Anatomy and Phys - Ch. 6

Bone Tissue

an organ made up of several tissues working together

bone

support, protection, assistance in movement, mineral homeostasis, blood cell production, triglyceride storage

functions of the skeletal system

the skeleton serves as a structural framework and supports soft tissues

support

protects internal organs from injury (e.g., cranial cavity protects the brain, ribcage protects the heart and lungs)

protection

most skeletal muscles attach to bones, the muscles pull on bone when they contract to produce movement

assistance in movement

bone tissue makes up about 18% of the weight of the human body and stores about 99% of the body’s calcium

stores several minerals (calcium and phosphorus) and can release calcium when needed

mineral homeostasis

consists of developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers

present in developing bones of the fetus and some adult bones (hip, ribs, sternum, vertebrae, skull, and ends of lone bones)

red bone marrow

production of blood cells through red bone marrow

hemopoiesis

consists of mainly adipocytes, stores lipids for energy

yellow bone marrow

long cylindrical main portion; bone shaft

diaphysis

distal and proximal ends of bones; where other bones (typically long) articulate with other bones

epiphysis

proximal and distal regions between diaphysis and epiphysis containing the epiphyseal plate where much bone is growing during adolescence and childhood

metaphysis

layer of hyaline cartilage that allows the bone to grow in length; growth plate

epiphyseal plate

When a bone stops growing, the cartilage is replaced with bone ___.

epiphyseal line

hyaline cartilage covering both epiphyses that reduces friction and absorbs shock; most long bones have this on both ends (tips of fingers do not)

articular cartilage

covers the outer surface wherever there is no articular cartilage and provides attachment for tendons and ligaments; highly vascular

periosteum

layer of the periosteum made up of dense irregular connective tissue

outer fibrous layer

layer of the periosteum made up of osteoprogenitor cells

inner osteogenic layer

cylindrical space within diaphysis filled with yellow marrow (lipids or triglycerides) that starts off small early on and, over time, hollows out and fills with bone marrow

medullary cavity

thin inner membrane lining the medullary cavity, single layer of osteoprogenitor cells and a small amount of connective tissue

endosteum

consists of widely separated cells surrounded by a hardened extracellular matrix

bone (osseous) tissue

consists of 15% water, 30% collagen fibers, and 55% crystalized mineral salts

extracellular matrix of bone tissue

combination of calcium phosphate and calcium hydroxide

hydroxyapatite

process by which mineral salts are deposited in a framework of collagen fibers; osteoblasts push out collagen fibers into space where it is going to start making bone

calcification

unspecialized bone stem cells derived from mesenchyme; only bone cell to undergo cell division

osteoprogenitor cells

synthesize and secrete collagen fibers and other organic material - surround themselves in extracellular matrix and become osteocytes

bone-building cells

osteoblasts

cell that secretes extracellular matrix

-blast

mature bone cells that maintain the bone’s daily metabolism by passing gases and nutrients between the blood stream and other bone cells

osteocytes

cell that maintains and monitors the tissue

-cyte

develop from white blood cells; release enzymes and acids that breakdown bone’s extracellular matrix

bone “eating” cells

osteoclasts

cell that breaks down extracellular matrix

-clast

makes up the diaphysis (shaft) of long bones and the external layer of all bones; resists stresses produced by weight and movement; composed of repeating structural units - osteons

compact bone tissue

repeating structural units that make up compact bone tissue

osteon

space for blood vessels, nerves, and lymphatic vessels that are running through the length of the bone

osteonic (central) canal

spaces where blood vessels and nerves from the periosteum penetrate the compact bone; horizontal canals

perforating (Volkmann’s) canals

layers around central canal that create osteons

lamellae

circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the osteonic canal

concentric lamellae

the areas between neighboring osteons that are fragments of older osteons that have been partially destroyed during bone rebuilding or growth

interstitial lamellae

bone lamellae that are arranged around the entire outer and inner circumference of the diaphysis of a long bone; develop during initial bone formation

