 |
|
Categoriy |
Chylo-
micron |
VLDL |
IDL |
LDL |
HDL |
|
Size (in nano meter) |
75-1000 |
30-80 |
25-40 |
20 |
7.5-10 |
|
Protein |
2 |
8 |
10 |
20 |
50 |
|
Cholesterol |
2 |
4 |
5 |
7 |
4 |
|
Cholesterol Esters |
3 |
16 |
25 |
46 |
16 |
|
Triglyceride |
90 |
55 |
40 |
6 |
5 |
|
Phospholipids |
3 |
17 |
20 |
21 |
25 |
|
Origin |
Intestine |
Liver |
VLDL/ HDL catabolism |
IDL |
Liver, Intestine |
|
Normal value (mg/dl) |
125-200 |
10 to 30 |
40 to 125 |
90 - 150 |
25 - 60 |
|
Table 2:
Composition of Lipoproteins |
|
Kuman & klerk, 2005 |
Absorption
Some glycerol, short
chain fatty acids and medium chain fatty acids can be absorbed into
the blood stream diffusing through intestinal cells. Monoglycerides
and long chain fatty acids merge into micelles to transport through
the microvilli of intestinal cells. When micelles diffuse into
intestinal cells the monoglycerides and long chain fatty acids are
reassembled into triglycerides and carried away by chylomicrons.
Transport
Lipid is transported by the help of Chylomicrons and other
lipoproteins like LDL, VLDL, IDL & HDL. Chylomicrons transport diet
derived lipids (primarily triglycerides) from the intestine to cells
(Fig. 1). VLDL transport liver synthesized lipids (primarily
triglycerides) to cell. LDL carries and deposits cholesterol to
tissues: muscle, fat stores, mammary glands, heart, etc. HDL carries
cholesterol and phospohlipids from cells back to liver for recycling
or disposal.
Homeostasis
Most body cholesterol is made by the liver from Acetyl CoA (Fig. 1).
A very variable amount (0 to 1000 mg/day) is absorbed from diet.
After consumption of fat; fatty acid absorbed from the intestine &
converted to Acetyl CoA by glycolysis & beta oxidation, which
eventually promotes hepatic cholesterol production and tends to
increase plasma cholesterol level. Cholesterol levels in the blood
reflect approximately 40% to 60% endogenous cholesterol, with the
balance coming from dietary sources. Cholesterol is derived from
three sources: exogenously from the systemic circulation and
endogenously via intracellular synthesis & reverse cholesterol
transport. |
Exogenous
Pathway
Following digestion and absorption of dietary fat, chylomicrons
circulate through the intestinal lymphatic system and interact at
the capillaries of adipose tissue and muscle cells releasing TG to
the adipose tissue to be stored and made available for the bodyÕs
energy needs.
Endogenous
Pathway
The endogenous pathway involves the liver synthesizing lipoproteins.
TG and cholesterol esters are generated by the liver and packaged
into VLDL particles and then released into the circulation. VLDL is
then processed by LPL in tissues to release fatty acids and
glycerol.
Reverse Cholesterol Transport
A low plasma level of HDL is a risk factor for coronary artery
disease (CAD). The reverse cholesterol transport from is the
physiological process to counteract the deposition of cholesterol
via VLDL and LDL from peripheral cells and carries it to the liver.
Moreover, HDL particles have many additional anti atherogenic
features, such as anti inflammatory, anti agreggative and anti
oxydative properties.
PATHOPHYSIOLOGY
An increase in portal vein long chain free fatty acids would inhibit
hepatic Apo-B from undergoing degradation in the endoplasmic
reticulum and would increase the Apo-B undergoing hepatic secretion
as triglyceride containing |
|
