1. Bone Tissue

2. Functions of Bone Support - surrounding tissue
Protect - vital organs and other tissues
Movement - attachment for muscles
Mineral homeostasis - mineral balance for body
Blood cell formation - hematopoiesis
Storage – triglycerides in yellow marrow

3. Structure of Bone
Bone is a highly vascularized C.T. with a hard, mineralized extracellular matrix. It is found in the body in two different arrangements:
Compact bone is good at providing
protection and support.
It forms the diaphysis of long bones,
and the external layer of all bones.
Spongy bone is lightweight and
provides tissue support .
It forms much of the epiphysis
and the internal cavity of long bones.
Compact bone
Spongy bone 3

4. Structure of Long Bone
Articular cartilage is the thin layer of hyaline cartilage covering the epiphysis of long bones.
Articular cartilage is found where the bone forms an
articular (joint) surface - where one bone moves against another bone.
The periosteum is a tough sheath of dense, irregular connective tissue on the outside of the bone.
Hyaline cartilage is the articular cartilage of this long bone 4

5. Structure of Long Bone
The medullary cavity is a space within the diaphysis of long bones that contains fatty
yellow bone marrow in adults.
The endosteum is a membrane that lines the medullary cavity. 5

6. Anatomy of a Long Bone Diaphysis = shaft
Epiphysis = one end of a long bone
Metaphysis = growth plate region

7. Bone Structure In adolescents, through the end of
active growth, the epiphysis of the
long bones contains hyaline
cartilage and forms an “epiphyseal
growth plate”.
The growth plate is always
actively dividing and causing the
bone to elongate from each end. 7

8. Types of Bones
Discuss only a typical long bone at this point. Later, other bone types will be discussed. 8

9. Bone Surface Markings

10. Bone Surface Markings

11. Types of Bone Cells
Osteoblasts are bone building cells: They synthesize and secrete collagen fibers and other organic components.
Osteocytes are mature osteoblasts (maintenance).
Osteoclasts are large bone breakdown cells. 11

12. Compact Bone
contains units called osteons or Haversian systems formed from concentric lamellae (rings of calcified matrix).
Interstitial lamellae between osteons are left over fragments of older osteons.
Lacunae are small spaces between the lamellae which house osteocytes.
Canaliculi are small channels filled with extracellular fluid connecting the lacunae.
Blood and lymphatic vessels are found in the osteon’s Central canal.
Perforating (Volkmann’s)
canals allow transit of these vessels to the outer cortex of the bone.
Named After Clopton Havers (1650?–1702), English physician and anatomist. 12

13. Spongy Bone
Spongy bone lacks osteons. Instead, lamellae are arranged in a lattice of thin columns called trabeculae.
Trabeculae of spongy bone support and protect the red bone marrow and are oriented along lines of stress (helps bones resist stresses without breaking).
Hematopoiesis (blood cell production) occurs in spongy bone. 13

14. Bone Formation
Ossification or osteogenesis is the process of forming new bone. Bone formation occurs in four situations:
Formation of bone in an embryo
Growth of bones until adulthood
Remodeling of bone
Repair of fractures

15. Bone Formation
Osteogenesis occurs by two different methods, beginning about the 6th week of embryonic development.
Intra-membranous ossification produces spongy bone.
This bone may subsequently be remodeled to form compact bone.
Endochondral ossification is a process whereby cartilage is replaced by bone.
Forms both compact and spongy bone. 15

16. Bone Formation
Intra-membranous ossification is the simpler of the two methods.
It is used in forming the flat bones of the skull, mandible, and clavicle.
Bone forms from mesenchymal cells that develop within a membrane – without going through a cartilage stage (recall that mesenchyme is the tissue from which almost all other C.T. develop.)
Many ossification centers. 16

17. Intramembranous Ossification

18. Bone Formation
Endochondral ossification is the method used in the formation of most bones, especially long bones.
It involves replacement of cartilage by bone.
There are one primary and two secondary centers of growth. 18

19. Bone Formation 19

20. Bone Formation 20

21. Bone Formation
Bone Formation

22. Bone Growth in Length Epiphyseal plate or cartilage growth plate
cartilage cells are produced by mitosis on epiphyseal side of plate
cartilage cells are destroyed and replaced by bone on diaphyseal side of plate
Between ages 18 to 21, epiphyseal plates close.
cartilage cells stop dividing and bone replaces the cartilage (epiphyseal line)
Growth in length stops at age 21

23. Bone Growth in Width

24. Bone Remodeling
Ongoing since osteoclasts carve out small tunnels and osteoblasts rebuild osteons.
osteoclasts form leak-proof seal around cell edges
secrete enzymes and acids beneath themselves
release calcium and phosphorus into interstitial fluid
osteoblasts take over bone rebuilding
Continual redistribution of bone matrix along lines of mechanical stress
distal femur is fully remodeled every 4 months

25. Bone Growth and Remodeling
Bone Remodeling

26. Fractures
Anatomical appearance – one or both bones are “open” to the outside.
Open (compound) 26

27. Fractures
Anatomical appearance – bone breaks into many fragments.

28. Fractures Anatomical appearance – like breaking a green twig
Greenstick 28

29. Fractures
Anatomical appearance – the distal part is shoved up into the proximal part.
Impacted 29

30. Fractures

31. Fractures Colles’ is a fracture of the distal radius ± ulna. Colles’31

32. Fracture and Repair
The first step, which occurs 6-8 hours after injury, is the formation of a fracture
hematoma as a result of
blood vessels breaking in
the periosteum and
in osteons. 32

33. Fracture and Repair
The second and third steps involve the formation of a callus (takes a few weeks, to as many as six months).
Phagocytes remove cellular debris and fibroblasts
deposit collagen to
form a fibro-
cartilaginous callus... 33

34. Fracture and Repair
... which is followed by osteoblasts forming a bony
callus of spongy bone. 34

35. Fracture and Repair
The final step takes several months and is called remodeling :
Spongy bone is replaced by
compact bone.
The fracture line
disappears, but
evidence of the break
remains. 35

36. Calcium Homeostasis Skeleton is reservoir of calcium
Calcium ions (Ca2+ ) involved with many body systems
nerve & muscle cell function
blood clotting
enzyme function in many biochemical reactions
Small changes in blood levels of Ca2+ can be deadly (plasma level maintained 9-11mg/100mL)
cardiac arrest if too high
respiratory arrest if too low

37. Calcium Homeostasis
Parathyroid hormone (PTH) is secreted if Ca2+ levels falls
PTH gene is turned on & more PTH is secreted from gland
osteoclast activity increased, kidney retains Ca2+ and produces calcitriol
Calcitonin hormone is secreted from parafollicular cells in thyroid if Ca2+ blood levels get too high
inhibits osteoclast activity
increases bone formation by osteoblasts

38. Osteoporosis

39. Disorders of Bone Ossification
Rickets
calcium salts are not deposited properly
bones of growing children are soft
bowed legs, skull, rib cage, and pelvic deformities result
Osteomalacia
new adult bone produced during remodeling fails to ossify
hip fractures are common