Chapter 6: The Skeletal System: Bone Tissue

Question 1

What are the 6 functions of the skeletal system?

Answer 1

Support, protection, assistance in movement, mineral homeostasis, blood cell production, and triglyceride storage

Question 2

How does the skeletal system support us?

Answer 2

Structural framework of the body. Supports soft tissue and provides attachment points for tendons of skeletal muscles

Question 3

How does the skeletal system provide protection?

Answer 3

Protects internal organs from injury like cranial bones protect the brain

Question 4

How does the skeletal system assist in movement?

Answer 4

Skeletal muscles attach to bones; when they contract they pull on bones to produce movement

Question 5

How does the skeletal system provide mineral homeostasis?

Answer 5

It stores several minerals, especially calcium and phosphorus which contributes to strength of bones. On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and distribute minerals to other body parts

Question 6

How does the skeletal system produce blood cells?

Answer 6

Within certain bones, connective tissue called RED BONE MARROW produces RBCs, WBCs and platelets in a process called hemopoiesis. With increasing age, most red bone marrow turns to yellow. It’s present in developing bones of the fetus and some adult bones. Like the hip (pelvic) bone, ribs, sternum, vertebrae, skull and ends of bones of the humerus and femur

Question 7

How does the skeletal system function in triglyceride storage?

Answer 7

Yellow Bone Marrow consists mainly of adipose cells which store triglycerides

Question 8

What are the 7 parts of the long bone?

Answer 8

Diaphysis, epiphysis, metaphysis, articular cartilage, periosteum, medullary cavity, endosteum

Question 9

What is the diaphysis of long bone?

Answer 9

Bone’s shaft/body (main part)

Question 10

What is the epiphysis of long bone?

Answer 10

Proximal and distal ends of bone

Question 11

What is the metaphysis of long bone?

Answer 11

Regions between the diaphysis and epiphysis. Contains an epiphyseal growth plate (in growing bone), a layer of hyaline cartilage that allows diaphysis to grow. Carilage in epiphyseal plate is replaced by bone… resulting bony structure called the epiphyseal line

Question 12

What is the articular cartilage of long bone?

Answer 12

Thin layer of hyaline cartilage covering the epiphysis where the bone forms an articulation (joint) with another bone. Absorbs shock and freely movable joints. Lacks perichondrium and blood vessels to repairing damage is limited

Question 13

What is the periosteum of long bone?

Answer 13

Tough connective tissue sheath and its associated blood suppply that surrounds the bone surface wherever it’s not covered by articular cartilage. Protects bone, assists in fracture repair, helps nourish bone tissue, serves as an attachment point fr ligaments and tendons. It’s attached to underlying bone via PERFORATING FIBRES (thick bundles of collagen that extend from periosteum into the bone ECM).

Question 14

What is the medullary of long bone?

Answer 14

Hollow, cylindrical space within diaphysis that contains fatty yellow bone marrow and many blood vessels in adults

Question 15

What is the endosteum of long bone?

Answer 15

Thin membrane that lines medullary cavity. Contains single layer of bone-forming cells and small amount of connective tissue

Question 16

How is bone tissue (osseous tissue) formed

Answer 16

Bone tissue contains lots of ECM surrounding widely separated cells. Most abundant mineral salt is calcium phosphate which is combined with calcium hydroxide to form crystals of HYDROXYAPATITE. The crystals combine with minerals like calcium carbonate and ions like mg, flouride, P, sulfate. As the materials are deposited in the framework formed by collagen fibres of the ECM they crystalize and the tissue hardens (this is called CALCIFICATION and is initiated by osteoblasts). Calcification requires collagen fibres

Question 17

What are the 4 types of cells present in bone tissue?

Answer 17

Osteogenic cells, osteoblasts, osteocytes, and osteoclasts

Question 18

What are osteoprogenitor cells in bone?

Answer 18

Unspecialized bone stem cells derived from mesenchyme. Only bone cells that undergo division (resulting in osetoblasts). Found along inner part of periosteum, in the endosteum and in the canals within bone that contains blood vessels

Question 19

What are the osteoblasts of bones?

Answer 19

Bone building cells. Synthesize and secrete collagen fibres and other organic components needed to build the ECM of bone tissue and initiate calcification

Question 20

What are osteocytes of bone?

