1. BIO 137 Anatomy & Physiology I
Bone Tissue
BIO 137 Anatomy & Physiology I

2. The Skeletal System Organs Bones Cartilages Tendons Ligaments
Functions
Support
Protection
Movement
Hematopoiesis
Mineral Store
Energy Store

3. Tissues of the Skeletal System
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 – 80% of bone in skeleton
Spongy bone - 20% of bone in skeleton
is seen as

4. Compact Bone Most rigid connective tissue
Continuous, solid extracellular matrix found between cells
Matrix composed of mineral salts and collagen
Hardness due to mineral salts in matrix
Collagen provides strength and resilience

5. Spongy Bone Made of Bony plates called trabeculae
Space between trabeculae filled with red bone marrow
Found in flat bones between sheets of compact bone
Found in epiphyses of long bones
Spongy bone reduces a bone’s weight

7. Long Bone Structure
Epiphysis - Expanded ends of a long bone, articulates with other bones
Articular cartilage (hyaline cartilage) on outer surface
Composed of mostly spongy (cancellous) bone surrounded by thin layers of compact bone
Red bone marrow with
Hematopoietic stem cells
located here
Hyaline cartilage is the articular cartilage of this long bone

8. Long Bone Structure Diaphysis – shaft of bone
Central medullary cavity
Hollow tube in diaphysis filled with yellow marrow
Medullary Cavity is lined by endosteum
Osteoclasts located in endosteum
Metaphysis – region between diaphysis and epiphysis
Growth plate here

9. Lone Bone Structure
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 .
The endosteum is composed of
osteoclasts, osteoblasts, and
connective tissue.
Nutrient foramen – canal where vessels enter/exit a bone

10. Long Bone Structure
The periosteum is a tough sheath of dense, irregular connective tissue on the outside of the bone.
It contains osteoblasts that
help the bone grow in thickness,
but not in length.
Continuous with tendons and ligaments
It also assists with fracture repair
The periosteum is only found on areas where there is no articular cartilage

11. Chemical Constituents of Bone
Bone is 15% water, 30% organic proteins, 55% mineral salts (hydroxyapatite crystals).
Organic constituents
Collagen fibers provide flexibility and tensile strength.
Inorganic hydroxyapatite crystals (mineral salts)
Calcium Phosphate (Ca3PO4)2
Calcium Carbonate (CaCO3 – marble)
Other trace elements: magnesium, fluoride, sulfate

12. Bone Cells Osteogenic Stem Cell Osteoclasts Osteoblasts Osteocytes
Derived from mesenchyme
Forms osteoblasts
Only Mitotic bone cell
Osteoclasts
Bone breakdown (resorption)
Osteoblasts
Bone forming cells, deposit bony matrix around themselves
Osteocytes
matured osteoblasts
Completely surrounded by bony matrix
Carries out daily cellular activities

13. Histology of Bone Tissue
Compact bone is composed of repeating structural units called Osteons or Haverisan Systems
Osteons have concentric circles of matrix called lamellae surrounding a Central (Haversian) canal
Blood vessels and nerves here
Osteoblast cells mature into
Osteocytes after matrix is
laid down

14. Histology of Bone Tissue
Lacunae spaces in osetons hosue osteocytes
Canaliculi – small channels that connect lacunae of osteocytes
Nutrient and waste transport
Gap junctions for communication
Perforating (Volkmann’s) canals – transverse canals that connect vessels of central (Haversian) canals

15. Haversian System of Compact Bone

17. Blood and Nerve Supply of Bone
Bone is richly supplied with blood; Periosteal arteries and veins supply the periosteum and compact bone.
Nerves accompany the blood
vessels
The periosteum is rich in
sensory nerves sensitive to
tearing or tension

18. 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

19. 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.

20. 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
Many ossification centers.

21. Intramembranous Bone Formation

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

23. Endochondral Bone Formation

24. Bone Formation
Ossification contributing to bone length is usually complete by years of age.
Bones can still continue to thicken and are capable of repair even after the epiphyseal growth plates have closed.

25. 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 causing the
bone to elongate from each end.

26. Bone Structure
In adults, the epiphyseal cartilage is no longer present and elongation of bones has stopped.
The epiphyseal growth plate
becomes an “epiphyseal line”,
as growing cartilage is
replaced by calcified bone.

