Chapter 7: Skeletal System

Question 1

Four Classes of Bones

Answer 1

long, short, flat, irregular (*sesamoid)

Question 2

Long Bones

Answer 2

have longitudinal axes and expanded ends (allow for greater efficiency)
Examples: radius, ulna, femur, tibia, fibula.

Question 3

Short Bones

Answer 3

cube-like

Examples: carpals and tarsals

Question 4

Flat Bones

Answer 4

plate-like with broad surfaces

Examples: skull, ribs, and scapula

Question 5

Irregular Bones

Answer 5

various shapes

Examples: vertebrae and facial bones

Question 6

Sesamoid Bones

Answer 6

round bones that are small and nodular and embedded with tendons by joints.
Example: patella (kneecap)

Question 7

Parts of Long Bone

Answer 7

Epiphysis, Articular Cartilage, Diaphysis, Periosteum, Processes, Medullary Cavity, Endosteum, Marrow

Question 8

Epiphysis

Answer 8

expanded portion of the long bone which articulates (meets) with another bone.
made of spongy bone - which has bony plates called trabeculae

Question 9

Articular Cartilage

Answer 9

hyaline cartilage that coats the articulating part of the epiphysis.
articulate: where it meets with something else

Question 10

Diaphysis

Answer 10

shaft of the long bone between epiphysis.

wall of diaphysis is compact bone which has a continuous extracelllular matrix with no gaps

Question 11

Periosteum

Answer 11

tough, vascular, fibrous membrane that covers the diaphysis of the bone.
functions to form and repair bone tissue

Question 12

Processes

Answer 12

provides site for attachments of tendons or ligaments

Question 13

Bones usually have compact bone overlying spongy bone

Answer 13

none

Question 14

Medullary Cavity

Answer 14

runs through the diaphysis which is semi-rigid tube with a hollow chamber.

Question 15

Endosteum

Answer 15

lines the cavity and the spaces of spongy bone and contains bone-forming cells

Question 16

Marrow

Answer 16

the tissue that fills the spaces of the bone

red & yellow

Question 17

Microscopic Structure of Bone

Answer 17

osteocytes: bone cells located in tiny, bony chambers called lacunae, which form concentric circles around central canals (Haversian canals)
function: transport nutrients (calcium/inorganic salts) and waste (worn out cells) to & from nearby cells
cell processes of osteocytes pass through canaliculi
extracellular matrix is composed of collagen and inorganic salts which gives bones strength and resilience

Question 18

Compact Bone

Answer 18

osteon: cylinder shaped unit of compact bone.
many osteons cemented together forms the substance of compact bone
each central canal contains BV and nerves
perforating canals (Volkmann’s canals) connect central canals and contain larger BV and nerves

Question 19

Spongy Bone

Answer 19

composed of osteocytes and extracellular matrix
bone cells lie within trabeculae and get nutrients from substances diffusing into the canaliculi that lead to thin, bony plates

Question 20

Bone Development & Growth

Answer 20

parts of the skeleton begin to form during the first few weeks of prenatal development
bones form by replacing existing CT
bones continue to grow and develop into adulthood
intramembranous bones originate within sheetlike layers of CT
endochondral bones begin as masses of cartilage that are later replaced by bone tissue

Question 21

Intramembranous Bones

Answer 21

broad, flat bones of the skull
during osteogenesis, membrane-like layers of unspecialized CT appear at the sites of future bones
dense BV supply the CT layers with nutrients so they can continue to grow
the cells then enlarge & become further differentiated (more defined) into osteoblasts (bone forming cells)
osteoblasts then deposit bony matrix around themselves
as a result spongy bone forms in all directions along the BV within the CT
later, some spongy bone becomes compact bone as spaces fill with bony matrix
as development continues, osteoblasts may become surrounded by matrix and become secluded within lacunae
that matrix encloses the processes of osteoblasts and gives rise to canaliculi
once those are isolated, the osteoblasts become osteocytes.

