This document discusses bone histology and physiology. It contains information on the three main types of bone cells - osteoblasts, osteocytes, and osteoclasts - and their functions in bone formation and resorption. It also describes the structure of bone tissue and the skeletal system's roles in support, protection, movement, mineral homeostasis, blood cell production, and triglyceride storage. Key aspects of bone physiology covered include mineral storage and regulation of calcium and phosphate levels in the body.

1. BONE HISTOLOGY
Prof. & Head. of Oral & Maxillofacial Surgery Sinhgad
Dental College & Hospital Pune.
Dr. J. B. Garde
M.D.S.
Nobel Fellow 2008

2. Bone Physiology

3. Bone cells
 As for all connective tissue, bone consists
of cells and extracellular matrix.
 There are three types of cells in mature
bone tissue:
 Osteoblasts
 Osteocytes
 Osteoclasts

5. Function
 Osteoblasts and osteocytes are involved in
deposition of bone matrix
 Osteoblasts are located at the surface of
bone tissue, whereas osteoclasts are
located within the calcified matrix
 Osteoclasts are involved in the
resorption of bone tissue.

7. An osteoclast cell attached
to the bone surface. Where
it is in contact with the
bone it forms a ‘ruffled
zone’ under which
resorption takes place.

9. Histology of bone tissue
 Like other connective tissues, bone
is a matrix containing cells as
opposed to a structure made of cells
 The matrix is made of hydroxyapatite
which is predominately tricalcium
phosphate
Ca3 (PO4)2

10. Functions of bone and the
skeletal system
Bone tissue and the skeletal system perform
several functions:
Support
Protection
Movement
Mineral homeostasis
Blood cell production
Triglyceride storage

11. Support
The skeleton is a structural
framework for the body
supporting soft tissues and
provides attachment points for
the tendons of most skeletal
muscles

12. Protection
The skeleton protects many
internal organs from injury. For
example, the skull (cranial bones)
protects the brain and the
vertebrae protect the spinal cord.

13. Movement
As skeletal muscles attach to
bones, when muscles contract
they pull on bones. Thus,
muscles and bones can produce
movement

14. Mineral homeostasis
Bone tissue stores important
minerals, especially calcium and
phosphorus. Bone releases these
minerals (on demand) to different
parts of the body to maintain
homeostasis

15. Hormones affecting growth
Parathyroid hormone and
1,25-dihydroxyvitamin D3
stimulate bone resorption.
Calcitonin inhibits bone
resorption.

16. Blood cell production
In some bones, red bone marrow
(a connective tissue) produces
erythrocytes, leucocytes and
platelets, via a process called
haemopoiesis.

17. Bone Structure
 Periosteum – hard outer covering
 Cells for growth and repair
 Compact bone – hard strong layer
 Bone cells, blood vessels, protein with Ca and P
 Spongy bone – at ends of long bones
 Has small open spaces to lighten weight
 Marrow cavity – hollow in middle of long bones

19. Bone Structure

20. Haversian System
 Structure of compact bone
 Rings of bone tissue with blood vessels
and nerves in the center

21. Haversian System

22. Bone Development
 Initial skeleton of cartilage in infants
 Replaced with bone by osteoblasts
 More than 300 bones at birth – fuse to 206
 Always growing and breaking down
 Osteoblasts – form new bone cells
 Osteoclasts – break bone cells down
 Osteocytes – mature bone cells

23.  Bone Physiology
 Calcium, Phosphate, storage, fluxes
 Regulation of mineral homeostasis
Bone Physiology and Mineral
Homeostasis

24. Structure of Bone
Trabecular bone
Compact bone

25. Structure of Bone
Haversian Canal with a blood vessel
Osteoid
Calcified bone matrix

26. Bone Cells
Osteoblasts
Osteoblast precursors
Osteocytes

27. Bone Cells
- osteoclast and bone remodeling

29. Bone Cells
- osteoclast and bone remodeling

30. Bone Cells
- osteoclast and bone remodeling

31. Bone Cells
- osteoclast and bone remodeling

32.  Calcium
 Magnesium
 Phosphorus
Body Minerals

33. • Skeleton – mechanical strength
• Signaling
• Second messenger
• Hormone/neurotransmitter release…
• Muscle contraction…
• Calcium – function
Minerals

34. • 99% - bone and teeth
• Hydroxyapatite crystals - [Ca10(PO4)6(OH)2]
• Reservoir
• 1% - in solution (mostly extracellular fluid)
• Ionized (50%)
• Protein-bound (40%, mostly albumen)
• Complexed (10%, phosphate, citrate, sulfate…)
• Calcium – forms
Minerals

35. • Extracellular Calcium
• Total serum calcium: 2.1 - 2.6 mM
• Ionized calcium: 1.1 - 1.3 mM
• functionally critical
• Free (ionized) Intracellular Calcium
• Approximately 100 nM
• Calcium – concentration
Very tightly controlled!!!
Minerals

36.  Cooperative binding
 Ligands other than
Ca
 Inhibition of
adenylate cyclase
 Activation of
phospholipase C
(increase of IP3 and
DAG)
 Parathyroid, C cells
in thyroid, kidney…
• Calcium – receptors
Minerals
COOH
NH2
intracellular
extracellular

37. Minerals
 85% - bone and teeth
 Hydroxyapatite
 Reservoir
 15% - extracellular fluid and soft tissues
 Phosphate esters
 Phosphorylated intermediates
 Serum phosphorus
 Ionized (55%)
 Protein-bound (10%)
 Complexed (35%, Na, Ca, Mg)
• Phosphorus – forms