Chapter 6: Skeletal System
I. Bone Structure
A. Bone Classification
1. The four classes of bone according to shape are long, short, ________,
and irregular.
2. Examples of long bones are forearm and ________ bones.
3. __________ bones are shaped like cubes.
4. Examples of short bones are wrist bones and _______ bones.
5. _________ bones are plate like structures.
6. Examples of flat bones are some skull bones, ribs, and ________.
7. _________________ bones have a variety of shapes.
8. Examples of irregular bones are ________ and some facial bones.
9. Round bones are also called __________bones.
10. Sesamoid bones are small and nodular and embedded within
_______ adjacent to joints.
11. An example of a ____________ bone is the patella.
B. Parts of a Long Bone
1. An expanded end of a _________ bone is called an epiphysis.
2. An ____________ articulates with another bone.
3. __________ cartilage is located on the articulating portion of an
epiphysis.
4. The shaft of a long bone is called a _________.
5. ________________ is a tough, vascular, fibrous membrane covering
the diaphysis of a bone.
6. Periosteum functions to form and repair ____________ tissue.
7. Processes provide sites for attachments of ___________ or ligaments.
8. The wall of the diaphysis is composed of _____________bone.
9. Compact bone has a continuous extracellular matrix with no gaps.
10. The epiphyses are largely composed of ____________ bone.
11. Spongy bone consists of bony plates called __________.
12. A bone usually has compact bone overlying spongy bone with the
relative amounts of each varying in differently shaped bones.
13. A semirigid tube with a hollow chamber called the medullary cavity
runs through the _____________ of the long bone.
14. Endosteum lines the medullary cavity and spaces of ___________
bone.
15. Endosteum contains bone-forming cells, the stem cells called
osteoprogenitor cells and the bone building ____________cells
16. The tissue that fills the spaces of bone is called marrow.
17. The two forms of marrow are red and ___________.
C. Microscopic Structure
1. Introduction
a. Bone cells are called _________________.
b. ___________ are tiny, chambers that contain osteocytes.
c. Lacunae form concentric canals around central canals, central
canals are also known as _____________canals
d. Osteoctyes transport nutrients and wastes to and from nearby
cells.
e. Cellular processes of osteocytes pass through narrow canal like
structures called ___________.
f. The extracellular matrix of bone is composed of collagen and
___________ salts.
2. Compact Bones
a. An __________ is a cylinder-shaped unit of compact bone.
b. The substance of compact bone is formed from many osteons
cemented together.
c. Each central canal contains blood vessels and __________.
d. ___________ canals connect central canals of osteons.
e. Perforating canals contain larger _________ vessels and
nerves.
3. Spongy Bone
a. Spongy bone is also composed of cells called ____________
and extracellular material.
b. Unlike compact bone, the bone cells do not aggregate around
central canals.
c. Instead the cells lie within ________________.
d. Osteocytes get nutrients from substances diffusing into
canaliculi that lead to the surface of trabeculae.
II. Bone Development and Growth
A. Introduction
1. Parts of the skeleton begin to form during the first few weeks of
_____________ development.
2. Bony structures continue to grow until ___________.
3. Bones form by replacing existing _____________ tissues.
4. ________________ bones originate within sheetlike layers of
connective tissue. (membranes)
5. Endochondral bones originate as masses of cartilage that are later
replaced by _____________ tissue.
B. Intramembranous Bones
1. Examples of intramembranous bones are the broad, flat bones of the
skull and _________.
2. Osteogenesis is bone _________________.
3. During their development, membrane like layers of relatively
undifferentiated connective tissue appear at the sites of their future bones.
4. Dense networks of blood vessels supply the connective tissue layers.
5. Osteoblasts are ______-forming cells.
6. _______________ deposit bony matrix around themselves.
7. Spongy bone can become __________ bone as spaces fill with bone
matrix.
8. As development continues, osteoblasts may become surrounded by
matrix.
9. Extracellular matrix enclosing the processes of osteoblasts gives rise to
canaliculi.
10. Once isolated, osteoblasts become _________________.
11. Periosteum comes from cells of the undifferentiated connective tissue
that persist outside of the developing bone.
12. Compact bone is formed by osteoblasts on the inside of periosteum.
13. Intramembranous ____________ is the process of replacing
connective tissue to form an intramembranous bone.
C. Endochondral Bones
1. Most of the bones of the skeleton are formed by ___________
ossification.
2. Endochondral bones develop as masses of _____________ cartilage.
3. Eventually the cartilage _____________.
4. As the cartilage decomposes, a periosteum forms from
connective tissue that encircles the developing structure.
5. _________ vessels and undifferentiated connective tissue cells invade
the disintegrating tissue.
6. Some of the cells differentiate into ____________.
7. Osteoblasts form spongy bone in the spaces previously housed by
cartilage.
8. Endochondral ossification is the process of forming an endochondral
bone by the replacement of hyaline _____________.
9. The primary ossification center is an area in the _____________of a
long bone in which the bony tissues begin to replace hyaline cartilage.
