Anatomy Bone Composition Part 3

What is the primary component of bone?

bone connective tissue (cells and extracellular matrix)

What are the four types of bone CT?

osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

What are osteoprogenitor cells?

beginning cells

What are osteoblasts?

form from osteoprogenitor stem cells, synthesize and secrete osseous material (make and drop bone cells), differentiate into osteocytes

What are osteocytes?

mature bone cells derived from osteoblasts, detect stress on bone; trigger new bone formation

What are osteoclasts?

large, multinuclear, phagocytic cells, involved in bone resorption, get rid of excess bone, make bone look "new" after fracture

What is compact bone composed of?

composed of small cylindrical structures called osteons

What are osteons?

basic functional and structural unit of mature compact bone, oriented parallel to bone diaphysis, appears as bull's eye target; look like cylinders

What are the 4 components of osteons?

central canal, lamellae, osteocytes, canaliculi

What is the central canal?

cylindrical channel at center of osteon, blood vessels and nerves extend through channel

What is the lamellae

rings of bone connective tissue, surround central canal, composed of COLLAGEN fibers (which give bone strength and resilience)

What is canaliculi?

tiny interconnecting channels within bone connective tissue that extend from each lacuna and travel through lamellae and connect to lacunae and central canal, connect to lacunae to communicate

What are perforating canals?

only found in long bone, not part of osteon, perpendicular to central canals, connect central canals within different osteons.

What is trabeculae and where can it be found?

trabeculae is bone with spaces, open lattice of narrow rods and plates of bones (bone marrow fills the spaces), mesh of crisscrossing bars, found in spongy bone

What is the function of trabeculae?

resistance to stresses

When does cartilage begin to grow?

begins during embryologic development

What is interstitial growth?

growth in length (occurs within internal regions of cartilage)

What is appositional growth?

growth in width (occurs on cartilage's outside edge)

What is ossification?

the formation and development of bone connective tissue

When does ossification begin?

around 8 - 12 weeks into embryonic development and continues through childhood and adolescence

What is intramembranous ossification?

bone growth within a membrane (ex. skull)

What does intramembranous ossification produce?

flat bones of skull, some of the facial bones, mandible, central part of the clavicle

What is endochondral ossification?

begins with a hyaline cartilage model, produces most bones of skeleton, including bones of upper and lower limbs, pelvis, vertebrae, and ends of clavicle

What is the ORDER of endochondral ossification?

1. Fetal hyaline cartilage model develops

2. Cartilage calcifies, a periosteal bone collar forms

3. Primary ossification center forms in diaphysis

4. Secondary ossification centers form in epiphyses

5. Bone replaces cartilage, except articular cartilage and epiphyseal plates

6. Epiphyseal plates ossify and form epiphyseal lines

What is bone remodeling?

ongoing replacement of old bone tissue by new bone tissue, continues into adulthood, occurs at different rates, 20% of skeleton replaced yearly, dependent on the coordinated activities of osteoblasts, osteocytes, and osteoclasts. Influenced by hormones and mechanical stress

What is mechanical stress?

occurs in weightbearing movement and exercise, required for normal bone remodeling

What hormones stimulate bone growth and remodeling?

growth hormone, thyroid hormone, sex hormones

What does the growth hormone do?

directly stimulates growth of cartilage in epiphyseal plate

What does the thyroid hormone do?

regulates normal activity at epiphyseal plates

What are the two ways aging affects bones?

decreased tensile strength of bone and bone loss of calcium and other minerals

What does decreased tensile strength of bone do?

reduces the rate of protein synthesis by osteoblasts, relative amount of inorganic material increases, becomes brittle and susceptible to fracture

What does bone loss of calcium and other minerals do?

bones become thinner and weaker, there is insufficient ossification, osteopenia starts

What is osteopenia?

occurs slightly in all people with age, begins at age 35-40, osteoblast activity declines; osteoclast activity previous levels, vertebrae, jaw bones, epiphyses loose large amount of mass

What is osetoporosis?

reduced bone mass sufficient to compromise normal function, reduced hormones with age also add to reduction in bone mass

What are fractures?

breaks in bone

What are the three types of fractures?

stress fracture, simple fracture (closed), compound fracture (open)