Osteology

Objective of the lecture

• Definition of osteology and bone

• Classification of bones

• Bone structure

• Bone development

• Bone markings

Osteology

Definition:

Greek (osteon=bone logos=science)

The branch of anatomy that deals with the structure and function of bones.

Osteology

• There are 206 bones in the skeleton of the adult. • Axial skeleton: Vertebral column - 26 (sacrum - 5 fused and coccyx - 3-4 fused)

80 Ribs and sternum - 25

Skull - 22

Auditory ossicles - 6

Hyoid bone - 1

• Appendicular Upper limb - 64

skeleton: Lower limb - 62

126

Total 206

275 bones 12 weeks (6-9 inches long)

Classification of bones - position

• Axial

• Apendicular

Skull Vertebral column Thoracic cage Shoulder girdle Upper limb Pelvic girdle Lower limb

• Long

• Short

• Flat

• Irregular

• Sesamoid

https://opentextbc.ca/anatomyandphysiology

Classification of bones - shape

• Support- framework that supports body and cradles its soft organs

• Protection- for delicate organs, heart, lungs, brain

• Movement- bones act as levers for muscles

• Mineral storage- calcium & phosphate

• Blood cell formation- hematopoiesis

Function of the Skeletal System

Long Bones

Longer than wide They have body (diaphysis) and 2 ends (epiphysis)

All limb bones with the exception of wrist, ankle and patella

Short bones

Cube shaped - close dimensions in length and width

Bones of wrist and ankle

Flat bones

Thin and wide

Sternum, scapula, ribs

and most of cranial bones

Irregular bones

Complicated shape

Vertebrae, hip bones and

facial bones of the skull

Sesamoid bones

Usually small and rounded

Embedded in tendons

Part of the biomechanics of the joints

Gross anatomy of bone

https://opentextbc.ca

Flat bones

Bone cells and tissue

Osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide. Immature osteogenic cells are found in the deep layers of the periosteum and the marrow. They differentiate and develop into osteoblasts.

The osteoblast is responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts do not divide, they synthesize and secrete the collagen matrix and calcium salts. They are derived from osteoprogenitor cells, a mesenchymal stem cell line.

The osteoclast is responsible for bone resorption. Found on bone surfaces, multinucleated, and originates from monocytes and macrophages. “Bone version” of macrophages. Howship’s lacuna.

The osteocyte is the primary cell of mature bone and the most common type of bone cell. Located in a space called a lacuna and surrounded by bone tissue. Maintains the mineral concentration of the matrix via the secretion of enzymes. Lacks mitotic activity. Communicate with each other and receive nutrients via long cytoplasmic processes that extend through canaliculi within the bone matrix.

Extracellular Matrix

• The extracellular matrix (ECM) refers to the molecules that provide biochemical and structural support to the cells. It is made of organic and inorganic matter.

• The ECM of bone is highly specialised. In addition to collagen and the associated proteins usually found in connective tissue, bone is impregnated with mineral salts, in particular calcium hydroxyapatite crystals. These crystals associate with the collagen fibres, making bone hard and strong. This matrix is organised into numerous thin layers, known as lamellae.

• Inorganic salts make bone hard and resistant to crushing.

• Collagen gives strength and resilience to bone.

Bone cells and tissue

• Compact bone – Structural

• Trabecular bone – Structural

• Bone Marrow – Structural and RBC

• Vessels – Nutritional and Innervation

Components of Bone

Compact and Spongy Bone

• Woven bone (primary bone) – Appears in embryonic development and fracture repair, as it can be laid down rapidly.

• Lamellar bone (secondary bone) – The bone of the adult skeleton. It consists of highly organised sheets of mineralised osteoid. This organised structure makes it much stronger than woven bone. Lamella bone itself can be divided into two types – compact and spongy.

