Lipid Metabolism

Lipid Metabolism

# I. Types of Lipids in the Body

Lipids are one of the main components of the body and are classified into 3 types:

• Transport form: Includes fatty acids, phospholipids, and some other lipids. They are transported in the blood as lipoproteins.

• Combined form: Lipids can combine with carbohydrates or other lipids to participate in the structure of cell components in tissues and organs in the body.

• Storage form: Triglycerides are neutral fats that are delivered and stored in adipose tissue. When the body needs energy, triglycerides will be mobilized from adipose tissue to participate in energy metabolism or the synthesis of new substances.

# II. Transport Forms

• Very Low Density Lipoprotein (VLDLC): Contains a lot of triglycerides.

• Intermediate Density Lipoprotein: Has less triglycerides than VLDLC.

• Low Density Lipoprotein (LDL): Contains almost no triglycerides, with moderate levels of cholesterol and phospholipids.

• High Density Lipoprotein (HDL): Contains up to 30% protein.

After meals, the amount of lipoprotein in the blood increases and then gradually returns to normal. Cholesterol in the blood also increases but does not exceed 15% of the normal level.

# III. Roles of Lipids in the Body

Lipids play an important role in the body:

• Energy supply:

• Lipids are the body’s largest energy reserve, accounting for about 40%, mainly triglycerides.

• 1 gram of lipid provides 9.3 Kcal of energy.

• The degradation of triglycerides provides energy for the body (not directly, but through the intermediary production of ATP).

• Glycerol -> pyruvic acid -> acetyl CoA -> Krebs cycle.

• Fatty acids (beta oxidation) -> carbon fragments -> acetyl CoA -> Krebs cycle + ATP.

• Participation in cell structure:

• Lipids participate in many structural components of cells and form the body in all tissues:

• Cell membranes and membranes of organelles within cells (lipids).

• Structures of nerve tissues, especially the myelin sheath of nerve axons (sphingomyelin).

• Thromboplastin – a substance necessary for blood clotting (cephalin).

• The surfactant layer of the alveoli (lecithin).

• Cholesterol is the main component of steroid hormones, the main raw material for producing bile acid and bile salts.

• Participation in the functional activities of the body:

• Lipids participate in many structural components of cells, thus participating in many functional activities of cells:

• Blood clotting process.

• The function of transmitting nerve impulses.

• Participate in the process of metabolism and reproduction.

• Digestion process.

• Cholesterol deposited in the stratum corneum of the skin prevents water from permeating the skin.

# IV. Lipid Needs in the Body

• Lipids are an indispensable food source for the body.

• Provide 18-25% of the total energy needs per day.

• The main source comes from animal fat, vegetable oil.

• Some complex lipids are synthesized by the liver (phospholipids, cholesterol) and are supplied by two sources: endogenous + exogenous (food).

# V. Regulation of Lipid Metabolism

Lipid metabolism is regulated by two mechanisms:

• Nervous mechanism:

• The hypothalamus is involved in lipid metabolism.

• Stress, heat, cold, and emotions affect the activity of the endocrine system, which in turn affects lipid metabolism.

• Humoral mechanism:

• Hormones that increase lipid catabolism:

• Adrenaline: adrenal glands.

• Glucagon: pancreatic islets.

• GH: pituitary gland.

• T3, T4: thyroid gland.