1.
after the secondary ossification centers have appeared and epiphyses have largely ossified, hyaline cartilage remains at only two places: (1) on the epiphyseal surfaces, where it forms the articular cartilages
(2) between the diaphysis and epiphysis, where it forms the epiphyseal plates
2.
appositional growth (cartilage): "growth from outside"
chondroblasts in the surrounding perichondrium produce the new cartilage tissue by actively secreting matrix
3.
blood vessels: bones are well vascularized
- 3-11% of the blood in the body is in the skeleton
4.
bone deposition: accomplished by osteoblasts
- cells lay down organic osteoid on bone surfaces and calcium salts crystallize within this osteoid
5.
bone markings (3 categories): - projections that are the attachment sites for muscles and ligaments
- surfaces that form joints
- depressions and openings
6.
bone resorption: accomplished by osteoclasts
7.
calcification zone: cartilage matrix becomes calcified and the chondrocytes die
8.
canaliculi: "spider legs"
- thin tubes
- osteocytes (mature bone cells), their bodies occupy small cavities in the solid matrix called lacunae
"little canals" run through the matrix, connecting neighboring lacunae to one another and to the nearest capillaries, such as those in the central canals
- within the canaliculi, the extensions of neighboring osteocytes touch each other and form gap junctions
9.
central canal (Haversian canal): canal that runs through the core of each osteon
- lined by endosteum
- contains its own blood vessels, which supply nutrients to the bone cells of the osteon, and its own nerve fibers
- endosteum that lines the central canal is an osteogenic layer
- unlike the growth rings in trees, lamellae of bone tissue are added to the inner surface of the osteon, thus decreasing the diameter of the central canal
10.
circumferential lamellae: occur in the external and internal surfaces of the layer of compact bone
- extends around the entire circumference of the diaphysis
- resist twisting of the entire long bone
11.
classification of bones: long bones
short bones
flat bones
irregular bones
12.
closed reduction: bone ends are coaxed back into position by the physician's hands
13.
compact bone is entirely replaced: every 10 years
14.
compound: broken ends of the bone prodtrude through the skin
15.
deep layer (periosteal membrane): osteogenic, containing bone-depositing cells (osteoblasts) and bone-destroying cells (osteoclasts)
- indistinguishable from the fibroblasts within this layer
16.
diaphysis: shaft
forms the long axis of a long bone
17.
diploe: internal spongy bone in flat bones
18.
elastic cartilage: similar to hyaline cartilage; matrix contains many elastic fibers along with the delicate collagen fibrils; more elastic than hyaline cartilage & better able to tolerate repeated bending; epiglottis and outer ear
19.
endochondral ossification: other bones develop as hyaline cartilage, which is replaced through this process
- bones are: endochondral bones or cartilage replacement bones
20.
endochondral ossification: all bones from the base of the skull down, except for the clavicles, are endochondral bones
- begins late in the second month of development and is not completed until the skeleton stops growing in early adulthood
- growing endochondral bones increase both in length and in width
21.
endochondral ossification, process: (1) a bone collar forms around the diaphysis
(2) cartilage calcifies in the center of the diaphysis
(3) periosteal bud invades the diaphysis, and the first bone trabeculae form; by the third month of development, bone tissue continues to form around the diaphysis from the periosteum and has begun to appear in the center of the diaphysis; this bone tissue makes up the primary ossification center
(4) diaphysis elongates, and the medullary cavity forms; areas of bone formation in the epiphyses are called secondary ossification centers; larger long bones of the body can have several ossification centers in each epiphysis
(5) epiphyses ossify, and cartilaginous epiphyseal plates separate diaphysis and epiphyses
22.
endosteum: thinner connective tissue membrane that covers internal bone surfaces
- covers the trabeculae of spongy bone
- lines the central canals of osteons
- is osteogenic, containing both osteoblasts and osteoclasts
23.
epiphyseal line: between the dipahysis and each epiphysis of an adult long bone
- line is a remnant of the epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone
24.
epiphyseal plates: also called growth plates
- responsible for lengthening the bones during the two decades following birth
25.
epiphyses: bone ends
- joint surface is covered with a thin layer of hyaline cartilage (articular cartilage)
26.
fact: below the resting zone, the cartilage cells form tallecolumns, like coins in a stack: (blank)
27.
fact: calcified cartilage is not bone: bone and cartilage are always distinct tissues
28.
fact: cartilage stops growing in the late teens when the skeleton itself stops growing, and chondrocytes do not divide again: cartilage regenerates poorly in adults
29.
fact: periosteum is richly supplied with nerves and blood vessels: why broken bones are painful and bleed profusely
30.
