TRIGLYCERIDES:  (continued):

MOVEMENT OF LIPIDS  -  LIPOPROTEINS: 

Lipids and proteins combine together without the aid of a covalent bond to form what is known as lipoproteins.  A cell in the intestinal wall makes it possible for the lipids – phospolipids,  free cholesterol, cholesterol ester and triglycerides -  to come together as a cluster.  Then  the cluster is bundled up with a coat of protein in order to form a lipoprotein.   Lipoprotein functions in the blood plasma as a vehicle to transport  cholesterol as well as triglycerides and is referred to as plasma lipoprotein.

Apolipoproteins mix with lipids to create several varieties  of  lipoprotein particles.   The prefix Apo  denotes the protein in its lipid free state.  Different  blends of  lipids and proteins produce particles of different densities,  such as chylomicrons, high-density lipoproteins.etc.   Every blend of lipoproteins has specific functions to perform.  The following table illustrates this: (it is based on weight percentage.)

                 HUMAN BLOOD PLASMA LIPOPROTEINS  -  MAJOR CAATEGORIES:

Lipoprotein       protein      phospolipid     free cholesterol      cholesterol    Triglycerides

Esters.

Chylomicron               2              9                           1                         3                    85

VLDL                        10            18                          7                        12                   50

LDL                            23            20                          8                        37                   10

HDL                           55            24                           2                       15                      4

Chylomicron:    They are the least dense and largest of lipoproteins containing a large proportion of  triglycerols.   Intestinal walls do contain epithelial cells. ( The endoplasmic reticulam of the epithelial cell systhesize  chylomicron  )   Chylomicrons move through  the villi of the intestine and absorbed into the lymphatic system from where it  easily enters the blood stream.  Chylomicrons makes it possible for the  triglycerides to  tissues  for their immediate consumption or to be stored as fat for future use.

Very Low Density Lipoproteins (VLDL) :   Liver assess the availability of fatty acids and if  what is availabale is more than the immediate requirement for use as fuel, it converts the excess availability into triglycerols and wrap it up with appropriate apolipoprotein which is known as  Very Low Density Lipoprotein.   VLDL is transported from liver  through blood plasma    to muscles for its immediate energy needs and to adipose tissues for storage as fat.      

Low Density Lipoprotein (LDL) :    When VLDL distributes triglycerols, its contents of other lipids such as phospolipids, cholesterol, cholesteryl esters etc., remain high.  The loss of triglycerols necessitates some quantity of VLDL  to be converted into what is known as Lowe Density Lipoprotein (LDL).  LDL is known as bad cholesterol.  When it is carried in the blood plasma it has a tendancy to litter the cholesterol on its way making the blood vessels prone to getting clogged.  A clogged blood vessel is the rudimentary cause for many chronic diseases some of which may even turn very dangerous.

High Density Lipoproteins: (HDL) :  Another important lipoprotein  class is known as High Density Lipoproteins (HDL):  The HDL  springs from small intestine as well as liver.  It mainly contains protein rich particles with very negligible amount of cholesterol and cholesteryl esters.  (Refer table given above).  It is termed as good cholesterol  as it works as a scavenger and collects  a majority of  cholesterol littered by LDL.

TRIGLYCERIDES:  (continued):

MORE ABOUT LIPIDS:

The sources of majority of lipids  in your body  are from animal fats and/or other animal products.  The source of animal fats did come from carbohydrates found in plants.  Carbohydrates are classified as (1) Complex carbohydrates and (2) Refined carbohydrates.   Complex carbohydrates are those which are used straight from the plants.  Refined carbohydrates  are those whose ingredients have undergone a process of refining.   The refining process takes away most of the enzymes, fiber, vitamins and minerals.  Your body needs all those vital ingredients for further food processing and digestion,. One exaample of  Complex  carbohydrate is potatoe.  Pasta is a good example of refined caarbohydrate.    Whatever excess of refined carbohydrate available in the system is converted into triglycerides  then fatty acids and finally as  fats and stored for future use.

Not  all fataty acids  are equal in length;  some are short chained and still others are long chained.   Shorter the chain , faster it solves in water.  The solubility of longer chained fatty acids are comparatively slower.

