Endocrine Physiology ca homeostasis

1. Endocrine
system
Physiology

2. Presented by/
Dr/ dina hamdy merzeban

3. Endocrine control of calcium metabolism

4. Calcium distribution in the
body

5. Calcium
distribution
in the body

6. The function of
ECF Ca 2+:

7. The function of ECF Ca 2+:
Neuromuscular
excitability:
Excitation-
contraction
coupling
Stimulus-
secretion
coupling:
Maintenance of
tight junctions
between cells:
Clotting of
Blood:

8. The function of ECF
Ca 2+:

9. The function of ECF Ca 2+:

10. The function of ECF
Ca 2+:
Calcium forms part of the intercellular cement
that holds particular cell tightly together. In
addition it is involved in cell motility and cilia
action.
Maintenance of tight junctions between
cells:

11. The function of ECF Ca 2+:
Clotting of
Blood:
Calcium serves as a cofactor in
several steps of the cascade of
reactions that lead to clot
formation. Also it acts as a second
messenger in many cells.

12. Control of Ca2+
metabolism

13. Control of Ca2+ metabolism includes regulation of both:
Calcium homeostasis:( 9-11mg%)
Involves the immediate
adjustments required to maintain
constant free plasma Ca2+
concentration on a minute to minute
basis. (Rapid exchanges between
bone and ECF and to a lesser
extend by modifications in urinary
excretion of Ca2+).
Calcium balance: Involves the
more slowly responding
adjustments required to maintain a
constant total amount of Ca2+ in
the body

14. Regulators of Ca2+ metabolism
three hormones
The principal
regulator is the
parathyroid
hormone
Vitamin D calcitonin

15. Regulators of Ca2+
metabolism
three tissues
bone
kidney
intestine

16. Parathyroid gland

17. Parathyroid gland
Location: Four
glands imbedded
on posterior
surface of Thyroid
Secretes:
Parathyroid
hormone
Function:
Calcium
regulation

18. Parathyroid gland contain two types of endocrine cells
Chief cells
Produce
parathyroid
hormone
Increases
blood
concentration
of Ca2+

19. Parathyroid hormone
The primary hormone
controlling Ca2+ is
parathyroid hormone, PTH
is essential for life
PTH raises the Ca++
concentration in the plasma
This hormone also lowers
PO4 3- in the blood
There is an inverse
relationship between Ca++
& PO4 3- levels in the
blood plasma; the product
of their two concentrations
must be constant

20. Mechanism of
action of PTH

21. The actions of
PTH

22. Action of
PTH on
bone

23. First

24. First
PTH quickly releases Ca++ from the small labile pool in bones
It stimulates the transfer of Ca2+ from the bone fluid across the osteocytic-
osteoblastic bone membrane into the plasma by means of PTH activated
Ca2+ pumps located in the osteocytic osteoblastic bone membrane
Ca2+ is quickly replaced in this area from mineralized bone

25. Second

26. PTH's chronic effect
Under conditions of chronic
hypocalcemia PTH influences the slow
exchange of Ca2+ between bone itself
and ECF by promoting actual localized
dissolution of bone
It stimulates osteoclast to eat up bone,
increasing the formation of more
osteoclasts, and transiently inhibiting
the bone forming activity of osteoblast
Prolonged excess PTH secretion over
months or years eventually lead to the
formation of cavities throughout the
bone, that are filled with very large,
overstuffed osteoclasts

27. Action of PTH on kidney
PTH INCREASES
REABSORPTION OF
CALCIUM & REDUCES
REABSORPTION OF
PHOSPHATE
NET EFFECT OF ITS
ACTION IS
INCREASED CALCIUM
& REDUCED
PHOSPHATE IN
PLASMA
IT ENHANCES THE
ACTIVATION OF
VITAMIN D BY THE
KIDNEY

28. Action of PTH on
intestine
PTH INDIRECTLY
INCREASES BOTH
CA2+ AND PO43-
ABSORPTION FROM THE
SMALL INTESTINE BY
HELPING ACTIVE VITAMIN
D

29. The PTH induced removal of
extra PO43- from the body
fluids is
essential for preventingrepr
ecipitation of Ca2+ freed
from bone. Because of the
solubility characteristic of
Ca3 (PO4)2 salt.