Answer 20

Mature bone cells. Maintains daily metabolism like exchanging nutrients and waste within the blood. No division

Question 21

What are osteoclasts of bone?

Answer 21

Huge cells derived from fusion of many monocytes (a WBC). Concentrated in the endosteum. Plasma membrane folded into a ruffled border where the cell releases lysosomal enzymes that digest proteins and mineral components of the ECM. This breakdown of ECM is called resorption. Also helps regulate blood calcium levels. Carve out bone.

Question 22

What are the 2 types of bone?

Answer 22

Compact or spongy

Question 23

Briefly describe compact bone tissue

Answer 23

Contains osteons which consists of concentric lamellae around a central canal. Strongest. Concentric lamellae surround a netowkr of blood vessels and nerves in the central canal. Between concentric lamellae are small spaces called lacunae which contain osetocytes. Radiating from the lacunae is the canaliculi which contains the ECM… inside are finger life processes of osteocytes which communicate with eachother via gap junctions. Canaliculi contaiin lacunae with one another and with central canals which provide routes for nutrients and O2 to reach osteocytes and removing waste. Compact bone tissue is tickest in those parts of the bone where stress is applied in few directions

Question 24

What are interstitial lamellae?

Answer 24

Fragments of older osteons partly destroyed by bone rebuilding. Areas of neighbouring osteons

Question 25

What is circumferential. Lamellae?

Answer 25

Arranged around entire outer and inner circumference of the shaft of a long bone are lamellae called circumferential lamellae. Connected to periosteum by perforating fibres

Question 26

Briefly describe spongy bone tissue

Answer 26

No osteons. Located in interior part of a bone protected by compact bone. Has lamellae arranged in irregular pattern of thin columns called trabeculae. Between trabeculae are macroscopic spaces filled with red bone marrow in bones that produce RBCs and yellow bone marrow (adipose tissue) in others. Trabeculae consists of concentric lamellae, osteocytes in lacunae and canaliculi. In long bones it forms core of epiphysis and narrow rim bordering the medullary cavity of diaphysis. Located where bones are not heavily stressed or where stress is applied in all directions.

Question 27

Name 2 big ways that spongy bone differs from compact?

Answer 27

1) spongy bone is light so bone moves easier when pulled by skeletal muscles. 2)The trabeculae of spongy bone supports and protects red bone marrow

Question 28

What is the periosteal arterties?

Answer 28

Small artieries accompanied by nerves enter the diaphysis through many perforating canals and supply the periosteum and out part of the compact bone

Question 29

What is the nutrient artery?

Answer 29

Centre of the diaphysis. Passes through a hold in compact bone called nutrient foramen

Question 30

What arteries supply the ends of long bones?

Answer 30

Metaphyseal and epiphyseal arteries.

Question 31

What are metaphyseal arteries?

Answer 31

Together with nutrient artery supplies the red bone marrw and bone tissue of the metaphysis

Question 32

What are epiphyseal arteries?

Answer 32

Supplies the red bone marrow and bone tissue of the epiphyseal.

Question 33

What are the 3 veins that carry blood away from bone?

Answer 33

1) Nutrient veins (one or two) (accompany the nutrient artery and exit through diaphysis). 2) Epiphyseal veins and metaphyseal veins (many of them) (Accompany their respective arteries and exit through the epiphyses and metaphyses). 3)Periosteal (many small) (accompany their respective arteries and exit through the periosteum). .Periosteum is rich in sensory nerves.

Question 34

WHat are the two patterns bone formation follows?

Answer 34

1) Intramembranous ossification (bones form directly within mesenchyme) and 2) endochondral ossification (bones form within hyaline cartilage that develops from mesenchyme).

Question 35

What bones undergo intramembranous ossification?

Answer 35

Flat bones of the skull, most of the facial bones, mandible (lower jaw), and medial parts of clavicles

Question 36

What are the steps of formation of bone via intramembranous ossification?

Answer 36

1) Development of ossification centre, 2) calcification, 3) Formation of trabeculae, 4) Development of periosteum (compact bone replaces surface layers of spongy bone)

Question 37

What are the steps involved in the formation of endochondral bone?

