Chapter 6: The Skeletal System

5 skeletal system functions (SMP BS)

1. Support (bone and cartilage)
2. Protection (skull, ribs, sternum, vertebrae)
3. Movement (tendons, ligaments)
4. Storage (Ca++, P, fat)
5. Blood cell production (bone marrow)

Which type of cartilage do most bones develop from?

hyaline cartilage

What is the matrix of hyaline cartilage made of?

collagen fibers (strength) and proteoglycans (resiliency)

Chondroblasts

specialized cells that form the matrix of hyaline cartilage

Chondrocytes

specialized cells in lacunae that maintain the matrix of hyaline cartilage

Perichondrium

Dense irregular connective tissue membrane covering cartilage

Articular cartilage

hyaline cartilage that covers ends of bones in joints

Does articular cartilage have a perichondrium?

no

Appositional growth in cartilage

when chondroblasts in the perichondrium add new cartilage to the (outside) edge of the existing cartilage

Interstitial growth in cartilage

when chondrocytes divide within the cartilage

Bone matrix composition

35% organic collagen fibers (proteoglycans also) that provide flexible strength & 65% inorganic hydroxyapatite (CaPO4 crystals) that bear weight

What would happen if the calcium was removed from the bone?

the bone would be too bendy

What would happen if the collagen was removed from the bone?

the bone would be too brittle

Which of these is correctly matched?
A. Organic: collagen
B. Inorganic: collagen
C. Organic: hydroxyapatite/CaPO4crystals
D. Inorganic: protein fibers

A. Organic: collagen

Osteoblasts

cells surrounded by bone matrix that carry out ossification/osteogenesis and communicate through gap junctions

Osteocytes

mature bone cells found in lacunae that maintain matrix

Lacunae

occupied spaces by osteocyte cell body

Canaliculi

occupied canals by osteocyte cell processes

Osteoclasts

large, multi-nucleated cells with a ruffled border formed by the contact of the PM of osteoclasts/bone matrix that breakdown/reabsorb already existing bone via H+ ions (decalcify the bone matrix) and enzymes (digest protein component of matrix)

How do osteoclasts break down bone?

by secreting H+ and protein-digesting enzymes that dissolve calcium phosphate in bone

Stem cells (Osteochondral Progenitor cells)

become either chondroblasts or osteoblasts

Woven bone

immature bone present during fetal development or in the early stages of repair where collagen fibers are randomly oriented

Lamellar bone

mature bone present after remodeling where collagen fibers are oriented in one direction in each lamella

lamellae

concentric, circumferential, and interstitial layers of the bone matrix

Cancellous/Spongy bone

bone made of trabeculae that have spaces filled with blood vessels and bone marrow, are covered with a single layer of cells (osteoblasts/clasts), and are oriented along stress lines

trabeculae

interconnecting rods or plates of bone (like scaffolding

Compact bone

denser bone with fewer spaces, so the blood vessels enter the bone itself

Central/Haversian canals

grooves that run parallel to the bone shaft contain blood vessels, nerves, & L. C. T.

endosteum

membranous lining of the hollow cavity of the bone

periosteum

A dense fibrous membrane that covers the surface of bones and serves as an attachment for tendons and muscles

Perforating/Volkmann's canals

grooves that run perpendicular to the bone shaft and serve as entry points for blood vessels from the periosteum or endosteum

Osteon/Haversian system

the microscopic, functional, and repeating unit of compact bone that consists of a Haversian canal, its contents, lamellae, lacunae w/ osteocytes, and canaliculi

How do osteocytes receive nutrients and remove waste?

the canal system

Long bone shape

bones that are longer than wide (Ex: upper and lower limbs)

Short bone shape

bones that are nearly cube shaped (Ex: carpals and tarsals)

Flat bone shape

bones that are thin, flattened, or curved (Ex: ribs, sternum, skull, or scapulae

Irregular bone shape

bones that are complex shapes (Ex: vertebrae, facial bones)

Diaphysis

shaft of a long bone (compact bone mostly)

Epiphysis

end of a long bone (cancellous bone mostly)

Epiphyseal plate

growth plate made of hyaline cartilage until growth stops

Epiphyseal line

remnant of the epiphyseal plate that forms after the bone stops growing in length

Medulary cavity

central, hollowed-out area in the shaft of a bone that contains red blood marrow (all red marrow in children but yellow marrow in the limb bones & skull in adults)

Sharpey's fibers

periosteal fibers that penetrate through the periosteum into the bone that strengthen tendon or ligament attachment

Do flat bones have a diaphysis?

no

Which paired terms are most correct?
A. Epiphysis - shaft of long bone
B. Epiphysis - most is made of compact bone
C. Diaphysis - flat, short, irregular bones
D. Diaphysis - shaft of long bones

D. Diaphysis - shaft of long bones

What does it mean when you see the epiphyseal line?
A. The diaphyseal plate has closed
B. The epiphyseal plate has closed
C. Active cartilage growth is taking place
D. Growth in length is continuing

B. The epiphyseal plate has closed

Intramembranous ossification

bone develops in a connective tissue membrane from embryonic mesenchymal cells

Process of intramembranous ossification (9 steps)

1. Mesenchymal cells in the membrane become osteochondral progenitor (OCP) cells
2. The OCP cells become osteoblasts
3. The osteoblasts produce bone matrix that surrounds the collagen fibers of the connective tissue membrane
4. The osteoblasts then become osteocytes
5. The osteocytes form tiny trabeculae of woven bone
6. More osteoblasts gather on the trabeculae and produce more bone.
7. The resulting spongy bone cells specialize to form red bone marrow
8. Cells surrounding the developing bone specialize to form the periosteum
9. Osteoblasts from the periosteum lay down bone matrix to form an outer surface of compact bone