30. The solubility product =
plasma concentration of
Ca2+ X plasma
concentration of PO 3- =
constant.

31. A rise of their
concentrations
will raise this
value above the
solubility
product and
results in the
precipitation of
the salt

32. Regulation of PTH levels
PTH secretion is increased in response to a
fall in plasma Ca2+ concentration and
decreased by a rise in plasma Ca2+ levels
A rise in PO43- will decrease extracellular
Ca2+ causing an increase in PTH
1, 25 2 D3 inhibits the formation of PTH and
so decreases its secretion

33. calcitonin

34. Calcitonin
Calcitonin is a polypeptide hormone secreted by the parafollicular or “C” cells of the
thyroid gland
It is released in response to high plasma calcium
Calcitonin acts on bone osteoclasts to reduce bone resorption
Net result of its action is a decline in plasma calcium & phosphate
It is not essential for maintaining either Ca2+ homeostasis or balance, it is important in
extreme hypercalcemia

35. calcitonin

36. Calcitonin ON BONE
First: On short term
basis calcitonin
decreases Ca2+
movement from the
bone fluid into the
plasma
Second: On long term
basis calcitonin
decreases bone
resorption by
inhibiting the activity
of osteoclasts

37. Calcitonin on kidney
It stimulates
excretion of
Ca2+ and
PO43- in urine
It inhibits 1a
hydroxylase
activity of the
proximal tubules

38. Regulation of calcitonin secretion
Increase plasma Ca2+ stimulates calcitonin secretion and a fall in
plasma Ca2+ inhibits calcitonin secretion
Calcitonin plays a role in protecting skeletal integrity when there
is a large Ca2+ demand as in pregnancy or breast feeding
it hastens the storage of newly absorbed Ca2+ following a meal.

39. Vitamin D

40. Sources
FOOD UV LIGHT MEDIATED
CHOLESTEROL METABOLISM

41. Synthesis
It must be
activated by
two sequential
biochemical
alterations that
involve the
addition of two
hydroxyl
groups
The first of
these reactions
occurs in the
liver and the
second in the
kidneys

42. Vitamin D3
The term vitamin D
refers to group of
sterols that are
formed by action of
ultraviolet rays
Synthesis begins in
skin when cholesterol
derivative is
converted to active
vitamin D3 by sunlight

43. Function of
vitamin D

44. Function of vitamin D
Increase
Ca2+ and PO43-
absorption in
the intestine
It stimulates
Ca2+ and PO43-
reabsorption in
the kidney
Increases the
responsiveness
of bone to PTH

45. Regulation of
plasma ca

46. Regulation of plasma ca

47. Regulation of
plasma ca

48. Regulation of
plasma ca

49. Calcium Disorders
• The affected individual can be asymptomatic or
symptoms can be severe
• Hypercalcemia reduces the excitability of
muscle and nervous tissue, leading to muscle
weakness, decreased alertness, poor memory
and depression
• Other effects are the thinning of bones
• development of kidney stones
• digestive disorders such as peptic ulcers,
nausea and constipation
• Hyperparathyroidism has been called a disease
Hyperparathyroidism: can occur by
excess PTH secretion

50. Calcium Disorders
• The affected individual can be asymptomatic or symptoms can be severed
• Hypercalcemia reduces the excitability of muscle and nervous tissue, leading to
muscle weakness, decreased alertness, poor memory and depression
• Other effects are the thinning of bones, development of kidney stones and
digestive disorders such as peptic ulcers, nausea and constipation
• Hyperparathyroidism has been called a disease of bones, stones and abdominal
groans
Hyperparathyroidism: can occur by excess PTH secretion
PTH hyposecretion leads to hypocalcemia and
hyperphosphatemia. This increases neuromuscular excitability.

51. PTH
hyposecretion
Tetany is a clinical state of increased neuro-
muscular excitability caused by a slight decrease in
the plasma level of ionized calcium
In complete absence of PTH: Death
results within a few days, usually
because of asphyxia caused by
hypocalcemic spasm of respiratory
muscles
A deficiency of vitamin D decreases
intestinal absorption of calcium
Causes: Iatrogenic or autoimmune attack against
the parathyroid glands

52. •Vitamin D
deficiency
rickets in children or
osteomalacia in adults.
decreases intestinal
absorption of calcium.
This can lead to