Compact Bone

is good at providing protection and support.

" It forms the diaphysis of long bones, and the external layer of all bones.

Spongy Bone

lightweight and provides tissue support .
" It forms much of the epiphysis and the internal cavity of long bones.

Cartilage

is a poorly vascularized C.T. with a matrix composed of chondroitin sulfate and various fibers.

" Fiber types distinguish hyaline cartilage (fine collagen) from fibrocartilage (collagen bundles) or elastic cartilage (elastic fibers)

This is a layer of hyaline cartilage that reduces friction between bones involved in a joint.

a) periosteum
b) distal epiphysis
c) nutrient foramen
d) articular cartilage
e) epiphyseal plate

d.) articular cartilage

Articular Cartilage

is the thin layer of hyaline cartilage covering the epiphysis of long bones.
" Articular cartilage is found where the bone forms an articular (joint) surface - where one bone moves against another bone.

This is a layer of hyaline cartilage that allows the diaphysis to grow in length.

a) periosteum
b) distal epiphysis
c) nutrient foramen
d) articular cartilage
e) epiphyseal plate

E. epipheasyl plate

This is the fibrous covering on the surface of bone that is involved in thickening of the bone.
a) periosteum
b) endosteum
c) marrow
d) epiphysis
e) metaphysis

a. periosteum

Periosteum

a tough sheath of dense, irregular connective tissue on the outside of the bone.

" It contains osteoblasts, in an inner osteogenic layer, that help the bone grow in thickness, but not in length.
" It also assists with fracture repair and serves as an attachment point for tendons and ligaments.

medullary cavity

is a space within the diaphysis of long bones that contains fatty yellow bone marrow in adults. It minimizes bone weight where it is needed least.

endosteum

is a membrane that lines the medullary cavity. It also contains a layer of osteoblasts.

perichondrium

is a dense irregular connective tissue membrane that surrounds cartilage

chondrocytes

cells that form cartilage

These are considered bone-building cells.

a) fibroblasts b) osteoclasts c) osteocytes d) osteoblasts e) all of these choices

d. osteoblasts

osteoblasts

are bone building cells: They synthesize and secrete collagen fibers and other organic components. Initiate calcification.

osteocytes

are mature osteoblasts (maintenance). Surrounded by extracellular matrix.

These are considered bone-dissolving cells.
a) osteogenic cells
b) osteoclast
c) osteocytes
d) osteoblasts
e) all of these choices

b.) osteoclast

osteoclasts

are large bone breakdown cells.
" As white blood cells, osteoclasts migrated from the bone marrow to become “fixed macrophages” in the substance of the bone. Secrete acid and enzymes at the ruffled border.

Which of following selections lists bone cells in the order from unspecialized stem cell to highly specialized mature bone cell?

a) osteogenic cells, osteoclasts, osteocytes
b) osteogenic cells, osteoblasts, osteocytes
c) osteogenic cells, osteocytes, osteoblasts
d) osteoblasts, osteogenic cells, osteocytes
e) None of these choices.

b) osteogenic cells, osteoblasts, osteocytes

Other important tissues of the skeletal system and their functions:

Epithelium (endothelium) form the capillary walls

" Nerves (the periosteum is especially tender)

" Red marrow – hematopoiesis

" Yellow marrow – fat storage

Chemical constituents of bone

Bone is 25% water, 25% organic proteins, 50% mineral salts (hydroxyapatite crystals, from calcium phosphate and calcium hydroxide combination)

! Organic constituents
• Collagen fibers provide flexibility and tensile strength.

" Inorganic hydroxyapatite crystals (mineral salts) • Calcium Phosphate (Ca3PO4)2
• Calcium Carbonate (CaCO3 – marble)
• Other trace elements: magnesium, fluoride, sulfate

This is the region of a long bone that articulates with other bones.
a) diaphysis
b) epiphysis
c) metaphysis
d) periosteum
e) dmarrow

b. epiphysis

The shaft of a long bone

diaphysis

epiphysis

form the distal and proximal ends of a long bone.

metaphysis

are the areas where the epiphyses and diaphysis join.

Osteons in compact bone tissue are aligned

a) horizontal to the metaphysis.
b) parallel to the epiphysis.
c) parallel to the length of the diaphysis.
d) randomly between the epiphyseal plates.
e) parallel to the perforating canals.

C.

Interstitial lamellae

between osteons are left over fragments of older osteons.

