Chapter 6 Bones and Skeletal Tissue

Question 1

What are the three regions of the axial skeleton? How many bones are found there?

Answer 1

80 bones found in: 1 - The Skull 2 - Vertebral column 3 - Thoracic Cage

Question 2

What are 7 functions of the skeleton?

Answer 2

1 - Blood cell formation 2 - Mineral Storage (e.g. calcium and phosphate) 3 - Anchors for skeletal muscle 4 - Triglyceride storage (stored as yellow marrow) 5 - Hormone Production (e.g. osteocalcin) 6 - Structure or support 7 - Protection (e.g., skull protects brain)

Question 3

What are the four bone classifications?

Answer 3

Long bones (e.g., humerus) Flat bones (e.g., sternum) Short bones (e.g., talus, includes sesamoids e.g., patella) Irregular (e.g., vertebra) - these bones simply don’t fit into any of the above.

Question 4

What are the two primary regions of the skeleton?

Answer 4

Axial - bones of skull, the rib cage and the vertebral column. These are for protection, support, and carriage. Appendicular - bones of the upper and lower limbs and the girdles that attache the limbs. These are for locomotion and manipulation of the environment.

Question 5

Where are compact and spongy bone found?

Answer 5

Compact - Outer layers of spongy bone look smooth and solid. Spongy - Internal to outer layers is trabecular bone, a honeycomb of trabeculae “little beams.” The spaces therein are filled with marrow.

Question 6

What are the structures of a long bone?

Answer 6

Diaphysis - a tubular shaft that forms the long axis. Contains a medullary cavity. Epiphysis - The bone ends covered by a layer of hyaline cartilage. Membranes - The periosteum and endosteum Blood Vessels and Nerves

Question 7

What are the epiphyseal line and epiphyseal plate?

Answer 7

These are found between the diaphysis and epiphysis. The line is a remnant of the plate (growth plate). It is the part that grows to lengthen bone.

Question 8

What are the periosteum and endosteum?

Answer 8

The periosteum covers the entire outer surface of the bone barring joint surfaces. Its vascular and innervated. It is secured to bone by perforating fibers. Outer layer is dense irregular tissue. Inner is osteogenic layer, it contains stem (osteoprogenitor) cells and osteoclasts. The endosteum lines the inner trabeculae and canals of bone. Same as osteogenic layer of periosteum.

Question 9

What are the four bone cells found in bone tissue?

Answer 9

Osteoprogenitor cells - they are mitotically active squamous cells that can differentiate into osteoblasts. Osteoblasts - secrete bone matrix made of collagen (90%) and Ca+ binding protein. Calcification. Become osteocytes. Osteocytes - mature cells found in lacunae. stress detectors and indicate need for construction or deconstruction as necessary. Osteoclasts - Giant multinucleate cells located at bone resorption sites. Their edge is ruffled to increase surface are for enzyme activity and to seal off areas from surrounding matrix.

Question 10

What are osteons?

Answer 10

A structural unit of compact bone. These are weight bearing pillars that are arranged parallel to the long axis of the bone.

Question 11

What is lamella?

Answer 11

Each matrix tube that forms the osteon is referred to as lamella. Compact bone is also referred to as lamellar bone. They look like rings in a tree trunk.

Question 12

What is the osteoid?

Answer 12

The osteoid makes up 1/3 of the bone matrix and includes the organic compounds such as ground substances and collagen fibers. These are secreted by osteoblasts. These contribute to its structure, tensile strength, and flexibility.

Question 13

What are the inorganic compounds in bone?

Answer 13

These are hydroxyapatites, or mineral salts. Primarily calcium phosphates. These resist compression. ~About 65% of bone by mass.

Question 14

What are 5 phases of endochondral ossification?

Answer 14

1 - Bone collar forms around diaphysis of the hyaline cartilage model. 2 - Cartilage calcifies in the center of the diaphysis and then develops cavities. 3 - Periosteal bud invades the internal cavities and spongy bone forms 4 - The diaphysis elongates and a medullary cavity forms 5 - The epiphyses ossify

Question 15

What are two types of bone?

Answer 15

Endochondral bone - whereby bone develops by replacing cartilage. Membranous bone - whereby bone develops from a fibrous membrane.

