cartilage and bone

cartilage

specialized form of connective tissue produced by chondrocytes

what are the characterisitics of cartilage?

1. prominant extracellular matrix

2. avascular

3. encapsulated by pericondrium

what does it mean that the cartilage is avascular (effect)?

all nutrients need to diffuse through the matrix to reach chondrocytes; slow healing process

what are chrondrocytes essential for?

production of and maintenance of extracellular matrix

why is the formation of a hematoma important in bone repair?

hematoma provides a scaffold for inflammatory cells and signals for recruiting osteoprogenitor cells

How does the transition from a soft callus to a hard (bony) callus occur in the healing process?

endochondral ossification

what is crucial to the survival of chondrocytes?

composition of extracellular matrix since there are no blood vessels present

what are bound to proteoglycans in cartilage?

collagen type 2 and fibers

what is the most common type of cartilage?

hyaline cartilage

what characterizes hyaline cartilage?

1. type 2 collagen fibers

2. GAGs

3. proteoglycans

4. mutli-adhesive glycoproteins

what characterizes fibrocartilage?

high content of orderly arranged type 1 collagen fibers

what is fibrocartilage a combination of?

hyaline cartilage and dense connective tissue

what characterizes elastic cartilage?

elastic fibers and elastic lamenallae

lacunae

house the chondrocytes in cartilage

what distinguishes hyaline cartilage?

homogenous amporphous matrix that appears glassy

function of hyaline cartilage

1. provide low friction surface for joints

2. lubricate synovial joints

3. distribute applied forces of bone

what is hyaline cartilage in the embryo?

acts as the precursor to long bone

where is hyaline cartilage in post-neonatal life?

1. rings of trachea

2. plates in larynx and nose

3. caps end of bones in articulating joints

how is cartilage formed?

1. mesenchymal cells in embryo differentiate into chondroblasts

2. chondroblasts become trapped in lacuna and form chondrocytes

3. mesenchymal tissue surrounds the developing cartilage to form the fibrous covering, the perichondrium

4. inner layers of perichondrium generate new chondroblasts

what distinguishes fibrocartilage?

high and orderly content of type 1 and 2 collagen fibers

where is fibrocartilage typically located?

1. where tendons attach to bones

2. intervertebral discs

3. pubic symhysis

4. cardiac skeleton

what distinguishes elastic cartilage?

presence of elastin in cartilage matrix

where is elastic cartilage found?

1. epiglottis

2. external ear

what cartilage do not have a perichondrium?

fibrocartilage

what cartilage will not undergo calcification?

elastic cartilage

what are the main cell types present in hyaline cartilage?

1. chondroblasts

2. chondrocytes

what are the main cell types present in elastic cartilage?

1. chondroblasts

2. chondrocytes

what types of joints are most prone to cartilage degeneration?

1. weight-bearing (knees, hips, shoulders)

2. heavily used (back)

bone

specialized form of connective tissue that consists of extracellular components with organic and inorganic components

what is the organic component of bone?

1. type 1 collagen

2. osteoid (ground substance)

what is the inorganic component of bone?

calcium hypoxyapatite

what is the distinguishing feature of bone?

the mineralization of the matrix which produces an extremely hard tissue capable of providing support and protection

what is the function of bone?

1. lever for muscle action

2. protection of organs

3. hemopoietic organ

4. reservoir store for calcium and phosphorous

explain the process of bone formation

1. osteoprogenitor cells derive from mesenchymal cells

2. mesenchymal cells divide to give rise to osteoblasts

3. osteoblasts on the surface of the bone will deposit the organic components of the bone matrix (osteoid)

4. the osteoid becomes mineralized (Calcium phosphate and hydroxyapatite crystals)

5. osteoblasts continue depositing matrix until they become trapped inside lacuna

6. once trapped, osteoblasts mature into osteocytes, which regulate bone function

what type of cells are osteoblasts?

basophillic

what type of cells are osteocytes?

flat, large, mutinucleated cells that border bone surfaces

how do osteocytes communicate with one another?

via canaliculi

what is the function of osteoclasts?

phagocytic cells that reabsorb bone matrix as necessary during bone development and remodeling/repair

where are osteocytes derived from?

fusion of hemopoietic cells in bone marrow

compoct/dense/cortical bone

dense layer forming outside of bone

spongy/cancellous/medullary bone

spongelike network consisting of trabeculae to form the interior of cobe

long bone

longer in one dimension; consists of a shaft and two ends

what are examples of long bone?

1. tibia

2. metacarpals

short bones

nearly equal in length and diameter

what is an example of short bones?

carpal bones

flat bone

thin and platelike; consist of two layers of relatively thick compact bone with intervening layer of spongy bone

example of flat bone

1. bones of skull cap

2. sternum

example of irregular bone

vertebra

in order what are the anatomical parts of long bone?

