Lipids, proteins, nucleic acids and polysaccharides, constitute the structure of the cells. Lipids are structured in a way that have heads hydrophilic and hydrophobic tails. To keep their tails in water, they form a spherical structure known as a micelle. Extended structures of micelles is known as lipid bilayers and these become the main components of cell membranes. Lipids which are composed primarily of normal chains act as energy storage. Being the main components of the hormones, also take part in events marking biochemists in the body.
Triacylglycerol, the most abundant type of lipid, is mostly obtained from the food we eat. This type of lipid has two types: fats and oils. The only difference between these two is that fats are solid at room temperature while the oils are liquid. This substance is a reservoir of energy because it contains more hydrogen atoms which can be oxidized and transformed into energy in comparison to proteins and carbohydrates. Triacylglycerol is stored in adipose cells that constitute the adipose tissue. These tissues are abundant in the subcutaneous layer of the skin and into the abdominal cavity. Adipose tissues are very effective in energy storage allowing humans to survive for two or three months without food. In addition, they function as insulation against the very cold weather.
Triacylglycerol is insoluble in water, whereas digestive enzymes are soluble. To be able to extract nutrients digestion takes place in lípidos-agua interfaces. The rate of digestion depends on the surface of the interface. The Peristaltic movement in the bowel, pancreatic lipase and bile acid increases the rate of digestion of lipids.
The triacylglycerol has been completely damaged, that is absorbed by the cells of the intestinal walls. After absorption, it is ready to be transported to different cells in the body by the bloodstream. However, being soluble in blood, a triacylglycerol to be transported in complex with proteins. Lipoproteins are particles which are composed of a core of triacylglycerols and contain esters surrounded by an outer layer of protein and cholesterol.
Lipoproteins are five main types: intermediate of chylomicrons, low-density (VLDL) lipoproteins, lipoprotein of high-density (HDL), low-density (LDL) lipoproteins and lipoprotein (IDL) density. Four early lipoprotein transport triacylglycerols in whole body while the latter that carries triacylglycerols in the tissues of the liver. Chylomicrons, VLDL, IDL and LDL transfer its content triacylglycerol through its accession to the tissues. After this, the three first shrink lipoproteins and transformed into rich in cholesterol LDL. Cells are rich in LDL cholesterol to maintain the structure of their membranes by bore the particle in a process known as receptor-mediated Endocytosis.
When recipients of defective cells, LDL cholesterol accumulates in the blood, putting a person at increased risk of cardiovascular problems. HDL, on the other hand, acts as the "good cholesterol" and collects LDL to lead them towards the liver for disposal.