chapter 18

Chapter 18: Nutrition and Metabolism

18.6 Appetite Control

• Appetite:
    - Drive that compels us to seek food.
    - Control center is located in hypothalamus.
    - Regulated by several hormones and neurotransmitters including:
      - Insulin
      - Leptin
      - Neuropeptide Y
      - Ghrelin

Substances that Control Appetite

• Substances:
    | Substance | Site of Secretion | Function |
    |-------------------|--------------------|---------------------------------------------------|
    | Insulin | Pancreas | Stimulates adipocytes to admit glucose and store fat; promotes glycogen synthesis. |
    | Leptin | Adipocytes | Suppresses appetite and increases metabolic rate after eating. |
    | Neuropeptide Y | Hypothalamus | Enhances appetite. |
    | Ghrelin | Stomach | Enhances appetite. |

18.7 Vitamins

• Vitamins:
    - Organic compounds required in small amounts for normal metabolic processes.
    - Essential nutrients.
    - Classified based on solubility:
      - Fat-soluble vitamins: A, D, E, and K.
      - Water-soluble vitamins: B vitamins and vitamin C.

Vitamin Fallacies and Facts

Fat-Soluble Vitamins

• Characteristics:
    - Associated with lipids and influenced by factors affecting lipid absorption (e.g., presence of bile salts).
    - Stored in various tissues; excess can lead to overdose.
    - Resistant to heat.
    - Includes vitamins A, D, E, and K.

Vitamin A

• Characteristics:
    - Exists in several forms; synthesized from carotenes; stable in heat, acids, and bases, but unstable in light.

• Functions:
    - Antioxidant needed for synthesis of visual pigments, mucoproteins, and mucopolysaccharides; necessary for normal development of bones and teeth and maintenance of epithelial cells.

• Sources:
    - Liver, fish, whole milk, eggs, leafy green vegetables, yellow and orange vegetables and fruits.

• Excess:
    - Nausea, headache, dizziness, hair loss, birth defects.

• Deficiencies:
    - Night blindness, degeneration of epithelial tissues.

Vitamin D

• Characteristics:
    - Group of steroids, resistant to heat and oxidation, acids, and bases; stored in the liver, skin, brain, spleen, and bones.

• Functions:
    - Promotes absorption of calcium and phosphorus; aids in the development of teeth and bones.

• Sources:
    - Produced in skin exposed to UV light; also found in milk, egg yolk, fish liver oils, and fortified foods.

• Excess:
    - Diarrhea, calcification of soft tissues, renal damage.

• Deficiencies:
    - Rickets, bone decalcification and weakening.

Vitamin E

• Characteristics:
    - A group of compounds; resistant to heat and visible light; unstable in the presence of oxygen and UV light; stored in muscles and adipose tissue.

• Functions:
    - Antioxidant; prevents oxidation of vitamin A and polyunsaturated fatty acids; may help maintain the stability of cell membranes.

• Sources:
    - Oils from cereal seeds, salad oils, margarine, shortenings, fruits, nuts, and vegetables.

• Excess:
    - Nausea, headache, fatigue, easy bruising and bleeding.

• Deficiencies:
    - Rare.

Vitamin K

• Characteristics:
    - Exists in several forms; resistant to heat but destroyed by acids, bases, and light; stored in the liver.

• Functions:
    - Required for synthesis of prothrombin, which is essential for blood clotting.

• Sources:
    - Leafy green vegetables, egg yolk, pork liver, soy oil, tomatoes, cauliflower.

• Excess:
    - Jaundice in formula-fed newborns.

• Deficiencies:
    - Prolonged clotting time.

Water-Soluble Vitamins

• Includes:
    - B vitamins (thiamine, riboflavin, niacin, pantothenic acid, vitamin B6, cyanocobalamin, folic acid, biotin) and Vitamin C.

• Characteristics:
    - Cooking and food processing can destroy some of them.
    - B vitamins are vital for normal cellular metabolism.
    - B vitamins generally found in the same foods, forming the vitamin B complex.

