Parathyroid Gland - Techno Ayurveda

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The Parathyroid Gland
Dr. Mahesh Kundagol

Parathyroid Gland Anatomy
Four Parathyroid
glands are usually
found posterior to the
thyroid gland
Total weight of
parathyroid tissue is
about 150mg

Anatomy & Location of Parathyroid Gland

Parathyroid Gland - Overview
Calcium & Phosphate Metabolism
Distribution & Balance of Ca & PO 4
Hormones involved
– Parathyroid Hormone
– Calcitonin
– Vit. D
Diseases associated with the Parathyroid
Gland

Ca 2+ Distribution & Balance

Ca 2+ Distribution & Balance cont..

PO 4- Distribution & Balance

PO 4- Distribution & Balance cont.

Bone

Parathyroid Hormone (PTH)
• A peptide hormone that increases plasma
Ca 2+
• Causes increase in plasma Ca 2+ by:
1. Mobilization of Ca 2+ from bone
2. Enhancing renal reabsorption
3. Increasing intestinal absorption (indirect)

Biosynthesis, Storage & Secretion of PTH
PTH is synthesized as the preprohormone
(Preproparathyroid Hormone) by parathyroid
gland chief cells
The active form of PTH is cleaved from the
preprohormone before release from the gland
PTH is synthesized continously (it is either
released from the gland or degraded)
PTH is released by exocytosis in response to
reduced plasma calcium
Vitamin D feeds back to reduce PTH secretion as
a secondary mechanism

Regulation of PTH release by Plasma
Ca 2+ Levels
• PTH is released by chief cells in the
parathyroid gland.
• Chief cells contain receptors for Ca 2+
• A decrease in plasma Ca 2+ levels mediates
the release of PTH
• Conversely, hypercalcemia inhibits PTH
release

BONE
Biological Activity of PTH
– PTH stimulates bone osteoblasts to increase
growth & metabolic activity
– PTH stimulated bone resorption releases
calcium & phosphate into blood
KIDNEY
– PTH increases reabsorption of calcium &
reduces reabsorption of phosphate
– Net effect of its action is increased calcium &
reduced phosphate in plasma
INTESTINE
– Increases calcium reabsorption via vitamin D

Bone Growth and Calcium
Metabolism
Epiphyseal plate – new bone growth site
Chondrocytes, osteoblasts & calcification build bone

Bone Growth and Calcium
Metabolism
Figure 23-19: Bone growth at the epiphyseal plate

Control of Calcium Balance &
Metabolism
Parathyroid H
– Vitamin D
– Sun/diet
Calcitonin
– Thyroid
– C-cells
(Phosphate balance)
Figure 23-23: Endocrine control of calcium balance

Calcitonin
A thyroid hormone
produced by C-cells
Physiological
effects are opposite
to those of PTH
Rapid acting, short
term regulator of
plasma Ca levels

Calcitonin Lowers Blood Ca
Calcitonin is made by the C cells of the thyroid
gland
A large peptide "prohormone" is made and then
cut down to the 32 amino acid calcitonin
Stimulates osteoblasts, inhibits osteoclasts
Causes removal of Ca from plasma to calcify new
bone
Lowers plasma Ca (opposes PTH)
Minor role in adult due to PTH feedback
Major role in children due to the rapid nature of
bone remodeling and its effect on osteoclastic
activity

Vit. D
Vit. D family comprises of several diferent
compounds, all having similar functions.
Most important is Vit. D 3 (cholecalciferol)
Derived from irradiation of 7-
dehydrocholesterol in skin by UV rays
Causes Ca absorption fron intestinal tract
Active form of this hormone is 1,25-
dihydroxycholecalciferol (calcitriol)

Active Vitamin D (Calcitrol) is Made in 3 Steps by
Different Organs
‣ The skin uses ultraviolet sunlight to make vitamin
D3 (cholecalciferol) from cholesterol
‣ The vitamin D3 is converted to 25-
Hydroxycholecalciferol in the liver
‣ Stimulated by PTH
‣ The 25-Hydroxycholecalciferol is made into
calcitriol (1, 25-Dihydroxycholecalciferol) in the
kidney
‣ Stimulated by PTH
The main effect of calcitriol is to increase
intestinal absorption of Ca

Other hormones affecting Ca
concentration and bone development:
Estrogens: promote bone growth. When
estrogens are reduced at menopause,
osteoporosis is accelerated.
Testosterone: stimulates bone and cartilage
growth
Growth hormone: promotes bone and
cartilage growth and increases intestinal
absorption of Ca

Disorders of Calcium Balance
Hypercalcemia – hormone excess
• caused by either excessive bone
resorption or increased calcium absorption
• hard to diagnose, often asymptomatic
- stones
- bones
- groans
- moans
- overtones

Hypocalcemia
• PTH or vitamin D deficiency
• calcium receptor deficiency
• rickets and osteomalacia
- disordered cartilage, poor bone
formation at epiphyseal plates
- leads to skeletal defects

Osteoporosis: Disease of Bone Growth &
Calcium Metabolism
Bone reabsorption
exceeds deposition
Osteoclasts mobilize
Ca ++ to plasma
Factors: inadequate
Ca ++ intake, genes,
hormones, smoking
Figure 23-21: Osteoclasts are responsible for bone resorption

Defenses against hypocalcemia
and hypercalcemia
Organ Hypocalcemia Hypercalcemia
Parathyroid ↑PTH secretion ↓PTH secretion
Kidney ↓GFR ↓filtered Ca ++
↑Ca ++ reabsorption
↑GFR ↑filtered
Ca ++
↑1,25(OH) 2
D 3
↓Ca ++ reabsorption
↓1,25(OH) 2
D Gastrointestinal tract ↑Ca
++
absorption ↓Ca ++ absorption 3
Skeleton ↑bone resorption ↓bone resorption

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