The human skeleton consists mainly of cortical and trabecular bone. There are three main types of bone cells - osteocytes, osteoclasts, and osteoblasts. Osteoblasts form new bone, osteoclasts resorb bone, and osteocytes maintain bone structure. Bones provide structure, protection, storage, and leverage. Hormones like estrogen, calcitonin, parathyroid hormone, and thyroxine regulate bone metabolism. Vitamin D and calcium are important for bone health and absorption. Osteoporosis occurs when bone resorption exceeds formation, decreasing bone density and strength and increasing fracture risk. It is diagnosed using DEXA scans and treated with supplements, bisphosphonates,

1. By Nishay Patel

2. Basics About Bone
Facts
•The human skeleton consists of 80% cortical bone and 20%
trabecular bone.
•More than 99% of the body’s calcium is in the skeleton.
•There are long, short, flat and irregular bones in the body.
Functions
• Support
• Leverage
• Protection
• Storage of Calcium salts and Phosphate ions
•Production of Erythrocytes
Parietal bonevertebracarpals
humerus

3. Bone cell types
• OSTEOCYTES – are mature bone cells which maintain bone
structure by recycling calcium salts in the bony matrix and
assisting in repairs
•OSTEOCLASTS – secrete acids which dissolve bony matrix and
release stored mineral ions (calcium and phosphate ions),
responsible for bone resorption.
•OSTEOBLASTS – responsible for the formation and
mineralisation (calcification) of new bone matrix.

4. Bone Growth Mechanism
• Osteoblasts are responsible for creating new bone
(osteogenesis). Osteoblasts secrete the bony matrix and
when they become surrounded by this it differentiates into
an Osteocyte.
• Osteocytes aid in the process of bone repair by recycling
calcium salts in the bony matrix.
• In long bones, Chondrocytes divide within the growth plate
and secrete collagen. As they get embedded into the plate
they secrete the hormone Indian hedgehog which controls
bone repair.

5. Bone Repair Mechanism
1. Immediately after fracture, the extra vascular blood cells form a
blood clot, called a FRACTURE HEMATOMA.
2. A network of spongy bone unites the inner surfaces, known as an
INTERNAL CALLUS and an EXTERNAL CALLUS of cartilage and bone
stabilizes the outer edges.
3. Cartilage of the external callus has been replaced by new bone,
and spongy bone now unite the broken ends.
4. A swelling initially marks the location of the fracture. Over time
this region will be remodelled.

6. Hormones that control
bone metabolism
1. Oestrogen –protect bone from the resorptive effects of PTH
and increase osteoblast proliferation. They also inhibit
cytokines that recruit osteocytes.
2. Calcitonin-a peptide hormone that inhibits bone breakdown by
binding to a receptor on osteoclasts inhibiting their action.
3. Parathyroid hormone-causes bone resorption by indirectly
stimulating osteoclasts. It causes cells of bones to release
calcium into the bloodstream. Osteoporosis can occur if too
much hormone is released.
4. Thyroxine-stimulates osteoclast action, reducing bone density
and liberating calcium.

7. Calcium And Vitamin D
• Calcium is an important nutrient for building bone and
slowing the pace of bone loss.
• Vitamin D mobilises calcium from bone helps to absorb
calcium. It promotes maturation of osteoclasts and indirect
stimulation of their activity. It also decreases collagen
synthesis by osteoblasts.
• Vitamin D deficiency causes rickets, or bone softening, in
children, and in adults can cause osteomalacia.
• Adequate intake of calcium and vitamin D is necessary for
good bone health.

8.  Occurs when bone loss exceeds bone formation
leading to a decrease in bone density and strength.
 Fractures are more likely to occur.
 Incidence increases with age and post menopausal
women are at highest risk.
 Diagnosis of osteoporosis – defined as low bone
mineral density (BMD) as measured at hip and/or spine
 Measured by dual energy x-ray absorptiometry (DEXA)

9.  Calcium and Vitamin D supplements should be
provided to all patients
 Oral bisphosphonates are 1st line therapy, with
Alendronate as first choice.
 MOA: bisphosphonates attach to hydroxypatite binding sites on
bony surfaces. When osteoclasts begin to resorb bone, the
bisphosphonate is released and impairs the ability of osteoclasts to
continue resorption. They also inhibit FPP synthase, thereby
inhibiting osteoclast activity.
 2nd line: Risedronate or Etidronate
 3rd line: Strontium
 Alternative treatments: IV bisphosphonates, PTH

10.  Rang and Dales Pharmacology pp.430-439
 www.health.harvard.edu
 Bones and joints ppt by Sugden D
 Bones and joints disorders by Williams J