1. Dr. Shaikh Mujeeb Ahmed Assistant Professor AlMaarefa College
Parathyroid Hormone
ENDO BLOCK 412
Dr. Shaikh Mujeeb Ahmed
Assistant Professor
AlMaarefa College

2. Lecture Objectives
At the end of this lecture the student should be able to
Describe the role of calcium in the body
Enumerate the factors affecting plasma calcium
Describe the mechanisms controlling plasma Ca++ concentration
Describe the chemical nature, source and actions of parathyroid hormone
Describe the chemical nature, source and actions of calcitonin hormone
Describe the role of vit.D in regulation of Ca++ conc.
Describe Pathophysiology of hypo & hyperparathyroidism
Describe the effects of Vit.D deficiency

3. Bound to plasma protein (50%)
Calcium Distribution
Total Body Ca++
Body fluid (1%)
ECF (0.1%)
Free form (50%)
Bound to plasma protein (50%)
ICF in soft tissues (0.9%)
Skeleton & teeth (99%)

4. Vital role of Ca++ Neuromuscular excitability
Excitation contraction coupling in cardiac, smooth & skeletal muscle
Stimulus secretion coupling
Excitation secretion coupling
Maintenance of tight junctions between cells
Clotting of blood

5. Endocrine Control of Calcium Metabolism
Three hormones regulate plasma concentration of Ca2+ (and PO43-)
Parathyroid hormone (PTH)
Calcitonin
Vitamin D

6. Ca++ homeostasis & Ca++ balance
Ca++ adjustment on Minute to minute basis
Exchange between bone and ECF
Ca++ balance
Slowly responding adjustment
Ca++ intake Vs Ca++ excretion
Parathyroid hormone (PTH) the principal regulator of Ca++ metabolism , acts directly or indirectly on all three of these effector sites.

7. Parathyroid hormone secreted by the parathyroid glands,
four rice grainsized glands located on the back surface of the thyroid gland, one in each corner

9. Cont… PTH is essential for life
The overall effect is increase plasma Ca++
Complete absence of PTH ensues death within few days.
It acts on bone, kidneys and intestine
PTH acts to lower plasma PO43- conc.

10. PTH raises plasma Ca2+ by withdrawing Ca2+ from the bone bank.
induces a fast Ca2+ efflux into the plasma from the small labile pool of Ca2+ in the bone fluid.
Second, by stimulating bone dissolution, it promotes a slow transfer into the plasma of both Ca2+ and PO43- from the stable pool of bone minerals in bone itself.

12. Both Ca2+ & PO43- are released in plasma
PTH’s chronic effect is to promote localized dissolution of bone to release Ca2+ into plasma.
Stimulate osteoclast
Both Ca2+ & PO43- are released in plasma
PTH deals with PO4 by its action on kidneys

13. PTH acts on the kidneys to conserve Ca2+ and eliminate PO43-
Absorb more Ca++
Decrease reabsorption of PO43-
an inverse relationship exists between the plasma concentrations of Ca2+ and PO43-
Activation of Vit. D
PTH indirectly promotes Ca++ & PO43- absorption from the intestine by helping Vit.D

14. Regulation of PTH secretion
PTH secretion increases when plasma Ca2 falls and decreases when plasma Ca2 rises.
this relationship forms a simple negative- feedback loop for controlling PTH secretion

15. Calcitonin Polypeptide hormone produced by C cells of thyroid gland
Decreases plasma Ca ++ levels
on a short-term basis calcitonin decreases Ca ++ movement from the bone fluid into the plasma.
Second, on a long-term basis calcitonin decreases bone resorption by inhibiting the activity of osteoclasts via the cAMP pathway.
Calcitonin also inhibits Ca ++ and PO43- reabsorption from the nephron

16. ACTIONS OF CALCITONIN ON BONE
Decresaed osteoclastic number
Decreased osteoclastic activity
Actions are proportional to baseline rate of bone turnover

18. VITAMIN D
cholecalciferol, or vitamin D, a steroid like compound essential for Ca++ absorption in the intestine.
Activated by the addition of two (-OH) groups.
The first reaction occurs in the liver & the second in kidneys.
The active form of vit.D is 1,25-(OH)2- vitamin D3 also known as calcitriol.

19. Figure 19.26: Activation of vitamin D.

20. Figure 19.27: Interactions between PTH and vitamin D in controlling plasma calcium.
Fig , p. 736

21. Disorder of parathyroid hormone
PTH hypersecretion – hyperparathyroidism
Characterized by hypercalcemia & hypophosphatemia
Clinical features:
Muscle weakness
Decrease alertness, poor memory & depression
Cardiac disturbances
Mobilization of Ca2+ & PO43- from skeletal store may results in thinning of bone, fractures, skeletal deformities
Increase incidence of Kidney stones

22. Hyperparathyroidism
Bones
Stones
Abdominal groans

24. PTH hyposecretion Hypoparathyroidism
Inadvertent removal of parathyroid gland
Hypocalcemia and hyperphospatemia
Increased neuromuscular excitability
Muscle cramps twitches
Tingling and pins and needle sensation
Irritability & paranoia

25. SIGNS AND SYMPTOMS OF HYPOPARATHYROIDISM
Positive Chvostek’s (facial muscle twitch) sign
Positive Trousseau’s (carpal spasm) sign
Delayed cardiac repolarization with prolongation of the QT interval
Paresthesia
Tetany

26. Hypocalcemic tetany

27. VITAMIN D DEFICIENCY Decrease Ca++ absorption from intestine.
PTH increases plasma Ca++ from bone
Demineralization of bones - softening
Rickets in children
Osteomalacia in adult.

28. Comparison of normal and osteoporotic bone.
Note the reduced density of osteoporotic trabecular bone compared to normal trabecular bone.
p. 730

29. 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT. 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level. 3 2 1
CALCITRIOL stimulates
increased absorption of
Ca2+ from foods, which
increases blood Ca2+ level.
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 5 6 1
PTH also stimulates
the kidneys to release
CALCITRIOL.
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level. 3 4 2 5 1
High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level. 2

30. References Human physiology, Lauralee Sherwood, seventh edition.
Text book physiology by Guyton &Hall,11th edition.
Text book of physiology by Linda .S .Costanzo third edition