Weeks 9 and 10

Reading:UCSD Nutrition:Chapters 6-7
New Nutrition:Unit 3

1. Premise: Our bodies are made up of both organic and inorganic molecules.

A. Over 90% of our body weight is composed of molecules containing carbon (C), hydrogen (H), oxygen (O) and nitrogen (N).

B. The remainder is made up of the so-called inorganic elements and their compounds (minerals and salts), many of which are essential for life. Some of which are there and do not seem to be beneficial or toxic. And others, such as lead (Pb), mercury (Hg) and cadmium (Cd) which are poisons.

2. Premise: Water is special.

A. Water is arguably the most essential nutrient in the TPN bag, since it has so many vital functions among which are its interaction with minerals. Some of the most important activities of water are:

  • a solvent to dissolve inorganic salts to form ions (charged molecules) or organic molecules such as sugars, amino acids, protein, etc.
  • a chemical reactant.
    Example: CO2 + H2O AE H2CO3 (carbonic acid)
  • a source of acid (H+)and base (OH-) by dissociation
    H2O AE H+ + OH-
  • a transport fluid to circulate nutrients and remove waste
  • a coolant by evaporation in sweat and breathing
  • a lubricant in bone and joints

3. Premise: Electrolytes play an important role in nutrition.

A. The ability of a salt to dissolve in water is a function of the positive (cationic) and negatively (anionic) charged particles (i.e. Na+ and Cl-) to be surrounded by water and thus dissociate. Such a solution will conduct electrical current and is called an electrolyte.

B. The balance of salts and water, electrolyte balance, is a delicate one. Disturbances either in gain or loss of salt or of water can have serious health consequence.

4. Premise: There are essential minerals which play many roles in cells and tissues.

A. There are seven essential "bulk" mineral elements required:
  • Cations
  • Sodium (Na+) Potassium (K+)
    Calcium (Ca2+) Magnesium (Mg2+)
  • Anions
  • Chloride (Cl-) Phosphate (PO43-)
    Sulfate (SO42-) Carbonate (CO32-)

    Note that carbonate is obtained by its body in the reaction of CO2 + H2O (see above) and subsequent dissociation and is not required as a nutrient. Carbonate and bicarbonate function as important buffers to maintain acid/base balance, pH.

    5. Premise: Each mineral element plays many roles in cells and tissues.

    A. Osmotic balance: Three major fluid compartments of our body:
    • Intercellular: that aqueous solution within each of the cells
    • Intracellular (also called extracellular or interstitial): that solution which bathes all cells but is external to the cells
    • Blood plasma: the circulating blood, minus the red cells

    Water moves freely across bio-membranes in response to the concentration of salts and other solute molecules. Salt and solute concentrations are regulated by active and passive processes in the membranes including transporters, hormones, and permeability properties. When salt concentrations are not regulated there are serious consequences:

    • Retention of sodium chloride (NaCl) leads to retention of water (edema, swelling )
    • Loss of glucose in urine as in diabetes, causes water loss and dehydration

    B. Bioelectric phenomenon are associated with nerve transmission, nerve-muscle connections, and the senses of vision, hearing, smell, touch and taste. Each depends on changes of the ionic concentration inside and outside the cells regulated by its membrane.
    • In resting cells, extra-cellular sodium is high and potassium low. In the cell itself, sodium is low and potassium high. When stimulated, the membrane changes it permeability. Sodium rushes in; potassium rushes out. An electrical impulse results.
    • Calcium and magnesium ions play a key role in regulating nerve and muscle membrane behavior.
    • Dietary consequences for improper intake of salts and water are manifest as loss of nerve and muscle function.
    • Chloride is an ion that usually passively follows the movement of positively charged ions.

    C. Muscle contraction involves both membrane regulation of salt concentration and the participation of calcium in the act of muscle fiber shortening and elongation.
    • Irregular contractions of the heart, arrythmias are associated with altered salts
    • Low serum Ca can upset muscular contractility.

    D. Structural integrity of tissues and bones depends primarily on calcium and phosphate
    • The insoluble mineral of bone is primarily calcium and phosphate. Inadequate calcium compromises bone maintenance. Calcium deficiency is a serious dietary problem among young and old alike.
    • Cell membranes require calcium and magnesium to cross-link their proteins and lipids to maintain stability.
    • The interaction among cells to form tissues requires calcium.
    • Lubricating fluids in joints and bone contain sulfate derivatives of complex carbohydrates.

    E. Mineral cofactors are required for the catalytic activity of important enzymes
    • Na+ and K+ activate some enzymes in carbohydrate metabolism
    • Magnesium binds substrates to the active centers of enzymes in respiration
    • Calcium stabilizes active forms of some proteins
    • Phosphate ions are directly involved in the oxidative burning of sugars, fats and amino acids and the conservation of released energy as adenine triphosphate (ATP). Synthesis of polymers of glycogen, lipids and proteins from their component parts is driven by high energy phosphorylated intermediates.

    F. Energy conservation and utilization

    6. Premise: There are 11 elements which are known to be required in trace amounts for growth, development and health. They are active through five principal mechanisms:

    A. Catalytic cofactors: Many reactions require trace elements as catalytic cofactors. For example:
    • Zinc is required in over 200 reactions including nucleic acid and protein synthesis.
    • Manganese is required to synthesize connective tissue and bones (collagen).

    B. Oxidation/reduction: Some metal ions, particularly iron, copper, and manganese are involved in the energy metabolism of cells. Iron is involved in the electron transport that ultimately converts oxygen to water. Copper participates in electron transport as well as synthesis of nerve membranes and formation of collagen.

    C. Oxygen binding and transport Oxygen is carried by the red cells of the blood from the lungs bound to hemoglobin which contains iron at its active heme center. Oxygen is released to the tissues where it is picked up by a similar protein, myoglobin, before it accepts electrons and protons to form water.

    D. Metabolic regulation Iron, copper and zinc can regulate the activities of protein and nucleic acid synthesis. Proper immune response requires these trace elements.

    E. Structural integrity The three dimensional architecture of proteins and nucleic acids depends upon zinc and manganese as well as iron and copper. These metals bind and hold large molecules in active configurations. An example is the requirement of zinc for proper conformation of the taste- bud proteins in the tongue. Without zinc, taste and smell are lost. Iodide is incorporated into the amino acids which synthesize thyroid hormones.

    7. Premise: There are several dietary factors which limit trace element status.

    A. Availability: Most foods do not contain adequate amounts of trace metals. The richest sources of iron, copper, zinc and manganese are red meats, fish, chicken and legumes. Fortified flour provides a significant fraction of dietary iron. Supplements are necessary for those who choose a vegetarian diet. Iron deficiency leads to inadequate synthesis of hemoglobin and red cells (anemia).

    B. Solubility: the form in which a metal is present in the diet influences its solubility and thus its ability to be absorbed. Thus complexes of metal with sugars and amino acids can be more effectively adsorbed.

    C. Transport: Some metal complexes move quickly across the gut into the blood; others are not permeable. They are then carried by the blood to cells where they are incorporated into essential molecules or stored.

    D. Regulation: Trace metals, particularly iron and copper, are not effectively excreted. They accumulate and can cause toxicity. Loss of iron is primarily by loss of blood as in menstrual bleeding and ulcers.

    8. Premise: The two most common dietary deficiencies are related to the essential minerals.

    A. Selection of foods and/or supplements to assure adequate uptake is critical:
    • Iron and other trace elements from meat, fish, poultry, eggs, beans or from multi-mineral supplements (iron, copper, zinc, manganese)
    • Calcium from dairy products (milk, yogurt, cheese, ice cream) or supplements

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