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PROPERTIES OF TRIACYLGTYCEROLS

1. Hydrolysis : Triacylglycerols undergo stepwise enzymatic hydrolysis to finally liberate free fatty acids and glycerol.

The process of hydrolysis, catalysed by lipases is important for digestion of fat in the gastrointestinal tract and fat mobilization from the adipose tissues.

2. Saponification : The hydrolysis of triacylglycerols by alkali to produce glycerol and soaps is known as saponification.

3.Rancidity: Rancidity is the term used to represent the deterioration of fats and oils resulting in an unpleasant taste. Fats containing unsaturated fatty acids are more susceptible to rancidity.

Hydrolytic rancidity occurs due to partial hydrolysis of triacylglycerols by bacterial enzymes.

Oxidative rancidity is due to oxidation of unsaturated fatty acids.

This results in the formation of unpleasant products such as dicarboxylic acids, aldehydes, ketones etc.

 

Antioxidants : The substances which can prevent the occurrence of oxidative rancidity are known as antioxidants.

Trace amounts of antioxidants such as tocopherols  (vitamin E), hydroquinone, gallic acid and c,-naphthol are added to the commercial preparations of fats and oils to prevent rancidity. Propylgallate, butylatedhydroxyanisole (BHA)  and butylated hydroxytoluene (BHT) are the antioxidants used in food preservation.

Lipid peroxidation in vivo: In the living cells, lipids undergo oxidation to produce peroxides and free radicals which can damage the tissue. .

The free radicals are believed to cause inflammatory diseases, ageing, cancer , atherosclerosis etc

Iodine number : lt is defined as the grams (number)  of iodine absorbed by 100 g of fat or oil. lodine number is useful to know the relative

unsaturation of fats, and is directly proportional to the content of unsaturated fatty acids

Determination of iodine number will help to know the degree of adulteration of a given oil

Saponification number : lt is defined as the mg  (number) of KOH required to hydrolyse (saponify) one gram of fat or oiL

Reichert-Meissl (RM)  number: lt is defined as the number of ml 0.1 N KOH required to completely neutralize the soluble volatile fatty acids distilled from 5 g fat. RM number is useful in testing the purity of butter since it contains a good concentration of volatile fatty acids (butyric acid, caproic acid and caprylic acid).

Acid number : lt is defined as the number of mg of KOH required to completely neutralize free fatty acids present in one gram fat or oil. In normal circumstances, refined oils should be free from any free fatty acids.

The small intestine

Digestion within the small intestine produces a mixture of disaccharides, peptides, fatty acids, and monoglycerides. The final digestion and absorption of these substances occurs in the villi, which line the inner surface of the small intestine.

This scanning electron micrograph (courtesy of Keith R. Porter) shows the villi carpeting the inner surface of the small intestine.


The crypts at the base of the villi contain stem cells that continuously divide by mitosis producing

  • more stem cells
  • cells that migrate up the surface of the villus while differentiating into
    1. columnar epithelial cells (the majority). They are responsible for digestion and absorption.
    2. goblet cells, which secrete mucus;
    3. endocrine cells, which secrete a variety of hormones;
  • Paneth cells, which secrete antimicrobial peptides that sterilize the contents of the intestine.

All of these cells replace older cells that continuously die by apoptosis.

The villi increase the surface area of the small intestine to many times what it would be if it were simply a tube with smooth walls. In addition, the apical (exposed) surface of the epithelial cells of each villus is covered with microvilli (also known as a "brush border"). Thanks largely to these, the total surface area of the intestine is almost 200 square meters, about the size of the singles area of a tennis court and some 100 times the surface area of the exterior of the body.

Incorporated in the plasma membrane of the microvilli are a number of enzymes that complete digestion:

  • aminopeptidases attack the amino terminal (N-terminal) of peptides producing amino acids.
  • disaccharidasesThese enzymes convert disaccharides into their monosaccharide subunits.
    • maltase hydrolyzes maltose into glucose.
    • sucrase hydrolyzes sucrose (common table sugar) into glucose and fructose.
    • lactase hydrolyzes lactose (milk sugar) into glucose and galactose.

Fructose simply diffuses into the villi, but both glucose and galactose are absorbed by active transport.

  • fatty acids and monoglycerides. These become resynthesized into fats as they enter the cells of the villus. The resulting small droplets of fat are then discharged by exocytosis into the lymph vessels, called lacteals, draining the villi.

Effects and Toxic Actions on Organ Systems

1. Local anesthetics (dose dependent) interfere with transmission in any excitable tissue (e.g. CNS and CVS).

2. CNS effects

 a. Central neurons very sensitive.

 b. Excitatory-dizziness, visual and auditory disturbances, apprehension, disorientation and muscle twitching more common with ester type agents.

 c. Depression manifested as slurred speech, drowsiness and unconsciousness more common with amide type agents (e.g. lidocaine).

 d. Higher concentrations of local anesthetic may eventually produce tonic-clonic[grand mal]  convulsions.

 e. Very large doses may produce respiratory depression which can be fatal. Artificial respiration may be life-saving.

 3.CVS effects

 a. Local anesthetics have direct action on the myocardium and peripheral vasculature by closing the sodium channel, thereby limiting the inward flux of sodium ions.

 b. Myocardium usually depressed both in rate and force of contraction. Depression of ectopic pacemakers useful in treating cardiac arrhythmias.

 c. Concentrations employed clinically usually cause vasodilation in area of injection.

 d. Vasoconstrictors such as epinephrine may counteract these effects on myocardium and vasculature.

4.  Local Tissue Responses

 a. Occasionally focal necrosis in skeletal muscle at injection site, decreased cell motility and delayed wound healing.

 b. Tissue hypoxia may be produced by action of excessive amounts of vasoconstrictors.