Steroids and Sterols (Cholesterol) Lecture Notes PDF

# Steroids & Sterols (Cholesterol) - Structure and Biomedical Importance ## Cholesterol Structure and Function - Cholesterol is a fat-like substance found in the body. - It is essential for building cell membranes and hormones. - It is also a precursor to vitamin D. - Cholesterol is synthesized in...

# Steroids & Sterols (Cholesterol) - Structure and Biomedical Importance ## Cholesterol Structure and Function - Cholesterol is a fat-like substance found in the body. - It is essential for building cell membranes and hormones. - It is also a precursor to vitamin D. - Cholesterol is synthesized in the liver and other tissues. - Cholesterol is transported in the blood by lipoproteins. - There are two main types of lipoproteins: LDL and HDL. - LDL is considered "bad" cholesterol because high levels increase the risk of heart disease. - HDL is considered "good" cholesterol because it helps remove LDL from the body. - The image shows a cell membrane with a hydrophilic head and hydrophobic tails. - Cholesterol is located near the tails, embedded within the membrane. - Cholesterol is amphipathic, meaning it has both water-soluble and water-insoluble parts. ## Cholesterol: A Significant Molecule - Cholesterol is a key component of cell membranes. - It helps regulate membrane fluidity. - It is a precursor to steroid hormones, such as estrogen, testosterone, and cortisol. - It is a precursor to vitamin D. - It is important for the function of the nervous system and brain. ## Gallstones - Gallstones are solid formations that can develop in the gallbladder. - They can cause pain, inflammation, and other complications. - The image shows numerous gallstones inside a gallbladder. ## Angina & Myocardial Infarction - Angina is chest pain due to a lack of oxygen to the heart muscle. - Myocardial infarction, or heart attack, is when a part of the heart muscle dies from a lack of oxygen. - The image shows the heart with arteries, one of which is narrowed by a cholesterol buildup, resulting in a blood clot. ## Hypercholesterolemia - Hypercholesterolemia, high cholesterol, is a condition when there is an excess of cholesterol in the blood. - It can increase the risk of heart disease. - The image shows a man's face, highlighting xanthelasmas (yellow deposits near the eyes) and corneal arcus (a white or gray ring around the cornea). ## Atherosclerosis - Atherosclerosis is a disease in which plaque builds up inside the arteries and narrows the arteries. - The image shows an artery, which is hardening and narrowing due to plaque buildup. ## Health Consequences - High cholesterol can lead to a number of health problems, including: - Angina - Myocardial infarction (heart attack) - Stroke - Peripheral artery disease - Atherosclerosis - Gallstones ## Dietary and Lifestyle Management of Cholesterol - A heart-healthy diet includes: - Fruits - Vegetables - Whole grains - Fish - Lean meats - Low-fat dairy products - Nuts - Seeds - Legumes (dried beans and peas) - Exercise on most days of the week for at least 30 minutes. - Limit saturated and trans fats. # The Metabolism and Transport of Cholesterol ## Cholesterol Synthesis - Cholesterol is synthesized in the liver from acetyl coenzyme A (acetyl-CoA). - Acetyl-CoA is derived from the breakdown of carbohydrates and fats. - About 75% of the body's cholesterol needs are met by endogenous synthesis. ## Cholesterol Transport - Cholesterol is transported in the blood by lipoproteins. - Lipoproteins are made up of a core of lipids surrounded by a shell of protein. - The image shows the basic components of a lipoprotein. - Apoptoprotein - Phospholipid Layer - Free Cholesterol - Triacylglycerol - Cholesterol ester ## Lipoprotein Classes - There are several classes of lipoproteins, including: - Chylomicrons: Transport dietary lipids from the intestines to the liver and body tissues. - Very-low-density lipoproteins (VLDL): Transport triglycerides from the liver to the tissues. - Low-density lipoproteins (LDL): Carry cholesterol from the liver to the tissues. - High-density lipoproteins (HDL): Carry cholesterol fromtissues back to the liver for removal. ## LDL and HDL Cholesterol - LDL cholesterol is often called "bad" cholesterol because high levels can lead to the buildup of plaque in the arteries. - HDL cholesterol is