Lipids Total, Lipids Role in Our Body

Lipids

Sample

1. This is done on the serum of the patient.
2. Fasting samples for 8 to 12 hours is needed.

Indication

1. Total lipid is advised to assess lipid metabolism.
2. It is helpful for the diagnosis of hyperlipidemia.

Pathophysiology

Definition:

1. The lipids are a heterogeneous group of compounds related more by their physical characteristics rather than their chemical properties.
2. The lipids have the common properties of:
   1. Relatively insoluble in water.
   2. Soluble in nonpolar solvents like ether, benzene, and alcohol.
3. Lipids are essential dietary constituents due to their importance of:
   1. Fat-soluble vitamins.
   2. High energy.
   3. Essential fatty acids are present in natural foods.
4. Lipids include fats, oils, steroids, waxes, and related compounds.
5. The major lipids are:
   1. Cholesterol.
   2. Triglycerides.
   3. Phospholipid.

Importance of the lipids:

1. Lipids serve as an efficient source of energy when stored in adipose tissue.
2. Lipids serve as a thermal insulator in the subcutaneous tissues and organs.
3. Nonpolar lipids act as an electrical insulator allowing the rapid progression of depolarization waves along myelinated nerves.
4. The fat contents of the nerve tissue are high.
5. The combination of lipids and protein as lipoproteins are important cellular constituents.
6. It is part of the cell membranes, mitochondria within the cytoplasm.
7. It is means of transporting lipids in the blood.
8. Lipids are important to understand atherosclerosis, obesity, and polyunsaturated fatty acids in the nutrients and health.

Properties of lipids:

1. Lipid is defined as soluble in the organic solvent (ether, hexane, or chloroform) and insoluble in water.
   1. These are carbon and hydrogen-containing compounds and are mostly hydrophobic.
   2. Lipids are insoluble in liquid media like plasma. Therefore these must be packaged into lipoproteins particles.
   3. Lipids have a hydrophilic exterior with the help of a phospholipids coat.
   4. The phospholipid layers have various types of apolipoproteins.
   5. In the central part of lipoproteins are cholesterol and triglycerides.
   6. Every lipoprotein contains:
      1. Cholesterol.
      2. Triglycerides.
      3. Phospholipids.
      4. Apolipoproteins

Metabolism of lipids:

1. Lipids are synthesized from dietary fat.
2. Ingested lipids are taken up by the intestinal epithelial cells and packaged into lipoproteins called a chylomicron.
3. Chylomicron is the lipoprotein that transports lipids from the intestinal epithelium to other somatic cells, particularly liver cells, where these are endocytosed via apolipoprotein E.
4. In the liver, cholesterol and triglycerides are packed into another type of lipoprotein called  Very low-density lipoprotein  (VLDL), secreted into the blood.
   1. VLDL has increased the amount of Triglycerides (TG).  VLDL is the mean for the transport of TG to the other somatic cells.
   2. Hepatocytes also produce high-density lipoproteins (HDL).
      

      Lipid metabolism

      

      Cholesterol sources

      

      Cholesterol absorption

Lipids play an important role in life :

1. These are precursors of the hormone
2. Help indigestion.
3. Provide a store of energy.
4. They provide metabolic fuels.
5. They are part of the cell membranes.
6. Make certain hormones.
7. Lipids yield fatty acid on hydrolysis.
8. Lipids can form esters.
9. Cholesterol and triglycerides are the main lipids measured in routine blood chemistry tests.
   

   Cholesterol important facts

Classification of the lipids:

Lipids are a group of substances that consists of :

1. Glycerol ester includes:
   1. Triglycerides.
   2. Diglycerides.
2. Monoglycerides.
   1. Phosphoglycerides.
3. Free fatty acids.
4. Phospholipids.
5. Sterols include:
   1. Cholesterol
   2. Steroid hormone.
   3. Bile acids.
   4. Vit.D.
6. Carotenoids.
7. Vitamins A, E, and K.

Another classification of Lipids is as follows :

1. Neutral fat consists of fatty acids (oleic, linoleic, Stearic, Arachidonic, and Palmitic acids) in triglycerides.
2. Waxes.

