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  1. Definition: The term lipid is defined as soluble in the organic solvent (such as ether, hexane or chloroform), and insoluble in water.
  2. These are carbon and hydrogen containing compounds and mostly hydrophobic.
  3. Lipids are synthesized from the dietary fat.

  1. Lipids play important role in life :
    1. These are precursor of the hormone
    2. Help in digestion.
    3. Provide store of energy.
    4. They provide metabolic fuels.
    5. They are part of the cell membranes.
    6. Make certain hormones.   


  1. Lipids yield fatty acid on hydrolysis.
  2. Lipids can form esters.
  3. Cholesterol and triglycerides are the main types of lipids measured in routine blood chemistry tests.

  1. Lipids are a group of substances which consists of :
    1. Glycerol ester includes:
      1. Triglycerides.
      2. Diglycerides.
      3. Monoglycerides. P
      4. Phosphoglycerides.
    2. Free fatty acids.
    3. Phospholipids.
    4. Sterols include:
      1. Cholesterol
      2. Steroid hormone.
      3. Bile acids.
      4. Vit.D.
    5. Carotenoids.
    6. Vitamins A, E, and K.
  2. Another classification of Lipids is as follows :
    1. Neutral fat consists of fatty acids (oleic, linoleic, Stearic, Arachidonic, and Palmitic acids) in the form of 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
    1. Sterols:
      1. Cholesterol and esters (major biologic significance).
      2. Steroids.
      3. Bile acids.
    2. Substances associated with lipids:
      1. Carotenoids.
      2. Vit.K.
      3. Vit. E.
  3. Simple lipids.
    1. Neutral fats.
    2. Waxes.
    3. Phospholipids.
  4. Compound Lipids.
    1. Glycolipids:
      1. Cerebrosides.
      2. Gangliosides.
    2. Lipoproteins.
  5. 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 types of lipids measured in routine blood chemistry.
    3. Conjugated lipids are with the combination of phosphate or sugar to lipid molecules.
  6. Lipids 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 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.
  7. Triacylglycerols are esters of three fatty acids and a glycerol molecule.

  1. The terms fat, oil, and lipid are often used interchangeably.
  2. Hyperlipidemia is the presence of elevated or abnormal levels of lipids and/or lipoproteins in the blood.
    1. The peak level of raise lipids (Hyperlipemia) occurs after 3 to 6 hours after the meal.
    2. Plasma cholesterol level increases with the age.
    3. In the latter half of the pregnancy, plasma cholesterol is raised about 30% of the women normal level. 
    4. Men cholesterol level is higher than the women.
  3. Lipids and lipoproteins are a highly modifiable risk factor for cardiovascular disease.
  4. One of the most clinically relevant lipid substances is cholesterol, especially for atherosclerosis and cardiovascular disease.
  5. Hyperlipoproteinemia is elevated levels of lipoproteins.

Functions of lipids

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

Raised level of Lipids is seen in:

  1. In hypothyroidism, both free and ester-cholesterol is raised.
  2. In nephrotic syndrome, β-lipoprotein are greatly raised. Total plasma lipids exceed 2 g/dL. The plasma is milky.
  3. In lipoid nephrosis, total cholesterol level is 300 to 1000 mg/dL.
  4. These are raised in Ketosis, generally in the untreated Diabetes mellitus. The plasma lipid level ranges between 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, LDLHDL is advised.

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