Thiamine (B1)

• Characteristics:
    - Destroyed by heat and oxygen, especially in alkaline environments.

• Functions:
    - Part of the coenzyme required for oxidation of carbohydrates; coenzyme required for ribose synthesis.

• Sources:
    - Lean meats, liver, eggs, whole grain cereals, leafy green vegetables, legumes.

• Excess:
    - Uncommon; may cause vasodilation and cardiac dysrhythmias.

• Deficiencies:
    - Beriberi, muscular weakness, enlarged heart.

Riboflavin (B2)

• Characteristics:
    - Stable to heat, acids, and oxidation; destroyed by bases and UV light.

• Functions:
    - Part of enzymes and coenzymes such as FAD, required for oxidation of glucose and fatty acids necessary for cellular growth.

• Sources:
    - Meats, dairy products, leafy green vegetables, whole grain cereals.

• Excess:
    - None known.

• Deficiencies:
    - Dermatitis, blurred vision.

Niacin (B3)

• Characteristics:
    - Stable to heat, acids, oxidation; converted to niacinamide by cells; synthesized from tryptophan.

• Functions:
    - Part of coenzymes NAD and NADP required for oxidation of glucose and synthesis of proteins, fats, and nucleic acids.

• Sources:
    - Liver, lean meats, peanut butter, legumes.

• Excess:
    - Flushing, vasodilation, wheezing, liver problems.

• Deficiencies:
    - Pellagra, dermatitis, diarrhea, mental disorders.

Pantothenic Acid (B5)

• Characteristics:
    - Destroyed by heat, acids, and bases.

• Functions:
    - Part of coenzyme A required for oxidation of carbohydrates and fats.

• Sources:
    - Meats, whole grain cereals, legumes, milk, fruits, vegetables.

• Excess:
    - None known.

• Deficiencies:
    - Rare; may cause loss of appetite, mental depression, muscle spasms.

Vitamin B6

• Characteristics:
    - Group of three compounds; stable to heat and acids; destroyed by oxidation, bases, and UV light.

• Functions:
    - Coenzyme required for protein synthesis and various amino acids, conversion of tryptophan to niacin, production of antibodies, and nucleic acid synthesis.

• Sources:
    - Liver, meats, bananas, avocados, beans, peanuts, whole-grain cereals, egg yolk.

• Excess:
    - Numbness, clumsiness, paralysis.

• Deficiencies:
    - Rare but can include convulsions, vomiting, seborrhea lesions.

Biotin (B7)

• Characteristics:
    - Stable to heat, acids, and light; destroyed by oxidation and bases.

• Functions:
    - Coenzyme required for metabolism of amino acids and fatty acids and nucleic acid synthesis.

• Sources:
    - Liver, egg yolk, nuts, legumes, mushrooms.

• Excess:
    - None known.

• Deficiencies:
    - Rare; may cause elevated blood cholesterol, nausea, fatigue, anorexia.

Folacin, Folic Acid (B9)

• Characteristics:
    - Occurs in several forms; destroyed by oxidation in an acid environment or by heat in an alkaline environment; stored in liver where converted into folinic acid.

• Functions:
    - Coenzyme required for metabolism of certain amino acids and for DNA synthesis; promotes production of normal red blood cells.

• Sources:
    - Liver, leafy green vegetables, whole grain cereals, legumes.

• Excess:
    - None known.

• Deficiencies:
    - Megaloblastic anemia, spina bifida.

Cyanocobalamin (B12)

• Characteristics:
    - Complex, cobalt-containing compound; stable to heat; inactivated by light, strong acids, and strong bases; absorption regulated by intrinsic factor from gastric glands; stored in liver.

• Functions:
    - Part of coenzyme required for synthesis of nucleic acids and metabolism of carbohydrates; plays a role in myelin synthesis; required for normal red blood cell production.

• Sources:
    - Liver, meats, milk, cheese, eggs.

• Excess:
    - None known.

• Deficiencies:
    - Pernicious anemia.

Ascorbic Acid (Vitamin C)

• Characteristics:
    - Chemically similar to monosaccharides; stable in acids but destroyed by oxidation, heat, light, and bases.