There are two types of fatty-acids based on the basis of saturation.   They are (a) sdaturated fatty-acids  (b)  un-saturated fatty acids,  (c) poly-unsaturated fatty acids, and, (d) transfatty acids.     Saturation means that if  every bond  in the  chain of carbon atoms is holding a hydrogen atom without any letup,  we take it that the chain is a saaturated fatty-acid.   Technically speaking, saturated fatty-acids  are straight chain molecules with exactly the same carbon numbers  without any double bonds, each of which is holding, without let up, a hydrogen atom.

Sometimes, it is seen  that the chain of carbon of a fatty acid does have points where hydrogens are missing.      Such points are referred to as  points of  unsaturation.  It only means that there is scope  for  futher addition of hydrogen atoms to the chain of carbon.  Such a chain of fatty-acid where there is one or a number of  points of  unsaturation happened,  we call it unsaturated fatty acid. 

 If,  in a carbon chain, there are two or more number of  points found to have  missing hydrogen atoms,  i.e,  two or more points of unsaturation occurred,  it is said to be a Polyunsaturated fatty-acid.

Ttrans fatty-acids, or, Trans fats,  are a particular type of unsaturated fat,  They occur minimally in nature, but  mainly formed during the course of converting an unsaturated fat to saturated fat by  a  special  industrial  process  known as  hydrogenation.

TRIGLYCERIDES:  (continued):

HOW HUMAN BODY USES FAT:

Your  food contains many nutrients  such as csaarbohydrates, proteins, vitamins, sodium, nitrogen  and, of course, fats, besides many other minerals. Your body also secretes  a number of enzymes ( an enzyme is a soluble, Colloidal  –  meaning  a glue-like non-crystalline  substance with very large molecules   -   substance produced  by living cells.  It works as a catalyst  and brings about  acceleration of chemical reactions without itserlf undergoing any change.)  in order to  help the digestion process.  Some of the  Enzymes that are important for digestion  of  nutrients  are   Carbohydradse  for carbohydrates,  protease for protein,  and lipase for fats  are available in the pancreatic juices secreted by the pancreas.  Your body prefers to digest first carbohydrates and proteins  preferring to keep the fat waiting for its turn.  This, the body does, because carbohydrates and proteins provide quite a good amount of glucose which can be readily accessed.   Before digestion the lipids undergo  a process of   bodily seperation. mostly through subtraction, i.e, as soon as the process of digestion  of carbohydrates and protaeins begin, the lipids are left behind.  All such left benind lipids  fuse into large globules.   In the stomach  food is stored and processed in layers.  The  food that remains very near the wall of the stomach is the one that is attened first.  The atmosphere inside stomach is acidic as it secretes gastric juices including hydrochloric acid.   The acids and enzymes first start woking with proteins and carbohydrates leaving fats which now form into larger globules  and float on the top of the stomach which is the furtherest point to pyloric valve which lets the partially digested food  (known as chime) into the deodenum for further procesdsing.  The fats being on the top side of the stomach,  gets attention only after other partially digested foods are sent out.   This is  the reason why we feel satiated and full when we eat non-vegetarian foods.

When the large sized fat globules reach duodenum they get a fine springle of bile salts  which emulsify and sent them into the  small intestine.   Here the large fat globules are broken into very small droplets  by an emulsifier.

This enables the enzymes that are required to work with the droplets come very next to them to enanble them to  attack the bonds.   The required enzymes are secreted mostly in the pancreas  and flow into the duodenum through the ampulla of vater and proiceed to intestine where the real digestive process  starts.  We will see  how fat is digested in the intestine  in the next article.

DIGESTION OF LIPIDS:

The human stomach partially digests the food it receives and makes it into a soup like substance known as chime.  This chime is pushed into the deudonum through the phyloric-valve.  The chime is acidic as the food in the stomach gets treatment from hydrochloric acid it produces.  As soon as the  partially  digested food in the form of chime reaches deudonum the intestinal wall triggers the release of two harmones, (1) cholecystokinin (CCK) and  (2) secretin.  The purpose of these harmones is to stimulate secretion of  pancreatic juices.   It also triggers the release of bile salts from the gall-bladder  which also reach the deudonum through the opening known as  ampulla of vater in the pancreatic duct.