circumferential lamellae

small spaced between the lamellae that contain osteocytes

lacunae

small channels that are filled with extracellular fluid that allow processes from osteocytes to connect with one another

canaliculi

little beams surrounding many red bone marrow filled spaces

trabeculae

consists of trabeculae surrounding many red bone marrow filled spaced, does not contain osteons, light weight

structure of spongy bone tissue

forms most of the structure of short, flat, and irregular bones and the epiphysis of long bones; supports and protects the red bone marrow

function of spongy bone tissue

enter the bone through numerous perforating canals; join with arteries in osteonic canals and further branch through transverse canals

location of periosteal arteries

transport blood vessels from one osteonic canal to the next

function of periosteal arteries

enter the bone near the center of the diaphysis through a hole called the nutrient foramen; passes into the medullary cavity and branches proximally and distally

location of nutrient arteries

supplies compact bone in the diaphysis

function of nutrient arteries

enter the metaphysis of a long bone through perforating canals

location of metaphyseal arteries

with branches of the nutrient artery, supplies the red and yellow bone marrow and spongy bone of the metaphyses

function of metaphyseal arteries

enters the epiphyses of a long bone through perforating canals

location of epiphyseal arteries

supply the red and yellow bone marrow and spongy bone of the epiphyses

function of epiphyseal arteries

____ is rich in sensory nerves, some of which carry pain sensations that are very sensitive to tearing or tension.

Periosteum

True/False: Bone is richly supplied with blood, thus it heals slowly.

False

True/False: Blood vessels are more abundant in portions of bone that contain red bone marrow.

True

process of bone formation that occurs throughout the lifetime of an individual in 4 different situations

ossification (osteogenesis)

1. initial bone development as an embryo and fetus

2. growth during childhood and adolescence

3. remodeling of bone during adulthood

4. repair of fractures throughout life

4 instances of Ossification

intramembranous ossification and endochondral ossification

2 types of embryonic bone formation

True/False: Intramembranous ossification does not go through a cartilage stage.

True

True/False: Bone formation begins during the 6th week of embryonic development.

True

forms the flat bones of the skull, most of the facial bones, the mandible (lower jaw), and the medial part of the collar bone in 4 stages

intramembranous ossification

Mesenchymal cells cluster at several ossification centers and differentiate into osteoprogenitor cells and then into osteoblasts

Osteoblasts secrete ECM until surrounded by it

Step 1 of Intramembranous Ossification: development of the ossification center

secretion of ECM stops, osteoblasts become osteocytes

osteocytes extend processes into bone canaliculi that radiate in different directions

within a few days, calcium and other mineral salts are deposited and the ECM hardens

Step 2 of Intramembranous Ossification: calcification

bone matrix forms and develops into trabeculae that fuse with one another to form spongy bone around network of blood vessels in the tissue

connective tissue associated with blood vessels differentiates into red bone marrow

Step 3 of Intramembranous Ossification:

formation of trabeculae

mesenchyme condenses on outside of bone, develops into the periosteum

layer of compact bone replaces surface layer of spongy bone

spongy remains in center

*much of newly formed bone is remodeled as bone transforms into its adult size and shape*

Step 4 of Intramembranous Ossification: development of the periosteum

forms most bones, especially long bones, in 6 steps

endochondral ossification

mesenchyme clusters together, develops chondroblasts which secrete cartilage ECM, producing cartilage model (made of hyaline cartilage)

covering called perichondrium develops around model

Step 1 of Endochondral Ossification:

development of the cartilage model

chondroblasts that surrounded themselves in the cartilage ECM become

chondrocytes

chondrocytes divide and further secretion of cartilage ECM

continued growth of cartilage model = chondrocytes in middle die, leaving behind empty spaces

Step 2 of Endochondral Ossification:

growth of the cartilage model

Chondrocytes from ___ cause interstitial cartilage growth in length.

