Parathyroid and Calcitonin Physiology

Physiology of Calcium homeostasis, Parathyroid hormone, calcitonin and vitamin C

1. Parathyroid
and Calcitonin
Prof. Dr. Rashid Mahmood
(Courtesy: Prof. Dr. M. Yousaf, Dr. Abroo Kainat)
A patient post thyroidectomy admitted in surgical ward presents
in morning round with twisting of fingers while checking her Blood
pressure. Her serum calcium is very low (6mg/dl; Normal 9-
11mg/dl) on that day .
1.What is your diagnosis ?
2.Name the Hormones responsible for Calcium homeostasis, and
describe the role of each.
3.What is the management of above patient?
4.What are the effects of low level and high level of calcium?

2. Learning Objectives
•Goal/Aim: To give the understanding of the
physiology of Calcium Homeostasis
•Specific Objectives: By the end of this lecture
the students will be able to:
i.Describe the regulation of blood Calcium
ii.Describe the effects of Parathyroid hormone
iii.Describe the effects of Calcitonin
iv.Describe the effects of Vitamin D
2© Prof. Dr. Rashid Mahmood

3. Triad of Ca++ Homeostasis
•To regulate THREE
Calcium
Phosphorus
Bone
•Regulated by THREE:
Parathyroid Hormone (PTH)
Calcitonin
Vit. D
•Regulated at THREE sites:
Kidney
Intestines
Bone
3© Prof. Dr. Rashid Mahmood

4. Importance of the topic
•Normal calcium level important
for:
1.Contraction of skeletal muscles
2.Contraction of smooth muscles
3.Cardiac muscle contraction
4.Transmission of nervous
impulses
5.Clotting of blood
6.Secretory activity of the glands
4© Prof. Dr. Rashid Mahmood

5. Daily calcium exchange
(1000
5© Prof. Dr. Rashid Mahmood

6. Assessment Q. No. 1
•Name the hormones that control Calcium
metabolism
6© Prof. Dr. Rashid Mahmood

7. Learning Objectives
•Goal/Aim: To give the understanding of the
physiology of Calcium Homeostasis
•Specific Objectives: By the end of this lecture
the students will be able to:
i.Describe the regulation of blood Calcium
ii.Describe the effects of Parathyroid hormone
iii.Describe the effects of Calcitonin
iv.Describe the effects of Vitamin D
7© Prof. Dr. Rashid Mahmood

8. PTH
•Physiologic Anatomy
•Chemistry/ Structure
•Functions
•Site of action
•Mechanism of action
•Regulation
8© Prof. Dr. Rashid Mahmood

9. Physiologic Anatomy
9© Prof. Dr. Rashid Mahmood

10. Parathyroid Gland
Chief cells:
hormonal
production
Oxyphil
cells: no
known
functions
10© Prof. Dr. Rashid Mahmood

11. Chemistry of PTH
•Protein in nature
•84 amino acids
•A fragment of 34 amino acids have some
parathyroid hormonal activity
11© Prof. Dr. Rashid Mahmood

12. Functions of PTH
•Maintenance of blood Calcium level
•Maintenance of blood Phosphate level
•Activation of Vitamin D
•Actions on
Bone
Intestine
Kidney
12© Prof. Dr. Rashid Mahmood

13. Maintenance of blood Calcium level
by PTH
•Normal blood calcium level = 9-11 mg/dl
•PTH→ ↑blood calcium level
Resorption from the bones
Reabsorption from the renal tubules
Absorption from GIT
13© Prof. Dr. Rashid Mahmood

14. PTH Hormonal effects on Bone
Action Rapid phase Slow phase
Onset of action within minutes days and weeks
Action on
Osteoclasts
↑activity of
Osteocytes (Mainly
Osteoclasts)
already present (↑
activity of osteocytic
pump)
Formation of new
Osteoclasts
Reabsorptive action of amorphous
calcium salts and
PO
4
(Osteolysis)
Resorption of bone
itself osteoporosis
14
Rapid phase & Slow phase

15. Effects of PTH
15© Prof. Dr. Rashid Mahmood
CaSR= Calcium
Sensing receptor

16. Functions of PTH
16© Prof. Dr. Rashid Mahmood

17. PTH effects on Kidney
17
↑ reabsorption
of Mg, H
+
↓reabsorption
of Na
+
, K
+
and
amino acids
© Prof. Dr. Rashid Mahmood

18. PTH: Main functions
18© Prof. Dr. Rashid Mahmood

19. Effects of PTH on blood Ca
++
and PO
4
19© Prof. Dr. Rashid Mahmood

20. Effects on intestine
•PTH→ formation of
1,25,dihydroxycholecalciferol→formation of
Calcium binding protein
»Calbindin
Calcium stimulated ATPase
Alkaline phosphatase
↑ calcium
absorption
20© Prof. Dr. Rashid Mahmood

21. Mechanism of action of PTH
•Cyclic AMP mechanism
21© Prof. Dr. Rashid Mahmood

22. Regulation of secretion of PTH
•Hypocalcemia is the most important
stimulus for PTH production & secretion
•Hypocalcemia→ hypertrophy of
parathyroid gland e.g.
In pregnancy
During lactation
In rickets
•Hypercalcemia →↓activity and size of
parathyroid gland
22© Prof. Dr. Rashid Mahmood

