chylomicrons travel through the
lymphatic system and eventually enter the bloodstream, where they deliver
lipids to various tissues in the body.
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METABOLISM OF LIPIDS:
LIPOLYSIS:
Ø Lipolysis
is the metabolic process through which triglycerides are broken down into fatty
acids and glycerol.
Ø Fatty
Acid Utilization for ATP Production: Fatty acids undergo
beta-oxidation within cells to generate acetyl-CoA, which enters the citric
acid cycle (Krebs cycle) and eventually leads to the production of ATP.
Ø Glycerol
Conversion to Glucose: Glycerol, the other product of
lipolysis, can be converted into glucose through a process known as gluconeogenesis.
BETA OXIDATION OF FATTY ACID (PALMITIC
ACID):
1.
Activation:
Palmitic acid first undergoes activation in the cytoplasm, where it combines
with CoA to form palmitoyl-CoA. This step requires an input of energy in the
form of ATP.
2.
Transport into the Mitochondria:
Palmitoyl-CoA is transported into the mitochondria, crossing both the outer and
inner mitochondrial membranes.
3.
Beta-Oxidation (Repeating Cycle):
·
Step 1:
The palmitoyl-CoA undergoes a reaction in which the first two carbons are
cleaved off, producing acetyl-CoA and a shortened fatty acyl-CoA chain (now 14
carbons long).
·
Step 2:
The shortened fatty acyl-CoA chain undergoes another round of beta-oxidation,
releasing another acetyl-CoA and further shortening the chain.
This process repeats until the entire fatty acid is
broken down into multiple acetyl-CoA molecules.
4.
Acetyl-CoA Enters the Citric Acid
Cycle: The acetyl-CoA produced in each round of
beta-oxidation enters the citric acid cycle, where it is further metabolized to
produce NADH, FADH2, and GTP, which contribute to the production of ATP in the
electron transport chain.
DISEASES RELATED TO ABNORMAL METABOLISM OF LIPIDS:
1. KETOACIDOSIS
Ketoacidosis is a serious metabolic condition
characterized by high levels of ketone bodies in the blood, leading to
increased acidity.
Dehydration in Ketoacidosis:
Dehydration is a common feature of ketoacidosis. The breakdown of fats for
energy during ketoacidosis produces ketones, which are acidic. The body
attempts to eliminate these ketones through increased urination, leading to
significant fluid loss and dehydration. This can be life threatening.
2. FATTY
LIVER
Definition:
Fatty liver, also known as non-alcoholic fatty liver disease (NAFLD), is a
condition characterized by the accumulation of excess fat in the liver cells.
This buildup of fat can lead to inflammation and liver damage over time.
Reasons for Fatty Liver:
1.
Obesity:
·
Excess body weight, especially visceral
fat around the abdomen, is a significant risk factor for fatty liver.
2.
Type 2 Diabetes:
·
Individuals with type 2 diabetes often
have insulin resistance, which can contribute to the accumulation of fat in the
liver.
3.
Dietary Factors:
·
Diets high in refined carbohydrates,
sugars, and saturated fats can contribute to the accumulation of fat in the
liver.
4.
Sedentary Lifestyle:
·
Lack of physical activity is associated
with obesity, insulin resistance, and an increased risk of fatty liver.
3. HYPERCHOLESTEROLEMIA
Hypercholesterolemia
is a medical condition characterized by elevated levels of cholesterol in the
blood.
REASONS:
1.
Dietary Choices:
Consuming a diet high in saturated fats, commonly found in processed foods and
fried items, can elevate cholesterol levels.
2.
Lack of Exercise:
A sedentary lifestyle contributes to higher cholesterol levels. Regular
physical activity helps maintain healthy cholesterol levels.
3.
Genetics:
Inherited factors, known as familial hypercholesterolemia, can lead to elevated
cholesterol levels even in individuals with a healthy lifestyle.
COMPOUNDS FORMED FROM CHOLESTEROL:
1.
