CMQ

Let’s start with a few definitions.

Nutrition is the food, vitamins, and minerals that are ingested and assimilated into the body.

Assimilation is the process of getting nutrient molecules into the cells of the body and chemically preparing them for use in the chemical reactions of the body.

Metabolism is the process of using nutrient molecules as energy sources and as building blocks for our own molecules.

Catabolism is the breaking down of nutrient molecules, releasing their stored energy; oxygen is used in catabolism.

Anabolism is the process that builds nutrient molecules into complex substances.

Nutrients are food components digested and absorbed by the body.

Macronutrients are nutrients needed in large daily quantities; these are carbohydrates, fats, and proteins.

Micronutrients are nutrients needed in tiny daily quantities; these are the vitamins and minerals.

Next, we’ll review some of the metabolic functions of the liver.

The liver secretes bile, which breaks down large fat globules.

It helps maintain normal blood glucose level.

The liver helps metabolize carbohydrates, fats, and proteins; it synthesizes several kinds of protein compounds.

It removes toxins from the blood and stores useful substances.

Now we’ll review the macronutrients: carbohydrates, lipids, and proteins.

Carbohydrates exist in several forms including monosaccharides, disaccharides, and polysaccharides. The monosaccharide glucose is the preferred energy nutrient of the body.

Proteins are primarily anabolized and secondarily catabolized.

The use of amines from protein in the glucose pathway for energy is called gluconeogenesis.

Essential amino acids are those that must be in the diet because the body cannot make them.

There are three series of chemical reactions in glucose metabolism: glycolysis, the citric acid (or Krebs) cycle, and the electron transport system.

Glycolysis changes glucose to pyruvic acid; it is anaerobic in that it uses no oxygen. Glycolysis occurs in cytoplasm and yields a small amount of energy, generating two adenosine triphosphate (ATP) molecules.

The citric acid cycle changes pyruvic acid to carbon dioxide; it is aerobic because it requires oxygen. The citric acid cycle occurs in mitochondria and yields a large amount of energy (mostly as high-energy electrons).

The electron transport system, also located in mitochondria, transfers energy from high-energy electrons (from the citric acid cycle) to ATP molecules.

The mitochondrial part of the pathway (the citric acid cycle and electron transport system) is aerobic and generates up to 30 ATP molecules per original glucose molecule.

Carbohydrates are primarily catabolized for energy.

ATP is the molecule in which energy obtained from the breakdown of nutrients is stored; it serves as a direct source of energy for cellular work.

Glucose that is not needed immediately for making ATP is stored as glycogen (a long chain of glucose subunits) in liver and muscle cells.

Glycogenesis is the anabolic process of joining glucose molecules together in a chain to form glycogen (to store glucose for later use).

Glycogenolysis is the catabolic process of breaking apart glycogen chains, releasing individual glucose molecules for use in making ATP.

Blood glucose (commonly, but imprecisely called blood sugar) normally stays between about 80 and 110 mg per 100 mL of blood during fasting; insulin accelerates the movement of glucose out of the blood into cells, thereby decreasing blood glucose and increasing glucose catabolism.

Triglycerides (or fats) are the most abundant lipid in our diet.

• Like carbohydrates, lipids are energy molecules. Before being used for energy, fats are broken down into fatty acids and glycerol.
• Lipids are catabolized to yield energy and anabolized to form adipose tissue.

Proteins are primarily anabolized and secondarily catabolized. Only small amounts of proteins are catabolized for energy.

The use of amines from protein in the glucose pathway for energy is called gluconeogenesis.

Essential amino acids are those that must be in the diet because the body cannot make them.

Micronutrients include vitamins and minerals.

Vitamins are organic molecules that are needed in small amounts for healthy metabolism.

Minerals are inorganic molecules found naturally in the earth, required by the body for normal function.

Regulatory centers in the hypothalamus play a primary role in controlling food intake.