Compact and Spongy Bone Compact Bone

• Tightly packed tissue

• The outer layer, under the periosteum of the diaphysis and epiphysis

• Cortical bone

• Microscopic structural unit of compact bone is called an osteon, or Haversian system

Spongy Bone

• Cancellous or Trabecular bone

• Found in epiphyses of long and also in short ,flat and irregular bones

• Built of numerous branching bony plates - in complete osteons

• Spaces reduce weight

Compact Bone

• The structural unit is Haversian system or osteon

• Osteon • Cylinder • Longitudinal orientation • 5-20 concentrically arranged lamellae of

bone matrix • Lamellae have crisscross pattern at 90⁰ • Running through the center of each osteon

is the central canal • Central canal contains

• blood vessels • nerve tissue • Lymphatic

• Volkmann’s or perforating canal

Compact bone

http://medcell.med.yale.edu/histology/bone_lab.php

The layers of a long bone, beginning at the external surface, are therefore: • Periosteal surface of compact bone • Outer circumferential lamellae • Compact bone (Haversian systems) • Inner circumferential lamellae • Endosteal surface of compact bone • Trabecular bone

Spongy (Trabecular) Bone

https://opentextbc.ca

• Contains osteocytes in lacunae /not arranged in concentric circles/ • Lattice-like network - trabeculae

/formed along the lines of stress -”Wolf’s law”/

• 20% bone mass - 80% bone surface • Pores filled with marrow /red marrow

in some - hematopoiesis/

Bone Marrow

Consists of stroma, myeloid tissue, fat, lymphatic tissues Red marrow

Involved with the production of RBC

Consists of hematopoietic tissue

Highly vascularized

Yellow marrow Not as vascularized as red marrow

Large amount of fat cells

Percentage increases with age

Bone Development

Intramembranous Ossification

• Compact and spongy bone develops directly from sheets of mesenchymal (undifferentiated) connective tissue.

• Direct differentiation of cells within mesenchymal condensations into bone forming cells (osteoblasts)

• The flat bones of the face, most of the cranial bones, the clavicles and periosteum.

https://opentextbc.ca

Bone Development

Endochondral Ossification

• Develops by replacing hyaline cartilage.

• Cartilage serves as a template to be completely replaced by new bone - takes much longer.

• Bones at the base of the skull and long bones.

Interstitial growth

Appositional growth

Bone Repair

Stages in Fracture Repair

The healing of a bone fracture follows a series of progressive steps: (a) A fracture hematoma forms.(b) Internal and external calli form. (c) Cartilage of the calli is replaced by trabecular bone. (d) Remodeling occurs.

Nutrients and Bone Health

Nutrient Role in bone health

Calcium

Needed to make calcium phosphate and calcium carbonate, which form the hydroxyapatite crystals that give bone its hardness

Vitamin D Needed for calcium absorption

Vitamin K Supports bone mineralization; may have synergistic effect with vitamin D

Magnesium Structural component of bone

Fluoride Structural component of bone

Omega-3 fatty acids Reduces inflammation that may interfere with osteoblast function

Hormones That Affect the Skeletal System

Hormone Role

Growth hormone Increases length of long bones, enhances mineralization, and improves bone density

Thyroxine Stimulates bone growth and promotes synthesis of bone matrix

Sex hormones

Promote osteoblastic activity and production of bone matrix; responsible for adolescent growth spurt; promote conversion of epiphyseal plate to epiphyseal line

Calcitriol Stimulates absorption of calcium and phosphate from digestive tract

Parathyroid hormone

Stimulates osteoclast proliferation and resorption of bone by osteoclasts; promotes reabsorption of calcium by kidney tubules; indirectly increases calcium absorption by small intestine

Calcitonin Inhibits osteoclast activity and stimulates calcium uptake by bones

Diseases of the Skeletal System:

• Osteoporosis - bone reabsorption outpaces bone deposit; bones become lighter and fracture easier

• Rickets - vitamin D deficiency

• Osteomalacia - soft bones, inadequate mineralization in bones, lack of vitamin D

• Pagets Disease - spotty weakening in the bones, excessive and abnormal bone remodeling

• Rheumatoid arthritis - autoimmune reaction