Blood Lipids Notes (BCM 225)

**BCM 225 NOTE** **Blood lipids** Blood lipids, also known as blood fats, are lipids present in the bloodstream, either in a free state or bound to other molecules. They are primarily transported within a phospholipid capsule, and the type of protein in this outer shell determines the particle\'s...

**BCM 225 NOTE** **Blood lipids** Blood lipids, also known as blood fats, are lipids present in the bloodstream, either in a free state or bound to other molecules. They are primarily transported within a phospholipid capsule, and the type of protein in this outer shell determines the particle\'s fate and its impact on metabolism. Cholesterol and triglycerides are examples of these lipids. The concentration of blood lipids is influenced by their intake and excretion from the intestine, as well as their uptake and secretion from cells. Hyperlipidemia, characterized by elevated or abnormal levels of lipids and/or lipoproteins in the blood, is a significant risk factor for cardiovascular disease. **Types of Blood Lipids** **Cholesterol** is a waxy substance produced by the body and found in animal products. It plays several roles in the body and is a crucial component of cells. The term \"cholesterol\" actually refers to two types: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Lipoproteins transport cholesterol through the bloodstream. LDL is considered harmful (think \"L\" for lousy) because it can lead to cholesterol build-up in the arteries, forming plaques. HDL is beneficial (think \"H\" for healthy) as it helps the body eliminate cholesterol. **Triglycerides** are another type of fat produced by the body and found in food. High triglyceride levels are mainly due to lifestyle choices such as poor diet, smoking, alcohol consumption, and lack of exercise, though genetics can also play a role. **Problems from Hyperlipidemia** High cholesterol can cause plaque build-up on the walls of blood vessels, leading to blocked arteries, high blood pressure, stroke, heart disease, or heart attack. Elevated triglycerides increase the risk of metabolic syndrome, which raises the likelihood of heart disease and other conditions, including diabetes. **Lifestyle Treatments for Hyperlipidemia** To lower both cholesterol and triglycerides, it\'s recommended to eat a healthy, low-fat diet and increase physical activity, which can also help raise HDL cholesterol. To reduce LDL cholesterol, you should: - - - - - To lower triglycerides, you should: - - - - - **Medications for Hyperlipidemia** Your doctor may prescribe medication, such as statins. For most people with hyperlipidemia, the benefits of statins outweigh potential side effects. Before prescribing medication, your doctor will consider your history of heart attack or artery blockages, as well as factors like age, weight, family history, and the presence of smoking, high blood pressure, or diabetes. ### Fatty Acids **Intestinal Intake**: Short- and medium-chain fatty acids are absorbed directly into the bloodstream through intestinal capillaries and travel via the portal vein. Long-chain fatty acids, however, are too large to enter the small capillaries directly. Instead, they are coated with a membrane of phospholipids and proteins, forming large transporter particles called chylomicrons. These chylomicrons enter lymphatic capillaries and are then transported into the bloodstream at the left subclavian vein, bypassing the liver. The concentration of blood fatty acids temporarily increases after a meal. **Cell Uptake**: Post-meal, the rise in blood fatty acid levels leads to increased uptake by various cells, primarily liver cells, adipocytes, and muscle cells. This process is stimulated by insulin from the pancreas, stabilizing blood fatty acid levels after a meal. **Cell Secretion**: After a meal, some fatty acids absorbed by the liver are converted into very low-density lipoproteins (VLDL) and secreted back into the bloodstream. When a significant amount of time has passed since the last meal, the blood fatty acid concentration decreases, prompting adipocytes to release stored fatty acids into the blood as free fatty acids to supply energy to muscle cells. These secreted fatty acids are then taken up by other cells until they enter fatty acid metabolism. ### Cholesterol The fate of cholesterol in the blood is largely determined by its lipoprotein composition, with some types favoring transport to body tissues and others to the liver for excretion into the intestines. According to the 1987 report of the National Cholesterol Education Program, Adult Treatment Panels, total blood cholesterol levels should be: - - - Blood cholesterol levels typically increase with age, peaking around 60 years old. Seasonal variations also occur, with higher levels in winter, possibly linked to lower vitamin C intake. **Intestinal Intake**: During lipid digestion, cholesterol is packed into chylomicrons in the small intestine and delivered to the portal vein and lymph. These chylomicrons are eventually taken up by liver hepatocytes through interactions between apolipoprotein E and LDL receptors or lipoprotein receptor-related proteins. **In Lipoproteins**: Cholesterol, being minimally soluble in water, is transported in the bloodstream by water-soluble lipoproteins that carry cholesterol and triglycerides internally. The apolipoproteins on the lipoprotein surface determine the cells from which cholesterol will be removed and to which it will be supplied. The largest lipoproteins, chylomicrons, transport fats from the intestinal mucosa to the liver, carrying mostly triglycerides. In the liver, chylomicrons release triglycerides and some cholesterol. The liver converts unburned food metabolites into VLDL, which are secreted into plasma and converted to intermediate-density lipoproteins (IDL) and then to low-density lipoprotein (LDL) particles and non-esterified fatty acids. Most LDL particles in healthy individuals are large and buoyant (lb-LDL) and are cardiovascularly neutral. However, small and dense LDL (sd-LDL) particles are strongly associated with atheromatous disease in the arteries. Total LDL is often referred to as \"bad cholesterol,\" though only a fraction is harmful. Standard chemistry panels typically measure total triglyceride, LDL, and HDL levels in the blood. Measuring sd-LDL is expensive, but it can be inferred indirectly by estimating VLDL levels, typically done by measuring triglyceride levels after at least eight hours of fasting. **Intestinal Excretion**: After being transported to the liver by HDL, cholesterol is delivered to the intestines via bile production. However, 92-97% is reabsorbed in the intestines and recycled through enterohepatic circulation. **Cell Uptake**: Cholesterol circulates in the blood in LDL and is taken into cells by LDL receptor-mediated endocytosis in clathrin-coated pits, then hydrolyzed in lysosomes. **Cell Secretion**: In response to low blood cholesterol, various cells, mainly in the liver and intestines, synthesize cholesterol from acetyl-CoA via the enzyme HMG-CoA reductase, which is then released into the blood. ### ### ### Related Medical Conditions **Hyperlipidemia**: Hyperlipidemia is the presence of elevated or abnormal levels of lipids and/or lipoproteins in the blood. It is a highly modifiable risk factor for cardiovascular disease and can predispose individuals to acute pancreatitis. High cholesterol, particularly, is a significant factor in atherosclerosis and cardiovascular disease. **Hyperlipoproteinemia**: This condition involves elevated levels of lipoproteins. **Hypertriglyceridemia**: This condition involves elevated levels of triglycerides. **Hypercholesterolemia**: Hypercholesterolemia is the presence of high cholesterol levels in the blood. It is not a disease but a metabolic derangement that can contribute to various diseases, especially cardiovascular disease. Familial hypercholesterolemia is a rare genetic disorder affecting cholesterol metabolism. **Hypocholesterolemia**: Abnormally low cholesterol levels are referred to as hypocholesterolemia