often called "good" cholesterol because it helps remove LDL from the arteries and reduce the risk of heart disease. ## Cholesterol and Disease - When there are high levels of LDL cholesterol in the blood, it can accumulate in the walls of arteries, leading to: - Atherosclerosis. - Coronary heart disease. - Stroke. - Peripheral vascular disease. ## Management of High Cholesterol - High blood cholesterol can be managed through: - Lifestyle changes (diet, exercise, weight loss, smoking cessation). - Medications, such as statins. # Functions of Lipids * Functions of lipids include: - Helps in the absorption of fat-soluble vitamins. - Lipoproteins are the transporting form of lipids. - Fats serve as surfactants by reducing surface tension. - Improve taste and palatability. - Acts as electrical insulators in neurons. - Serve as a storage form of energy. - Are a structural component of cell membranes. - Precursors of many steroid hormones and vitamin D. - Act as a thermal insulator. - Protect internal organs. # Biomedical Importance of Cholesterol - Cholesterol plays several vital roles in the body: * Cell Membrane Structure - Cholesterol is a crucial component of cell membranes, contributing to their structural integrity. - It helps regulate membrane fluidity, preventing it from becoming too rigid or excessively fluid. - The hydroxyl group in cholesterol helps it interact with the hydrophilic portion of cell membranes. - It helps to maintain the cell membrane's permeability to small molecules. - The image demonstrates the location of cholesterol within a cell membrane. <start_of_image>* Precursor to Steroid Hormones - Cholesterol serves as a precursor to steroid hormones, including: - Estrogen. - Testosterone. - Cortisol. - These hormones are essential for a wide range of biological processes, such as sexual development, reproduction, and stress response. - The image depicts various steroid hormones derived from cholesterol. * Precursor to Vitamin D - Cholesterol is a precursor to vitamin D. - Vitamin D is produced in the skin when exposed to sunlight. - Vitamin D is essential for calcium absorption and bone health. - The image illustrates the process of vitamin D synthesis from cholesterol. * Nervous System Function - Cholesterol is essential for maintaining neurotransmitter function and building brain and nerve tissue. - Myelin is a fatty substance that surrounds nerve cells, allowing for rapid transmission of nerve impulses. - Myelin is composed of 70-80% cholesterol. - Cholesterol is a key factor in the formation of synapses, the junctions between nerve cells where communication occurs. - Good sleep can enhance learning ability and memory formation, as it increases cholesterol synthesis during sleep. ## Cholesterol Degradation - Cholesterol can be degraded into: - Bile acids - Steroid hormones - Vitamin D - The image shows a diagram of cholesterol degradation and its metabolic pathways. ## Cholesterol Occurrence - Cholesterol is naturally present in the body in low concentrations. - It is also obtained from various food sources, primarily animal products. * Endogenous Cholesterol - About 75% of the body's cholesterol is derived from endogenous production, primarily in the liver. - Endogenous cholesterol synthesis contributes significantly to maintaining cholesterol levels. * Exogenous Cholesterol - About 25% of the body's cholesterol is obtained from exogenous sources, mainly from dietary intake. - Animal products like egg yolks, meat, poultry, shellfish, and milk are primary sources of dietary cholesterol. - The body absorbs approximately 30% of exogenous cholesterol, while the rest is eliminated. - The image depicts the liver producing and releasing cholesterol, and its intake from dietary sources, primarily animal products. ## LDL and HDL: Good and Bad Cholesterol - **LDL (Low-Density Lipoprotein)** - Often referred to as "bad" cholesterol. - It carries cholesterol from the liver to various tissues throughout the body. - When LDL levels are elevated, it can accumulate in arteries, leading to plaque buildup and atherosclerosis. - The image highlights the structure of LDL. - **HDL (High-Density Lipoprotein):** - Often referred to as "good" cholesterol. - It carries cholesterol from the tissues back to the liver for elimination. - Elevated HDL levels are associated with reduced risk