Chapter 6: The Skeletal System: Bone Tissue

Question 1

Describe the 6 main functions of bone tissue

Answer 1

1. Supports soft tissue and provides attachment for skeletal muscles
2. Protects internal organs
3. Assists in movement, along with skeletal muscles
4. Mineral homeostasis: stores and releases minerals on demand
5. Blood cell production: homeopoiesis is the process in which red bone marrow produces blood cells
6. Triglyceride storage: yellow bone marrow stores triglycerides (fats/energy reserve)

Question 2

A long bone is one that has greater length than width. Describe the store and function of the following parts:

Diaphysis 
Epiphysis 
Metaphyses 
Articular cartilage 
Periosteum 
Medullary cavity 
Endosteum

Answer 2

Diaphysis: bone shaft/main part

Epiphysis: proximal & distal ends of bone

Metaphyses: regions between the diaphysis & epiphysis

Articular cartilage: layer of hyaline cartilage covering the part of the epiphysis where the bone forms a joint with another

Periosteum: connective tissue sheath & associated blood supply that surrounds surface not covered by articular cartilage

Medullary cavity: hallow space within diaphysis that contains fatty yellow bone marrow and blood vessels

Endosteum: a thin membrane that lines the medullary cavity

Question 3

In a growing bone each metaphysis contains and _______ plate containing cartilage that allows it grow in length; when the bone ceases to grow the cartilage is replaced by bone known as the _________

Answer 3

epiphyseal (growth) plate; epiphyseal line

Question 4

The periosteum is composed of an outer ______ layer that consists of dense irregular connective tissue and an inner _____ layer that consists of cells

Answer 4

fibrous ; osteogenic

Question 5

Perforating (Sharpey’s) fibers attach the periosteum to the underlying bone

True or False

Answer 5

True

Question 6

Bone or osseous tissues most abundant mineral salt is calcium phosphate that combines with other mineral salts to form crystals of ____________.

Answer 6

hydroxyapatite

Question 7

What is calcification? what iniaties it?

Answer 7

Calcification: mineral salts formed by the collagen fibers of the ECM crystallize and hardens

Initiated by osteoblasts

Question 8

Describe the features of the 4 types of cells present in bone tissue:

Osteogenic
Osteoblasts
Osteocytes
Osteoclasts

Answer 8

Osteoprogenitor: only bone cell to undergo cell division (stem cell) and develop into osteoblasts

Osteoblasts: synthesize and secrete collagen and other organic comments that form the extracellular matrix of bone tissue (initiated calcification)

Osteocytes: mature bone cells that maintain metabolism by exchanging watse/nutrients

Osteoclasts: functions in resorption, the breakdown of bone ECM (maintenance/repair)

OSTEOBLASTS Build Bone while OSTEOCLASTS Carve bone

Question 9

Compact vs. Spongy bone tissue

Answer 9

Compact: the strongest form of bone tissue that is found beneath the periosteum of all bone sand makes up the bulk of diaphysis

Spongy: does not contain osteons and is always located in the interior of the bone

Question 10

What are the histological features of compact bone tissue?

osteons (concentric lamellae and central canal)
lacuna (canaliculi)
circumferential lamellae (perforating fibers)

Answer 10

Composed of osteons (havarian system) which consists of concentric lamellae (circular plates of mineralized ECM) arranged around a central canal

Between the lamellae are spaces known as lacuna which
are connected to the central canal by tiny canaliculi pathways which are filled with ECF and provide routes for oxygen and nutrients

Circumferential lamellae are arranged around the entire outer and inner circumference of the bone shaft - connected to the periosteum ba perforating fibers

Question 11

How does spongy bone tissue differ from compact bone tissue?

