The Trace Elements Flashcards
1
Q
How does charge affect bioavailability of minerals?
A
- absorption of minerals with the same charge may depend on the relative amounts in a meal
2
Q
Amounts of minerals in food maybe depend on…
A
Where the food was grown
3
Q
Dietary components may enhance or inhibit…
A
Absorption
4
Q
How is iron absorbed in the diet?
A
- iron is absorbed from the diet in the heme (animal source) or nonheme (plant sources) form
- charge important in iron absorption; Fe2+ (heme or ferrous form) is more soluble and more easily absorbed than the Fe3+ (nonheme or ferric) form
- consumption of nonheme iron with acids (especially vitamin C) and meats aids absorption
5
Q
Where is iron found in the diet?
A
- clams, chili beans, beef liver, eggs, liver, kidney beans, lentils, spinach
- protein sources
- milk is a poor source of iron
6
Q
What is the process of iron absorption, transport, and storage?
A
- heme or ferrous (2+) nonheme iron is absorbed, then converted to the ferric form (3+) by a copper-containing protein in mucosal cells
- some iron is stored in mucosal cells by binding to ferritin, but this is excreted when the cell dies
- transferrin is the protein that carries iron in blood; iron is stored in the liver, bone marrow, myoglobin, and spleen, ferritin-bound
7
Q
What is the function of iron?
A
- a component of myoglobin and hemoglobin
- part of proteins in the CAC and ETC along with transport for O2 and CO2
- part of catalase, drug-metabolizing enzymes (cytochrome P450), and has immune functions as well
8
Q
Where is iron depleted from first?
A
- iron stores, then plasma, then RBCs
9
Q
The only way we lose iron is through..
A
Bleeding (menstruation and pregnancy)
10
Q
What mineral is most likely to be deficient?
A
- iron
- up to 80% of world’s population is deficient
11
Q
What group is most likely to be iron deficient?
A
- women and children are most often deficient – women due to menstruation and children due to the increased needs during growth
12
Q
What is microcytic hypochromic?
A
Small, pale cells because heme group is deficient in RBCs
13
Q
What is iron toxicity?
A
- iron can be toxic acutely (it’s a common cause of poisoning in children), or built up gradually to cause iron overload
- too much iron encourages ROS
14
Q
Normal hematocrit values?
A
Men: 0.420 - 0.520
Women: 0.370 - 0.460
15
Q
Normal hemoglobin?
A
Men: 140 g/L
Women: 123-157 g/L
16
Q
What is hemochromatosis?
A
- condition where you absorb too much iron
- common genetic defect in the Caucasian population, but it often goes undetected by health care providers
- iron overload can cause oxidative damage leading to chronic diseases and premature death
17
Q
Serum vs. plasma?
A
- serum is similar to plasma but without clotting factors and platelets
18
Q
How is hemochromatosis treated?
A
- patients should be advised to watch iron intake, do not take supplements containing iron and have blood checked regularly for ferritin
19
Q
What is the prevalence of inadequate zinc intake?
A
- high across all age groups, especially older men
20
Q
Where is zinc found?
A
- zinc is available in meats and vegetables, but is less easily absorbed from plants due to binding by phytates (present in plant foods)
21
Q
How is zinc absorbed?
A
- zinc homeostasis is controlled in the GI tract - there are protein transport systems for intake and export from the mucosal cells; metallothionein controls the transfer into the blood
- will hold onto zinc in high levels
- metallothionein also binds copper, so high zinc levels can inhibit copper absorption
22
Q
What are zinc fingers?
A
- common DNA binding motif on proteins, allow the regulation of DNA transcription
- these “fingers” enable binding of proteins to regulatory regions of DNA via cross-linking
- some vitamins, and hormones such as estrogen, testosterone and thyroid hormones bind to zinc finger proteins to regulate gene expression
23
Q
How is copper absorbed?
A
- copper absorption is affected by high intakes of other minerals (iron, manganese and molybdenum), most notably zinc
- metallothionein, which is induced by high zinc intake, has greater affinity for copper than zinc and can prevent copper’s entrance into the bloodstream
- phytates in foods can actually increase copper absorption by binding zinc
- deficiency uncommon, only seen with TPN
24
Q
What is the role of mineral antioxidants?
A
- many trace elements function as as antioxidants
- act in different areas to neutralize ROS
- ex. vit E in cell membrane
25
Q
What is manganese?
A
- Mn is part of superoxide dismutase in mitochondria; also required for enzymes for amino acid, carbohydrate and cholesterol metabolism
- when intake is low manganese absorption increases, absorption decreases when intake is high
- elimination occurs through bile
26
Q
What is selenium?
A
- Se is part of glutathione peroxidase, it spares vitamin E by reducing the production of free radicals
- deficiency can cause muscle weakness and discomfort, also poor heart function as seen in Keshan disease
- in countries where the food is grown and eaten locally soil content has an impact on the intakes of minerals; in China areas with low selenium are correlated with Keshan disease, areas with high levels showed fingernail changes and hair loss
27
Q
What is iodine?
A
- iodine is a component of thyroid hormones thyroxine (T4) and triiodothyronine (T3)
28
Q
What is the function of thyroid hormones?
A
- these hormones regulate protein synthesis, basal metabolic rate, and growth and development by controlling gene expression
- a selenium-containing enzyme converts T4 to T3 in the cell for receptor protein binding to control gene expression
- T3 can enter nucleus
29
Q
How are thyroid hormones regulated?
A
- thyroid hormone levels are controlled by release of thyroid-stimulating hormone (TSH) from pituitary gland when blood levels are low
- with TSH, the thyroid gland takes up iodine and synthesizes hormones, which feeds back and turns off TSH
- thyroid hormones cannot be produced in absence of iodine; deficiency of iodine results in reduction of metabolic rate with fatigue and weight gain
30
Q
What occurs with iodine deficiency?
A
- goiter is the result of iodine deficiency, the thyroid gland is enlarged due to continued stimulation of the gland by TSH
- thyroid hormones are needed for growth; stillbirth or spontaneous abortion may occur in pregnancy, cretinism in live births
- goitrogens can cause deficiency, but this is unusual in Canada due to fortification (salt)
- cassava contains goitrogens (turnip and cabbage)
31
Q
What is fluoride?
A
- fluoride deficiency results in greater numbers of dental cavities
- fluoride has an affinity for calcium, it is associated with calcified tissues
- water is fluoridated for the prevention of cavities, but there is concern about toxicity due to high intakes of fluoride (ingestion of toothpaste)
- too much fluoride can result in pitting and staining of the teeth called “fluorosis”