within

Chrondrocytes on the ___ cause appositional cartilage growth in thickness

outside

nutrient artery penetrates cartilage and stimulates

chondrocytes in the diaphysis replaced by osteoprogenitor cells, then become osteoblasts

osteoblasts deposit bone ECM over cartilage remnants

primary ossification spreads from center towards ends of the cartilage model

Step 3 of Endochondral Ossification:

development of the primary ossification center

ossification center grows toward ends, osteoclasts break down bone in the center, leaving empty space

most of wall of diaphysis replaced with compact bone

Step 4 of Endochondral Ossification:

development of the medullary cavity

takes place around time of birth

chondrocytes replaced by osteoprogenitor cells, become osteoblasts

osteoblasts deposit bone ECM over cartilage remnants

spongy bone remains in epiphyses

Step 5 of Endochondral Ossification:

development of the secondary ossification centers

hyaline cartilage covering epiphyses becomes articular cartilage

prior to adulthood, hyaline cartilage remains between diaphysis and epiphyses as epiphyseal (growth) plate*

*This region is responsible for lengthwise growth of long bones

Step 6 of Endochondral Ossification:

formation of the articular cartilage and epiphyseal plate

addition of bone material on the diaphyseal side of the epiphyseal plate (growth plate)

interstitial growth

addition of bone material from the outside (periosteum)

appositional growth

Bone growth in length involves 2 major events:

1) interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate

2) replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification

closest to epiphysis

small, scattered chondrocytes

anchors the epiphyseal plate to the epiphysis of the bone

zone of resting cartilage

slightly larger chondrocytes, stack of coins arrangement

interstitial growth as they divide and secrete ECM

chondrocytes divide to replace those that die at the diaphyseal side of the epiphyseal plate

zone of proliferating cartilage

large, maturing chondrocytes arranged in columns

zone of hypertrophic cartilage

few layers of mostly dead chondrocytes

cartilage ECM calcifies

osteoclasts dissolve calcified cartilage, osteoblasts and capillaries from diaphysis invade the area

osteoblasts secrete bone ECM (replacing cartilage with bone) in endochondrial ossification

zone of calcified cartilage

when the epiphyseal cartilage cells stop dividing and bone replaces the remaining cartilage - epiphyseal plate fades and leaves behind this bony structure

epiphyseal line

osteoprogenitor cells under periosteum differentiate into osteoblasts, osteoblasts secrete bone ECM

surrounded by ECM = osteocytes

ridges form on either side of a periosteal blood vessel - ridges grow and create a groove for the blood vessel

Step 1 of Appositional Growth

ridges fold together, become a tunnel (central canal) that encloses blood vessel — future osteon

Step 2 of Appositional Growth

osteoblasts on inside of “tunnel” deposit bone ECM — forms new concentric lamellae

Step 3 of Appositional Growth

process continues and repeats as new blood vessels grow in the periosteum

Step 4 of Appositional Growth

the ongoing replacement of old bone tissue with new that involves resorption and deposition; controlled by hormones and blood calcium levels and is an integral part of calcium homeostasis; also removes injured bone, replacing it with new stronger bone tissue

remodeling

removal of minerals and collagen fibers from bone by osteoclasts; bone to blood

resorption

addition of minerals and collagen fibers to bone by osteoblasts; blood to bone

deposition

a branch of dentistry concerned with the prevention and correction of poorly aligned teeth

orthodontics

minerals, vitamins, hormones

factors affecting bone growth and remodeling

True/False: Large amounts of calcium and phosphorus are needed while bones are growing and are necessary for remodeling

True

stimules osteoblast activity

Vitamin A

needed for the synthesis of collagen

Vitamin C

increases the absorption of calcium from food

Vitamin D

can stimulate osteoblasts and promote cell division at the epiphyseal plate during childhood

IGF’s (insulin-like growth factors)

sex hormones at puberty that are responsible for increased osteoblast activity and cause a dramatic effect on bone growth (“growth spurt”)

androgens (male) and estrogens (female)

any break in a bone

fracture

by severity, shape/position of fracture line, or based on the physician who first described them

ways in which fractures are named