Outer circumferential lamellae

encircle the bone beneath the periosteum.

inner circumferential lamellae

encircle the medullary cavity.

Which of the following structures contain osteocytes?

a) haversian canals
b) Volkmann’s canals
c) concentric lamellae
d) lacunae
e) canaliculi

d. lacunae

These are extensions of the lacunae and are filled with extracellular fluid.
a) Volkmann’s canals
b) haversian canals
c) osteons
d) canaliculi
e) periosteum

D

lacunae

are small spaces between the lamellae which house osteocytes

canaliculi

re small channels filled with extracellular fluid connecting the lacuna

Blood and lymphatic vessels are found in the osteon’s .....

central canal

perforating (volkmans) canal

allow transit of these vessels to the outer cortex of the bone.

Spongy bones lack osteons

Instead, lamellae are arranged in a lattice of thin columns called trabeculae. " Trabeculae of spongy bone support and protect the red bone marrow and are oriented along lines of stress (helps bones resist stresses without breaking).

hematopoiesis

(blood cell production) occurs in spongy bone.

Ossification

or osteogenesis is the process of forming new bone. Bone formation occurs in four situations:

" Formation of bone in an embryo
" Growth of bones until adulthood
" Remodeling of bone
" Repair of fractures

Osteogenesis occurs by two different methods, beginning about the 6th week of embryonic development.

Intra-membranous ossification

endochondral ossification

intra-membranous ossification

produces spongy bone.
• This bone may subsequently be remodeled to form compact bone.

endochondral ossification

is a process whereby cartilage is replaced by bone. • Forms both compact and spongy bone.

the method used in the formation of most bones, especially long bones. " It involves replacement of cartilage by bone. " There are one primary and two secondary centers of growth.

Which of the following selections correctly lists the sequence of events that occur during intramembranous ossification?

a) Ossification center develops > Calcification > Formation of trabeculae > Development of new periosteum.
b) Calcification > Ossification center develops > Formation of trabeculae > Development of new periosteum.
c) Ossification center develops > Formation of trabeculae > Calcification > Development of new periosteum.
d) Development of new periosteum > Ossification center develops > Calcification > Formation of trabeculae.
e) Ossification center develops > Calcification > Development of new periosteum > Formation of trabeculae.

A.

Intra-membranous ossification is the simpler of the two methods.

" It is used in forming the flat bones of the skull, mandible, and clavicle. " Bone forms from mesenchymal cells that develop within a membrane – without going through a cartilage stage (recall that mesenchyme is the tissue from which almost all other C.T. develop.) " Many ossification centers.

During endochondral ossification in a fetus, bones initially develop as a cartilage model surrounded by a connective tissue covering called the
a) periosteum.
b) endosteum.
c) perichondrium.
d) perimysium.
e) trabeculae.

C

Growth in length by chondrocytes is called ______ growth?
a) Interstitial
b) Appositional
c) Exogenous
d) Primary
e) Secondary

a

Growth in width (on the outer surface) by chondrocytes is called ______ growth? a) Interstitial
b) Appositional
c) Exogenous
d) Primary
e) Secondary

b

Which of the following statements about bone remodeling is FALSE?
a) It occurs throughout your lifetime.
b) It involves bone resorption.
c) It involves bone deposition.
d) It occurs at different rates at different locations.
e) It occurs at a faster rate in compact bone than spongy bone.

e

Why must a balance exist between osteoclasts and osteoblasts

If too much new tissue is formed, the bones become abnormally thick and heavy (acromegaly).

" Excessive loss of calcium weakens the bones, as occurs in osteoporosis.

" They may also become too “soft”, as seen in the bone diseases rickets and osteomalacia.

Which of the following two minerals are needed in large quantities when bones are growing?
a) calcium and chlorine
b) magnesium and sulfur
c) calcium and phosphorous
d) manganese and sulfur
e) potassium and phosphorous

C

Minerals are an important component for bone growth and remodeling

Large amounts of calcium and phosphorus and smaller amounts of magnesium, fluoride, and manganese are required for bone growth and remodeling.

During adulthood, which of the following does NOT significantly contribute to bone remodeling and growth?
a) parathyroid hormones
b) vitamin D
c) epinephrine
d) sex steroids
e) human growth hormone

C.

Vitamins are necessary for normal bone metabolism:

" Vitamin A stimulates activity of osteoblasts. " Vitamin C is needed for synthesis of collagen. " Vitamin D is essential to healthy bones because it promotes the absorption of calcium from foods in the gastrointestinal tract into the blood. " Vitamins K and B12 are needed for synthesis of bone proteins.

