Micronutrients Flashcards
Requirements of normal erythopoiesis
Iron
Folate
B12
Low B12 symptoms
Tingling in extremities
Concentrations problems
Macrocytosis
Reasons for low B12
Diet
Malabsorption
Abnormal acid, IF, pancreatic secretions and ileal absorptive function
Pernicious anaemia
Autoimmune disorder where individual develops antibodies against intrinsic factor and/or parietal cells causing decreased IF. Not enough to bind B12 so it can’t be absorbed in the terminal ileum.
B12 malabsorption due to small intestinal issues
B12 binds IF normally but abnormal terminal ileum i.e. through surgical removal or Crohns inflammation means it is not absorbed in the small intestine
Pernicious anaemia diagnosis
Antibodies to parietal cells of IF detected in blood test
Gastric biopsies can provide evidence of autoimmune gastritis, low acid output or other autoimmune diseases
Pernicious anaemia treatment
High doses of B12 required every week for 4-6 months then every 3 months
Response to treatment must be monitored to ensure B12 levels are high, haemoglobin and reticulocytes are responding and neurological symptoms have abated
Loss of specialised receptors on terminal ileum leads to:
Failure to absorb B12
Failure to reabsorb bile salts
Bile salts lost through colon causing irritation and secretory diarrhoea. Decreased bile salts means less fat emulsification and impaired fat absorption.
Mechanism by which partial gastrectomy can lead to low B12
No antrum = no G cells = no gastrin
No gastrin = less gastric acid, less B12 released from food
No pylorus = bile reflux = stomach atrophy
Atrophy = decreased parietal cells = decreased IF therefore less B12 absoprtion
Low B12 in celiac disease
Loss of small intestine villi therefore loss of endocrine cells that secrete secretin and CCK involved in pancreatic stimulation
Schilling test
Radioisotope test used to determine if patient has lack of IF
Rarely used now - time consuming, involves radioisotopes and results can be difficult to interpret
B12 is also known as:
Cobalamin
Steps of vitamin B12 absorption
1) B12 in food released during peptic digestion
2) Parietal cells secrete haptocorrin
3) Parietal cells secrete IF which binds released B12
4) B12-IF uptaken by brush border receptors in small intestine
5) B12-IF cleaved. IF taken back into enterocyte. 80% B12 binds haptocorrin, 20% B12 binds holotranscobalamin
6) B12-haptocorrin goes to liver, B12-holotranscobalamin taken up by all cells for DNA synthesis
7) Pancreatic proteases degrade B12-haptocorrin (currently stored in liver)
Megaloblastic anaemia
Slightly larger and irregularly shaped blood cells than normal
Water soluble vitamins
Vitamin C
All the Bs
Folic acid
Biotin
Fat soluble vitamins
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Absorption of water soluble vitamins
Partly digested by mucosal hydrolyses
Absorbed into mucosal cell and transported to hepatic portal vein
Stored in liver
Absorption of fat soluble vitamins
Form minor components of micelles
Uptake into mucosal cells
Export into lymphatics and then plasma as chylomicrons
Stored in body lipids
Factors affecting bioavaliability
Efficiency of digestion Nutrient intake Foods consumed simultaneously Food preparation method Synthetic or natural nutrient
Vitamin B1
Thiamin
Metabolism of energy yielding
Vitamin B2
Riboflavin
Intermediates via redox reactions
Vitamin B3
Niacin
Vitamin B6
Pyridoxine
Transamination
Vitamin B12
Cobalamin
Transmethylation
Vitamin B9
Folate/folic acid
Vitamin B5
Pantothenic acid
Constituent of coenzyme A
Vitamin B7
Biotin
Carboxylation using coenzyme A
Sources of thiamin
Whole grain, fortified and enriched products
Pork
Thiamin defincieny
Wet (heart) and dry (neuro) beriberi
Wernickes encephalopathy
Caused by alcoholism
Folate deficiency
Macrocytic anaemia
Poor growth and neural tube defects
Caused by alcohol intake, pregnancy, some drugs
Sources of folate
Leafy greens
Legumes, seeds, fortified cereals
Sources of vitamin D
Oily fish
Raw mushrooms
Eggs
Vitamin D deficiency
Rickets
Osteomalacia
Vitamin D absorption
UV light from sun + precursor in liver made from cholesterol makes previtamin D3
+ foods = Vitamin D3 (inactive)
In liver, vitamin D3 hydroylated
In kidneys, hydroxylated again to active form
Folate absorption
Folate occurs as polyglutamate in food. When digested, glutamate breaks off and CH3 added.
Folate absorbed and delivered to cells
Seven major minerals
Calcium Phosphorous Potassium Sulfur Sodium Chloride Magnesium
Iron homeostasis
1 g stored in body
300 mg in myoglobin and respiratory enzymes
2.5 g in RBCs
2 mg taken in from diet
1 - 2 mg lost in feces
20 - 25 mg recycled daily for RBC formation
Iron recycling
Haemoglobin containing iron in RBCs carries oxygen
Bleeding = loss
Liver and spleen dismantle RBCs, package iron into transferrin and store excess iron in ferritin
Sweat, skin and urine = loss
Transferrin carries iron in blood
Some delivered to myoglobin of muscle cells
Bone marrow incorporates iron into haemoglobin of RBCs and stored excess iron in ferritin
Iron absoprtion
Iron in food
Mucosal cells in the intestine (duodenum) store excess iron in mucosal ferritin
If the body needs iron, mucosal ferritin releases iron to mucosal transferrin which hands iron to another transferrin that travels through the blood to the rest of the body
If the body doesn’t need iron, it’s excreted in shed intestinal cells
Heme iron
25% absorbed
Haemoglobin and myoglobin from animal products
5 - 10% dietary iron
Non-heme iron
Vegetable, pulses, supplements
17% absorbed
Absorption of heme iron
Absorbed into mucosal cell as intact porphyrin complex
Affected by iron deficiency but not composition of meal and gastrointestinal secretions
Absorption of non-heme iron
Must be present in duodenum in soluble form
In stomach, ionised by gastric juice and neutralised
Ferric iron precipitated and is uptaken at the brush border into the cell by membrane iron binding protein
Affected by meal composition
Vitamin C is important for iron absorption because:
It is a dietary reducing agent. DMT1 (iron membrane receptor) can only uptake Fe+2 so Fe+3 from non-animal products needs to be reduced
Haem oxygenase
Enzyme that cleaves haemoglobin from iron in animal products freeing up Fe+2 for storage
Hepcidin protein
Peptide hormone from liver that regulates iron
Haemochromatosis
Chronic disorder involving excess absorption and inappropriate storage of iron
Factors affecting heme iron absorption
Iron status of subjects
Heme iron present in meat
Factors affecting non-heme iron absorption
Iron status of subjects
Amount of bioavailable non-heme iron
Balance between dietary factors enhancing and inhibiting iron absorption
Factors enhancing iron absorption
Vitamin C
Meat and fish (meat factor protein)
Organic acids
Factors inhibiting iron absorption
Phylates Iron binding polyphenols Dietary fibre Tannins Calcium
Factors decreasing iron absorption
Intestinal motility
Steatorrhoea
3 stages of iron deficiency
1) Depleted storage iron - low serum ferritin
2) Iron restricted erythopoiesis - low serum transferrin saturation
3) Iron deficiency anaemia - low haemoglobin
Importance of iron
Myelination
Neuronal growth and differentiation
Neurotransmitter regulation
Blood brain barrier closes off to iron at about 2 years old so intake critical in iron deficient populations before this age
