Chapter 6

What are the components of the skeletal system?

bones + connective tissues that stabilize or connect bones (cartilages, joints, ligaments, etc)

Ligaments

also known as articulations; form wherever 2 bones meet

the skeletal system components are derived from what embryonic layer of development?

mesoderm

what are the 5 main functions of the skeletal system?

support, storage of minerals and lipids, blood cell production, protection, and leverage

The skeletal system provides ____ support for the entire body

structural

Bones provide attachments for…

soft tissues and organs

The bone stores what type of mineral reserves?

calcium and phosphorus ion reserves in calcium salts

What does yellow bone marrow do?

stores lipids for energy reserves

What is produced in the red bone marrow?

RBCs, WBCs, and other blood elements

What do skeletal structures surround?

soft tissues and organs

Bones function as ____

levers

What does it mean to say bones function as levers?

they change size and direction of forces generated by skeletal muscles

what is the result of bones functioning as levers

body movements

Bone/Osseous Tissue

supporting connective tissue containing specialized cells in a matrix

What are the two main components of the matrix?

calcium salts and extracellular protein fibers

What are the calcium salts in the form of?

calcium phosphate Ca3(PO4)2

Calcium salts account for what fraction of the weight of bone?

2/3

Extracellular protein fibers (collagen) account for what fraction of bone weight?

1/3

Long Bones

where the length is larger than the width

Example of a long bone

humerus

Short Bones

length is approximately equal to the width

Examples of short bones

carpal and tarsal bones

Flat bones

thin and plate-like

example of flat bone

parietal bone

irregular bones

complex shapes; don’t fit into any other category

example of an irregular bone

vertebra

sutural bones

small. bones found between flat bones of the skull

sesamoid bones

develop within tendons at articulations

The diaphysis and the epiphyses are features of what bone?

long bone

Diaphysis

central shaft

What does the diaphysis surround?

a marrow cavity (medullary cavity)

What is the medullary cavity filled with?

center filled with yellow bone marrow

Epiphyses

the expanded portions at each end

What are epiphyses covered with?

articular cartilage

what type of cartilage is articular cartilage?

hyaline cartilage

Epiphyses are articulate with…

an adjacent bone at a joint

compact bone is known as

dense bone

Compact bone is relatively _______

solid

Where is compact bone found?

forms the wall of the diaphysis and covers spongy bone of each epiphysis

spongy bone is also called

trabecular bone

how can you describe spongy bone?

interlacing network of bony rods separated by spaced

where can you find spongy bone?

fills the epiphyses and lines the marrow cavity

What is the outer surface of long bone covered by?

periosteum

How can you describe the inner layer of the periosteum?

cellular

How do you describe the outer layer of the periosteum?

fibrous

The outer fibrous layer of the periosteum isolates….

bone from surrounding tissue

The outer fibrous layer of the periosteum forms…

attachments with fibers of tendons and ligaments

What is covered by the endosteum?

inner surfaces and spongy bone of marrow cavity

when is the endosteum active?

during bone growth, repair, and remodeling

Osteocytes use what for the exchange of ions and small molecules?

gap junctions

where are osteocytes found?

lacunae

Where are lacunae found?

between sheets of calcified matrix called lamellae

Canaliculi

small channels

what do canaliculi contain that is part of the osteocytes?

cytoplasmic extensions

canaliculi radiate…

through the matrix

What do canaliculi do?

connect the lacunae to blood vessels for nutrient and waste exchange

What is the basic functional unit of compact bone?

osteon

Lamellae

osteocytes arranged in concentric layers

lamellae or layers surround…

a central/Haversian canal

Central canals

run parallel to surface of the bone and contain blood vessels

perforating canals

link blood vessels of central canal with blood vessels of periosteum and marrow cavity

perforating canals run..

perpendicular to the bone surface

What type of bone covers all bone surfaces except inside joint capsules?

compact bone

Joint capsules

articular cartilage that protects opposing bone surfaces

what does the parallel arrangement of osteons allow for?

allows for resisting stress in specific directions

compact bone withstands..

forces applied on either end of a long bone

compact bone cannot tolerate…

moderate stress applied to the side of the shaft

What are 2 main points about spongy bone?

has no osteons, central canals, and perforating canals and contains red bone marrow

Trabecular

lamellae that form rods of plates

Spongy bone still contains…

osteocytes, lacunae, and canaliculi

Along with red bone marrow, spongy bone contains what?

blood vessels

Where can red bone marrow be found in spongy bone?

found in the spaces between trabeculae

Spongy bone is found in locations that are _____ heavily stressed

not

Spongy bone is found in locations with stresses arriving from many different ______

directions

What is an example of stresses arriving from different directions?

epiphyses of long bones where stresses are transferred across joints

Spongy bone is much ____ than compact bone

lighter

What does the light weight of spongy bone allow for?

reduces weight of the skeleton and easier for muscles to move bones

Osteoblasts

produce new bone through ossification

“blasts”

precursors

Osteocytes

are the most abundant cells in bone that maintain bone structure by recycling calcium salts

osteoclasts

release minerals through osteolysis or resorption

“class”

break

Osteogenic cells

mesenchymal stem cells that divide by mitosis to produce osteoblasts

where are osteogenic cells found?

found in the cellular layers of the periosteum and perichondrium and in the endosteum​

What are the only bone cells that divide?

osteogenic cells

“genic”

to create

Mesenchymal cells

make up the mesenchyma which is derived from the mesoderm during embryonic development

What three things do mesenchymal cells give rise to?

chondrocytes, muscle cells, and adipocytes

Osteoclasts are derived from…

the same stem cells that give rise to monocytes (the larges type of WBC)

When does embryonic development of bone begin?

6 weeks

What does bone development start as?

cartilage formation

Ossification

when cartilage is replaced with bone during the developmental stage

What are the 2 types of ossification?

intramembranous and endochondral ossification

When does calcification occur?

during ossification

Intramembranous ossification occurs when?

during fetal development

What happens during intramembranous ossification in fetal development?

bone develops within sheets of fibrous connective tissue

Where does bone development begin in intramembranous ossification?

ossification center

Intramembranous ossification Step 1

osteoblasts differentiate from connective tissue stem cells and form new bone matrix

Intramembranous ossification Step 2

bone matrix formation extends outward

Intramembranous ossification Step 3

osteoblasts surrounded by matrix change into osteocytes