of heart disease. - The image depicts the structure of HDL. ## Desirable Blood Cholesterol Levels: - The optimal blood cholesterol levels for adults are as follows: - Total Cholesterol: Less than 200 mg/dL - LDL Cholesterol: Less than 100 mg/dL - HDL Cholesterol: 40 mg/dL or higher - Triglycerides: Less than 150 mg/dL - These recommended levels are crucial for maintaining healthy blood cholesterol and reducing the risk of heart disease. ## Hypercholesterolemia - Hypercholesterolemia is a condition where there are very high levels of cholesterol in the blood. - It is a significant risk factor for developing heart disease. # Clinical Importance of Lipids - Lipids and their metabolism are involved in a variety of clinical conditions. - Several diseases are associated with abnormal lipid chemistry or metabolism. * Common Lipid Disorders: - Hypercholesterolemia: Elevated cholesterol levels. - Hypertriglyceridemia: Elevated triglyceride levels. - Hyperlipoproteinemia: Abnormal levels of lipoproteins in the blood. - Ketosis: Increased ketone bodies in the blood. - CVD (Cardiovascular Disease): A broad category of heart and blood vessel diseases, often linked to high cholesterol. - Fatty Liver: Accumulation of fat in the liver. - Obesity: Excess body fat. - Cancer: Though not directly linked to lipids, certain cancers may involve altered lipid metabolism. * Uncommon Lipid Disorders: - Metabolic disorders of cerebrosides: Disorders affecting the metabolism of cerebrosides, which are lipids found in the brain. - Lipidoses / lipid storage diseases: Accumulation of specific lipids in the tissues, leading to various clinical manifestations. - Multiple sclerosis: An autoimmune disease involving the nervous system, possibly influenced by altered lipid metabolism. - Infant respiratory distress syndrome: Respiratory problems in newborns, sometimes linked to lipid deficiencies. - Xanthomatosis: Deposits of cholesterol-rich material in the skin. - Retinitis pigmentosa: A retinal degenerative disease that can cause night blindness and eventual vision loss. - Phrynoderma / Toad skin: A skin condition associated with essential fatty acid deficiency. - Disorders of EFAs deficiency: Problems arising from a lack of essential fatty acids, which are necessary for various bodily functions. - Zwelleger's disease: A rare genetic disorder affecting the metabolism of lipids and other substances. # Can Cholesterol Problems be Prevented? - Yes, some heart-healthy lifestyle changes can significantly lower your risk or prevent the development of high cholesterol: - **Lose extra pounds and maintain a healthy weight.** - **Quit smoking.** - **Eat a low-fat, low-salt diet that includes many fruits, vegetables, and whole grains.** - **Exercise on most days of the week for at least 30 minutes.** - **Stop Drinking alcohol.** - **Managing blood cholesterol through dietary and lifestyle approaches is one of the most important measures to reduce the risk of heart disease.** # Risk Factors - The following factors increase the risk of high cholesterol and heart disease: - **Age:** Risk increases with age. - **Gender:** Men are more likely to develop heart disease than women, but the risk increases for women after menopause. - **Family history:** A family history of heart disease increases your risk. - **High blood pressure.** - **Type 2 diabetes.** - **Smoking.** - **Physical inactivity.** - **Excess body weight.** - **Low HDL cholesterol levels.** - **High LDL cholesterol levels.** - **C-reactive protein (CRP):** A marker of inflammation. - **Homocysteine:** An amino acid that can damage blood vessels. - **Lp(a) protein:** A type of lipoprotein that contributes to plaque buildup. - **Metabolic syndrome:** A cluster of risk factors, including high blood pressure, high blood sugar, and abdominal obesity. - **Syndrome X:** Similar to metabolic syndrome, characterized by heart metabolism issues. # Cholesterol and Heart Disease: Key Points - Cholesterol is an important molecule for cell membranes, hormones, and vitamin D production. - High levels of LDL (bad cholesterol) and low levels of HDL (good cholesterol) increase the risk of heart disease. - Atherosclerosis is a disease that develops when plaque built up inside the arteries. - Heart-healthy lifestyle changes and medications can manage and reduce the risk of high cholesterol.