1. Phospholipids :
   1. Lecithin.
   2. Cephalins.
   3. Sphingomyelin.
2. Glycolipids :
   1. Cerebrosides.
   2. Gangliosides.
3. Lipoproteins.
   1. HDL
   2. HDL-Cholesterol
   3. LDL
   4. LDL-Cholesterol.
   5. VLDL
4.  Sterols:
   1. Cholesterol and esters (major biologic significance).
   2. Steroids.
   3. Bile acids.
5. Substances associated with lipids:
   1. Carotenoids.
   2. Vit. K.
   3. Vit. E.

1. Lipids may be classified as:
   1. Simple lipids.
      1. Neutral fats.
      2. Waxes.
   2. Complex Lipids.
      1. Phospholipids.
      2.  Glycolipids:
         1. Cerebrosides.
         2. Gangliosides.
   3. Lipoproteins.
2. Lipid-associated substances are :
   1. Triacylglycerols are the major component of most foods, typically making up more than 95 to 99% of the total lipids.
   2. Cholesterol and triglycerides are the main lipids measured in routine blood chemistry.
   3. Conjugated lipids are with the combination of phosphate or sugar to lipid molecules.
3. Cholesterol is the best-known steroid and its association with atherosclerosis.
   1. Cholesterol is the precursor of other important steroids like bile acids, adrenocortical hormones, sex hormones, vitamin D, cardiac glycosides, sitosterol of the plants, and some alkaloids.
   2. Cholesterol is distributed in almost all of the body cells. It is abundant in the nervous tissue.
   3. It is the main component of the lipoproteins.
   4. It is a major part of the cell membranes.
   5. It is found in animal fats but not the plant’s fats.
4. Lipids on thin layer chromatography show the following pattern.
   

   Lipids thin layer chromatography

Facts about the lipids:

1. Lipids are carried in the blood by special proteins made in the liver. The two main forms of protein-bound cholesterol are called LDL and HDL cholesterol.
   1. As these are water-insoluble, so these are carried by the proteins.
   2. Free fatty acids are the very small amount of the blood, and these are bound to a loose complex with albumin.
   3. Major lipid components in the plasma found are triglycerides, Cholesterol, and phospholipids.
   4. These are transported in the blood as lipoproteins with large molecules of proteins as apolipoproteins.
   5. The largest and least dense molecule of lipoprotein is Chylomicron, and this is followed by:
      1. Very low-density lipoprotein (VLDL).
      2. Low-density lipoproteins (LDL).
      3. Intermediate density lipoproteins (IDL).
      4. High-density lipoproteins (HDL).
         1. Most of the triglycerides of non-fasting plasma reside in the chylomicrons.
         2. While fasting plasma sample triglycerides are mostly VLDL.
         3. Most of the cholesterol is present in LDL.
         4. A small fraction of the cholesterol, 15 to 25%, is in HDL.
2. Triacylglycerols are esters of three fatty acids and a glycerol molecule.
   

   Lipid absorption

3. The terms fat, oil, and lipid are often used interchangeably.

Hyperlipidemia is the presence of elevated or abnormal levels of lipids and lipoproteins in the blood.

15. 1. The peak level of raised lipids (Hyperlipemia) occurs 3 to 6 hours after the meal.
    2. Plasma cholesterol level increases with age.
    3. In the latter half of the pregnancy, plasma cholesterol is raised about 30% of the women’s normal level.
    4. Men’s cholesterol level is higher than in women.
16. Lipids and lipoproteins are highly modifiable risk factors for cardiovascular disease.
17. One of the most clinically relevant lipid substances is cholesterol, especially atherosclerosis and cardiovascular disease.
18. Hyperlipoproteinemia is elevated levels of lipoproteins.

Functions of lipids

1. The main biological function of lipids is to store energy.
2. Lipids form structural components of the cell membrane.
3. Lipids form messenger and signaling molecules.
4. Lipids can easily be stored in the body and work as a source of energy.
   

   Lipids function

Raised level of Lipids is seen in:

1. In hypothyroidism, both free and ester-cholesterol are raised.
2. In nephrotic syndrome, β-lipoprotein is significantly raised. Total plasma lipids exceed 2 g/dL. The plasma is milky.
3. In lipoid nephrosis, the total cholesterol level is 300 to 1000 mg/dL.
4. These are raised in Ketosis, generally in untreated Diabetes mellitus. The plasma lipid level ranges from 0.7 to 2.0 g/dL.
5. In diabetes mellitus, the level reported is reached 22 g/dL.

Now to assess the total lipids, mostly Cholesterol, Triglycerides, LDL, HDL is advised.

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