Changes

==Calcium in the Body==

==Introduction==

 

Calcium is essential for many intracellular and extracellular functions. These include:

Calcium is essential for many intracellular and extracellular functions. These include:

* Enzymatic reactions and membrane stability

* Enzymatic reactions and membrane stability

* Structural integrity of bone and teeth

* Structural integrity of bone and teeth

Within the serum:

* 55% of the Calcium is ionised - this is the biologically active form.

* 10% of the calcium is in complexes such as citrate and phosphate - together with the ionised form, this constitutes ultrafilterable calcium.

* 35% of the calcium is bound to plasma proteins.

Extracellular calcium can be measured in two ways:

**Within the serum:

# As total calcium - normal levels are 2.45-2.83 mmol/l and are affected by serum protein levels

*** 55% of the Calcium is ionised - this is the biologically active form.

# As ionised calcium - normal levels are 1.13-1.33 mmol/l. This is the biologically active form.

*** 10% of the calcium is in complexes such as citrate and phosphate.

areful sample handling and prompt measurement are essential for reliable results which can also  be affected by acid-base disturbances

**** Together with the ionised form, this constitutes ultrafilterable calcium.

*** 35% of the calcium is bound to plasma proteins.

** Extracellular calcium can be measured in two ways:

**# '''Total calcium'''

**#* Normal levels are 2.45-2.83 mmol/l

**#* This measurement can be affected by serum protein levels

**# '''Ionised calcium'''

**#* Normal levels are 1.13-1.33 mmol/l

**#* Biologically active form

**#* Careful sample handling and prompt measurement are essential for reliable results.

**#* This measurement can be affected by acid-base disturbances

==Calcium Homeostasis==

==Calcium Homeostasis==

 

There are regulatory mechanisms which maintain calcium homeostasis:

There are two lines of defence to maintain calcium homeostasis:

#Buffering - exchangeable calcium is present in bone salts - amorphous calcium phosphate (CaHPO4) is in a state of reversible equilibrium with calcium and phosphorous in extracellular fluid. Exchangeable calcium is alsp present in mitochondria.

#Buffering

#Hormonal regulation - calcium levels in the body are regulated by hormones produced in the [[Parathyroid Glands - Anatomy & Physiology|Parathyroid Glands]], the C-Cells (also called parafollicular cells) of the [[Thyroid Gland - Anatomy & Physiology|Thyroid Gland]] and the kidneys.  

#*Exchangeable calcium in bone salts - Amorphous Calcium Phosphate (CaHPO4) is in a state of reversible equilibrium with calcium and phosphorous in extracellular fluid.

#*Exchangeable calcium in mitochondria

#Hormonal regulation

 

Calcium levels in the body are regulated by hormones produced in the [[Parathyroid Glands - Anatomy & Physiology|Parathyroid Glands]], the C-Cells (also called parafollicular cells) of the [[Thyroid Gland - Anatomy & Physiology|Thyroid Gland]] and the kidneys.  

*'''Chief Cells''', also known as ''Principal Cells'', of the Parathyroid Gland secrete '''Parathyroid Hormone''' (PTH) which INCREASES Calcium level in the blood.

*'''Chief Cells''', also known as ''Principal Cells'', of the Parathyroid Gland secrete '''Parathyroid Hormone''' (PTH) which INCREASES Calcium level in the blood.