Cholesterol, Symptoms Of Low HDL
What is cholesterol?
Cholesterol is a normal component of blood plasma and tissues (especially bile and nerves). Cholesterol is an insoluble lipid whose molecule is composed of a sterol nucleus and does not contain any fatty acids and has one OH group that allows the emulsification of fats in water. The nucleus consists of 17 C atoms in the ring nucleus and a side chain consisting of 8 C atoms. It is the most common steroid in the body. It is present in free and bound form (esterified with fatty acids, most often with linoleic-75%). Esterification is performed by the enzyme LHAT (lecithin-cholesterol transferase).
How is cholesterol created?
It is ingested through animal foods (beef, offal, eggs) and as such is called exogenous cholesterol. On average, 500-1000 mg of exogenous cholesterol is ingested daily. It is also synthesized in the body and it is endogenous cholesterol which is mainly synthesized by the liver and intestinal mucosa. It is synthesized two to three times more than it is ingested with food.
You’ve heard of HDL and LDL (what is “good” and what is “bad” cholesterol?)
LDL cholesterol is also called “bad cholesterol” because it carries 75% of fat (50% of cholesterol) to the blood and is the main carrier of cholesterol. HDL cholesterol also called “good cholesterol”, contains 50% protein and only 20% cholesterol. LDL carries cholesterol to blood vessels, causing the formation of atheromatous plaque and the development of heart disease. In contrast, HDL removes cholesterol from blood vessels and carries it to the liver where it is excreted from the body through the bile. It means that HDL transmits “bad cholesterol from the circulation to the liver, and thus cleanses the blood of bad cholesterol and prevents the occurrence of atherosclerosis.
A person can voluntarily increase HDL cholesterol:
- by quitting smoking
- by practicing physical activity
HDL values are influenced by gender (women have more because estrogen affects its increased production) and diet.
It is believed that small amounts of alcohol affect the increase of HDL, but given the other harmful effects of alcohol, it is better to practice a healthy diet and physical activity.
What are chylomicrons?
The cholesterol pathway in the body ends with chylomicrons. These are the largest particles of lipoprotein (750-1200 Angstroms) and they transfer exogenous lipids (especially triglycerides) from the gut to other organs, bypassing the liver.
Chylomicrons contain the most triglycerides, followed by phospholipids, cholesterol, and the least protein. They go to the lymph vessels, D. thoracic, and from there into the blood. Along the way, chylomicrons release triglycerides to muscles and fat cells. Chylomicrons remain in the circulation for a short time, only a few hours after a meal (six hours). They are rapidly removed from plasma because they come into contact with lipoprotein lipase. It is an enzyme whose secretion is provided by insulin and glucose and is activated by heparin.
The absorption of cholesterol from food in the intestines is faster than the removal of cholesterol from the blood, which is why it is not recommended to eat fatty foods 6-12 hours before taking blood. Under the action of lipoprotein lipase (LP), chylomicron loses fatty acids that are released into the peripheral circulation, where they are used as an energy source and the synthesis of other lipids. The rest of the chylomicron (a chylomicron that has lost some of its lipids in its pathway) goes to the liver. In the case of lipoprotein lipase deficiency, chylomicronemia occurs. In the liver, endogenous cholesterol is synthesized from the remains of chylomicrons, ie. lipoproteins that are divided by density into HDL (High-Density Lipoprotein), LDL (Low-Density Lipoprotein), and VLDL (Very Low-Density Lipoprotein).
What about excess cholesterol?
Cholesterol particles (LDL particles) are partially removed by hepatocytes, but the main role is played by LDL receptors located on the cell surface. The LDL particle is retracted to the cell liposome, and the receptor separates and moves toward the membrane to take on new LDL particles. LDL particles after separation from the receptor continues to move deeper into the cell and Apo protein is broken down into amino acids, and cholesterol esters are hydrolyzed, releasing cholesterol that serves:
- to build the cell membrane
- is re-esterified
- stored in a cell
- leaves the cell (in hepatocytes for bile synthesis)
The amount of cholesterol that will be found in the cell is determined by the number of LDL receptors, which take place on the principle of negative feedback. An increased amount of cholesterol in the cell prevents the synthesis of LDL receptors, and a reduced amount of cholesterol in the cell is caused by the inhibition of LDL receptor production. Thus, LDL receptors are responsible for the removal of LDL cholesterol from plasma, and the number of LDL receptors is key to the regulation of plasma LDL cholesterol.
Brown and Goldstein was awarded the Nobel Prize in 1986 for the discovery of lipoprotein receptors on the membrane of liver cells that remove cholesterol from the circulation and inhibit cholesterol synthesis in the liver. They also found that if a person has fewer receptors than usual or they are less sensitive, blood cholesterol levels increase. The number of these receptors is thought to be inherited. According to the interpretation of these scientists, the level of cholesterol in the cell is regulated by three mechanisms:
- inhibits the production of enzymes (hydroxymethyl glutaryl coenzyme A reductase) to produce endogenous cholesterol
- stimulates the enzyme (acyl cholesterol acyltransferase) and thus cholesterol esters are formed
- cholesterol in the cell triggers the feet back mechanism so that the cell stops creating new receptors and thus interrupts the entry of exogenous cholesterol into the cell
Other researchers believe that the removal of cholesterol from the circulation depends on whether the receptors recognize lipoproteins, which depends on the specific protein they carry.
