Trace Elements Flashcards
Iron
Functions primarily as a carrier for oxygen (part of hemoglobin and myoglobin)
Important in immune function, cognitive development, temperature regulation, energy metabolism
Hemoglobin Structure: 4 protein subunits (globin) + porphyrin coordinated with Fe in the +2 state (heme), iron in the heme is coordinated to the four nitrogen atoms of the porphyrin, 6th position around the iron of the heme is occupied by O2
Ferritin = major iron storage protein within cells
Transferrin = iron transport protein (more iron is transported when body stores are low or needs increase)
For iron to be taken up by cells in the body, the transferrin-iron complex must bind transferrin receptors
If iron is low, the expression of the gene for transferrin receptors is increased and the expression of the gene for ferritin is reduced
If iron is high, the expression of the gene for transferrin receptors is reduced, resulting in less iron getting into cells and the gene for ferritin is increased, resulting in increased iron stored in enterocyte
Iron Deficiency
When iron is deficient, hemoglobin cannot be produced
Insufficient hemoglobin –> red blood cells are microcytic and hypo chromic and unable to deliver sufficient oxygen to the tissues (iron deficiency anemia)
At risk groups: infants, children, adolescents, athletes, women of reproductive age, pregnant women
Zinc
Essential in the diet for growth and development
Involved in the functioning of over 300 different enzymes, including superoxide dismutase, important for protecting cells from free radical damage
The amount of zinc can be regulated by increasing or decreasing the synthesis of proteins that transport Zn in versus those that transport Zn out of mucosal cells
Involved in function of superoxide dismutase (protects cells from free radical damage)
Used in enzymes that function in the synthesis of DNA and RNA
Used in enzymes involved in carb metabolism and in acid-base balance
Plays a role in the storage and release of insulin, mobilization of vitamin A from the liver and stabilization of cell membranes
Influences hormonal regulation of cell division
Important for immune system function
Deficiency: acrodermatitis enteropathica, symptoms poor growth and development, skin rashes, hair loss, diarrhea, neurological changes, reduced reproduction, reduced immune function, skeletal abnormalities
Toxicity: GI irritation, vomiting, loss of appetite, diarrhea, abdominal cramps, headaches, main problem is copper deficiency
Copper
Cu-containing enzyme, cytochrome c oxidase, is a key component of the electron transport chain located in the inner mitochondrial membrane
Lysyl oxidase- required for the cross-linking of collagen which are essential for the formation of strong and flexible connective tissue
Iron metabolism: Cu-cointaining enzymes are used to convert FeII to FeIII
Cu-containing enzymes are important for production of some neurotransmitters
Copper enzyme is used to produce the pigment melanin
Cu is an essential component of superoxide dismutase, an enzyme that provides antioxidant protection for cells
Several Cu-dependent transcription factors regulate specific genes
Zinc can decrease the bioavailability of copper
Copper absorption: transported to live bound to albumin, liver produces ceruloplasmin, which binds copper and transports it to other tissues
Copper Deficiency
At risk: infants with chronic diarrhea, burn patients
Rare genetic disorder: Menkes, results in a copper deficiency due to a defect in intestinal copper absorption
Symptoms: anemia, abnormalities of bone development
Copper Toxicity
Rare genetic disorder: Wilson’s disease, results in Cu overload, due to inability to excrete Cu in bile
Manganese
Constituent of some enzymes and an activator of other enzymes
Manganese-requiring enzymes are involved in amino acid, carbohydrate and cholesterol metabolism, cartilage formation, urea synthesis and antioxidant protection
Needed for the activity of superoxide dismutase (like copper and zinc)
Selenium
Se can replace sulfur in sulfur-containing amino acids (cysteine and methionine)
Selenium containing enzyme convert T4 to T3
Deficiency can lead to Keshan disease, affecting the heart muscle, symptoms include muscular discomfort and weakness
Toxicity - nausea, diarrhea, fingernail and hair changes, fatigue, irritability
Iodine
More than half the iodine in the body is found in the thyroid gland
Iodine is an essential component of thyroid hormones-thyroxine (T4) and triiodothyronine (T3) made from the amino acid tyrosine
T4 predominant in the blood and converted to the active form T3 by the selenoprotein
Thyroid hormones work by affecting gene expression in target cells
Thyroid hormones promote protein synthesis, and regulate basal metabolic rate, growth, and development
Regulation of Thyroid Hormone Levels
In response to cold or stress, the hypothalamus releases thyrotropin-releasing hormone (TRH) which stimulates the pituitary to release thyroid-stimulating hormone (TSH)
TSH will also be released if thyroid hormone levels are low
TSH stimulates thyroid gland to take up iodine and synthesize thyroid hormones
When supply of iodine is adequate, thyroid hormones can be made and their presence turns off synthesis of thyroid-stimulating hormone
Iodine Deficiency
Goiter: thyroid enlargement is classic sign of iodine deficiency
As iodine intake decreases, secretion of TSH increases- TSH stimulates thyroid hypertrophy and hyperplasia
Neurocognitive impairment
Fluoride
Major functions: effects on the mineralization of bone and teeth
Chronic toxicity = fluorosis (characterized by changes in bone, kidney and possibly nerve and muscle damage)
Acute toxicity = nausea, vomiting, diarrhea, acidosis and cardiac arrhythmias
