Micronutrition Metabolism Flashcards
What are minerals?
inorganic elements that have physiological function within the body
What does it mean to say “essential” (mineral)?
must be supplied in diet (food/fluids) and vary in amounts
How much of the total body weight do minerals constitute %?
4%
What are the potential roles of the minerals, with its constraints?
- difficult in assessing status, thereby, defining requirements
myriad interactions among minerals and other nutrient and non-nutrients in diet - sometimes, natural experiments of genetic disorders can thrown light on potential roles of minerals in disease processes
Dietary sources of Calcium:
- milk/milk products
- cereal/cereal products
- fish
- tofu
- green vege, dried fruit
- nuts, pulses
What is the % of calcium in human body weight?
1-2%
What is the % calcium in body’s mineral mass?
40%
What is the kg of calcium in human body weight?
1 kg
How much calcium % is in bones and teeth?
99%
how much calcium % is in extracellular fluid, blood, muscle and other tissues?
1%
What formed must calcium be in for it to be absorbed?
ionized
What two routes are calcium absorbed in intestines?
- Paracellular: passive calcium transport through tight junctions between mucosal cells
- Transcellular route: involve active transport by mucosal calcium transport protein
What is the mucosal transport protein called?
calbindin
What is calbindin like?
- saturable
- subject to physiological and nutritional regulation via vit. D
Is the paracellular route dependent on anything? Explain
Yes, dependable on concentration
But, No. It’s nonsaturable, independent of nutritional/physiological regulation,
Explain the process of calcium digestion, absorption and transport:
- Ca2+ cross bursh border membrane of enterocyte through calcium channel TRPV6
- Ca2+ binds to calbindin D which carries calcium across cytosol of enterocyte
- Ca2+ -ATPase pumps calcium across basolateral membrane for entrance into blood
- Some Ca2+ is absorbed between cells, typically with high luminal Ca2+ concentrations
In a mixed diet, how much % calcium is absorbed?
10-30%
What are examples of calcitropic hormones, and at what levels of calcium are they triggered?
- parathyroid hormone (PTH) = low calcium
- 1,25(OH)2D3 = low calcium
- calcitonin = high calcium
What are the functions of calcium?
- only nutrient whose storage form serves functional role = bone
- muscle/nerve stimulation
- blood clotting, wound healing
- hormones
- growth and metabolism
- prevention of osteoporosis, hypertension and protection against colon cancer
What is the bone made of in %?
60-70% mineral
30-40% water and protein
What is the structure of bone?
crystalline structure of Ca + phosphate, laid down on organic matrix of collagen
What are the two types of bones and the % of it?
- cortical bone (75%)
- trabecular bone (25%)
Which type of bone has a fast turnover rate? (t/o)
trabecular bone
What regulates bone metabolism?
osteoblast and osteoclast
How much % of adult skeleton is replaced each year?
10%
What are osteoblasts?
- bone forming cells
- secrete collagen and form matrix
- become calcified
- form osteocytes
What are osteoclasts?
- resorb bone by dissolving Ca and phosphate
- release minerals to circulation
What is the purpose of bone remodelling?
- prevent accumulation of damaged/fatigued bone by regeneration
- allow bone to respond to changes in mechanical forces
- facilitate mineral homeostasis and turnover
What is peak bone mass and when does it occur?
20-30yo
- 90-95% achieved during growing years
- declines after 30
- greater in males and afro-caribbeans
What is the rate of calcium accumulation in skeleton?
150mg/day
What are some calcium metabolic functions?
- promotes blood clotting
- involved in muscle contraction (calmodulin)
- involved in cellular reactions (cellular second messenger of hormonal action)
What is the recommended intake of calcium for pregnant women?
700mg/day
What is the recommended safe upper limit of calcium in adults?
2500mg/day
What is the recommended lower limit LRNI of calcium in adults?
400mg/day
What two things can possibility inhibit absorption of calcium?
phytates and fibre
How much phosphorus is in the body in % and g?
0.65-1.2%
600g
How much phosphorus % is in bone?
85%
How much phosphorus is in soft tissues?
15%
What are sources of phosphorus?
- cheese/cheddar
- yoghurt
- lentils
- milk
- chicken, roasted
- ground beef
- soy milk, peanut butter
What form is phosphorus usually found in?
- combination with minerals
- commonly in pentavalent form in combination with oxygen (PO4^(3-))
What is the value of plasma phosphorus?
3.5mg/100ml
Name 7 phosphorus-containing compounds in the body?
- DNA
- RNA
- ATP
- Creatine phosphate
- c-AMP
- Inositol 3-phosphate
- Phospholipids
What are the functions of phosphorus?
- bone mineralisation
- phospholipids (major mem. component)
- activation of molecules
- nucleotide/nucleoside phosphates
- acid-base balance
- temporary storage and transfer of energy derived from metabolic fuels
What specifically are the functions of phosphates as nucleotides/nucleosides?