Answer 37

1) Development of the cartilage model. 2) Growth of the cartilage model (interstitial growth.. increasing length… and appositional growth… increasing width). 3) Development of primary ossification centre ( a region where bone tissue replaces cartilage… primary ossification proceeds INWARDS from external surface of the bone). 4) Development of medullary cavity (osteoclasts break down some newly formed trabeculae leaving a cavity in the diaphysis). 5) Development of secondary ossification centres (no medullary cavity forms because spongy bone remains in the interior of epiphyses… secondary ossification proceeds OUTWARDS from centre of epiphyses toward centre of bone). 6) Formation of articular cartilage and the epiphyseal plate (hyaline cartilage that covers the epiphyses becomes the articular cartilage)

Question 38

What are the 2 things involved in growth in length of bone?

Answer 38

1) Interstitial growth of cartilage on the epiphyseal side of the epiphyseal plate. 2) Replacement of cartilage on the diaphyseal side of the epiphyseal plate with bone by endochondral ossification.

Question 39

What are the 4 parts of hyaline cartilage?

Answer 39

1) Zone of resting cartilage (Nearest the epiphyses. Small scattered chondrocytes. Cells don’t function in bone growth… they anchor the epiphyseal plate to the epiphysis). 2) Zone of proliferating cartilage (Larger chondrocytes. Chondrocytes undergo interstitial growth as they divide and secrete ECM. Replaces those that die at diaphyseal side of epi plate). 3) Zone of hypertrophic cartilage (Large, maturing chondrocytes arranged in columns). 4) Zone of calcified cartilage (few cells thick. Chondrocytes that are dead because the ECM around them has calcified. Osteoclasts dissolve the calcified cartilage and osetoblasts and capillaries from the diaphysis invade the area. The osteoblasts lay down bone ECM, replacing calcified cartilage).

Question 40

Where is chondrocytes proliferate and cartilage replaced?

Answer 40

Chondrocytes proliferate on the epiphyseal side of the plate. Cartilage is replaced by bone on the diaphysial side of the plate.

Question 41

When does the epiphyseal plate close?

Answer 41

Closes when the epiphyseal cell cartilage stops dividing and bone replaces it.

Question 42

Why is looking at the epiphyseal plate useful?

Answer 42

Useful in determining bone age, predicting adult height, and establishing age at death.

Question 43

What are the steps in appositional growth?

Answer 43

1) Osteoblasts become surrounded by ECM and develop into osteocytes which forms bone ridges on either side of the periosteal blood vessel. The ridges slowly enlarge and create a groove for the periosteal blood vessel. 2) Ridges fold together and fuse, the groove becomes a tunnel that encloses the blood vessel. The former periosteum becomes the endosteum that lines the tunnel. 3) Osteoblasts in the endosteum deposit bone ECM, forming new concentric lamellae which proceeds inward towards the periosteal blood vessel and the tunnel fills in. 4) As an osteon is forming, osteoblasts under the periosteum deposit new circumferential lamellae further increasing bone thickness.

Question 44

How does the medullary cavity enlarge?

Answer 44

Bone tissue lining the medullary cavity is destroyed by osteoclasts in the endosteum.

Question 45

What are the 2 processes that bone remodelling involves?

Answer 45

1) bone resorption and 2) bone deposition

Question 46

What is bone resorption?

Answer 46

Removal of minerals and collagen fibres from bone by oseteoclasts

Question 47

What is bone deposition?

Answer 47

Addition of minerals and collagen fibres to bone by osteoblasts

Question 48

What does remodelling do and what triggers it?

Answer 48

Remodelling removes injured bone and may be triggered by exercise, sedentary life, and changes in diet

Question 49

Describe the process of resorption?

Answer 49

Osteoclasts attach to bone surface at endosteum or periosteum and forms a leak proof seal at edges of ruffled border. Then releases lysosomal enzymes and several acids into the sealed pocket. The enzymes digest collagen fibres and other organic mineras. The degraded bone proteins and ECM materials (Ca and P) enter an osteoclast via endyctosis and undergo exocytosis on side opposite the ruffled border. Products of bone resorption diffuse into nearby blood capillaris. Osteoblasts move in to rebuild bone

Question 50

What are the 3 factors than affect metabolism of bone?

