All of Bone Composition

Anat.

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)

What is the diaphysis?

elongated, usually cylindrical shaft, provides leverage and weight support, compact bone with thin plates of spongy bone extending inward

What is medullary cavity?

hollow cylindrical space within the diaphysis, contains red bone marrow in children, contains yellow bone marrow in adults

What is epiphysis?

expanded region at each end of long bone

Where is the proximal epiphysis?

end of the bone closest to body trunk

Where is the distal epiphysis?

end of bone furthest from trunk

What is the epiphysis composed of?

outer thin layer of compact bone, inner region of spongy bone

What is articular cartilage?

covers the joint surface, thin layer of hyaline cartilage,

What is the function of articular cartilage?

reduces friction, absorbs shock in moveable joints.

What is metaphysis?

region of mature bone between diaphysis and epiphysis

What is the epiphyseal plate?

growth plate, thin layer of hyaline cartilage, is converted to bone over time

What is the function of the epiphyseal plate?

provides for lengthwise bone growth, forms the epiphyseal line when done growing

What is the periosteum?

coverings and linings of bone on the outside

What is the endosteum?

covers all internal surfaces of bone within medullary cavity, incomplete layer of cells, surrounds medullary cavity

What is bone marrow?

soft CT of bone, there are two types

What are the two types of bone marrow?

red and yellow

What is red bone marrow?

it is hemopoietic, located in spongy bone and medullary cavity of long bones in childrens, and skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus and femur in adults

What does hemopoietic mean?

blood cell forming

What is yellow bone marrow?

product of red bone marrow degeneration as children mature, it is a fatty substance, can convert back to red bone marrow

When does yellow bone marrow turn back into red bone marrow?

during severe amemia (condition with reduced red blood cells)

What are the 4 components of the skeletal system?

bones, cartilage, ligaments, other CT

What are bones?

primary organs of the skeletal system, rigid framework of the body

What is compact bone?

dense outer layer of bone, 80% of bone mass

What are two other names for compact bone?

dense or cortical

What is spongy bone?

internal to compact bone, has holes in it, 20% of bone mass

What is cartilage?

semirigid connective tissue, more flexible than bone

What are the two types of cartialge?

hyaline cartilage, fibrocartilage

What is hyaline cartilage?

covers the ends of some bones, within growth plates. model for bone formation, attaches ribs to sternum

What is fibrocartilage?

Weight-bearing cartilage that withstands compression, intervertebral discs, pubic symphysis, menisci of knee.

What are ligaments?

Connect bone to bone

What are tendons?

Connect muscle to bone

What are the functions of bone?

support, protection, levers for movement, hemopoiesis, storage of mineral and energy reserves

What is hemopoiesis?

blood cell production, occurs in red bone marrow connective tissue

What minerals and energy reserves are stored by bone?

calcium and phosphate

What are the four classes of bone by shape?

long, short, flat, irregular

What do long bones look like?

longer than they are wide

What do short bones look like?

length nearly equal to width

What do flat bones look like?

flat, thin surfaces, may be slightly curved

What do irregular bones look like?

elaborate, sometimes complex shapes

What is an example of a long bone?

femur and humerus

What is an example of a short bone?

carpals and tarsals

What is an example of a flat bone?

cranial bones, ribs

What is an example of an irregular bone?

vertebrae