Transport of lipids from the intestine to other tissues is by -

NEET PG
#1

Transport of lipids from the intestine to
other tissues is by -
a) Chylomicrons
b) LDL
c) HDL
d) VI DL

Correct Answer - A
Ans. is ‘a’ i.e., Chylomicrons
Transport of lipids
o There are two pathways of lipid transport in the body ?

  1. Transport of dietry lipid (Exogenous pathway)
  • It is the transport of 1 ipid.from intestine to liver.
  • Chylomicrons transport the dietry lipid from intestine to liver.
  • In Diet the major lipids are triglyceride and Aolesterol.
  • Cholesterol is absorbed as such in proximal small intestine and is
    esterified to cholesteryl ester (ChE). o Triglycerides are hydrolysed
    by lipases to glycerol and fatty acids which are absorbed in intestine.
    o Inside intestinal cells triglyceride is synthesized by fatty acids.
  • Chylomicrons are synthesized in the small intestine that contain
    triglyceride, cholesteryl ester, cholesterol, phospholipids and
    apoprotein B-48 (apo B-48).
  • These chylomicrons are secreted in the intestinal lymph and reach
    the systemic circulation via thoracic duct.
  • In the circulation Apo E and Apo C are transfered to
    chylomicrones by HDL, so now chylomicrons contain Apo B-48, Apo
    E, & Apo C.
  • In the circulation, Triglycerides of chylomicrones are hydrolysed
    by lipoprotein lipase (LPL) present on endothelial cells of vessels
    of skeletal muscles, adipose tissue and heart.
  • The released fatty acids are utilized locally by these tissues.
  • The chilomicron particle progressively shrinks in size by action of
    LPL and, cholesterol, phospholipids and apo C are transferred to
    HDL, creating chylomicron remnants that contains more cholesterol,
    less triglycerides, apo E & apo B-48.
    *Chylomicron remnants are removed by liver by the LDL
    receptors that require apo E as ligand.
    Note - Apo C-II, that is transfered from HDL to chylomicrons act as a
    cofactor for lipoprotein lipase. Apo A-V promotes LPL mediated
    triglyceride lipolysis in VLDL and chilomicrons.
  1. Transport of Hepatic lipids (Endogenous pathway)
  • VLDL is synthesized in liver that contains high triglyceride, ChE,
    cholesterol, phospholipid and Apo B-100.
  • (VLDL particles resembel chylomicrones in composition except that
    VLDL contains Apo B-100 instead of ApoB-48).
  • VLDL particles are secreted in the plasma and as with
    chylomicron, Apo E and Apo C are transferred from HDLto VLDL.
    Now VLDL contains Apo B-100, Apo E and Apo C.
  • In plasma, triglycerides of VLDL are hydrolysed by same
    lipoprotein lipase (see above) and apo C is transferredto HDL and
    the remmants are called IDL.
  • 40-60% of IDL is removed by liver via LDL receptor mediated
    endocytosis, this process require Apo E whichacts as ligand for LDL
    receptors.
  • Remaining 1 DL is remodeled by hepatic lipase to form LDL that
    contains maximum cholesterol.
  • 70% of LDL is removed by liver via LDL receptor and 30% is
    utilized by peripheral tissues as a source ofcholesterol.