Verily, there are a number of enzymes available in the pancreatic juice.   In so far as fats and oils i.e, lipids are concerned only  lipase  is important.. First, the bile salts emulsify the lipids into tiny droplets  and second enzyme lipase breaks them down into droplets of fatty acid and  monoglycerides.  It happens that the enzymes sometime free two ends of  a triglyceride of fatty acids leaving the middle fatty acid attsached.  This is referred to as monoglyceride.

(Triglycerides and monoglyceriders. )

Fatty acids and monoglycerides go through the epithelial cells of  the villi of the ileum, the 12 feet long intestinal portion which follows the 8 feet intestinal portion known as jejunum  where they are again  converted back into triglycerides. ( For your information, small intestine has three parts viz., deudonum, jejunum and ileum. )  After this, they are passed on to the lymphic system.  Now, the triglycerides in the lymphic system are carried away from the ileum and delivered to the blood stream.

You are aware that lipids are soluble only in fats as they are fat soluble.   In other words, they cannot be solved in water.   But your blood stream and the lymphatic system both are mainly  comprised of water.  However, short-chain fatty-acids are considered to be water soluble to some extent  and they are absorbed by the cells of the intestinal wall.

The long-chain fatty acids are connected again to monoglycerides  or  to  glycerol to create new triglycerides   To move about, they require lipoproteins.   We will discuss all about lipoproteins in the next article.  .

1.  TRIGLYCERIDES:

It is one of the three major class of dietary Lipids.  Lipids can be classified as any water soluble fat, oil or fat-like substance extractable  by solvents such as alcohol.   Fat,  in our daily food, contains  (1) visible  i.e, that which is easily seen  and  (2) Non-visible  i.e, that whcih cannot be readily seen.  Visible fats are  fats and oils  such as butter, ghee, , coconut oil, mustard oil, sunflower oil, hydrogenated  oil substances such as margarine  etc.  Non-visible fats are fats and oils that are contained in colourful pasteries, avocados, processed-foods, nuts  etc.  There is a general feeling  that fats are bad for our health and wellbeing,.  The assumption is very wrong.  Lipids are, in fact, very eassential, and must be part of  your dailly food  in order for you to be healthy and strong.   Lipids are very necessary  as they work as a source of  energy fuel .  It is a very essential component  of every cell membrane in our  body.    You know there are trillions of cells in our body!

                            LIPID – FAMILY

                            ||————————————||——————————–||

                            TRIGLYCERIDES                PHOSPOLIPIDS                STEROLS

Triglycerides can broadly be  catagorized as an ester i.e., a chemical compound  obtained by acid  –  alcohol interaction.,   It, generally, contains three fataty acids ( Tri  =  three ) attached to a molecule of Glycerol.  What is glycerol?  It is nothing but  a small water soluble carbohydrate.  In chemical terms it can be defined as  an organic alcohol  made up of  a  three carbon chains each of which is tied with an alcohol group.

                            THREE  FATTY ACIDS            +        GLYCEROL           =            TRIGLYCERIDE

About 90 to 95% of  the fats  in the foods that we eat  as well as those which remain in our body already are said  to be Triglycerides.    In actual fact, Triglycerides are considered to be  a form of storage of  food-energy that we eat in EXCESS of our bodily needs,.  Your Liver is a chemical facytory.  Triglycerides are manufactured in the Liver using carbohydrates as raw material.   Carbohydrates as well as triglycerides help in churning  out energy for metabolic activities of the body.  Whatever  Triglycerides that    we find in our food  are split in our digestive-tract  into  Fatty Acids and monoglycerides.   Whenever you eat more carbohydrates  than is required for your bodily needs  -  the present  day life  is fast-phased  and people find no time for cooking their own food,  no choice but to indulge in fast -foods,  such as pizza, hamburgers, pasta, sweets and cakes, breads, ready to eat food items  etc,   -   they are converted into triglycerides  and then into Fatty acids and stored as fat.