Cholesterol Structure and Importance

Cholesterol Structure and Biomedical Importance

• Cholesterol is a steroid and sterol.
• It's a crucial component of cell membranes, acting as a bidirectional regulator of membrane fluidity.
• At high temperatures, it stabilizes the membrane and increases its melting point.
• At low temperatures, it intercalates between phospholipids, preventing clustering and stiffening.
• Higher cholesterol concentrations increase membrane thickness and reduce permeability to small molecules.
• Cholesterol's hydroxyl group is oriented towards the aqueous phase, making this end hydrophilic.
• Cholesterol's structure comprises a cyclopentanoperhydrophenanthrene ring system.
• It has a hydroxyl group at carbon 3, a double bond between carbons 5 and 6, an eight-carbon side chain at carbon 17, and methyl groups at carbons 10 and 13.
• Total carbon atoms are 27.

Cholesterol and Diseases

• High cholesterol is a risk factor for conditions like atherosclerosis, heart disease, and myocardial infarction.
• High LDL cholesterol is considered “bad” cholesterol because it can deposit in artery walls, contributing to plaque buildup, narrowing, and potentially blood clots.
• Low HDL cholesterol is considered “good” cholesterol, involved in transporting cholesterol from organs/blood to the liver to remove it, thus preventing accumulation (cleaning blood).
• Hypercholesterolemia is a condition characterized by very high cholesterol levels in the blood.
• Diseases like atherosclerosis, diabetes mellitus, hyperlipoproteinemia, fatty liver, and lipid storage diseases are associated with abnormal lipid metabolism.
• Emerging risk factors include CRP, homocysteine, and Lp(a) protein.

Sources of Cholesterol

• Endogenous cholesterol is produced in the body (liver, 75%).
• Exogenous cholesterol comes from food (animal products, 25%).
• Cholesterol in animal products (egg yolks, meat, poultry, shellfish, milk) is absorbed, and increased intake lowers absorption, excreting about 1g daily.

Cholesterol's Functions

• Cholesterol is essential for normal cell growth and repair.
• It's a precursor for steroid hormones (estrogen, progesterone, testosterone, corticosteroids, aldosterone).
• Essential for the synthesis of vitamin D.
• Needed for absorption of fat-soluble vitamins.
• Crucial for the production of bile acids, aiding fat digestion.
• Cholesterol is needed to maintain neurotransmitter and brain function, and build brain and nerve tissue. It is needed for good sleep, learning, memory formation, and nerve cell function (Myelin).

Cholesterol-Related Compounds

• Bile acids are synthesized from cholesterol in the liver and contain 24 carbon atoms (e.g., cholic acid, chenodeoxycholic acid).
• Cholesterol is a crucial component of cell membranes, giving them structural integrity and influencing their permeability and fluidity.

Cholesterol in the Body

• Free cholesterol (about 30%) and ester form (about 70%) are present in the body.
• Blood cholesterol levels depend on both genetics and the environment.
• Cholesterol's role in membrane fluidity is important in maintaining physiological function.
• It regulates membrane fluidity by preventing the tails from crystallizing at low temperatures, and stabilizes at high temperatures, thus maintaining fluidity. Cholesterol regulates membrane fluidity by preventing crystallization .

Lipoproteins

• Lipoproteins are essential for transporting lipids in the blood.
• Types of lipoproteins include chylomicrons, VLDL, LDL, and HDL.

Today's case and Gall stones

A 45-year-old obese lady experiencing vomiting and abdominal pain, radiating to her right shoulder, worsening after dinner, with a history of hypertension and hypercholesterolemia, had multiple gallstones revealed by ultrasound.

Treatment for Atherosclerosis

• A heart-healthy diet (fruits, vegetables, whole grains, fish, lean meats, poultry, low-fat dairy, nuts, seeds, legumes)
• Brisk walking (30 minutes)
• Quit smoking
• Control weight, blood sugar, hypertension

Explore the fascinating structure and biomedical significance of cholesterol in this quiz. Learn about its role in cell membranes, how it affects membrane fluidity, and its associated health risks such as heart disease. Test your knowledge on its chemical structure and functions in the body.