fact: spongy bone and marrow cavities lighten the heavy skeleton and provide room for the bone marrow: (blank)
31.
fact: trabeculae of spongy bone seem to align along stress lines in an organized pattern of tiny struts: (blank)
32.
fact: without its mineral content, bone bends too easily to support weight: the proper combination of organic and inorganic elements allows bones to be exceedingly durable, strong, and resilient without being brittle
33.
fibrocartilage: resists both strong compression and strong tension (pulling) forces; occurs in certain ligaments and certain cartilages that experience both these forces; consists of thick collagen fibers (as in dense regular connective tissue) surrounding the chondrocytes within lacunae; found in anulus fibrosus portion of the discs between the vertebrae and in the articular discs of some joints (ex: menisci of the knee)
34.
flat bones: thin, flattened, and usually somewhat curved
- most cranial bones of the skull, ribs, sternum, scapula
35.
fourth type of cell found within bone tissue: osteoclasts
36.
functions of bone: (1) support
(2) movement: skeletal muscles attach to the bones by tendons and use the bones as levers to move the body and its parts; support and movement are mutually dependent functions
(3) protection
(4) mineral storage: most important are calcium and phosphate
(5) blood cell formation and energy storage: red marrow makes the blood cells and yellow marrow is a site of fat storage
(6) energy metabolism: osteoblasts secrete a hormone that influences blood sugar regulation; the hormone (osteocalcin) stimulates pancreatic secretions that reduce blood sugar levels (insulin)
37.
healing of a simple fracture: (1) hematoma formation
(2) fibrocartilaginous callus formation
(3) bony callus formation
(4) bone remodeling
38.
hyaline cartilage: most abundant; provides support through flexibility and resilience; makes up the articular cartilage that covers the ends of adjoining bones in movable joints; forms the cartilaginous attachments of the ribs to the sternum; accounts for most of the cartilage found in the respiratory structures; forms the embryonic skeleton
39.
hypertrophic zone: the older condrocytes deeper in the stack that enlarge and signal the surrounding matrix to calcify
40.
inorganic components of bone: mineral salts that invade the bony matrix, making bone tissue hard
41.
interstitial growth (cartilage): "growth from within"
chondrocytes within the cartilage divide and secrete new matrix
42.
interstitial lamellae: incomplete lamellae that lie between the osteons
- remains of old osteons that have been cut through by bone remodeling
- extends around the entire circumference of the diaphysis
43.
intramembranous ossification: membrane bones form directly from mesenchyme without first being modeled in cartilage
- all bones of the skull, except a few at the base of the skull, are of this category
- the clavicles (collarbones) are the only bones formed by intramembranous ossification that are not in the skull
44.
intramembranous ossification process: - (1) during week 8 of embryonic development, mesenchymal cells cluster within the connective tissue membrane and become bone-forming osteoblasts
- (2) cells begin secreting the organic part of the bone matrix, called osteoid, which then becomes mineralized; once surrounded by their own matrix, the osteoblasts are called osteocytes
- (3) new bone tissue forms between embryonic blood vessels, which are woven in a random network; result is woven bone tissue, with trabeculae arranged in networks; more mesenchyme condenses just external to the developing membrane bone and becomes the periosteum
(4) trabeculae at the periphery grow thicker until plates of compact bone are present on both surfaces
45.
irregular bones: various shapes
- ex: vertebrae and hip bones
46.
lamella: each of the tubes in an osteon
- layer of bone matrix in which the collagen fibers and mineral crystals align and run in a single direction
- fibers and crystals of adjacent lamellae always run in roughly opposite directions; alternating pattern is optimal for withstanding torsion, or twisting, stresses
- also inhibiting crack propagation: when a crack reaches the edge of a lamella, the forces causing the crack are dispersed around the lamellar boundaries, thus preventing the crack from progressing into deeper parts of the bone and causing fracture
47.
long bones: longer than they are wide
- has a shaft and two distinct ends
48.
medullary cavity: - filled with yellow bone marrow
- very center of the diaphysis that contains no bone tissue at all
- aka marrow cavity
49.
membrane bones: develop from a mesenchymal membrane through a process called intramembranous ossification
50.
nutrient artery and nutrient vein: main vessels serving the diaphysis
- together run through a hole in the wall of the diaphysis, the nutrient foramen
51.
open reduction: bone ends are joined surgically with pins or wires; after the broken bone is reduced, it is immobilized by a cast or traction to allow the healing process to begin
52.
organic components of bone: - cells, fibers, and ground substance
- account for 35% of tissue mass
- collagen is abundant in bone tisuse
53.
osteoblasts: cells that actively produce and secrete the organic components of the bone matrix: the ground substance and the collagen fibers
- bone matrix secreted by osteoblasts is called OSTEOID
54.
