Calcium and phosphorus levels in the blood are tightly regulated through the actions of parathyroid hormone (PTH), calcitonin, and vitamin D. When blood calcium levels drop, PTH levels rise to promote calcium absorption from the intestine and kidneys and release from bones. Calcitonin acts in opposition to PTH by lowering calcium levels through inhibiting bone resorption and promoting calcium excretion by the kidneys. Vitamin D aids in intestinal calcium absorption and renal reabsorption. Together this hormonal system maintains blood calcium levels within a narrow range through balancing calcium exchange between the blood, bones, intestine and kidneys.

1. METABOLIC RELATIONSHIP IN
Ca/P REGULATION

2. Ca and P are macroelements
• Ca and P in the organism were found as Apatite
crystals in bones and teeth. Hydroxyapatite
crystals= Ca10(PO4)6(OH)2
• Calcium accounts for 1-2 % of body weight in
humans (% 1.7).
• In Animals % 1,4-2,6
• Over 99 percent of total body calcium is found
in teeth and bones

3. • Besides the role of calcium in the contribution to the
structure of bones, also plays role in some significant
cellular activities.
• Calcium has an indispensable role in many events such as
nerve and muscle functions, hormonal mechanism of
action, blood clotting, cellular motility.
• Calcium is absorbed from the small intestine with the help
of calcium-binding protein (calmodulin).
• Its excreted by the urine through the kidneys.
• In calcium deficiency, tetany and its related disorders in
muscle and nerve are seen.

4. • In developing animals, in pregnant women, in laying
hens, and nursing animals Ca should be sufficiently
given in a daily basis in an adequate proportion
• In general, this ratio is between 2/1 and 1/1 in feedstuff.
• Ca / P ratio in the blood should be kept around 2/1
• Ca (mg/dl) x P (mg/dl) = ideally to be 36.
– ie: 9 x 4 = 36
• If this falls <30, Osteomalacia is seen in the elderly and
rickets in the young animals.

5. Blood Ca/P Balance
• Various hormones, tissues and organs are in charge for providing Ca / P
balance in blood.
• Hormones:
– PTH, Calcitonin, 1,25 (OH)2 Vit D3 (and others…)
• Tissue-Organs:
– Parathyroid gland, thyroid gland, skin
– Bone tissue, kidney, intestine, mammary gland, fetus
• In the parathyroid gland, the calcium-sensing
receptor controls calcium homeostasis by regulating the release
of parathyroid hormone (PTH).

6. Blood Ca/P Balance
Is maintained by
• Intestinal absorption
• Uptake from kidneys
• Release and resorption by the bones

7. Ca uptake from the intestine
• 10-20% of the calcium in feed can be absorbed from the small
intestine.
 Vit D
 PTH
 Calcitonin
 Sex steroids
 Ration low in Ca promotes uptake
– Glucocorticoids
– Increase in Intestinal motility
– Protein deficiency
– Insufficiency or absence of bile acids decreases absorption

8. Uptake from Kidneys
• Vit D
• PTH
• Metabolic acidosis
• Calcitonin
• Increase in extracellular volume
• Diuretics
• Prolonged starvation
• High level of phosphates
• Inactivity
24.8.2022 Biyokimya AD Ders Notu 8
decreases
increases

9. Kemiklerde salınım/depolanma
• Vit D – increases release
• PTH - increases release
• Sex hormones –induces bone metabolism
Prostaglandins – (especially Pg E) high doses
induces resorption (storage).

10.  Plasma calcium homeostosis is mainly achieved by a hormonal
system consisting of parathormone (PTH), calcitonin (CT), and the
active metabolites of Vit D (1,25- (OH)2-CC).
 This regulatory system regulates the exchange of Ca between
plasma and three major organs (bone, intestine, kidney).
Blood calcium level

11. PTH
Blood Ca Ca Ca
Diet
PTH levels dtermined by Ca levels
When blood Ca level drops PTH levels increase
Increase in
osteoclastic
activity
Absorption from
intestines
Ca uptake
from kidneys

12. Blood calcium levels
• Release/resorption Ca from bones
• Absorption from intestines
• Reuptake of calcium following the filtration in
the kidneys
are kept within narrow limits

14. PTH
• Released from the parathyroid gland
• Hypercalcemic effect.
• It promotes the uptake of Ca from the distal
tubules in the kidneys. It inhibits the
absorption of phosphate and bicarbonate.
• Increases the mobilization of Ca from the
bones
• Increases the absorption of Ca by the aid of
Vit D3

15. Calcitonin
• It is released from thyroid gland parafolicular
cells
• Calcitonin increases Ca, P elemination from
kidneys
• Hypocalcaemic effect
• Inhibits most of the hormones secreted from
GIS
• It prevents bone resorption by inhibiting
osteoclasts in bones.

16. Vit D3
• Active form : 1,25 (OH)2- CC
• Increases Ca mobilization from
bones,
• Increases Ca absorption from
intestine,
• Increases Ca uptake from the
kidney tubules.

17. • PTH, increases the synthesis of1, 25 (OH)2
CC in kidneys
• Diet is an important source for
cholecalciferol (Vit D3)
• It is converted to 25 hydroxycholecalciferol
by the liver
• And finally to 1,25- dihydroxy cholecalciferol
by kidney proximal tubules
• Production controlled by negatif feed-back
mechanisms
• Hypocalcaemia induces PTH release
• Calcitonin was produced in response
hypercalcemia to by thyroid gland C-cells
• Calcitonin is a potent Ca regulator. Causes Ca and
P decrease in blood.
– Ca renal outcome: Normally, 98% of the
filtered Ca is reabsorbed.
– Bone-Ca balance: Cell membrane contains Ca
++ sensitive receptors.

18. • Sex hormones, glucocorticoids (cortisol), thyroxine, GH, glucagon
and other factors may also indirectly affect regulation.
• Cortisol and thyroid hormones (T3 and T4) inhibit Ca absorption
from the intestines.
• Estrogens and STH stimulate renal hydroxylase to accelerate Ca
absorption.
• Both PTH and CT secretion rate are related to calcemia