chapter 12

what are the names of the thyroid hormones that require iodine?

tyrosine thyroxine triiodothyronine

zinc plays an important role in the proper functioning of which two vitamins?

vitamin A and Vitamin D

which vitamin improve the absorption of nonheme iron? why?

vitamin C enhances nonheme iron absorption both by keeping the iron in its more absorbable form ad by forming a complex with iron that remains soluble and more bioavailable

how is copper absorption inhibited by zinc?

when zinc intake is high, it stimulates the synthesis of the protein metallothionein in the mucosal cells. although metallothionein binds zinc, it binds to copper more tightly. therefore when metallothionein is synthesized, it binds to copper, preventing it from being moved out of the mucosal cells into the blood. *stops absorption

what are two main functions of zinc and what role does it play in each function?

zinc is involved in over 300 different enzymes regulates gene expression by allowing protein to fold around the zinc fingers that then allow them to bind to dna and regulate gene expression

if there is more selenium present in the body which vitamin could be reduced?

Vitamin E because this vitamin stops the action of free radicals once they are produced.

what is the diffrencce betwen heme iron and non heme iron?

heme iron-animals. iron that is part of a chemical complex called a heme group, fond in proteins such as hemoglobin n blood and myoglobin in muscle. nonheme iron- plants. a poorly absorbed form of iron found in both plat and animal foods that is not part of the iron complex found in hemoglobin and myoglobin.

define metallothionein and explain its role

metallothionein binds zinc and limits its uptake into the blood. when zinc intakes are high, fewer of the zinc transport proteins are available to move zinc from the lumen into the cells and more zinc transporters move zinc out of the mucosal cells into the lumen and from the cytosol into storage. the synthesis of metallothionein increases. this allows the body to lose zinc when cells die. when zinc intake is low, more zinc transport proteins are available to move zinc from the lumen of the intestine to the mucosal cells and from strage into cystosol. little metallothionein is synthesized, so zinc is not retained in the mucosal cells and not lost when cells die.

iodine is needed for the synthesis of what?

thyroid hormones

outline the key steps in iron absorption and transport

1. heme iron is absorbed as part of the heme group. once inside the cell the iron is released. 2. nonheme iron is absorbed in the ferrous form (Fe2+) 3. once the iron is inside the mucosal cells, some iron may bind to ferritin for storage 4. when the mucosal cells die, iron bound to ferritin is excreted in the feces. more iron is lost when body stores are high. 5. iron that enters the blood is converted to ferric iron (Fe3+) 6. transferrin transports iron to liver, bone, and other cells. more iron is transported when body stores are high. 7. most iron loss is due to blood loss. when red blood cells die the iron is released for resuse.

provide an example of a selenoprotein that selenium assocciates with and define what function it performs

glutathione peroxidase is an enzyme that helps protect cells from oxidative damage.

what are groitrogens and what do they do?

groitrogens are found in turnips, cabbage they're substances found in food that interfere with the utilization of iodine or with thyroid function

what is the differnce between hemoglobin and myoglobin?

hemoglobin= iron-containing protein in red blood cells that binds oxygen and transports it through the bloodstream to cells myoglobin- an iron containing protein in muscle cells that binds oxygen

what condition is associated with excess iron, and why?

iron overload- caused by hemochromatosis which is an inherited condition, caused by a defect in the gene hepcidin and other proteins involved in iron uptake. this allows excess iron to enter circulation. treatment includes 2-4 months transfusions to reduce iron

what happens if iodide is deficeint in the body?

it reduces the production of thyroid hormones. causes fatigue and weight gain- enlarged thyroid