- structural role
- energy storage and transfer
- intracellular second messenger
But what are the (actual) functions of phosphorus?
- support tissue growth (individual development OR through pregnancy/lactation)
- replace excretory and dermal levels
What are possible sources of magnesium?
- almonds, cashews, peanuts
- spinach
- shredded wheat cereals
- soymilk
- black beans, edemame
- peanut butter, bread, etc
How is magnesium homeostasis maintained?
by controlling efficiency of intestinal absorption and magnesium losses through the urine
What is the % absorption of Mg in small intestines?
20-70%
What are the 3 mechanisms Mg crosses intestinal epithelium?
- passive diffusion
- solvent drag (following water movement)
- active transport
What are the functions of Mg?
- neuromuscular activity transmission
- cardiac muscle contraction
- cellular (second messenger) role
What specifically are the functions of Mg in cellular role?
- activates enzymes for CHO and protein metabolism
- transportation of Na and K across cell membranes
- influences utilisation of K, Ca and protein
- Mg deficits are frequently accompanied by K and/or calcium deficit
Salt is widely used for?
- modifying flavour
- alter texture/consistency of food
- control microbial growth
Where is chloride mainly found?
ECF, and fully water soluble as chloride anion
What enhances the uptake of sodium?
glucose and anions (citrate, propionates and bicarbonate enhance the uptake of sodium)
In a 70kg male, how much sodium is in his body?
90g
In a 70kg how much % sodium contained in mineral apatite of bone?
75%
What conserves sodium and increases the Na reabsorption in kidney?
angiotensin and aldosterone
What happens in Na depletion?
- stimulate renal production of renin (generates active angiotensin in circulation)
- stimulates vasoconstriction
- increase blood pressure
- decrease water loss
- stimulates aldosterone release from adrenal cortex
What does the atrial natriuretic hormone do?
- counteracts the Na retention mechanisms by suppressing renin and aldosterone release - by inducing water/Na excretion
- decreases bp and antagonize angiotensin
What would be stimulated as a result of raised plasma sodium concentration?
- renal reabsorption of water
- decreases urinary output via antidiuretic hormone from posterior pituitary
This is in contrast to sodium, but how is chloride distributed?
- passively distributed throughout the body
- moves to replace anions lost
How much iron is in the body?
2-4g
What are dietary sources of iron?
- red meat, liver (haem form)
- dark green, leafy vegetables
- fortified breakfast cereals
Describe haemoglobin:
- Fe centrally located in Hb molecule
- porphyrin ring
- red blood cells
Functions of haemoglobin:
- Hb transports oxygen in red blood cells
- necessary for all aerobic cells and tissue
- vital for all aerobic physical activity
Where are the iron stores?
- stored as ferritin and haemosiderin
- in liver, bone marrow and spleen
What is the DRV (dietary reference values) for iron in men and women?
men = 8.7mg/d women = 14.8mg/d
What are the terms to describe toxicity in iron?
haemochromatosis = Fe overload + tissue damage haemosiderosis = Fe overload w/out tissue damage
How much zinc in g is in the human body?
1.5-3.0g
Where is it found?
all organs, tissues and body fluid
What are some sources of zinc?
- oysters
- chicken
- cheddar cheese
- cashew, watermelon seeds, almond
- milk, yoghurt
- red meat, salmon
- cocoa
What are some functions of zinc?
- metalloenzyme component
- gene expression: zinc fingers
- membrane/cytoskeletal stabilisation
- immune function
- sexual maturation
- fertility and reproduction
What are zinc fingers?
proteins with secondary structure of shape, due to presence of zinc atom linked through cysteinyl or histidyl residues in protein
Where are zinc fingers found?
within transcription factors that bind to metal response/regulatory elements in promoter regions of genes to enhance/inhibit transcription
What is the recommended intake of iodine in adults?
150mcg/d
What is the recommended intake of iodine for pregnant/breastfeeding women?
250mcg/d
What is the main result of excessive iodine intake?
thyroid problems
What is the maximum intake of iodine?
600mcg/d
What are the sources of iodine?
- cow’s milk
- sea fish and shell fish
- seaweed
What are iodine’s metabolic functions?
- forms thyroid hormones (T3 and T4)
- regulates BMR and cellular metabolism
- needed for nervous system development in foetus, and pregnancy
What are the physiological effects of thyroid hormones?
- enhance lipolysis in adipose tissue
- enhance contraction in muscle
- promote anabolism in bone
- increase heart rate
- stimulate nutrient digestion and absorption
- stimulate metabolic rate and cellular oxygen consumption in metabolically active tissues
What are the functions of Manganese?
- urea formation
- antioxidant enzymes
What are the sources of Mn?
- tea, nuts, cereals
Deficiency of Mn:
interferes with absorption
What happens in toxicity of Mn?
- hallucinations, memory or motor coordination affected
- Parkinson’s like symptoms