• Functions:
    - Required for collagen production, conversion of folacin to folinic acid, metabolism of certain amino acids; promotes absorption of iron and synthesis of hormones from cholesterol.

• Sources:
    - Citrus fruits, tomatoes, leafy green vegetables.

• Excess:
    - Can exacerbate gout and kidney stone formation.

• Deficiencies:
    - Scurvy, lowered resistance to infection, slow wound healing.

18.8 Minerals

• Minerals:
    - Inorganic elements required in metabolism.
    - Typically extracted from the soil by plants.
    - Obtained from plant foods or animals that have consumed plants.

Characteristics of Minerals

• Comprise approximately 4% of body weight, with most concentrated in bones and teeth.

• Generally incorporated into organic molecules (e.g., iron in hemoglobin).

• Some exist as inorganic compounds (e.g., calcium phosphate of bone).

• Certain minerals are free ions in the blood (e.g., sodium, chloride, calcium ions).

• Serve as structural materials for all cells.

• Play roles in muscle contraction, nerve impulse conduction, blood coagulation, and pH regulation.

• Mineral toxicity:
    - Can occur from excessive ingestion or overexposure to pollutants, chemicals, or certain drugs.

Major Minerals

• Definition:
    - Major minerals (macrominerals) make up 0.05% or more of body weight.
    - Examples include:
      - Calcium
      - Phosphorus
      - Potassium
      - Sulfur
      - Sodium
      - Chlorine
      - Magnesium

• Calcium and phosphorus account for nearly 75% of the mineral elements by weight.

Calcium

• Distribution:
    - Primarily in the inorganic salts of bones and teeth.

• Functions:
    - Provides structure to bones and teeth; essential for neurotransmitter release, muscle fiber contraction, cardiac action potential, and blood coagulation; activates certain enzymes.

• Sources:
    - Milk, milk products, and leafy green vegetables.

• Excess:
    - Can result in kidney stones and deposition of calcium phosphate in soft tissues.

• Deficiencies:
    - Can lead to stunted growth, misshapen bones, fragile bones, and tetany.

Phosphorus

• Distribution:
    - Mostly found in the inorganic salts of bones and teeth.

• Functions:
    - Provides structure to bones and teeth; component in nearly all metabolic reactions; vital in nucleic acids, many proteins, enzymes, and vitamins; important for cell membranes, ATP, and body fluids.

• Sources:
    - Meats, cheese, nuts, whole grain cereals, milk, and legumes.

• Excess:
    - None known.

• Deficiencies:
    - Can lead to stunted growth.

Potassium (K)

• Distribution:
    - Widely distributed; often concentrated inside cells.

• Functions:
    - Helps maintain intracellular osmotic pressure and pH regulation; necessary for impulse conduction in neurons.

• Sources:
    - Avocados, dried apricots, meats, peanut butter, potatoes, and bananas.

• Excess:
    - Uncommon.

• Deficiencies:
    - Can result in muscular weakness, cardiac abnormalities, and edema.

Sulfur (S)

• Distribution:
    - Widely distributed; abundant in skin, hair, and nails.

• Functions:
    - Essential component of certain amino acids, thiamine, insulin, biotin, and mucopolysaccharides.

• Sources:
    - Meats, milk, eggs, and legumes.

• Excess:
    - None known.

• Deficiencies:
    - None known.

Sodium (Na)

• Distribution:
    - Widely distributed; mostly found in extracellular fluids, bound to inorganic salts of bone.

• Functions:
    - Maintains osmotic pressure of extracellular fluids; regulates water movement; essential for impulse conduction in neurons; helps regulate pH and transport of substances across cell membranes.

• Sources:
    - Table salt, cured ham, sauerkraut, and cheese.

• Excess:
    - Can lead to hypertension, edema, and cell shrinkage.

• Deficiencies:
    - Can cause nausea, cramps, and convulsions.

Chlorine (Cl)

• Distribution:
    - Closely associated with sodium; highly concentrated in cerebrospinal fluid and gastric juice.

• Functions:
    - Similar functions to sodium.