Question 22

Endochondral Bones

Answer 22

most skeletal bones are endochondral bones
develop from masses of hyaline cartilage
the surrounding matrix breaks down and soon the cartilage cells die and degenerate. As it decomposes, periosteum forms from CT then encircles structure.
osteoblasts form spongy bone in the space occupied by cartilage.
osteoblasts become osteocytes when the bony matrix completely surrounds them. Then they’re called osteocytes
osteoblasts beneath the periosteum (tissue that surround bone) deposit compact bone around spongy bone.

Question 23

Primary Ossification Center

Answer 23

occurs when in uterus.
when bony tissue replaces hyaline cartilage int he center of diaphysis.
the epiphysis of developing bone remains cartilaginous and continue to grow.

Question 24

Secondary Ossification Center

Answer 24

towards the end
this appears later in the epiphyses and spongy bone forms in all directions
as it is deposited in both the diaphysis and epiphysis a band of cartilage forms called epiphyseal plate (growth plate) and remains between ossification centers.

Question 25

Growth of Epiphyseal Plate

Answer 25

cartilaginous cells of epiphyseal plate forms 4 layers

1. (innermost/deepest layer) (deep to superficial) anchors the epiphyseal plate to bony tissue of the epiphysis (closest to end of epiphysis and the cells do not participate in growth)
2. rows of many young cells undergoing mitosis (cell division). the cartilaginous plate thickens as new cells appear.
3. (thickest layer because it’s where both old and new cells are occupying space) formed by older cells which are left behind as new cells appear and those enlarge and thicken the epiphyseal plate, which lengthens the bone.
4. composed of dead cells & calcified extracellular matrix (thin layer)

Question 26

Osteoclasts

Answer 26

osteoclasts break down the calcified matrix
also phagocytize parts of the bony matrix
after osteoclasts remove the extracellular matrix, osteoblasts deposit bone tissue in place of the calcified cartilage.
long bones lengthen while cartilaginous cells are active
once ossification centers of the diaphysis and epiphysis meet, the plates close and growth is not possible.
over the course of your life, osteoclasts resorb bone tissue and osteoblasts replace bone.

Question 27

Factors That Affect Bone Development, Growth, and Repair

Answer 27

nutrition, hormonal secretions, physical stress

Question 28

Nutrition

Answer 28

vitamin D to absorb calcium (received through UV light)
vitamin A for osteoblast & osteoclast activity
vitamin C for collagen synthesis

Question 29

Hormonal Secretions

Answer 29

growth hormone: stimulates division of cartilage cells in epiphyseal paltes
parathyroid hormone: stimulates increase in number & activity of osteoclasts
sex hormones: promote formation of bone tissue
- females reach maximum heights earlier due to estrogen effects on epiphyseal plates are stronger than testosterone

Question 30

Physical Stress

Answer 30

stimulates bone growth: Wolff’s Law

Question 31

Central Canal

Answer 31

tiny channel in bone tissue that contains a blood vessel; Haversian canal; tube within the spinal cord that is continuous with the ventricles of cerebrospinal fluid.

Question 32

Haversian Canal

Answer 32

proper name for central canal

Question 33

Canaliculi

Answer 33

only found in compact bone

microscopic canal that connects lacunae of bone tissue

Question 34

Osteocyte

Answer 34

mature bone cell

Question 35

Osteoclast

Answer 35

cell that erodes bone

Question 36

Osteoblast

Answer 36

bone-forming cell

Question 37

Osteon

Answer 37

cylinder-shaped unit containing bone cells that surround a central canal; Haversian system.

Question 38

Bone Function

Answer 38

gives shape to structures
support body weight
- lower limbs, pelvis, vertebral column
protect organs
- eyes, ears, brain, lungs, abdominal, internal reproductive organs
blood cell formation
- begins in the yolk sac in embryonic development
- later are made in liver, spleen, bone marrow.

Question 39

Marrow

Answer 39

soft netlike mass of CT within the medullary cavitites, irregular spaces of spongy bone, and central canals of compact bone.

Question 40

Red Marrow

Answer 40

functions in forming RBC, WBC, and platelets

• occupies cavities of most bones in infants
• as adults, found in spongy bone of skull, ribs, sternum, clavicles, vertebrae, and pelvis

Question 41

Yellow Marrow

Answer 41

as we age, yellow marrow replaces red marrow

yellow marrow stores fat