Answer 11

It is light and reduces overall weight

They are composed to trabeculae (not osteons) that support and protect the red bone marrow

Question 12

Explain the location and roles of the nutrient arteries (nutrient foramina), epiphyseal arteries, periosteal arteries, and metaphysical arteries

Answer 12

Nutrient arteries - pass through a hole in the centre of diaphysis called the nutrient foramen/foramina and then divides into proximal and distal branches to supply the inner part of the bone

Epiphyseal arteries - enter the epiphyses and supply red bone marrow and tissue of the epiphyses

Periosteal arteries - enter the diaphysis through perforating canals and supply the periosteum and outer option of bone

Metaphysical arteries - enter the metaphyses with nutrient artery and supply red bone marrow and bone tissue of metaphysis

Question 13

Veins that carry blood away from the long bones are evident in which 3 places?

Answer 13

Nutrient veins exit at the epiphyseal, metaphysical, and periosteal

Question 14

Intramembranous vs. endochondrial ossification

Answer 14

Bone formation follows one of two patterns:

Intramembranous: bone forms directly with the mesenchyme, which is arranged in sheetlike layers that resemble membranes

Endochondrial: bone forms within hyaline cartilage that develops from mesenchyme

Question 15

Describe the steps in intramebranous ossification

Answer 15

1. Development of ossification centre: osteoblasts secrete organic extracellular matrix
2. Calcification: calcium and other mineral salts are deposited and ECM calcifies
3. Formation of trabeculae: ECM develops into trabeculae that uses to form spongy bone
4. Development of periosteum: mesenchyme at the periphery of the bone develops into the periosteum

Question 16

Describe the steps in endochondral ossification

Answer 16

1. Development of cartilage: mesenchymal cells develop into chondroblasts, which form the cartilage model
2. Growth of cartilage: occurs by cell division of chondrocytes
3. Development of primary ossification centre: n this region of the diaphysis, bone tissue has replaced more of the cartilage
4. Development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity
5. Development of secondary ossification centres: occur in the epiphyses of the bone
6. Formation of articular cartilage & epiphyseal plate: both structures consist of hyaline cartilage

Question 17

Long bones grow in length by which 2 major events?

Answer 17

1. Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate
2. Replacement of cartilage on the diaphysial side of the epiphyseal plate (thickness remains constant but bone length increases)

Question 18

Describe how bones grows in thickness (4 steps)

Answer 18

1. Ridges in periosteum create grooves for periosteal blood vessel
2. Periosteal ridges fuse forming an endosteum-lined tunnel (with blood vessel inside)
3. Osteoblats in endosteum build new concentric lamellae inward toward centre of tunnel, forming a new osteon
4. Bone grows outward as osteoblasts in periosteum build new circumferential lamellae. Osteon formation repeats

Question 19

What is bone remodelling?

Answer 19

Ongoing replacement of the only bone tissue by new bone tissue involving:

Bone resorption - removal of minerals and collagen fibers from bone by osteoclasts

Bone deposition- additional of minerals and collagen fibers to bone by osteoblasts

Question 20

Describe the sequence of events in the repair of a fracture

Answer 20

1. Reactive phase: formation of fracture hematoma
   2a. Reparative phase: fibrocartilaginous callus formation
   2b: Reparative phase: bony callus formation
2. Bone remodelling phase: compact bone replaces spongy bone

Question 21

Define a stress facture

Answer 21

microscopic fissures in bone that forms without any evidence of injury to other tissues

Question 22

Describe how blood calcium level is regulated

Answer 22

Bones bugger the blood calcium levels, releasing Ca2+ into blood (via osteoclasts) and absorbing Ca2+ (via osteoblasts)

Ca2+ exchange is regulated by hormones:
- Parathyroid hormone (PTH) operates via negative feedback - when Ca2+ levels are low they stimulate formation of calcitriol (increases Ca2+)

• Calcitonin inhibits osteoclasts (decreases Ca2+)

Question 23

Define osteoporosis

Answer 23

Bone reparation (breakdown) outpaces bone deposition (formation), largely due to a depletion of Ca2+

Question 24

Define rickets and osteomalacia

Answer 24

Rickets is a disease in children in which growing bones become soft and easily deformed

Osteomalacia is the adult counterpart where new bones fail to calcify causing pain and tendernes