LDL particles are removed from the circulation
autoregulation (80%), ie. based on the three mechanisms listed above. This occurs most often in the cells of the liver, adrenal glands, gonads, ie. organs that are actively dividing and have extremely high cholesterol needs, as well as the largest number of receptors on their membranes;
Alternative route “Skavenger” route or so-called. receptor cysts. Cells that use this way of taking cholesterol are not protected from its excessive accumulation (smooth muscle cells, endothelial cells, and macrophages), which are cells that play a significant role in atherogenesis;
The danger of cholesterol buildup in cells exists in situations where there are no receptors, such as in the case of familial hypercholesterolemia or when the diet is rich in fats and cholesterol.
What affects the increase in blood cholesterol?
Factors affecting plasma cholesterol concentration:
- Excessive intake of cholesterol in daily meals
- Increased intake of saturated fatty acids in the daily meal (fatty acids are deposited in the liver and produce more acetyl-coenzyme A which is, as we said, a major factor in cholesterol
- Unsaturated fatty acids slightly reduce cholesterol concentration;
- Thyroxine deficiency increases cholesterol concentration (hypercholesterolemia in hypothyroidism);
- Estrogen decreases and androgens increase blood cholesterol levels;
Note ReadType Of Muscles And Function In The Body
Prevention of cholesterolemia
* Smoking cessation
* Adequate diet
* Physical activity
* Moderate alcohol consumption
* Reduce total energy intake
* Limit fats to 30% or less of total caloric intake (50-67 g of fat per day in a diet of 1500-2000 kCal)
* Saturated fatty acids should make up 8-10% of the total amount of fat ( 15-23 g)
* Polyunsaturated fatty acids should be ingested 10% (15-23 g)
* 15% monounsaturated fatty acids (15-33 g)
* reduce cholesterol to less than 300 mg per day
* 2.4 g of salt per day
* carbohydrates ) should be represented by 55-60% of the total energy value
* antioxidants (beta carotene, vitamins C and E)
* increase dietary fiber intake
* moderate doses of alcohol (120 g wine, 360 g beer, or 25 g whiskey)
Today it is known that if you want to lower the level of cholesterol in the blood, the reduction of cholesterol in food is less significant, while it is far more important to reduce the total caloric intake, especially the intake of saturated fatty acids (stearic and palmitic). It was previously thought that avoiding eggs, especially egg yolks (one egg 275 mg of cholesterol) can contribute to lowering total cholesterol. Since we know that cholesterol ingested with food (exogenous) is not fully utilized, as well as that long-term lack of nutrients from egg yolks leads to macular degeneration and impairs the function of vision, recommendations from one to three eggs per week are increased to 3-4 eggs.
Cholesterol in 100 g of food
Chicken liver 500 mg
Veal liver 370 mg
Egg (hard-boiled) 274 mg
Pork liver 260 mg
Sea crabs 195 mg
Pork 121 mg
Hamburger 120 mg
Cheese Gouda 114 mg
Sweet sour cream 111 mg
Cream cheese 110 mg
Cheese Cheddar 105 mg
Mayonnaise 105 mg
Beefsteak 101 mg
Virile (chicken) 100 mg
Bacon 93 mg
Chicken (drumstick) 91 mg
Chicken (white meat) 69 mg
Shellfish 67 mg
Sour cream (20%) 66 mg
Biscuits 60 mg Paste, pork 50 mg
Ice cream 44 mg
Tuna 31 mg
Milk 3.3% mm 14 mg
Yogurt 13 mg
Why do we need cholesterol?
Since cholesterol can be synthesized in the body, it is not an essential substance, but it is important because of the many functions it performs in the body:
* is an integral part of the structure of membranes in all cells of the body;
* is an essential component of bile, vitamin D, and hormones (adrenaline and steroid hormones as well as sex hormones (estrogen and testosterone );
* helps the absorption of fatty acids (esterified cholesterol-70%);
* esterified cholesterol transports fatty acids by circulation;
* protects the skin from evaporation (precipitates in the various parts of the skin);
In larger quantities, cholesterol is deposited in the nervous tissue, corpus luteum, and adrenal cortex. It is also found in blood and bile. It was first isolated from gallstones, hence its name.
What happens to cholesterol in our body?
Ingested with food, it is absorbed through the intestinal mucosa (ileum), and then through the lymphatic system, cholesterol reaches the Ductus Toracicus (the largest lymph vessel) to the venous blood. Cholesterol ingested with food is usually bound to fatty acids (esterified cholesterol) and fatty acids must be removed before absorption by enzymes in the small intestine. Not all cholesterol is ingested with food. This varies from person to person and ranges from 25-75% (55% average). It is emulsified in the small intestine under the action of bile salts on micelles. The same happens with triglycerides (glycerol and fatty acids). Triglycerides and cholesterol esters are not soluble in water, they bind to phospholipids and proteins and form lipoproteins (which are soluble in water). They are synthesized not only in the cells of the intestine but also in the liver. Lipoproteins differ in how much they contain triglycerides, cholesterol, phospholipids, and protein, as well as by type of protein.