1. epiphysis

2. metaphysis

3. diaphysis

4. metaphysis

5. epiphysis

what is the diaphysis in long bone?

the shaft

what is the epiphysis in long bone?

the expanded ends (2 in total)

what is the metaphysis in long bone?

flared portion between the diaphysis and epiphysis

what are bones covered by?

periosteum

periosteum

a sheath of dense fibrous connective tissue containing osteoprogenitor cells

what are bone cavities line by?

endosteum

endosteum anatomical make up

a layer of connective tissue that also contain osteoprogenitor cells

what is endosteum formed by?

one layer of endosteal cells that can differentiate into osteoblasts

what is the location of endosteum?

line cavities of compact bone as well as the trabeculae of spongy bone

osteon anatomical make up

concentric lamella of bone matrix surrounding the Haversian canal

haversian canal

contains the blood and nerve supply of the osteon

circumferential lamella

follow the entire inner and outer circumferences of the shaft of long bone

volmanns canals

channels in lamellar bone which blood vessels and nerves travel from the periosteal and endosteal surfaces to reach the osteonal canal

what is the difference between the haversian canal and volkmanns canals in mature lamellar bone?

• direction in which they run to reach the osteonal canal

• haversian will run parallel

• volkmann will run perpendicular

how does immature bone differ from mature bone?

immature bone is non-lamellar contain more cells per unit areamatrix has more ground substance

why is immature bone non-lamellar?

interlacing arrangement of collagen fibers

what type of bone is characterized by the presence of osteons?

long bone

what type of bone is the predominant bone type in epiphyses of adult long bones?

spongy bone

what type of bone is also known as cancellous bone?

spongy bone

what type of bone lines the medullary (marrow) cavity?

spongy bone

intramembrous ossification

compact bone and spongy bone develop directly from sheets of mesenchymal tissue

what is important to understand about the cells in intramembranous ossification?

the cells form bone DIRECTLY; there is NO cartilage intermediate

what type of bone does intramembranous ossification primarily occur in?

flat bones

what type of ossification allows long bones to grow in WIDTH?

intramembranous ossification

how do bones grow in LENGTH?

endochondral osssification

how are bones developed in endochondral ossification?

bones develops by replacing hyaline cartilage; cartilage serves as the template

what are the steps of endochondral ossification?

1. Blood vessels invade the perichondrium, converting it into the periosteum

2. Osteoblasts differentiate and form a bone collar around the diaphysis

3. The bone collar blocks nutrient diffusion, causing chondrocytes to hypertrophy, secrete enzymes, calcify, and die, leaving cavities

4. Chondrocyte death signals blood vessels to invade, bringing osteoclasts and osteogenic cells

5. Osteoblasts begin depositing osteoid in the cartilage cavities

6. Osteoid deposition and mineralization form the primary ossification center in the diaphysis

7. secondary ossification centers responsible for development of growth plate (physis) in the bone

what is the only cartilage that will remain after endochondral ossification?

1. articular cartilage

2. epiphyseal cartilage (growth plate)

what is the responsibility of the growth plate (epiphyseal cartilage)?

connects epiphysis to the diaphysis and allows for bone growth in LENGTH

when does epiphyseal cartilage disappear?

upon completion of bone development at adulthood

zone of reserve cartilage

typical hyaline cartilage

zone of proliferation

chondrocytes divide repeatedly, enlarge, and become organized into columns

zone of hypertrophy

chondrocytes are swollen and dying

zone of calcified cartilage

chondrocytes die and release substances that begin matrix calcification

zone of ossification

bone tissue first appears; eventually will be remodeled as lamellar bone

what does growth in length of long bones depend on?

presence of epiphyseal cartilage

which zone of epiphyseal cartilage is when the cartilage will start to go cell division?

zone of proliferation

which zone of epiphyseal cartilage is when the cartilage has not yet started to turn into bone?

zone of reserve cartilage

which zone of epiphyseal cartilage is when even though they look swollen and enlarged, it is still metabollicaly active?

zone of hypertrophy

which zone of epiphyseal cartilage is when cells begin to degenerate and die?

zone of calcified cartilage

which zone of epiphyseal cartilage when finished causes the growth plate to close?

zone of ossification

true/false: growth in the circumference of long bone does not involve endochondral ossification?

true; occurs through process called appositional growth

why does bone have an excellent capacity for bone repair?

excellent vascularizationosteoprogenitor cells within its periosteum, endosteum, and marrow cavity

explain the main steps of bone fracture repair

a fracture hematoma formssoft callus formshard bony callus formsbone is remodeled

why is it important for the fracture hematoma to form in bone repair?

torn blood vessels release blood clots to try and maintain balance of pressure placed on bone

what are the main cells in bone?

osteocytes