• Sources:
    - Same as for sodium.

• Excess:
    - Can result in vomiting.

• Deficiencies:
    - Can cause cramps.

Magnesium (Mg)

• Distribution:
    - Abundant in bones.

• Functions:
    - Required for metabolic reactions in the mitochondria that produce ATP; involved in the breakdown of ATP to ADP.

• Sources:
    - Milk, dairy products, legumes, nuts, and leafy green vegetables.

• Excess:
    - Can cause diarrhea.

• Deficiencies:
    - Can lead to neuromuscular disturbances.

Trace Elements

• Definition:
    - Micronutrients found in minute amounts, each making up less than 0.005% of body weight.

• Include:
    - Iron
    - Manganese
    - Copper
    - Iodine
    - Cobalt
    - Zinc
    - Fluorine
    - Selenium
    - Chromium

Iron (Fe)

• Distribution:
    - Primarily in blood; stored in liver, spleen, and bone marrow.

• Functions:
    - Part of the hemoglobin molecule; assists in vitamin A synthesis; incorporated into several enzymes.

• Sources:
    - Liver, lean meats, dried apricots, raisins, enriched whole grain cereals, legumes, and molasses.

• Excess:
    - Can cause liver damage.

• Deficiencies:
    - Can lead to anemia.

Manganese (Mn)

• Distribution:
    - Most concentrated in liver, kidneys, and pancreas.

• Functions:
    - Part of enzymes required for fatty acid and cholesterol synthesis, urea formation, and normal functioning of the nervous system.

• Sources:
    - Nuts, legumes, whole grain cereals, leafy green vegetables, and fruits.

• Excess:
    - None known.

• Deficiencies:
    - None known.

Copper (Cu)

• Distribution:
    - Most highly concentrated in liver, heart, and brain.

• Functions:
    - Essential for hemoglobin synthesis, bone development, melanin production, and myelin formation.

• Sources:
    - Liver, oysters, crabmeat, nuts, whole grain cereals, and legumes.

• Excess:
    - Rare.

• Deficiencies:
    - Rare.

Iodine (I)

• Distribution:
    - Concentrated in the thyroid gland.

• Functions:
    - Essential for synthesis of thyroid hormones.

• Sources:
    - Food content varies with soil content in different geographic regions; includes iodized table salt.

• Excess:
    - Can cause autoimmune thyroid disease.

• Deficiencies:
    - Leads to decreased synthesis of thyroid hormones.

Cobalt (Co)

• Distribution:
    - Widely distributed.

• Functions:
    - Component of cyanocobalamin; necessary for synthesis of several enzymes.

• Sources:
    - Liver, lean meats, and milk.

• Excess:
    - Can lead to heart disease.

• Deficiencies:
    - Can lead to pernicious anemia.

Zinc (Zn)

• Distribution:
    - Most concentrated in liver, kidneys, and brain.

• Functions:
    - Component of enzymes involved in digestion, respiration, bone metabolism, and liver metabolism; necessary for normal wound healing and maintaining integrity of the skin.

• Sources:
    - Meats, cereals, legumes, nuts, and vegetables.

• Excess:
    - Can cause slurred speech and problems walking.

• Deficiencies:
    - Can result in depressed immunity, loss of taste and smell, and learning difficulties.

Fluorine (F)

• Distribution:
    - Primarily found in bones and teeth.

• Functions:
    - Component of tooth enamel.

• Sources:
    - Fluoridated water.

• Excess:
    - Can cause mottled teeth.

• Deficiencies:
    - None known.

Selenium (Se)

• Distribution:
    - Concentrated in liver and kidneys.

• Functions:
    - Component of certain enzymes.

• Sources:
    - Lean meats, cereals, and onions.

• Excess:
    - Can cause vomiting and fatigue.

• Deficiencies:
    - None known.

Chromium (Cr)

• Distribution:
    - Widely distributed.

• Functions:
    - Essential for the use of carbohydrates.

• Sources:
    - Liver, lean meats, and yeast.

• Excess:
    - None known.

• Deficiencies:
    - None known.