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CALCIUM and IRON ABSORPTION

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by

Tekpei Loi

on 2 June 2015

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Transcript of CALCIUM and IRON ABSORPTION

• Most abundant minerals in human body

• 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

• Reservoir:
Skeleton


Regulation in absorption of calcium
CALCIUM ABSORPTION

2 Distinct mechanisms:

a)

ACTIVE
,
transcellular
absorption

b)
PASSIVE
,
paracellular
absorption

Depends on amounts of free calcium available.

CALCIUM
Mechanism of iron absorption
-Occurs in
proximal duodenum
.

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:

1.
Heme iron
-found primarily in
red meats

2.
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

1.
Oxygen carriers
• Haemoglobin

2.
Oxygen storage
• Myoglobin in the muscle cells

3.
Enzyme cofactor

4.
Drug metabolism
(cytochrome P450)

Factors
favoring
iron absorption
Hepcidin

- a main iron regulating protein,
decreases ferroportin
and thus decreases iron absorption.

-
produced by hepatocytes
when iron stores are full. Inflammation can also stimulate hepcidin production.

DIETARY CALCIUM ABSORPTION
IRON ABSORPTION
Regulation of iron absorption
DIETARY CALCIUM and IRON 
ABSORPTION

GROUP 1A
SHIREEN HANIZA
VARMAN
SHI HAO
AIMI NAJWA
TEK PEI
MAIN SOURCES OF DIETARY CALCIUM
MILK
DAIRY PRODUCTS
GREEN LEAFY VEGETABLES
SALMON & SARDINES WITH SOFT BONES
SUNFLOWER SEEDS & ALMONDS
ACTIVE absorption
• Occurs only in the duodenum
when calcium intake is low.
• Involves
-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
calcium-ATPase
.
• Transcellular absorption of calcium across the epithelial cell is enhanced by the carrier protein
calbindin
(by which its synthesis depends on vitamin D).

• Occurs in the
jejunum
and
ileum
and in the
colon
when dietary calcium levels are
moderate or high
.
• Ionized calcium
diffuses
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


PASSIVE absorption
LOW
[Ca2+]
HIGH
[Ca2+]
Dependent upon
parathyroid hormones(PTH) and calcitonin
Low
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
High
level of calcium ions stimulates release of calcitonin, causing calcium ions in plasma to rise to normal level.
Once
inside the enterocyte
,
there are two fates for iron:

1)
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.
2)

Leave the enterocyte
and enter the body via the basolateral transporter known as
ferroportin
.

After leaving the enterocyte


Iron that enters the internal environment of the body
from the basolateral surface of the enterocyte
is
rapidly bound to apotransferrin
, through
ferroportins
.

• This transfer is facilitated by a protein called
hephaestin
.


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.

Haem iron
Ferrous form
Acids(HCl, vitamin C)
Solubilizing agents(sugar, amino acids)
Iron deficiency(reduced hepcidin)
Increased erythropoiesis
Pregnancy
Factors
reducing

iron absorption
Inorganic iron
Ferric form
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
Muscle contraction
Heartbeat regulation
Nerve impulse conduction
CVS
Cell division
Healthy immune system
Factors favoring calcium absorption
• Vitamin D
• Acidic medium
• Lactose

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.
• Aging.
• Caffeine.
• Drugs.

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