hormones that control ca

1. Calcium homeostasis
EDITED BY
DR DINA MERZEBAN
PHYSIOLOGY LECTURER
FAYOUM UNIVERSITY
WWW.FACEBOOK.COM/MERZEBAN PHYSIOLOGY

2. Calcium homeostasis
 The ability to maintain internal equilibrium of blood calcium and
phosphate ion levels.
 It is maintaining blood calcium level within normal range.
 Blood calcium level: 9-11 mg/100 ml
 Hypercalcemia: An abnormally high concentration of calcium
ions in the blood; at worst, cardiac arrest may occur.
 Hypocalcemia: An abnormally low concentration of calcium ions
in the blood; at worst, cardiac arrest may occur.

3. The adult human body contains about 1 kg of calcium; 99% is
present in bones and 1% in blood and other tissues.
Plasma calcium level: 9 -11 mg/100 ml
1. 50% ionized calcium.
2. 40% protein-bound calcium (bound to albumin).
3. 10% complex diffusible calcium bound to phosphates,
bicarbonates and citrates.

4. Functions of Ca2+
1- Necessary for activation of clotting factors in plasma.
2- It controls membrane excitation in nerve and muscles.
3- It is needed for muscular contraction (SK. & cardiac), also it is essential for
cardiac rhythmicity.
4- It is needed for release of hormones by endocrine cells and release of
neurotransmitters by neuron.
5- It is necessary for the production of milk and formation of bone and teeth.
6- It acts as a second messenger for certain hormones.

5. Absorption of Ca2+ by GIT
Factors that increase the solubility of calcium salts increase its
rates of absorption:
1- PH:
 acid medium ⇈ Ca++ absorption, most Ca++ absorption
occurs in the duodenum due to acid chyme.
 alkalies form insoluble Ca soaps ⇊ Ca++ absorption.
 CaCl2 ingested as acidifying salt and lactose due to production
of lactic acid ⇈ Ca++ absorption.
2- Citrates in drugs aid Ca++ absorption due to formation of
soluble calcium citrate, while phosphates and oxalates ⇊ Ca++
absorption due to formation of insoluble Ca salts.

6. Absorption of Ca2+ by GIT
4- Protein diet ⇈ Ca++ absorption due to formation of soluble
complexes with amino acids.
5- Vitamin D promotes Ca++ absorption from the GIT.
6- Feed back mechanism (PTH effect):
 ⇊ concentration in ECF will ⇈ Ca++ absorption from the gut
through stimulation of PTH.

7. Calcium regulation Involves:
(1) Three hormones
Parathormone(PTH) Calcitonin active vitamin D3
(2) Three tissues
Bone Intestine Kidney
(3) Three bone cells
Osteoblast Osteocytes Osteocalst

8. Bone cells
Osteoblasts: These are bone-forming cells. They secrete collagen and
other bone matrix proteins, as well as alkaline phosphatase, which
promotes deposition of calcium phosphate crystals.
Osteocytes: When osteoblasts become entrapped in collagen matrix,
they differentiate into osteocytes.
Osteoclasts: These cells erode and resorb bones. They achieve this by
acidifying the area of bone surrounding them, which will dissolve calcium
phosphate crystals. They also secrete acid proteases, which dissolve
collagen.

11. Parathormone(PTH)

12. Parathormone action (PTH)
Secreted from parathyroid gland.
(A) On bone
1. Rapid phase: Osteolysis
transport of Ca from bone fluid to ECF by activating a pump in
osteocytic membrane (Osteoblast and osteocytes)
2. Slow phase:  Activity of osteoclasts Bone decalcification

13. Parathormone action (PTH)
(B) on Kidney
1- It decreases PO4 reabsorption in the proximal convoluted tubules
(PCT).
2- It increases Ca2+ reabsorption in distal convoluted tubules (DCT).
3- ↑↑ 1, 25 dihydroxycholecalciferol (1,25 DHCC) in PCV.
(C) on Intestine
PTH increases Ca2+ absorption in intestine by (1,25 DHCC).

16. Regulation of PTH secretion:
PTH is increased by:
(1) Low serum Ca2+ :
(2) High serum PO4:
PTH is decreased by: opposite changes.

18. Vitamin D3
Photosynthesis of vitamin D3 (1,25 DHCC)

19. Actions of 1,25 DHCC:
1) On intestine:
It stimulates Ca2+ and phosphate absorption.
2) On bone:
♠ Low Ca2+ & PO4 → It stimulates osteoclastic activity → bone
resorption
3) On kidney:
++ Ca2+ reabsorption from distal tubules.
++ phosphate reabsorption from proximal tubules.

20. Calcitonin
• It is a polypeptide hormone that is secreted by the parafollicular cells of thyroid
(C cells or clear cells).
• Hypocalcemic hormone
Actions
(1) On bones:
- It inhibits directly bone resorption and stimulate bone
deposition by:
a- Inhibiting activity & formation of osteoclasts.
b- Activation of osteoblasts
(2) On kidney:
It increases Ca & phosphate excretion in urine.

22. Parathormone Calcitonin Vitamin D3
Source: Parathyroid gland Parafollicular cells of thyroid
gland
7-dehydro-cholesterol
>Cholecalciferol
->25-hydroxy-cholecalciferol->1,25-
(OH)2-cholecalciferol
Actions:
1- On bones: a) Rapid phase:
“Osteolysis”
b) Slow phase:
Activity of osteoclasts.
Inhibits activity of
osteoclasts.
It both deposits and mobilizes Ca
and phosphates resulting in
remodeling of bone.
2- On kidneys Reabsorption of Ca2+
from DCT
Phosphate reabsorption
by PCT.
 Excretion of both Ca
and PO4
3- in urine
 Reabsorption of Ca from DCT.
 Reabsorption of PO4
3- from PCT.
3- On GIT: Reabsorption of Ca++
indirectly by activating vit.
D3
 Intestinal absorption of Ca and
phosphate

23. Tetany
• Definition:
It is a condition of increase neuromuscular excitability due to decrease ionized
Ca2+ . It resulted in extensive spasm of the skeletal muscle.
• Causes:
1- Hypoparathyroidism following thyroidectomy.
2- Alkalosis: by persistent vomiting, hyperventilation.
3- Renal failure: results in retention of phosphates → low Ca2+
& failure of α hydroxylation.
4- Rickets (vitamin D deficiency in children).

24. Types of tetany
Manifest tetany:
- Occurs when serum Ca2+ is below 7 mg%
- Carpopedal spasms occur in fingers & toes (accoucheur
hand).
- Laryngeal spasms and respiratory spasms leading to fatal
asphyxia.
Latent tetany (Hidden):
- Occurs when serum Ca2+ is above 7 mg% but < 9.4
mg% (7-9.4 mg%).
- It appears by tests to show increased excitability.

25. Latent tetany
tests to show increased excitability.
1- Chovstek's sign
-Tapping the skin in front of the ear → Twitching of
facial muscles (hyperexcitable facial nerve).
- A tap on the peroneal nerve at lateral aspect of
fibula below its head → dorsiflexion and abduction of the foot.
2- Trousseau sign
Occluding the circulation of the arm with the blood pressure
cuff for few minutes → carpal spasm (accoucheur hand).

26. Accoucheur hand: flexion of wrist & metacarpo-pharyngeal joints with
extension of interphalangeal joints and adduction of the thumbs in the palm.

27. Thank you