Medical Lecture Notes

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Tuesday, 9 January 2018



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  • The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, that are related more by their physical than by their chemical properties.
  • Lipids have the common property of being:
  1. relatively insoluble in water .
  2. soluble in non polar solvent such as either and chloroform . 
  • Lipids are important dietary constituents because:
  1. high energy value .
  2.  fat soluble vitamin (  A,D,E,K ) .
  3.  essential fatty acids .

Functions of lipids :

  • Fat is stored in adipose tissue, where it also serves as a thermal insulator in the subcutaneous tissues and around a certain organ.
  • nonpolar lipids act as electrical insulators ( myelinated nerve).
  • lipoprotein serve as a mean transporting lipids in the blood.
Biomedical Problems that are associated with lipids :
  • diabetes mellitus 
  • obesity
  • atherosclerosis . 

Lipids are classified as simple or complex :

  • Simple lipids
  • Complex lipids
  • Precursor and derived lipids

1. Simple lipids: 

  • Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state.
  • Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols.

2. Complex lipids: 

  • Esters of fatty acids containing groups in addition to alcohol and a fatty acid.
  • Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue. They frequently have nitrogen-containing bases and other substituents, eg, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine.
  • Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate.
  • Other complex lipids: Lipids such as sulfolipids and aminolipids. Lipoproteins may also be placed in this category.

3. Precursor and derived lipids: 

  • These include fatty acids, glycerol, steroids, other alcohols, fatty aldehydes, ketone bodies, hydrocarbons, lipid-soluble vitamins, and hormones.

Fatty acids:

  • these are aliphatic carboxylic acids
  • occur mainly as esters in natural fats and oils but do occur in the unesterified form as free fatty acids, a transport form found in the plasma.
  • that occur in natural fats are usually straight-chain derivatives containing an even number of carbon atoms.
  • The carbon atoms adjacent to the carboxyl carbon (Nos. 2, 3, and 4) are also known as the α, β, and γ carbons, respectively, and the terminal methyl carbon is known as the ω or n-carbon.
  • Saturated acids end in –anoic (no double bond)
  • Unsaturated acids with double bonds end in -enoic.

Unsaturated Fatty Acids Contain One or More Double Bonds

  1. Monounsaturated (monoterpenoid, monoenoic) acids, containing one double bond.
  2. Polyunsaturated (polyenoic) acids, containing two or more double bonds.
  3. Eicosanoids: These compounds, derived from eicosa (20-carbon) polyenoic fatty acids, comprise the prostanoids, leukotrienes (LTs), and lipoxins (LXs). Prostanoids include prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (TXs).
  • Most naturally occurring unsaturated fatty acids have cis double bonds
  • Double bonds in naturally occurring unsaturated longchain fatty acids are nearly all in the cis configuration.

  • Trans fatty acids are present in certain foods, arising as a by-product of the saturation of fatty acids during hydrogenation, or "hardening," of natural oils in the manufacture of margarine ( increased risk of diseases including cardio-vascular disease and diabetes mellitus).

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