ch 6 a and p better version

skeletal cartliage

made of highly resilient, molded cartilage tissue that consist of primarily water

NO BLOOD VESSELS OR NERVES

perichondrium

layer of dense connective tissue surrounding cartilage like a girdle

helps cartliage resist outward expension

CONTAINS BLOOD VESSELS FOR NUTRIENT DELIVERY

appositional growth

new matrix laid down on surface of cartilage

cartilage forming cells in perichondrum secrete matrix against external face of existing cartilage

function of bone

support for body organs

protection of spinal cord, brain, vital organs

anchorage as levers for muscle action

mineral storage of calcium and phosphorous

blood cell formation called hematopoiseis occurs in red bone marrow of certain bones

fat storage used for energy storage stored in bone cavities

hormone production of osteocalcin that helps regulate insulin secretion, glucose homeostasis, and energy expendiure

axial skeleton

long axis of body

skull, vertebral column, rib cage

appendicular skeleton

bones of upper and lower limbs

girdles attaching limbs to skeleton

long bones

longer than wide with a medullary cavity extending the length of shaft

ex- most limb bones

short bones

cube shaped bones

ex- wrist and ankle bones

sesamoid bones form within tendons

ex-patella

flat bones

thin, flat, slightly curved

ex-sternum ribs most cranial bones

irregular bones

complicated shape

ex- vertebrae and hip bone

compact bone

dense outer layer on every bone that appears smooth and solid

spongy bone

made up of honeycomb of small, needle like, or flat pieces of bone called trabeculae

open spaces between trabeculae are filled with red or yellow bone marrow

periosteum

covers outside of compact bone

endosteum

covers inside portion of compact bone

all long bones have

shaft (diaphysis)

bone ends(epiphyses)

membranes

diaphysis

tubular shaft that forms long axis of bone

consist of compact bone surrounding central medullary cavity that is filled with yellow bone marrow in adults

epiphyses

ends of long bones that consist of compact bone externally and spongy bone internally

articular cartilage covers articular surfaces

epiphyseal line

between diaphysis and and epiphyseal line

fibrous layer

outer layer consisting of dense irregular connective tissue containing sharpeys fibers that secure to bone matrix

osteogenic layer

inner layer abutting bone and contains primitive osteogenic stem cells that give rise to bone cells

endosteum

delicate connective tissue membrane covering internal bone surfaces

covers trabeculae of spongy bone

lines canals that pass through compact bone

contains osteogenic cells that can differntiate into other cells

red bone marrow

found within trabecular cavities of spongy bone and diploe of flat bones like sternum

in newborns where is red bone marrow found

medullary cavities and all spongy bone

where is red bone marrow located in adults

located in heads of femur and humerus but most active sites of hematopoesis are flat bone diploe and some irregular bones like hip bone

yellow bone marrow can convert to red if person becomes anemic

bone markings

sites of muscle, ligament, and tendon attachment on external surfaces

areas involved in joint formation or conduits for blood vessels and nerves

3 categories

3 categories of bone markings

projections- site of muscle an ligament attachment

surfaces- form joints

depressions and openings- for blood vessels and nerves

5 major cell types

osteoprogenitor (osteogenic) cells

osteoblasts

osetocytes

bone lining cells

osteoclasts

osteoprogenitor

called osteogenic cells

mitotically active stem cells in periosteum and endosteum

when stimulated they differentiate into osteoblast or bone lining cells

osteoblast

bone forming cells that secrete unmineralized bone matrix called osteoid

osteoblasts are mitotic

osteoid

made up of collagen and calcium binding proteins and calcium binding proteins

osteocytes

mature bone cells in lacunae that no longer divide

maintain bone matrix and act as stress or strain sensors

respond to mechanical stimuli such as increased force on bone or weightlessness

communicate with osteoblasts and osteoclasts so bone remodeling can occur

bone lining cells

flat cells on bone surfaces beleived to also help maintain matrix

on external bone surface lining cells are called PERIOSTEAL cells

on internal surfaces they are called ENDOSTEAL cells

osteoclasts

derived from same hematopoietic stem cells that become macrophages

giant mutlinucleate cells function in bone resorption BREAK DOWN OF BONE

when active, cells are located in depressions called resorption bays

compact bone AKA LAMMELLAR BONE

consist of osten (haverisan system)

canals and canaliculi

interstitial and circumferential lamellae

oste0n - haversian system

structural unit of compact bone

consists of elongated cylinder that runs parallel to long axis of bone

osteon cylinder consists of several rings of bone matrix called lamellae

central haversian canal

runs through core of osten

conations blood vessels and nerve fibers

perforating volkmanns canals

canals lined with endosteum that occur at right angles to central canal

connect blood vessels and nerves of periosteum, medullary cavity, and central canal

interstititial lamellae

not apart of osteon

fill gaps between forming osteons, others are remnants of osteons cut by bone remodeling

circumferential lamellae

deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis

help long bone resist to twisting

spongy bone

appears poorly organized but its actually organized along lines of stress to help bone resist any stress

trabeuculae confer strength to bone

organic components

osteogenic cells, osteoblasts, osteocytes, bone lining cells, osteoclasts, and osteoids

osteoid

make up 1/3 of organic bone matrix is secreted by osteoblasts

consists of ground substance and collagen fibers which contribute ti high tensile strength and flexibility of bone

