Chapter 6.2 Bones

Question 1

Why are bones considered organs?

Answer 1

They contain multiple tissues (bone, blood vessels, nerves, cartilage, epithelium)

Question 2

What are the main functions of bones?

Answer 2

Support, movement, protection, mineral storage, blood cell formation, fat storage, energy metabolism

Question 3

How do bones support the body?

Answer 3

Provide a rigid framework that supports body weight

Question 4

How do bones enable movement?

Answer 4

Act as levers for skeletal muscles (via tendons)

Question 5

How do bones protect organs?

Answer 5

Skull protects brain; vertebrae protect spinal cord; ribs protect thoracic organs

Question 6

Which minerals are stored in bone?

Answer 6

Calcium and phosphate

Question 7

What is red bone marrow’s function?

Answer 7

Blood cell formation

Question 8

What is yellow bone marrow’s function?

Answer 8

Fat (energy) storage

Question 9

What hormone do osteoblasts secrete that affects metabolism?

Answer 9

Osteocalcin

Question 10

What is bone tissue made of?

Answer 10

Cells + extracellular matrix with organic and inorganic parts

Question 11

What makes bone hard?

Answer 11

Inorganic mineral salts (hydroxyapatite; mainly calcium phosphate)

Question 12

What gives bone flexibility and tensile strength?

Answer 12

Organic components, especially collagen

Question 13

What percent of bone mass is organic vs inorganic?

Answer 13

~35% organic, ~65% inorganic

Question 14

Bone matrix “reinforced concrete” analogy: collagen vs minerals?

Answer 14

Collagen = tensile strength; minerals = compression resistance

Question 15

What happens if bone loses minerals (demineralized)?

Answer 15

It becomes flexible/soft (collagen remains)

Question 16

What happens if bone loses organic material (burned)?

Answer 16

It becomes brittle (minerals remain)

Question 17

What are the 4 key bone cell types?

Answer 17

Osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

Question 18

What do osteoprogenitor cells do?

Answer 18

Stem cells that become osteoblasts

Question 19

What do osteoblasts do?

Answer 19

Build bone by secreting osteoid

Question 20

What is osteoid?

Answer 20

Unmineralized organic bone matrix made by osteoblasts

Question 21

What do osteocytes do?

Answer 21

Maintain healthy bone matrix

Question 22

What do osteoclasts do?

Answer 22

Resorb (break down) bone

Question 23

Where do osteoclasts come from?

Answer 23

A white-blood-cell lineage (hematopoietic origin)

Question 24

What is bone remodeling?

Answer 24

Continuous bone resorption + deposition to maintain strength and respond to stress

Question 25

What are the 4 bone shape classes?

Answer 25

Long, short, flat, irregular

Question 26

What is a sesamoid bone?

Answer 26

A short bone that forms inside a tendon (example: patella)

Question 27

What is compact bone?

Answer 27

Dense outer layer of bone

Question 28

What is spongy (trabecular) bone?

Answer 28

Internal honeycomb of trabeculae filled with marrow spaces

Question 29

What are trabeculae?

Answer 29

Small beams/plates of spongy bone aligned along stress lines

Question 30

What are the main parts of a long bone?

Answer 30

Diaphysis (shaft) and epiphyses (ends)

Question 31

What covers the joint surface of epiphyses?

Answer 31

Articular (hyaline) cartilage

Question 32

What is the epiphyseal line?

Answer 32

Adult remnant of the epiphyseal plate (growth plate)

Question 33

What is the medullary cavity?

Answer 33

Central cavity in diaphysis (usually yellow marrow in adults)

Question 34

What is periosteum?

Answer 34

Outer connective tissue covering of bone (except articular surfaces)

Question 35

What does periosteum do?

Answer 35

Resists tension, nourishes bone, anchors tendons/ligaments, supports growth/repair (osteogenic)

Question 36

What are Sharpey’s (perforating) fibers?

Answer 36

Collagen bundles anchoring periosteum to bone

Question 37

What is endosteum?

Answer 37

Thin inner membrane lining internal bone surfaces (trabeculae + canals)

Question 38

Why are bones painful when fractured?

Answer 38

Periosteum is richly innervated

Question 39

How do bones withstand bending stress?

Answer 39

Compact bone at surface resists max tension/compression; interior uses spongy bone and cavities to reduce weight

Question 40

What is an osteon (Haversian system)?

Answer 40

Structural unit of compact bone with concentric lamellae around a central canal

Question 41

What is the central (Haversian) canal?

Answer 41

Contains blood vessels and nerves within an osteon

Question 42

What are perforating (Volkmann’s) canals?

Answer 42

Connect central canals to periosteum and marrow cavity

Question 43

What is a lamella?

Answer 43

A layer (ring) of bone matrix in an osteon

Question 44

Why do alternating lamellae resist twisting?

Answer 44

Collagen/mineral directions alternate between layers

Question 45

Where do osteocytes sit?

Answer 45

In lacunae

Question 46

What are canaliculi?

Answer 46

Tiny channels connecting lacunae for nutrient/waste transfer

Question 47

Why do osteocytes need canaliculi?

Answer 47

Bone matrix is too solid for diffusion through matrix

Question 48

What are interstitial lamellae?

Answer 48

Remnants of old osteons between osteons

Question 49

What are circumferential lamellae?

Answer 49

Layers encircling the bone’s outer/inner circumference to resist twisting

Question 50

Does spongy bone have osteons?

Answer 50

No (trabeculae are too small to contain osteons)

Question 51

How do osteocytes in spongy bone get nutrients?

Answer 51

From capillaries in endosteum via canaliculi

Question 52

What are the two types of ossification?

Answer 52

Intramembranous and endochondral

Question 53

Which bones form by intramembranous ossification?

Answer 53

Most skull bones and clavicles

Question 54

Which bones form by endochondral ossification?

Answer 54

Most bones below skull base (cartilage replacement)

Question 55

How do long bones lengthen after birth?

Answer 55

Growth at epiphyseal plates

Question 56

What happens when epiphyseal plates close?

Answer 56

Bones stop lengthening

Question 57

Rough age range for epiphyseal plate closure?

Answer 57

About 15–23 years (often earlier in females)

Question 58

How do long bones widen?

Answer 58

Appositional growth (periosteum adds bone; endosteum removes bone)

Question 59

Name key hormones that regulate bone growth.

Answer 59

Growth hormone, thyroid hormones, sex hormones (androgens/estrogens)