CHAPTER 6 (Skeletal System) (copy)

Bones
Cartilages
Tendons
Ligaments

Components of Skeletal System

Body support
Organ protect
Body movement
Mineral storage
Blood cell production

Functions of the Skeletal System

collagen

is a fibrous protein that provides flexibility but resists pulling or compression.

matrix

ground substance contains proteoglycans which are water trapping proteins that help cartilage to be smooth and resilient.

bone matrix

is about 35% organic and 65% inorganic material by weight.
The organic material is primarily collagen and proteoglycans.

Hydroxyapatite

The inorganic material is primarily a calcium phosphate crystal called

collagen fibers

lend flexible strength to the bone.

osteoblasts

are responsible for the formation of bone and the repair and remodeling of bone.
produce collagen and proteoglycans
also secrete high concentrations of Ca2+ and phosphate ions, forming crystals called hydroxyapatite.

ossification

The formation of new bone by osteoblasts is called

osteocytes

are cells that maintain bone matrix and form from osteoblast after bone matrix has surrounded it.
account for 90-95% of bone cells and are very long-lived.

lacunae

Osteocyte cell bodies are housed within the bone matrix in spaces called
Osteocytes are located in spaces called

canaliculi

Their cell extensions are housed in narrow, long spaces called

osteoclasts

are bone-destroying cells.
They contribute to bone repair and remodeling by removing existing bone, called bone reabsorption.
Bone breakdown is important for mobilizing crucial Ca2+.
As bone is broken down, the Ca2+ goes into the blood.

lamellar bone

Mature bone is called

lamellae

It is organized into thin, concentric sheets or layers, called
are concentric rings of bone matrix which surround the central canal.

spongy bone

has less bone matrix and more space

compact bone

has more bone matrix and less space.
is the solid, outer layer surrounding each bone.

trabeculae

Spongy bone consists of interconnecting rods or plates of bone called

osteon

The functional unit of compact bone is an

central canal

It is composed of concentric rings of matrix surrounding a
are lined with endosteum and contain blood vessels, nerves, and loose connective tissue.

diaphysis

is the center portion of the bone which is composed of compact bone surrounding a hollow center called the medullary cavity

epiphysis

the ends of a long bone are called

articular cartilage

Within joints, the end of a long bone is covered with hyaline cartilage called

epiphyseal plate

is located between the epiphysis and the diaphysis. Growth in bone length occurs at the

epiphyseal line

When bone stops growing in length, the epiphyseal plate becomes ossified and is called the

marrow

Cavities in spongy bone and the medullary cavity in the diaphysis are filled with soft tissue called

red marrow

is the location of blood forming cells.

yellow marrow

is mostly fat.

periosteum

The outer surface of a bone is covered by a connective tissue membrane called

endosteum

is a single cell layer of connective tissue that lines the internal surfaces of all cavities within bones.
includes osteoblasts and osteoclasts.

Endochondral ossification
Intramembranous ossification

Bone formation in the fetus follows two processes:

Intramembranous ossification

starts within embryonic connective tissue membranes.
occurs when osteoblasts begin to produce bone within connective tissue.
This occurs primarily in the bones of the skull.
Osteoblasts line up on the surface of connective tissue fibers and begin depositing bone matrix to form trabeculae.

Endochondral ossification

starts with a cartilage model.
Is bone formation within a cartilage model.
The cartilage model is replaced by bone.
Initially formed is a primary ossification center, which forms bone in the diaphysis of a long bone.
A secondary ossification center forms bone in the epiphysis.

appositional growth

Bone growth occurs by the deposition of new bone lamellae onto existing bone or other connective tissue.
As osteoblasts deposit new bone matrix on the surface of bones between the periosteum and the existing bone matrix, the bone increases in width, or diameter.
This process is called

endochondral ossification.

Growth in the length of a bone, which is the major source of increased height in an individual, occurs in the epiphyseal plate.
This type of bone growth occurs through

Parathyroid Hormone

Secreted by the parathyroid gland
Increases formation and activation of osteoclasts, the principal bone-reabsorbing cells
Stimulates reabsorption of Ca2+ from urine in the kidney, reducing the amount of Ca2+ excreted in the urine.
Indirectly increases Ca2+ uptake from the small intestine through the activation of calcitriol.

calcitonin

Secreted from C cells in the thyroid gland when blood Ca2+ levels are too high
Rapidly lowers blood Ca2+ levels by inhibiting osteoclast activity

206 bones

How many bones are in the human body?

axial skeleton

consists of the bones of the skull, the auditory ossicles, the hyoid bone, the vertebral column, and the thoracic cage.

appendicular skeleton

consists of the bones of the upper limbs, the lower limbs, and the two girdles.

girdle

refers to the two zones where the limbs are attached to the body.

pectoral girdle, pelvic girdle

two zones of girdle

long bones

are longer than they are wide; examples are upper and lower limb bones.

short bones

are approximately as wide as they are long; examples are the bones of the wrist and ankle.

flat bones

have a relatively thin, flattened shape; examples are bones of the skull and sternum.

irregular bones

include the vertebrae and facial bones, which have shapes that do not fit readily into the other three categories.