Steroid Hormones:
Cholesterol is a precursor for the synthesis of steroid hormones, including:
·
Estrogen:
Female sex hormone.
·
Testosterone:
Male sex hormone.
·
Progesterone:
Involved in the menstrual cycle and pregnancy.
·
Cortisol:
Involved in stress response and metabolism.
2.
Bile Acids:
Cholesterol is converted into bile acids in the liver. Bile acids aid in the
digestion and absorption of fats in the small intestine. Examples include
cholic acid and chenodeoxycholic acid.
3.
Vitamin D:
Cholesterol serves as a precursor for the synthesis of vitamin D in the skin
when exposed to sunlight.
KETONE BODIES:
Definition:
Ketone bodies are small, water-soluble molecules produced in the liver from
fatty acids during periods of low carbohydrate intake.
Types:
1.
Acetoacetate:
The first ketone body produced.
2.
Beta-hydroxybutyrate (BHB):
Derived from acetoacetate.
3.
Acetone:
A byproduct formed from the breakdown of acetoacetate. It's mostly exhaled or
excreted in urine.
Significance:
1.
Energy Source:
When glucose is scarce, ketone bodies provide an alternative fuel for the brain
and muscles.
2.
Brain Function:
Ketones can be beneficial for brain health and may provide energy during carb
deficiency.
LIPOPROTEINS:
Lipoproteins are complex molecules made up of both lipids (fats) and proteins. They are
produced in the liver and intestine and play a crucial role in transporting
lipids through the bloodstream to various tissues and organs in the body. This
is important because lipids are insoluble in water and
would not be able to travel in the bloodstream without the help of
lipoproteins.
TYPES
There are several types of lipoproteins, including:
1.
Chylomicrons: The largest and least
dense lipoproteins, they are formed in the intestine and transport dietary fats from the intestine to other tissues.
2.
Very Low-Density Lipoproteins (VLDL):
These are produced by the liver and transport triglycerides to other tissues.
3.
Intermediate-Density Lipoproteins (IDL):
These are intermediate products formed during the breakdown of VLDL.
4.
Low-Density Lipoproteins (LDL): Also
known as "bad" cholesterol, these are produced by the liver and carry
cholesterol to other tissues. High levels of LDL cholesterol can increase the
risk of developing cardiovascular disease.
5.
High-Density Lipoproteins (HDL): Also
known as "good" cholesterol, these lipoproteins are produced by the
liver and transport excess cholesterol from other tissues back to the liver for
processing and elimination. High levels of HDL cholesterol can help protect
against cardiovascular disease.
LIPID PROFILE:
A lipid profile test, also known as a lipid panel or
cholesterol panel, is a blood test that measures the levels of various lipids
(fats) and lipoproteins in the blood. The test typically measures total
cholesterol, LDL cholesterol (often referred to as "bad"
cholesterol), HDL cholesterol (often referred to as "good"
cholesterol), and triglycerides.
The recommended fasting time before a lipid profile test is typically
9-12 hours, although this may vary depending on the specific laboratory
or doctor's instructions. During this time, it's important to avoid consuming
any food, beverages (including coffee and tea), or medications (unless
otherwise instructed by your doctor).
The normal values for a lipid profile test can vary
slightly depending on factors such as age, gender, and overall health status.
However, the general recommended normal ranges are:
- Total
cholesterol: Less than 200 mg/dL (milligrams per deciliter)
- LDL
cholesterol: Less than 100 mg/dL (for those at low risk of heart disease)
or less than 70 mg/dL (for those at high risk of heart disease)
- HDL
cholesterol: Greater than 40 mg/dL for men and greater than 50 mg/dL for
women
- Triglycerides:
Less than 150 mg/dL
ATHEROSCLEROSIS:
Atherosclerosis is a condition characterized by the
buildup of plaque, which is made up of cholesterol, fat, and other substances, on
the inner walls of arteries.
Over time, this buildup can narrow and harden the
arteries, restricting blood flow to vital organs and tissues.
It is a progressive disease and a leading cause of
heart attacks, strokes, and peripheral vascular disease.