27. Epiphyseal plates

28. Long Bone Growth at Epiphyseal Plate
4 zones of cartilage at epiphyseal plate
Zone of Resting cells
Closest to epiphysis, don’t participate in growth, anchors plate to bony tissue of epiphysis
Zone of Mitotic cells
Rows of many cells undergoing mitosis
As ECM forms around cartilage thickens
Zone of Hypertrophic cells
Older cells enlarge and thicken plate, lengthening bone
Calcifying older cells begin to die
Zone of Calcified cartilage
Thin layer of dead cartilage
Osteoblasts lay down bone to replace calcified cartilage

29. (c) Lengthwise growth of bone at epiphyseal plate
Epiphysis
(c) Lengthwise growth of bone at epiphyseal plate
EPIPHYSEAL (GROWTH) PLATE:
Zone of resting cartilage
Zone of proliferating cartilage
Zone of hypertrophic cartilage
Zone of calcified cartilage
Diaphysis
Articular cartilage
New chondrocytes are formed
Old chondrocytes are replaced by bone
New diaphysis

30. Long Bone Growth at Epiphyseal Plate
2 MAJOR EVENTS
1. New cartilage cells are produced by mitosis at epiphyseal end of plate
2. Replacement of cartilage with bone on diaphyseal end of plate by endochondral ossification
Epiphyseal plate temporarily increases in width
Bones continue to lengthen until ossification centers meet and the epiphyseal plate ossifies under control of sex hormones at end of puberty

31. Growth At Epiphyseal Plate

32. Bone Growth in Thickness: Appositional Growth
A bone thickens as Compact bone is deposited below the periosteum
Osteoclasts will resorb (break down) bone on the inside to form the medullary cavity
The diaphysis of a long bone grows in thickness on the outside while the medullary cavity is enlarged on the inside

33. Bone Growth & Remodeling
Ongoing process that includes bone resorption by osteoclasts and deposition of bone by osteoblasts
Opposing processes
Total mass of bone in skeleton remains constant
At any one time, 5% of total bone mas is being remodeled

34. Factors affecting Bone Development, Growth & Repair
Normal bone growth depends on several factors:
Nutrition
Hormonal secretions
Physical exercise

35. Nutritional Requirements for Bone Development
Vitamin A
Required for normal osteoblast and osteoclast activity during normal development
Vitamin C
Required for collagen synthesis
Vitamin D
Promotes calcium absorption in the small intestines

36. Factors affecting Bone Development, Growth & Repair
Physical stress from exercise
Stimulates bone growth (deposition)
Lack of exercise makes bones atrophy (weaker) and thinner
Loss of bone mass

37. Hormones affecting Normal Bone Growth
Thyroid Hormones
Secreted by the thyroid gland
Stimulates osteoblasts
Deficiency:
Stunted growth

38. Hormones affecting Normal Bone Growth
Sex hormones: Estrogen and Testosterone
Promote formation of bone tissue
Abundant at puberty, stimulate long bone growth
Growth Spurt
Estrogen effect stronger than testosterone
Responsible for closing epiphyseal plates
Widening of female pelvis

39. Hormone Requirements for Bone Development
Growth hormone – secreted from the anterior pituitary gland
Regulates overall body growth
IGFs released from liver and bone in response to GH
Stimulates division of cartilage cells in epiphyseal plates during growing years and stimulates growth in thickness
Role in metabolism (discussed in Endocrine System)

40. Growth Hormone Disorders
Pituitary Dwarfism
Pituitary gigantism
Acromegaly

41. Growth Hormone Deficiency
Pituitary Dwarfism
GH deficiency in children
Short stature from retarded skeletal growth
Normal body proportions

42. Growth Hormone Excess Acromegaly GH excess in adulthood
Bones become thicker & soft tissues proliferate
Disfuguring

43. Growth Hormone Excess Pituitary Gigantism
GH excess in childhood before epiphyseal plates have closed
Rapid growth in height

44. Blood Calcium Homeostasis
Bone is the body’s major calcium reserve, storing 99% of calcium
Inorganic salts in matrix of bone composed mostly of calcium phosphate and calcium carbonate
Calcium required for blood clot formation, nerve impulse conduction and muscle cell contraction
Calcium homeostasis maintained by three hormones:
Parathyroid hormone
Calcitonin
Vitamin D

45. Blood Calcium Homeostasis
Parathyroid Hormone
Secreted by parathyroid glands in response to low blood calcium
Stimulates osteoclast activity = Bone resorption
Secrete acids and enzymes that dissolve inorganic mineral matrix of bone
Releases calcium and phosphorous into the blood

46. Parathyroid Hormone Other PTH targets: Osteoclasts – Bone resorption
Kidneys
Reabsorb calcium during urine formation
Secrete phosphate during urine formation
Intestines
Increases calcium absorption through activation of Vitamin D regulation
This is necessary for the intestines to absorb Ca++
Functions to increase the calcium concentration of the plasma (also increases concentration of phosphate)

48. Blood Calcium Homeostasis
Vitamin D
Necessary for proper absorption of calcium in the small intestines
Lack of vitamin D decreases calcium absorption in small intestines
Decreases calcium content in bone matrix, making bones soft and deformed
Rickets in children
Osteomalacia in adults
Derivative of Cholesterol is converted by sunlight to Vitamin D

49. Blood Calcium Homeostasis
Calcitonin
Released from thyroid gland in response to high levels of blood calcium
Inhibits osteoclast activity
Stimulates osteoblasts to form bone tissue
Stimulates the kidneys to secrete calcium
Functions to decrease plasma calcium concentration