Calcium

Sources

1- Milk and its products (cheese, yughert)

2- Beans, egg yolk Both Ca and P are required for bone formation and other non-skeletal functions.

Factor affecting Ca absorption

Body calcium

99 % of Ca present in bones and teeth in the form of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂

1 % present in body fluid

Blood calcium:

Blood Ca

Blood Ca level 9-11 mg/dl, No Ca in RBC

Plasma Ca is present in 2 forms:

1- Ionized (diffusible) 5-6 mg   

It is the active form if ↓ leads to tetany

2- Non Ionized (bound) 4-5 mg, bound to albumin if ↓ no tetany

Factors affecting blood Ca (Ca hemostasis)

Hormonal factor

1- Parathyroid hormone  (PTH)  

↑ blood Ca by increasing

1- Absorption of Ca from intestine

2- Reabsorption of Ca from kidney

3- Resorbtion ( mobilization of Ca from bone to blood

 4- ↑ P excretion

2- Calcitriol (1,25 dihydroxycholecalciferol) active vitamin D3, ↑ Ca by

increasing

1-Absorption of Ca from intestine

2-Reabsorption of Ca from kidney

3-Resorbtion (mobilization of Ca from bone to blood

Factors that decrease Ca level:

3- Calcitonin secreted from C cell of thyroid gland

↓ Ca in blood by deposition in bones

4- Estrogen

Has a role in Ca metabolism in bones as calcitonin ,

↓ Ca in blood by deposition in bones

In menopause , oestomalachia occurs due to ↓ estrogen

Other factors:

1- Solubility product : Optimum absorption of Ca occurs at a ratio of 2:1 or 1:1 with P.

2- pH :  Ca is soluble and ionized at normal pH 7.4, alkalosis ↓ Ca

Functions of Ca (role of Ca in metabolism)

1-Enters in structure of bone and teeth

2-Contraction of muscle

3-Transmission of nerve impulse

4- ↓ neuromuscular irritability

so its deficiency leads to tetany that is treated by Ca

5- Blood and milk clotting: 

Casein in milk + Ca in presence of rennin forms insoluble Ca paracasinate (milk clot) (give sense of fullness in infants).

6- Combines with calmodulin

 which acts as second messenger for some hormone

7-Activates various enzymes (glycogen phosphorylase ,kinase).

Excretion

Mainly in feces, small amount in urine

Requirement

Adult 800 mg/day,  

Pregnancy & lactation 800-1200 mg/day

Alterations in serum Ca

Hypercalcemia

Causes

1- Primary hyperparathyrodism due to adenoma in gland

2- Secondary hyperparathyrodism

3- ↑ intake of vitamin D

4- Cancer bones

5- Drugs

Effect hypercalcemia

  Stone kidney, vomiting, abdominal cramp, constipation

Hypocalcemia

1-Hypoparathyrodism (primary or surgical removal)

2- Alkalosis

3- Kidney disease

Due to ↓ formation of calcitriol

Calcium Deficiency in bone

1-Rickets: in growing Children.

2- Osteomalacia in adults.