10. Secondary ossification centers appear in ______________.
11. The ___________plate is a band of cartilage between the primary and
secondary ossification centers.
D. Growth at the Epiphyseal Plate
1. In a long bone, the diaphysis is separated from the epiphysis by an
____________ plate.
2. The cartilaginous cells form four layers.
3. The first layer is composed of resting cells that do not actively
participate in growth.
4. The first layer anchors the epiphyseal plate to the bony tissue of the
epiphysis.
5. The ___________ layer includes rows of many young cells undergoing
mitosis.
6. As new cells appear, the cartilaginous plate thickens.
7. The third layer is formed by older cells that are left behind as new cells
appear.
8. The cells of the third layer enlarge and thicken the epiphyseal plate.
9. The __________ layer is composed of dead cells and calcified
extracellular matrix.
10. ______________ cells break down calcified matrix of bone.
11. _______________cells originate from monocytes.
12. Osteoclasts secrete acids that dissolve the inorganic component of the
calcified matrix, and their ___________ enzymes digest the organic
components.
13. Osteoclasts phagocytize components of the bony matrix.
14. After osteoclasts remove the extracellular matrix, _____________
invade the region and deposit bone tissue in place of calcified cartilage.
15. A long bone continues to _____________ while the cartilaginous cells
of the epiphyseal plates are active.
16. Lengthening of the bone is no longer possible once the
_____________centers of the diaphysis and epiphysis meet and the
epiphyseal plates ossify.
17. The __________ cavity forms when osteoclasts erode bone tissue in
the diaphysis.
18. The bone in the central regions of the epiphyses and diaphysis
remains spongy.
19. Hyaline cartilage on the ends persists as __________cartilage.
E. Homeostasis of Bone Tissue
1. Throughout life, osteoclasts resorb bone tissue and ______________
replace bone.
2. About 3% to 5% of bone calcium is exchanged each year.
F. Factors Affecting Bone Development, Growth, and Repair
1. Factors that affect bone development, growth and repair include
______________, exposure to sunlight, hormonal secretions, and physical
exercise.
2. Vitamin_________ is necessary for proper absorption of calcium.
3. Lack of vitamin D can lead to the diseases rickets in children and
_______________in adults
4. Vitamin __________ is necessary for osteoblast and osteoclast activity
during normal development.
5. Vitamin _______________ is required for collagen synthesis.
6. __________ hormone stimulates division of cartilage cells in
epiphyseal plates.
7. In children, the absence of ___________ hormone leads to pituitary
dwarfism.
8. An excess of growth hormone before the epiphyseal plates ossify leads
to pituitary ______________.
9. In adults, an excess of growth ____________ leads to acromegaly.
10. Thyroxine can halt bone growth by causing premature ossification of
the ________________ plates.
11. Parathyroid hormone stimulates an increase in the number and activity
of ____________ which break down bone.
12. Estrogens and ______________ promote formation of bone tissue.
13. Sex hormones also stimulate ossification of the ____________ plates.
16. Females typically reach their maximum heights earlier than males
because the effects of estrogen on the epiphyseal plates are stronger than
_______________.
17. ______________ stress stimulates bone growth.
III. Bone Function
A. Support and Protection
1. Bones give shape to structures such as the head, face, _______ and
limbs.
2. The bones of ________ limbs, pelvis, and vertebral column support the
body’s weight.
3. The bones of the skull protect the eyes, ears, and __________.
4. The bones of the thorax protect the _________and lungs.
5. Bones of the pelvic girdle protect lower abdominal and internal
_____________ organs.
B. Blood Cell Formation
1. Hematopoiesis is ________ cell formation.
2. _________cell formation begins in the yolk sac.
3. Later in development, blood cells are made in the liver, the spleen, and
__________ bone marrow.
4. _____________ is a soft, netlike mass of connective tissue within the
medullary cavities of bond bones, in the irregular spaces of spongy bone,
and in the larger central canals of compact bone tissue.
5. Red marrow functions in the formation of red blood cells, _________
blood cells, and platelets.
6. Red ________ occupies the cavities of most bones in an infant.
7. With increasing age, ___________ marrow replaces red marrow.
8. Yellow marrow stores ___________.
9. In an adult, red marrow is primarily found in the spongy bone of the
skull, ribs, sternum, clavicles, vertebrae, and _________bones.
C. Inorganic Salt Storage
1. Extracellular matrix of bone tissue includes collagen and
___________mineral salts.
2. The salts account for about 70% of the extracellular matrix by weight.
3. Hydroxyapatites are tiny crystals of ____________ phosphate.
4. The body requires calcium for many metabolic processes including
blood clot formation, nerve impulse conduction, and muscle cell and
______________contraction.
5. When blood calcium is __________, parathyroid hormone stimulates
osteoclasts to break down bone tissue to release calcium salts.
6. Very high blood calcium levels inhibit ___________ activity.
7. Calcitonin stimulates ______________ to form bones.
8. Bone tissue contains lesser amounts of magnesium, sodium, potassium
and ___________ ions.