SKELETAL SYSTEM - PART 1

Functions

1. Support
2. Protect
3. Movement
4. Storage
5. Blood cell production

Cartilage

reduce friction and model for bone formation

Tendons

attach bone to muscle

Ligaments

attach bone to bone

connective

Bones, cartilage, tendons, and ligaments are
___________ tissues

collagen and minerals

Bone’s extracellular matrix; flexible and able to bear weight

collagen and proteoglycans

Cartilage’s extracellular matrix; good shock absorber

collagen

Tendons and ligaments’ extracellular matrix; very tough

Proteoglycans

- large polysaccharides attached to proteins
- part of ground substance
- store water

long, short, flat, irregular

Based on shape

compact and spongy (cancellous)

Type of bone tissue

Long bones

Femur, tibia, fibula, phalanges

short bones

Carpals, tarsals

flat bones

Ribs, sternum, skull

Irregular bones

Vertebrae and facial

Diaphysis

– shaft
– compact bone tissue (on outside)

Epiphysis

– ends
– spongy bone tissue

Articular cartilage

- covers epiphyses
- reduces friction

Epiphyseal plate

– site of growth
– between diaphysis and epiphysis

Medullary cavity

– center of diaphysis
– red or yellow marrow

Periosteum

membrane around bone’s outer surface

Endosteum

membrane that lines medullary cavity

Compact Bone Tissue

Location: outer part of diaphysis (long bones) and thinner surfaces of other bones

Osteon/Haversian system

- structural unit of compact bone
- includes lamella, lacunae, canaliculus, central canal, osteocytes

Lamella

rings of bone matrix

Lacunae

spaces between lamella

Canaliculus

- tiny canals
- transport nutrients and remove waste

Central canal

- center of osteon
- contains blood vessels

compact bone

compact bone

Spongy Bone Tissue

• Cancellous bone
• Location: epiphyses of long bones and center of other bones
• No osteons

Trabeculae

interconnecting rods, spaces contain marrow

spongy bone

Osteocytes

maintain bone matrix

Osteoblasts

build bone

Osteoclasts

carve bone

Ossification

process of bone formation (occurs in utero)

Osteoblast’s role

- build bone
- after an osteoblast becomes surrounded by bone matrix it becomes an osteocyte

Ossification center

where bone formation begins

Primary ossification center

- where bone 1st begins to appear
- forms diaphyses

Secondary ossification center

forms epiphyses

Intramembranous Ossification

• Bone formation within connective tissue membranes
• Osteoblasts build bone
• Ex. Skull bones

Endochondral Ossification

• Bone formation inside cartilage
• Cartilage models are replaced by bone
• Ex. All bones (except skull)

Steps in Endochondral Ossification

1. Chondroblasts build a cartilage model, the chrondroblasts become chondrocytes.
2. Cartilage model calcifies (hardens).
3. Osteoblasts invade calcified cartilage and a primary ossification center forms diaphysis.
4. Secondary ossification centers form epiphysis.
5. Original cartilage model is almost completely ossified and remaining cartilage is articular cartilage.

Third month of embryonic development

Ossification in long bones beginning

Fourth month

Most primary ossification centers have appeared in the diaphyses of bone.

Birth to 5 years

Secondary ossification centers appear in the epiphyses

5 years to 12 years in females, 5 to 14 years in males

Ossification is spreading rapidly from the ossification centers and various bones are becoming ossified

17 to 20 years

Bone of upper limbs and scapulae becoming completely ossified

18 to 23 years

Bone of the lower limbs and os coxas become completely ossified

23 to 25 years

Bone of the sternum, clavicles, and vertebrae become completely ossified

By 25 years

Nearly all bones are completely ossified

Infancy and youth

- long bones lengthen at epiphyseal plate
- long bones widen by adding more lamella

Appositional growth

increase in bone width and diameter

End of bone growth (in length)

epiphyseal plate is replaced by an epiphyseal line

Bone Remodeling

- removal of existing bone by osteoclasts and deposition of new bone by osteoblasts
- occurs in all bones
- responsible for changes in bone shape, bone repair, adjustment of bone to stress, and calcium ion regulation

Bone Repair

1. Broken bone causes bleeding and a blood clot forms.
2. Callus forms which is a fibrous network between 2 fragments.
3. Cartilage model forms first then, osteoblasts enter the callus and form cancellous bone this continues for 4-6 weeks after injury.
4. Cancellous bone is slowly remodeled to form compact and cancellous bone.

Bone and Calcium Homeostasis

• Bone is a major storage site for calcium
• Movement of calcium in and out of bone helps determine blood levels of calcium
• Calcium moves into bone as osteoblasts build new bone
• Calcium move out of bone as osteoclasts break down bone
• Calcium homeostasis is maintained by parathyroid hormone (PTH) and calcitonin

Hematopoietic Tissue

tissue that makes blood cells

Red marrow

location of blood forming cells

Yellow marrow

bone marrow that is yellow with fat; found at the ends of long bones in adults

Location of hematopoietic tissue in newborns

most bones (red marrow)

Location of hematopoietic tissue in adults

- red is replaced with yellow marrow
- red marrow is mainly in epiphyses of femur and humerus

Foramen

- hole
- Ex. Foramen magnum

Fossa

- depression
- Ex. Glenoid fossa

Process

- projection
- Ex. Mastoid process

Condyle

- smooth, rounded end
- Ex. Occipital condyle

Meatus

- canal-like passageway
- Ex. External auditory meatus

Tubercle

- lump of bone
- Ex. Greater tubercle

anatomical terms for features of bones

axial skeleton

Mastoid process

attached to neck muscles

External auditory meatus

ear canal

Nasolacrimal canal

- canal between nasal cavity and eye
- conducts tears

coronal suture

the suture between the parietal and frontal bones of the skull

lambdoid suture

suture between the parietal and occipital bones

sagittal suture

the suture uniting the two parietal bones

squamous suture

suture between the parietal and temporal bones

paranasal sinus

any of the paired sinuses in the bones of the face adjacent to the nasal cavity that are lined with mucous membrane that is continuous with the lining of the nasal cavities

paranasal sinuses

frontal bone

the large cranial bone forming the front part of the cranium: includes the upper part of the orbits

parietal bone

either of two skull bones between the frontal and occipital bones and forming the top and sides of the cranium

occipital bone

a saucer-shaped membrane bone that forms the back of the skull

temporal bone

a thick bone forming the side of the human cranium and encasing the inner ear

Styloid process

attachment site for tongue

Mandibular fossa

depression where lower jaw and skull meet

Glenoid fossa

where humerus meets scapula

temporal bone

temporomandibular joint

sphenoid bone

butterfly-shaped bone at the base of the skull

sphenoid foramina

ethmoid bone

ethmoid bone

sphenoid bone

maxillae

of or relating to the upper jaw

maxillae

Hard palate

roof of mouth

Foramen magnum

hole where spinal cord joins brainstem

palatine bones

zygomatic bones