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CALCIUM and IRON ＡＢＳＯＲＰＴＩＯＮ
Transcript of CALCIUM and IRON ＡＢＳＯＲＰＴＩＯＮ
• One of the hardest minerals to be absorbed from dietary sources
• >99% of total body calcium is found in the
TEETH and BONES
, the remaining is present in the blood, extracellular fluid, muscle and other tissues.
• Exist in the form of hydroxyapatite in bones: Ca₁₀(PO₄)₆(OH)₂
Regulation in absorption of calcium
2 Distinct mechanisms:
Depends on amounts of free calcium available.
Mechanism of iron absorption
Before entering enterocytes
Iron is brought into enterocyte through active transport involving the protein DMT-1 (divalent metal transporter-1)
• DMT-1 is not specific to iron, and can transport other metal ions such as zinc, copper, cobalt, manganese, cadmium or lead.
Sources of iron
2 major forms of dietary iron:
-found primarily in
Other forms of iron
-bound to some other organic constituent of food
-cooking tends to break these interactions and increase iron availability
Functions of iron
• Myoglobin in the muscle cells
- a main iron regulating protein,
and thus decreases iron absorption.
produced by hepatocytes
when iron stores are full. Inflammation can also stimulate hepcidin production.
DIETARY CALCIUM ABSORPTION
Regulation of iron absorption
DIETARY CALCIUM and IRON
MAIN SOURCES OF DIETARY CALCIUM
GREEN LEAFY VEGETABLES
SALMON & SARDINES WITH SOFT BONES
SUNFLOWER SEEDS & ALMONDS
• Occurs only in the duodenum
when calcium intake is low.
-import of calcium into the enterocyte
-transport across the cell
-export into extracellular fluid and blood.
• Calcium enters the intestinal epithelial cells through
voltage-insensitive (TRP) channels
and is pumped out of the cell via a
• Transcellular absorption of calcium across the epithelial cell is enhanced by the carrier protein
(by which its synthesis depends on vitamin D).
• Occurs in the
and in the
when dietary calcium levels are
moderate or high
• Ionized calcium
through tight junctions into the basolateral spaces around enterocytes and then into blood.
* Passive diffusion--movement of calcium ions between mucosal cells and dependent on luminal-serosal calcium ion concentration gradient
parathyroid hormones(PTH) and calcitonin
level of calcium ions stimulates the release of PTH
PTH--> stimulates conversion of 25-hydroxy vitamin D3 to 1,25-dihydroxy vitamin D3 in the kidneys
PTH-->acts on enterocytes in the gut to direct transcription of gene encoding Ca binding protein. Therefore, more Ca binding protein @ membrane of cells.
PTH secretion turns off once Ca level @ plasma are restored
level of calcium ions stimulates release of calcitonin, causing calcium ions in plasma to rise to normal level.
inside the enterocyte
there are two fates for iron:
Bound to ferritin
, an intracellular iron-binding protein.
-Mostly the iron bound to ferritin in the enterocyte will remain there.
-This iron will be lost from the body when the enterocyte dies and is sloughed off from the tip of the villus.
Leave the enterocyte
and enter the body via the basolateral transporter known as
After leaving the enterocyte
Iron that enters the internal environment of the body
from the basolateral surface of the enterocyte
rapidly bound to apotransferrin
• This transfer is facilitated by a protein called
When apotransferrin binds to iron, it is called transferrin
• Transferrin delivers iron to red blood cell precursors,that take up iron bound to transferrin via receptor-mediated endocytosis.
Acids(HCl, vitamin C)
Solubilizing agents(sugar, amino acids)
Iron deficiency(reduced hepcidin)
Alkali(antacids, pancreatic secretion)
Precipitating agents(phytates,tantacid, phosphate)
Iron excess(increased hepcidin)
infection or inflammation
Functions of calcium
Structural development and maintenance of healthy bones and teeth
Nerve impulse conduction
Healthy immune system
Factors favoring calcium absorption
• Vitamin D
• Acidic medium
Factor inhibiting calcium absorption
• Oxalic acid
• Phytic acid
• Excess fat in diet.
• Lack of exercise.
• Increased fiber intake.
• Emotional instability in situations of stress, tension, anxiety, grief, and boredom.