23. Effect of Ca level on PTH secretion
23© Prof. Dr. Rashid Mahmood

24. Assessment Q. No. 2
•Which ions are likely to be secreted more
than normal in urine if PTH is deficient?
24© Prof. Dr. Rashid Mahmood

25. Learning Objectives
•Goal/Aim: To give the understanding of the
physiology of Calcium Homeostasis
•Specific Objectives: By the end of this lecture
the students will be able to:
i.Describe the regulation of blood Calcium
ii.Describe the effects of Parathyroid hormone
iii.Describe the effects of Calcitonin
iv.Describe the effects of Vitamin D
25© Prof. Dr. Rashid Mahmood

26. Calcitonin
•Secreted by Thyroid gland
Parafollicular cells or C- cells
•Effects are opposite to parathyroid
hormone
•Lesser role as compared to PTH
•Decreases the calcium level in the blood
•Stimulated by ↑ serum Ca
++
level
26© Prof. Dr. Rashid Mahmood

27. Effect on Bones
•Calcitonin →
↓ Osteoclastic activity
↓ Activity of osteocytic calcium pump
↓ Osteolysis
↑ Osteoblastic activity
↓ calcium level in the blood
Remodeling process shifted towards more
deposition than resorption of bone 27

28. Effect on bones (contd.)
Prolonged effects
Calcitonin →
↓ Formation of new osteoblasts leads to
secondary decrease in Osteoblastic activity
Finally ↓activity of both osteoclasts and
osteoblasts
Hypocalcemic effect is transient
28© Prof. Dr. Rashid Mahmood

29. Assessment Q. No. 3
•Activity of which cells is increased in
bones under the effect of calcitonin?
29© Prof. Dr. Rashid Mahmood

30. Still have one more hormone to
go!!!
30© Prof. Dr. Rashid Mahmood

31. Learning Objectives
•Goal/Aim: To give the understanding of the
physiology of Calcium Homeostasis
•Specific Objectives: By the end of this lecture
the students will be able to:
i.Describe the regulation of blood Calcium
ii.Describe the effects of Parathyroid hormone
iii.Describe the effects of Calcitonin
iv.Describe the effects of Vitamin D
31© Prof. Dr. Rashid Mahmood

32. Vitamin D
•Potent effect to ↑ Ca
++
absorption from the
intestinal tract
•Cholecalciferol (vitamin D3 ) is formed in the
skin and activated by liver and kidneys
•In the absence of PTH , almost none of the 1,
25 dihydrocholecalciferol is formed
•Several effects on intestines, bones, and
kidneys
•↑ blood Ca
++
and PO
4
through ↑ absorption
from intestines & ↓ excretion by kidneys
32© Prof. Dr. Rashid Mahmood

33. Activation of Vitamin D & its actions on intestine
33
© Prof. Dr. Rashid Mahmood

34. Review of Calcium Homeostasis
© Prof. Dr. Rashid Mahmood 34

35. Review of Calcium Homeostasis
35
(Contd…)
© Prof. Dr. Rashid Mahmood

36. Calcium ,
PTH, Vit D
© Prof. Dr. Rashid Mahmood 36

37. Calcium
Homeostasis
Review
(Contd…)
37
© Prof. Dr. Rashid Mahmood

38. Take Home points (1/3)
•Calcium Homeostasis is essential for
normal living
•Calcium levels are regulated by mainly
three hormones: Calcitonin, PTH, and
activated Vitamin D
•Calcium levels also maintained by utilizing
exchangeable calcium with amorphous
salts in the bone and Calcium in the ECF
38© Prof. Dr. Rashid Mahmood

39. Take Home points (2/3)
•PTH increases blood Calcium levels by
resorption from Bone , Renal reabsorption
and Intestinal reabsorption of Calcium
through increased synthesis of active
vitamin D
•PTH is necessary for activation of vit. D
•PTH decreases blood PO
4
level

by

decreasing its reabsorption in kidneys.
This action is more marked than increase
absorption from intestines and bones
39

40. Take Home points (3/3)
•Calcitonin decreases blood calcium levels,
and increases bone deposition
•Activated Vitamin D has several effects on
intestines, bones, and kidneys. It
increases absorption of Ca
++
and PO
4
into
ECF
40© Prof. Dr. Rashid Mahmood

41. Assessment Q. No. 4
•PTH secretion is inhibited by
A.↑ activity of dihydrocholecalciferol
B.↑ serum Ca
++
level in blood
C.↑ serum Mg
++
level in blood
D.↓ Calcitonin
E.Thyroid surgery
41© Prof. Dr. Rashid Mahmood

42. References
•Guyton and Hall Textbook of Physiology , 13
th

Edition
•Ganong’s review of Medical Physiology,25
th
edition
•Human Physiology, from cells to system, Lauralee
Sherwood, 9
th
edition
© Prof. Dr. Rashid Mahmood 42

43. Next Topic
•Next Topic: Mineralocorticoids,
•Thu, 02/11/2017, 10.30 to 11.30
•Prior knowledge required for next
topic:
Anatomy & Histology of Adrenal Gland
Physiology of Glucocorticoids
Biochemistry of Glucocorticoids and
Mineralocorticoids
© Prof. Dr. Rashid Mahmood 43

44. The End
Thank You
Questions ?
Comments ?
[email protected]
[email protected]
ppt also available at
https://www.slideshare.net
© Prof. Dr. Rashid Mahmood 44