Hormones are key contributors to normal bone metabolism.

" During childhood, the hormones most important to bone growth are human growth hormone (hGH) and growth factors called IGFs (produced by the liver). Both stimulate osteoblasts, promote cell division at the epiphyseal plate, and enhance protein synthesis.

" Thyroid hormones and insulin also promote bone growth by stimulating osteoblasts and protein synthesis.

" The sex hormones (estrogen and testosterone) cause a dramatic effect on bone growth, such as the sudden “growth spurt” that occurs during the teenage years.
• The sex hormones also promote widening of the pelvis in the female skeleton.
• They are also responsible for closing the epiphyseal plates at the end of puberty.

" Parathyroid hormone (PTH) and calcitonin are critical for balancing the levels of calcium and phosphorus between blood and bone.
• Maintaining a normal serum Ca2+ level takes precedence over mineralizing bone (usually both can be done)

Bone mass reduction is promoted by which hormone? a) calcitriol
b) calcitonin
c) human growth hormone
d) parathyroid hormone
e) insulin

D.

Day to day control of calcium regulation mainly involves:

" PTH stimulates osteoclastic activity and raises serum calcium level.

" Calcitonin (thyrocalcitonin), and to a lesser extent hGH and the sex hormones, stimulate osteoblastic activity and lower serum calcium level.

" Vitamin D is needed for absorption of the Ca2+ and PO4– ions from the small intestine, and reabsorption of those same ions in the kidneys.

" The role of regulating serum Ca2+ levels and mineralizing bone is under hormonal control, and is carefully balanced.

An increase in bone growth is promoted by which hormones?
a) calcitriol (active Vitamin D) and parathyroid hormone
b) calcitonin and calcitriol (active Vitamin D)
c) human growth hormone and parathyroid hormone
d) parathyroid hormone and insulin
e) All of the other selections are correct.

B.

Fracture and repair

Partial, complete (fx is all the way through the bone), closed (simple), open (fx punctures the skin), “Green stick” (a small linear break in the bone cortex), impacted, comminuted, spiral, transverse, displaced

Other fractures are classified by the disease or mechanism which produced the fracture.

Pathological fracture (usually from a cancerous process or severe chronic disease), compression fracture (produced by extreme forces such as in trauma) • Stress fracture (produced from repeated strenuous activities such as running)

What is the correct order of fracture repair? a) Fibrocartilaginous callus, bony callus, hematoma, remodeling
b) Remodeling, hematoma, fibrocartilaginous callus, bony callus
c) Hematoma, fibrocartilaginous callus, bony callus, remodeling
d) Bony callus, fibrocartilaginous callus, hematoma, remodeling

C

Once a bone is fractured, repair proceeds in a predictable pattern:

! The first step, which occurs 6-8 hours after injury, is the formation of a fracture hematoma as a result of blood vessels breaking in the periosteum and in osteons.

! The second and third steps involve the formation of a callus (takes a few weeks, to as many as six months). " Phagocytes remove cellular debris and fibroblasts deposit collagen to form a fibro- cartilaginous callus... which is followed by osteoblasts forming a bony callus of spongy bone.

! The final step takes several months and is called remodeling: " Spongy bone is replaced by compact bone. " The fracture line disappears, but evidence of the break remains.

under mechanical stress...

bone tissue becomes stronger through deposition of mineral salts and production of collagen fibers by osteoblasts. Unstressed bones, on the other hand, become weaker. " Astronauts in space suffer rapid loss of bone density.

two principle effects of aging on bone:

loss of bone mass
brittleness

Brittleness

• Collagen fibers give bone its tensile strength, and protein synthesis decreases with age. • The loss of tensile strength causes the bones to become very brittle and susceptible to fracture

osteoporosis

a condition where bone resorption outpaces bone deposition. " Often due to depletion of calcium from the body or inadequate intake

Which of the following conditions results when the articular cartilages in a joint degenerate to the point where the bony ends of articulating bones touch?
a) osteogenic sarcoma
b) rickets
c) osteomalacia
d) osteoarthritis
e) osteopenia

D

Which of the following substances are stored in the structure of adult bones for use by other tissues in the body?
a) calcium
b) phosphorous
c) triglycerides
d) iron
e) More than one of these substances is stored in bone.

E