Blood - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 8

Tabl e 1. 6. Size and lipid content (%) of lipoproteins.

Chylomicron VLDL LDL HDL

Size (nm) 80-500 ∼ 50 ∼ 20 ∼ 10

Cholesterol ∼ 0.02 ∼ 0.07 ∼ 0.08 ∼ 0.04

Cholesterol esters ∼ 0.03 ∼ 0.12 ∼ 0.42 ∼ 0.15

Phospholipids ∼ 0.07 ∼ 0.18 ∼ 0.22 ∼ 0.30

Triglycerides ∼ 0.86 ∼ 0.55 ∼ 0.06 ∼ 0.04

Proteins ∼ 0.02 ∼ 0.08 ∼ 0.22 ∼ 0.47

facilitate the cotransport of numerous hydrophobic molecules, such as enzymes
and hormones, across the endothelium (Sect. 9.6 ). In the interstitial space, it also
serves as a major interstitial osmotic agent, hence transendothelial osmotic pressure
gradient. Extravasated albumin is recycled into blood circulation by lymphatic
vessels. Like IgG, albumin binds the major histocompatibility complex-related Fc
receptor at low pH. This interaction shields these proteins from degradation.
Like fibrinogen, globulins induce reversible RBC aggregation in stagnant blood
regions. 8 -globulins that transport chemical

species, such as thyroxine and retinol (vitamin-A);

Several kinds of globulins exist: (1) α

β -globulins such as transferrin;

and γ -globulins, most of the antibodies (0.1-0.4 g/dl of α 1-globulins, 0.5-1 g/dl of

α 2-globulins, 0.7-1.2 g/dl of β -globulins, and 0.5-1.6 g/dl of γ -globulins).

1.3.4 Plasma Lipids and Lipoproteins

The lipoprotein structure shields water-insoluble lipids (cholesteryl esters and
triglycerides) from water, as it encapsulates them with polar lipids and proteins.
However, core lipids can move between lipoproteins. The 4 main types of circulating
lipoproteins that differ in size, density, and content include chylomicrons, and
very-low-density (VLDL), low-density (LDL), and high-density (HDL) lipoproteins
(Table 1.6 ,Fig. 1.2 ).
Lipoproteins convey cholesterol esters (CsE) and triglycerides (TG) in blood. 9
Triglycerides are delivered to muscles and adipose tissues for energy production
and storage (blood TG concentration 1.6 g/l at 60 years

old). 10 Excess lipid and glucid intake leads to conversion into triacylglycerols in the

< 1.2 g/l at 20 years old and <

8 Hemodynamic stresses oppose aggregation, limit aggregation growth, and progressively break
existing erythrocyte rouleaux and possible rouleau networks.
9 Analysis of serum lipids commonly yields concentrations of LDLs, HDLs, and TGs.
10 Lipoprotein lipase removes triglycerides from chylomicrons and VLDLs for fat storage or energy
source in adipose tissues and muscles, respectively.