Wk 2 - Physiology: Vitamins and Minerals Flashcards
What is vitamin B12?
Vitamin B12 (Cobalamin) is a water-soluble vitamin that is derived from animal products such as red meat, dairy, and eggs.
______ is a glycoprotein that is produced by ______ in the stomach and necessary for the absorption of B12 in the ______.
Intrinsic factor is a glycoprotein that is produced by parietal cells in the stomach and necessary for the absorption of B12 in the terminal ileum.
What is the function of vitamin B12?
B12 is used as a cofactor for enzymes that are involved in the synthesis of DNA, fatty acids, and myelin.
What transports vitamin B12 in the extracellular fluid?
Transcobalamins - mainly TC2 (recognised by liver receptor and endocytosed)
Reduced B12 absorption lead to…
anaemia because of failure of red blood cell synthesis
What is pernicious anaemia?
Anaemia resulting from a lack of intrinsic factor (nb only 1% of B12 is absorbed by diffusion - NEED intrinsic factor for absorption!)
Pernicious anaemia is an autoimmune condition in which antibodies to intrinsic factor are produced. Anti-intrinsic factor antibodies bind to and inhibit the effects of intrinsic factor, resulting in an inability of B12 to be absorbed by the terminal ileum.
List some causes of vitamin B12 deficiency.
1. Autoimmune: Pernicious anaemia is an autoimmune condition in which antibodies to intrinsic factor are produced. Anti-intrinsic factor antibodies bind to and inhibit the effects of intrinsic factor, resulting in an inability of B12 to be absorbed by the terminal ileum.
2. Malabsorption:
- Parietal cells in the stomach produce intrinsic factor; therefore, any patient with a history of gastric bypass surgery may be at risk for developing a B12 deficiency because their new alimentary pathway bypasses the site of intrinsic factor production.
- In patients with normal intrinsic factor production, any damage to the terminal ileum, such as surgical resection due to Crohn disease, will impair the absorption of B12 and lead to a deficiency.
- Other damage to the small intestine, such as inflammation from Celiac disease or infection with the tapeworm Diphyllobothrium latum, may also result in a B12 deficiency.
3. Dietary Insufficiency: Vitamin B12 is stored in excess in the liver; however, patients who have followed a strict vegan diet for approximately three years may develop a B12 deficiency from a lack of dietary intake.
What is the effect of surgically removing the terminal ileum?
- Poor absorption of B12
- Bile acids are not reabsorbed – causing irritation and diarrhoea
What is iron?
Iron is a mineral necessary for human life.
What is the function of iron in the human body?
It plays an important role in DNA synthesis and many other metabolic processes. It is also an essential component of heme, within haemoglobin, the protein responsible for transporting oxygen throughout the body.
What is haemochromatosis?
- Hemochromatosis is a disorder associated with deposits of excess iron that causes multiple organ dysfunction.
- Normally, iron absorption is tightly regulated because the body is incapable of excreting excess iron.
- Hemochromatosis occurs when there are high pathologic levels of iron accumulation in the body.
- Hereditary hemochromatosis is the most common autosomal recessive disorder in whites.
Where is iron usually found in the body?
Majority is found in haemoglobin, rest is stored in reticuloendothelial cells and the liver (as Ferritin or Hemosiderin)
What is iron usually stored as in the body?
- Ferritin
- Hemosiderin
How does the body regulate its iron content?
Iron is unique among minerals in that our body has limited excretion ability. Thus, absorption (i.e. iron uptake) is tightly controlled by the hormone hepcidin.
Describe the process of dietary iron uptake in the body.
Iron absorption occurs through the differentiated epithelial cells (enterocytes) of the mid and upper villus, and predominantly in the proximal part of the small intestine.
- Uptake is via the DMT (divalent metal transporter)
- Role for transferrin in uptake from gut lumen (???)
- Once in epithelial cell some iron binds to ferritin
- Some iron passes into blood and is transported bound to transferrin
- The ferritin bound iron stays in the cell and return to lumen when cell is sloughed off top of villus
- Erythropoietin decreases epithelial cell ferritin production and therefore decreases iron which is held in the cell
- Erythropoietin production is stimulated by decreased oxygen concentration in the blood to the kidney (i.e. Blood oxygen content rather than just PO2)
