Lipids, together with proteins, nucleic acids, and polysaccharides, constitute the structure of cells. Lipids are structured in such a way that they have hydrophilic heads and hydrophobic tails. In order to keep their tails away from water, they form a spherical structure known as a micelle. Extended structures of micelles are known as lipid bilayers and these become the main components of cellular membranes. Lipids that are composed primarily of carbon-hydrogen chains serve as energy storage. Being the main components of hormones, they also take part in biochemical signalling events in the body.
Triacylglycerol, the most abundant kind of lipid, is mostly obtained from the food we eat. This type of lipid has two kinds: fats and oils. The only striking difference between these two is that fats are solid at room temperature while oils are liquid. This substance is a great energy reservoir because it contains more hydrogen atoms that can be oxidized and turned into energy, compared to proteins and carbohydrates. Triacylglycerol is stored in adipose cells that constitute the adipose tissues. These tissues are abundant in the subcutaneous layers of the skin and in the abdominal cavity. Adipose tissues are very efficient in storing energy as they allow humans to survive for two to three months without food. Also, they function as insulator against very cold weather conditions.
Triacylglycerol is insoluble in water while the digestive enzymes are soluble. To be able to extract nutrients, the digestion takes place in lipid-water interfaces. The rate of digestion is dependent on the surface area of the interface. The peristaltic movement in the intestines, pancreatic lipase, and bile acids increase the rate of lipid digestion.
When the triacylglycerol has been completely broken down, it is absorbed by the cells found on the intestinal walls. After absorption, it is ready to be transported to the different cells in the body through the bloodstream. However, to be soluble in blood, a triacylglycerol has to be transported in complex with proteins. Lipoproteins are particles that are composed of a core of triacylglycerols and cholesteryl esters surrounded by an outer layer of proteins and cholesterol.
Lipoproteins have five major types: chylomicrons, very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density lipoproteins (LDL), and high density lipoproteins (HDL). The first four lipoproteins transport triacylglycerols throughout the body while the last one transports triacylglycerols in the tissues to the liver. Chylomicrons, VLDL, IDL, and LDL transfer their triacylglycerol content by adhering to the tissues. After this, the first three lipoproteins shrink and are transformed into cholesterol-rich LDL. Cells take up the cholesterol-rich LDL to maintain the structure of their membranes by engulfing the particle in a process known as receptor-mediated endocytosis.
When the cholesterol-receptors of the cells become defective, LDL accumulates in the blood, putting a person at higher risk for cardiovascular problems. HDL, on the other hand, acts as the 'good cholesterol' and scavenges LDL to bring them back to the liver for disposal.
Triacylglycerol, the most abundant kind of lipid, is mostly obtained from the food we eat. This type of lipid has two kinds: fats and oils. The only striking difference between these two is that fats are solid at room temperature while oils are liquid. This substance is a great energy reservoir because it contains more hydrogen atoms that can be oxidized and turned into energy, compared to proteins and carbohydrates. Triacylglycerol is stored in adipose cells that constitute the adipose tissues. These tissues are abundant in the subcutaneous layers of the skin and in the abdominal cavity. Adipose tissues are very efficient in storing energy as they allow humans to survive for two to three months without food. Also, they function as insulator against very cold weather conditions.
Triacylglycerol is insoluble in water while the digestive enzymes are soluble. To be able to extract nutrients, the digestion takes place in lipid-water interfaces. The rate of digestion is dependent on the surface area of the interface. The peristaltic movement in the intestines, pancreatic lipase, and bile acids increase the rate of lipid digestion.
When the triacylglycerol has been completely broken down, it is absorbed by the cells found on the intestinal walls. After absorption, it is ready to be transported to the different cells in the body through the bloodstream. However, to be soluble in blood, a triacylglycerol has to be transported in complex with proteins. Lipoproteins are particles that are composed of a core of triacylglycerols and cholesteryl esters surrounded by an outer layer of proteins and cholesterol.
Lipoproteins have five major types: chylomicrons, very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density lipoproteins (LDL), and high density lipoproteins (HDL). The first four lipoproteins transport triacylglycerols throughout the body while the last one transports triacylglycerols in the tissues to the liver. Chylomicrons, VLDL, IDL, and LDL transfer their triacylglycerol content by adhering to the tissues. After this, the first three lipoproteins shrink and are transformed into cholesterol-rich LDL. Cells take up the cholesterol-rich LDL to maintain the structure of their membranes by engulfing the particle in a process known as receptor-mediated endocytosis.
When the cholesterol-receptors of the cells become defective, LDL accumulates in the blood, putting a person at higher risk for cardiovascular problems. HDL, on the other hand, acts as the 'good cholesterol' and scavenges LDL to bring them back to the liver for disposal.