Question 16

What bones are formed by intramembranous ossification?

Answer 16

Cranial bones and clavicles.

Question 17

What are the phases of intramembranous ossification?

Answer 17

1 - Ossification centers develop in fibrous connective tissue. Mesenchymal cells cluster and differentiate into osteoblasts. 2- Osteoid is secreted and calcifes. Osteoblasts secrete osteoid, which calcifies in days. Trapped osteoblasts become osteocytes. 3 - Immature spongy bone and periosteum form. Osteoid is laid between blood vessels. Periosteum is the result of vascularized mesenchyme condensing on outer bone. 4 - Compact bone replaces spongy bone (just deep to periosteum). The superficial trabeculae are remodeled into compact bone and deeper areas mature eventually filling with marrow.

Question 18

How do long bones grow?

Answer 18

1 - Proliferation zone - these cells divide quickly and push the epiphysis and diaphysis apart. 2 - Hypertrophic zone - older chondrocytes enlarge as lacunae erode, this forms large interconnecting spaces. 3 - Calcification zone - surrounding cartilage matrix calficies. Chondrocytes die and their matrix begisn to deteriorate and blood vessels invade.

Question 19

What is the process by which bone grows thicker?

Answer 19

Appositional growth, which involves remodeling.

Question 20

How much of the skeleton is replaced each year from remodeling?

Answer 20

5% - 10%

Question 21

What two activities occur in bone remodeling?

Answer 21

Resorption and Deposit

Question 22

What are the two loops that regulate bone remodeling?

Answer 22

Maintaining Ca2+ - a negative feedback loop involving the parathyroid regulates calcium ion levels. Keeping bone strong - mechanical stress determines where remodeling occurs.

Question 23

Why is extracellular Ca2+ homeostasis so important?

Answer 23

In order to maintain the resting membrane potential of all cells.

Question 24

What is the source and function of parathyroid hormone?

Answer 24

The parathyroid gland, in the thyroid releases Parathyoid Hormone (PTH) which signals osteoclasts to resorb bone which is then made available in the blood stream. As calcium levels rise in the blood PTH secretion ends.

Question 25

What are two critical factors in bone remodeling?

Answer 25

Hormonal Controls Mechanical Stress

Question 26

What is the law explaining bone structure remodeling in response to mechanical stress?

Answer 26

Wolf’s Law - where bones are used and stress they will be reconfigured accordingly.

Question 27

How is mechanical force detected in order for remodeling to occur?

Answer 27

Deforming bone pushes fluid containing ions through canaliculi. The resulting electrical current signals osteocytes to release chemicals in order to promote new formations.

Question 28

How do hormones and mechanical stress differ in determining bone remodeling?

Answer 28

Hormones are responsible for ‘if’ and ‘when’ it occurs. Mechanical Stress determines ‘where’ it occurs.

Question 29

How are bone fractures classified?

Answer 29

1 - Position of bone ends - displaced or non-displaced 2- Completeness - complete (all the way through) or incomplete 3 - Skin Penetration - open (compound) or closed (simple)

Question 30

How is a fracture treated and What are the four phases of bone fracture repair?

Answer 30

Treatement begins with reduction (realignment) or screwed together in an open (internal) reduction. Then it is immobilised for 6-8 weeks or more. 1 - A hematoma forms from hemorrhaged blood and deprived cells die. 2 - Fibrocartilaginous callus forms when blood vessels grow into the hematoma and then fibroblasts connect damaged areas with collagen fibers, while chondroblasts secrete cartilage matrix (which later calcifies). This acts as a splint. 3 - A bony callus forms within the fibrocartilaginous callus as osteoblasts begin to create new trabeculae, immature bone, to span the entire break. 4 - Bone is remodeled for months as excess is removed from the diaphysis and medullary cavity and the bone beings to respond to mechanical stress as normal.

Question 31

What is osteoporosis? What are the risk factors?

Answer 31

A group of diseases in which resoprtion outpaces deposition. 1 - decreased sex hormones 2 - insufficient bone stress 3 - insufficient calcium, vitamin d, or protein 4 - smoking 5 - genetics 6 - hormonal conditions e.g. diabetes 7 - alcohol or medications

Question 32

Answer 32

Question 33

Answer 33