Nutritional Requirements for RBCs Flashcards
Fe2+ is called_____
Fe3+ is called _____
Ferrous
Ferric
Iron is an important component in what 3 molecules?
Hemoglobin
Myoglobin
Cytochromes
Bacteria require iron for growth. How does the body prevent the bacteria from getting iron?
By storing iron bound to ferratin inside of enterocytes and macrophages where it is inaccessible to the bacteria.
Does the body have circulating iron?
No - circulating iron would be toxic to the body.
What are the 2 dietary sources of iron and their relative bioavailabilities?
Heme iron from animal products, which is easier to absorb and more bioavailable.
Non-heme iron from vegetables which is harder to digest and has lower bioavailability.
How much iron is consumed in the diet daily?
How much of that is absorbed? How much that is absorbed is excreted?
25mg
Approximately equal balance of absorption of 2mg of iron and excretion of 2mg of iron –> heavy reliance on mobilization from storage in enterocytes, hepatocytes and macrophages to meet iron demands
What 2 factors inhibit hepcidin? What increases [hepcidin]?
Iron levels and hepcidin levels trend in the _____ direction in a normal person
Hypoxia (HIF-1alpha) and erythropoesis
Inflammation
Trend in the same direction
Although ferratin is largely confined to the interior of cells for iron storage, a small amount is secreted in the blood. What do serum ferratin levels tell you about a person’s health?
Low serum Ferratin = iron deficiency
High serum ferratin may indicate chronic inflammation
Describe regulation of iron storage via DMT1.
Describe how iron levels regulate iron uptake in the intestinal crypts.
When serum iron is low, cells in the bottom of the intestinal crypt are stimulated to produce more DMT1 so that when the mature and reach the top of the crypt they will have an increased number of transporters to bring in more iron. This regulation happens at the level of transcription.
The opposite is true when serum iron is high.
Describe the transcriptional regulation that occurs due to iron levels.
When iron is low, iron response elements on the DNA are bound by iron response proteins and transcription of proteins that are important when iron is high (ferratin, ALA) are inhibited. Additionally, the mRNA of proteins involved in iron absorption and mobilization (transferrin, DMT1) is stabilized so more protein can be translated.
When iron is high, iron binds to the iron response proteins and allows transcription of storage proteins and destabilizes the mRNA of iron absorption and mobilization proteins.
____ and ____ stimulate the liver to make hepcidin.
____ and ____ inhibit the liver from producing hepcidin.
Hepcidin inhibits secretion of ferratin from _____ and ____.
High serum Iron and inflammation
Hypoxia and low serum iron
Enterocytes and macrophages
What does hepcidin do?
It binds to ferroportin and causes internalization and degradation of the protein. As such, less iron is released from enterocytes and macrophages.
What are the major contriutors to folate deficiency?
Decreased intake, poor absorption, increased demand
What are the sources of dietary folate?
Foliage
Fortified foods
What are the dietary sources of B12?
Eggs, milk, meat, poultry, oysters
What are the causes of B12 deficiency?
Malabsorption
Inadequate dietary intake
Nitrous oxide
Where is B12 absorbed?
Where is Folate absorbed?
Distal ileum
Jejunum
Vitamin B12 is made by ________ and is found in what dietary foods?
Microorganisms
Meat products but not plant foods
Describe the process of Vitamin B12 absorption.
B-12 enters the body from dietary animal products. When it enters the body it is bound to animal protein. In the stomach, pepsin produced from gastric chief cells separates B12 from the animal protein. At this point, B12 binds to R-protein, which is mostly synthesized by salivary glands and parietal cells in the stomach and protects the B12 from acidic degradation. The B12-R complex can be secreted in the bile or continue on to the small intestine. In the small intestine, the alkaline environment promotes dissociation of the B12 from the R protein so B12 associates with intrinsic factor, which is produced by parietal cells in the stomach. The B12-IF complex is absorbed in the distal ileum via cubilin receptors. Once inside the enterocyte, the B12 is bound to Transcobalamin I or II and released into the portal system which delivers it to tissues. B12 is stored in the liver.