Answer 50

1) Minerals (lots of Ca and P, and small amounts of Mg, Fl, and Mn needed for bone growth and remodelling), 2) Vitamins (Vit. A stimulates activity of osteoblasts, C needed for synthesis of collagen, D increases absorption of Ca from foods in GI into blood), 3) Hormones (IGFs stimulate osteoblasts, promote cell division @ epiphyseal plate and proteins needed to build new bone, thyroid hormones (T3 and T4) from the thyroid gland also promote bone growth by stimulating osteoblasts, insulin from pancreas increases synthesis of bone proteins).

Question 51

How do sex hormones affect bone growth?

Answer 51

Like estrogen and androgens (testosterone). Increase osteoblast activity, synthesis of bone, ECM and the sudden growth spurt in teen years. Estrogen promotes changes in skeleton that is typical of females (like wide pelvis). They usually shut down growth at epiphyseal plate (why females’ close earlier).

Question 52

What is a stress fracture?

Answer 52

A series of microscopic fissure in bone that forms without evidence of injury to other bone tissue. Results from repeated strenuous activities (like running, jumping, or dancing) and from diseases like osteoporosis.

Question 53

What are the 4 phases in repairing a bone fracture?

Answer 53

1) Reactive phase (mass of blood called a hematoma forms around the fracture site. Bone cells die here due to lack of circulation so inflammation response due to dead cells. Neutrophils, macrophages, and osteoclasts remove the dead or damaged tissue) 2a) Reparative phase: Fibrogenous Callous Formation (Blood vessels grow into the fracture hematoma and phagocytes clean up dead bone cells. Fibroblasts from periosteum invade fracture site and produce collagen fibres. And cells from periosteum develop into chondroblasts and produce fibrocartilage) 2b) Reparative Phase: Bony Callous Formation (Osteoprogenitor cells develop into osteoblasts which begin to produce spongy trabeculae. The fibrocartilage is converted into spongy bone and this callous is called bony callus). 3) Bone remodelling phase (Dead portions of original fragments of broken bone are gradually resorbed by osteoclasts. Compact bone replaces spongy bone around periphery of fracture)

Question 54

Why is calcium homeostasis important?

Answer 54

Nerve and muscle cells depend on stable level of calcium ions (Ca2+) in EC fluid, blood clotting reqires Ca2+ ions, some enzymes require Ca2+ as a cofactor (additional substance for enzymatic reaction to occur).

Question 55

What might happen if Ca+ is too high / too low?

Answer 55

Heart may stop if too high and breathing may stop if too low

Question 56

How does bone help buffer Ca2+ levels?

Answer 56

Releases Ca2+ into blood plasma (using osteoclasts) when levels decrease and bone absorbs Ca2+ (using osteoblasts) when levels rise

Question 57

How is Ca2+ exchange regulated?

Answer 57

It’s regulated by hormones. The most important hormone is the parathyroid hormone (PTH) secreted by parathyroid glands. It increases blood Ca2+ levels. PTH secretion operates via NEGATIVE feedback loop. The parathyroid gland is the control centre. PTH stimulates formation of calcitriol (active form of vit D), a hormone that promotes the absorption of calcium from foods in the GI tract in the blood… helps elevate levels.

Question 58

What happens when blood Ca2+ arises above normal?

Answer 58

Parafillicular cells in the thyroid gland secrete calcitonin (CT). CT inhibits activity of osteoclasts, speeds up Ca2+ uptake by bone and accelerates Ca2+ deposition in bones.

Question 59

What happens under physical stress?

Answer 59

When under stress bone tissue becomes stronger through increased deposition of mineral salts and production of collagen fibres by osteoblasts. High impact intermittent strains more strongly influence bone deposition than lower impact strains (ie running vs walking)

Question 60

What is the main mechanical stress on bone?

Answer 60

Those that result from the pull of skeletal muscles and the pull gravity.

Question 61

In middle age, there is a decrease in bone mass. Why?

Answer 61

Bone resorption by osteoclasts outpaces bone deposition by osteoblasts

Question 62

What are the 2 main effects of aging on bone tissue?

Answer 62

1) Loss of bone mass and 2) Brittleness

Question 63

Why is there a loss of bone mass in old age?

Answer 63

Due to demineralization… loss of Ca and other minerals from bone ECM

Question 64

Why do people’s bones become brittle in old age?

Answer 64

Decrease rate of protein synthesis. Collagen fibres give bone its tensile strength. So loss of tensile strength causes bones to become brittle and susceptible to fracture. This is due to diminished production of human growth hormone (HGH)