inoroganic cmpononets

hydroxyapatities

makeup of 65 percent of bone mass

consist of tiny calcium phosphate crystals in and around collagen fibers

responsible for hardness and resistance to compression

ossififcation-osteogenesis

process of bone tissue formation

formation of bony skeleton begins in month 2 of development

post natal bone growth occurs until early adulthood

bone remodeling and repair are lifelong

endochondral ossification

bone forms by replacing hyaline cartliage

bones are called carliage (endochondral) bones

form most of skeleton

intramembranous ossification

bone develops from fibrous membrane

bones are called membrane bones

endochondral ossification cont

forms essentially all bones inferior to base of skull except clavicles

begins late in month 2 of development

uses previously formed hylaine cartliage models

requires breakdown of hyaline cartlaige prior to ossification

begins at primary ossification center in center of shaft

5 main steps in proccess of endochhondral ossification

1. bone collar forms around diaphysis of cartliage model

2. central cartilage in diaphysis calcifies then develops cavities

3. periosteal bud invades cavities leading to formation of spongy bone

4. diaphysis elongates and medullary cavity form- secondary ossification centers appear in epiphyses

5. epiphyses ossify- hyaline cartliage remains inly in epiphyseal plates and articular cartliages

intramembranous ossification

begins with fibrous connective tissuse membranes formed by mesenchymal cells

forms frontal, parietal, occiptal, temporal, and clavicle bones

4 major steps of intramembraous ossification

1. Ossification centers are formed when mesenchymal

cells cluster and become osteoblasts

2. Osteoid is secreted, then calcified

3. Woven bone is formed when osteoid is laid down

around blood vessels, resulting in trabeculae

▪ Outer layer of woven bone forms periosteum

4. Lamellar bone replaces woven bone, and red bone

marrow appears

epiphyseal plates consists of 5 zones

1. Resting zone

2. Proliferation (growth) zone

3. Hypertrophic zone

4. Calcification zone

5. Ossification zone

resting zone

area of cartliage on epiphyseal side of epiphyseal plate that is relatively inactive

proliferation zone

area of cartliage on diaphysis side that is  rapidly

dividing

– New cells formed move upward, pushing epiphysis away from diaphysis,

causing lengthening

hypertrophic zone

older chondorcytes closer to diaphysis

cartliage lacune enlarge and erode forming interconnecting spaces

• Calcification zone

– Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate

ossififcation zone

Chondrocyte deterioration leaves long spicules of

calcified cartilage at epiphysis-diaphysis junction

– Spicules are then eroded by osteoclasts and are

covered with new bone by osteoblasts

– Ultimately replaced with spongy bone

– Medullary cavity enlarges as spicules are eroded

• Bone lengthening ceases

Females: occurs around 18 years of age

– Males: occurs around 21 years of age

 Growth hormone:

most important hormone in stimulating

epiphyseal plate activity in infancy and childhood

Thyroid hormone: 

 modulates activity of growth hormone, ensuring proper proportions

spongy bone replaced every

 3–4 years

Compact bone replaced

every 10 years

 Resorption

function of osteoclasts

– Dig depressions or grooves as they break down matrix

– Secrete lysosomal enzymes and protons+

(H ) that digest matrix

– Acidity converts calcium salts to soluble forms

osteoclast activation involves PTH and immune T cell proteins

bone deposition

osteoblasts

osteoid seam

band of unmineralized bone matrix that marks area of new matrix

calcification front

abrupt transitoin zone between osteoid seam and older mineralized bone

Remodeling occurs continuously but is regulated by two

control loops:

Maintaining+ Ca homeostasis

▪ Hormonal negative feedback loop involving

parathyroid hormone maintain 2

Ca + in the blood

– Keeping bone strong

▪ Mechanical and gravitational forces acting on bone

drive remodeling to keep bone strong

Parathyroid hormone (PTH)

 produced by parathyroid glands in response

to low blood calcium levels

– Stimulates osteoclasts to resorb bone, calcium is released into blood, raising levels

Calcitonin

produced by parafollicular cells of thyroid gland in response to

high levels of blood calcium levels

– Wolf’s law 

bones grow or remodel in response to demands placed on them

▪ Stress is usually off center, so bones tend to bend

▪ Bending compresses one side, stretches other side

– Diaphysis is thickest where bending stresses are

greatest

Nondisplaced

ends retain normal position

Displaced:

 ends are out of normal alignment

– Completeness of break

Complete

 broken all the way through

 Incomplete:

 not broken all the way through

Open (compound):

skin is penetrated

communited

bone fragments into 3 or more peices

common in older adults because bones are more brittle

compression

bone is crushed

common in porous bones

trauma like a fall

spiral

ragged break occurs when excessive twisting forces

sports fx

depressed

broken bone portion is pressed inward

skull fx

green stick

Bone breaks incompletely, much in the

way a green twig breaks. Only one side of

the shaft breaks; the other side bends.

Common in children,

Closed reduction

 physician manipulates to correct

position

Open reduction

surgical pins or wires secure ends

• Repair involves four major stages:

1. Hematoma forms

2. Fibrocartilaginous callus forms

3. Bony callus forms

4. Bone remodeling occurs

Osteomalacia

Bones are poorly mineralized

– Osteoid is produced, but calcium salts not adequately

deposited

– Results in soft, weak bones

– Pain upon bearing weight

• Rickets (osteomalacia of children)

Results in bowed legs and other bone deformities because

bones ends are enlarged and abnormally long

– Cause: vitamin D deficiency or insufficient dietary calcium

Bisphosphonates:

decrease osteoclast activity and

number

▪ Partially reverse osteoporosis in spine

Denosumab

 Monoclonal antibody shown to reduce fractures in

males with prostate cancer

▪ Improves bone density in elderly