Endochondral ossification

bone develops in cartilage

Centers of ossification

locations in the connective tissue membrane where ossification begins then expands to form a bone

Fontanels

large, membrane-covered spaces between developing skull bones

Long bone growth

occurs at the epiphyseal plate and involves the formation of new cartilage by interstitial cartilage growth then appositional bone growth

Appositional bone growth

new layers of bone are added on to the surface of old bone (beneath the periosteum)

Does articular cartilage ossify or persist through life?

it persists throughout life

Zones of epiphyseal plate (5)

1. Resting cartilage
2. Proliferation
3. Hypertrophy
4. Calcification
5. Ossified bone

Zone of resting cartilage

cartilage attaches to the epiphysis

Zone of proliferation

new cartilage is produced on the epiphyseal side of the plate as the chondrocytes divide and form stacks of cells

Zone of hypertrophy

chondrocytes mature and enlarge

Zone of calcification

matrix is calcified and chondrocytes die

Ossified bone (final zone of the epiphyseal plate)

calcified cartilage on the diaphyseal side of the plate is replaced by bone

Growth at articular cartilage

carried out by chondrocytes near the surface of the articular cartilage and results in the increased size of the epiphyses

Pituitary gigantism

excess growth hormone before growth plates close

Acromegaly

excess growth hormone after growth plates close

Achondroplastic dwarf

improper growth at the growth plate

Factors affecting bone growth (3)

1. Genetics
2. Nutrition
3. Hormones

How does nutrition affect bone growth?

lack of Ca++ and protein during growth causes bones to be small

Rickets

Vitamin D deficiency in children that causes a decrease in mineralization of bone matrix

Osteomalacia

softening of the bone caused by a lack of vitamin D in adulthood

Vitamin C is necessary for

osteoblasts, collagen, wound healing, and teeth to not fall out

Scurvy

Vitamin C deficiency

How do hormones affect bone growth?

1. Growth hormone from the anterior pituitary gland affects interstitial cartilage growth and appositional bone growth
2. Thyroid hormone affects all tissues
3. Sex hormones stimulate growth at puberty and the closure of epiphyseal plates

Basic multicellular unit (BMU)

a temporary group of osteoclasts and osteoblasts that last about 6 months which remove old bone matrix and replace it with new bone

How long does it take to renew the entire skeleton?

10 years (a decade)

What are the functions of bone remodeling?

bone growth, changes in shape, adjustments to stress, bone repair, and Ca++ ion regulation

How are new osteons formed in compact bone?

osteoclasts break down the matrix and form a tunnel, then osteoblasts form lamellae around the tunnel wall, forming a concentric lamella

4 steps to bone repair

1. Hematoma formation
2. Callus formation
3. Callus ossification
4. Bone remodeling

Hematoma formation

Blood from blood vessels clot

Callus formation

tissue forms at fracture site and connects broken ends

Internal part of callus formation

blood vessels grow into clot, osteoclasts dissolve debris, fibroblasts produce collagen and granulation tissue, chondroblasts produce cartilage, and osteoblasts invade, laying down bone

External part of callus formation

osteoblasts and chondroblasts help the bone/cartilage collar stabilizes into two pieces

Callus ossification

callus replaced by woven, cancellous bone

Bone remodeling

replacement of woven/bone by (lamellar) compact bone

What early structure helps stabilize a fracture during bone repair?
A. Chondroblasts
B. Callus
C. Hematoma
D. Periosteum

B. Callus

What cells or tissues do not play a major role in bone repair in the Callus formation stage?
A. Chondroblasts
B. Macrophages
C. Compact bone
D. Osteoblasts

C. Compact bone

Calcium homeostasis

calcium enters bone via osteoblasts and leaves via osteoclasts, affecting blood calcium levels, which are regulated by the parathyroid hormone and calcitonin

How does parathyroid hormone (PTH) affect blood calcium levels?

raises calcium in the blood by stimulating osteoclasts

How does calcitonin affect blood calcium levels?

lowers calcium in the blood by inhibiting osteoclast activity

Effects of aging on the skeletal system

1. Bone matrix decreases and becomes more brittle due to lack of collagen and less hydroxyapatite
2. Bone mass decreases (spongy bone first, then compact bone)

Bone loss causes an increase in fractures, deformity, loss of height, pain, stiffness, stooped posture, & loss of teeth

7 types of bone fractures

1. Open (compound) - bone break + open wound where the bone may be sticking out
2. Closed (simple) - no break in skin
3. Incomplete - not across bone
4. Greenstick (incomplete) - fracture on the convex side of the curve of a bone
5. Hairline - two sections of bone do not separate (skull)
6. Comminuted fractures - more than two pieces
7. Impacted - one fragment is driven into the cancellous portion of the other fragment

5 classifications of impacted bone fracture

1. Linear
2. Transverse
3. Spiral
4. Oblique
5. Stellate radiating out from a central point

If a 12-year-old were to fracture their epiphyseal plate, the result of the damage could be that the bone:
A. Grows abnormally brittle.
B. May stop growing at the plate.
C. May grow much thicker at the site of the injury.
D. Has a greatly increase potential for a sarcoma.

B. May stop growing at the plate.

What did the Adventist Health Study mentioned at the end of the PowerPoint find? (4 things)

1. Adventist men live 7.3 years longer and Adventist women live 4.4 years longer than other Californians.
2. Five behaviors (not smoking, plant-based diet, nuts several times per week, regular exercise and normal weight), increase life span by up to ten years.
3. Fruits and vegetables lowered risk of heart disease/cancer.
4. Increasing consumption of red and white meat was associated with increased risk of colon cancer