osteoclasts: derived from a lineage of white blood cells
- multinucleated
- break down bone by secreting hydrochloric acid, which dissolves the mineral component of the matrix, and lysosomal enzymes, which digest the organic components
55.
osteocytes: when osteoblasts are completely surrounded by bone matrix and are no longer producing new osteoid
- function to keep the bone matrix healthy
- if osteocytes die or are destroyed, the bone matrix is resorbed
56.
osteogenesis: begins in the embryo, proceeds through childhood and adolescence as the skeleton grows, and then occurs at a slower rate in the adult as part of a continual remodeling of the full-grown skeleton
57.
osteogenesis and ossification: process of bone-tissue formation
58.
osteogenesis, before week 8: skeleton of the human embryo consists only of hyaline cartilage and some membranes of mesenchyme, an embryonic connective tissue
- bone tissue first appears in week 8 and eventually replaces most cartilage and mesenchymal membranes in the skeleton
59.
osteogenic cells: stem cells that differentiate into bone-forming osteoblasts
60.
osteomalacia: applies to a number of disorders in adults in which the bones are inadequately mineralized
- even though osteoid matrix is produced, calcification does not occur, and the bones soften and weaken
- main symptom: pain when weight is put on the affected bone
- caused by inadequate amounts of vitamin D or calcium phosphate in the diet
- cured by drinking vitamin D-fortified milk and exposing the skin to sunlight
61.
osteon (Haversian system): long, cylindrical structures oriented parallel to the long axis of the bone and to the main compression stresses
- functionally: miniature weight-bearing pillars
- structurally: group of concentric tubes resembling the rings of a tree trunk in cross section
62.
osteoporosis: low bone mass and a deterioration of the microscopic architecture of the bony skeleton
- become porous and light
- estrogen deficiency is strongly implicated in osteoporosis
63.
osteosarcoma: form of bone cancer
- usually originates in a long bone of the upper or lower limb
64.
Paget's disease: characterized by excessive rates of bone deposition and bone resorption
- makes the bones soft and week
- activity of soteoblasts outpaces that of osteoclasts: bones can thicken, but in an irregular manner, and the medullary cavities may fill with bone
65.
Perforating canals (Volkmann's canals): lie at right angles to the central canals and connect the blood and nerve supply of the periosteum to that of the central canals and the marrow cavity
66.
perforating fibers (Sharpey's fibers): - thick bundles of collagen that run from the periosteum into the bone matrix
- what secures the periosteum to the underlying bone
67.
periosteal bud: consists of a nutrient artery and vein, along with the cells that will form the bone marrow
- contains bone-forming and bone-destroying cells (osteogenic stem cells and osteoclasts)
68.
periosteum: connective tissue membrane that covers the entire outer surface of each bone except on the ends of the epiphyses, where articular cartilage occurs
- provides insertion points for the tendons and ligaments that attach to a bone
69.
periosteum membrane sublayers (2): superficial layer of dense irregular tissue--resists tension placed on a bone during bending
- deep layer that abuts the compact bone
70.
proliferation zone: chondroblasts at the "top" of the stack that divide quickly, pushing the epiphysis away from the diaphysis, thereby causing the entire long bone to lengthen
71.
resting (quiescent) zone: cartilage cells nearest the epiphysis are relatively small and inactive
72.
rickets: like osteomalacia for kids
- more severe than osteomalacia
- caused by inadequate amounts of vitamin D or calcium phosphate in the diet
- cured by drinking vitamin D-fortified milk and exposing the skin to sunlight
73.
sesamoid bones (short bones): special type of short bone that forms within a tendon
- ex: kneecap/patella
- vary in size and number
- some clearly act to alter the direction of pull of a tendon
- others reduce friction and modify pressure in tendons, thus reducing abrasion or tearing
74.
short bones: roughly cube-shaped
- occur in the wrist and ankle
75.
simple fracture: bone breaks cleanly but does not penetrate the skin
76.
spongy bone aka: trabecular bone
77.
spongy bone is entirely replaced: every 3 or 4 years
78.
structure of a long bone: diaphysis
epiphyses
blood vessels
medullary cavity
membranes
79.
structure of short bones: - similar to long bones, but have no diaphysis
- contain bone marrow (between the trabeculae of their spongy bone), but no marrow cavity is present
80.
three types of cells in bone tissue that produce or maintain the tissue: osteogenic cells, osteoblasts, osteocytes
81.
treatment of a fracture: reduction: realignment of the broken bone ends
82.
when we are incapacitated...: bone is resorbed because it is not needed to support the body
83.
when we are physically active...: new bone is formed, strengthening skeletal support
