Chapter 6- Bones and skeletal tissues Flashcards
1
Q
Chondro-
A
Cartilage
2
Q
Osteo-
A
bone
3
Q
Functions of bones (6)
A
- Support
- Protection
- Attachment point
- Storage
- Blood cell formation
- Hormone production
4
Q
How do bones support the body
A
holds up the body and cradles organs- bone is second hardest substance produced by the body (teeth are the hardest)
Occurs in conjunction with skeletal muscle tissue
5
Q
Which general areas of the body do the bones protect (2)
A
- Central nervous system- the skull protects the brain, the vertebrae wrap around the spinal cord
- Visceral organs- rib cage wraps around organs in thorax and the upper abdominal cavity
6
Q
What attaches muscle to bone
A
skeletal muscle attaches to bone via tendons
7
Q
How do the muscles use the bones to allow for voluntary movement?
A
Tendons allow the muscles to use the bones as levers. Shortening (contracting) muscle pulls on the tendon which pulls on the bone, producing movement.
8
Q
What substances do bones store? (2)
A
Minerals- calcium
Fat- yellow marrow in the bones of adults
9
Q
Hematopoiesis
A
formation of blood cells in red bone marrow
10
Q
Which hormone is produced by bones?
A
Osteocalcin- regulates insulin release, glucose homeostasis, and energy expenditure
11
Q
Before the osseous skeleton is formed, what 2 things is it composed of?
A
Before the osseous skeleton forms, it is composed of cartilage and connective fibers
12
Q
Why is cartilage ideal for the skeleton before bone is formed?
A
Cartilage cells accommodate mitosis very well. Ground substance is viscous and makes it firm, but cartilage is still mostly water
13
Q
Characteristics of all cartilage types (4)
A
- Strength and resilience- it can be compressed and return to original shape
- Cartilage is mostly water- contributes to flexibility
- No nerve supply and avascular
- Surrounded externally by perichondrium (tissue sheet)
14
Q
Perichondrium
A
Tissue sheet that surrounds cartilage externally. Contains blood vessels and resists outward expansion of cartilage- prevents it from being too compressed
15
Q
2 basic components found in all types of cartilage
A
- Chondrocytes
2. Extracellular matrix- has fibers, more viscous
16
Q
Types of cartilage (3)
A
- Hyaline
- Elastic
- Fibrocartilage
17
Q
Hyaline cartilage
A
Most abundant type of cartilage. Chondrocytes are spherical, contains collagen fibers
18
Q
Where is hyaline cartilage typically found?
A
articular cartilage (forming joints), costal cartilage, respiratory cartilage, nasal cartilage
19
Q
Elastic cartilage
A
Similar to hyaline, but contain more elastic fibers
20
Q
Where is elastic cartilage typically found
A
Examples- external ear, epiglottis (like a trap door closing over the trachea when you swallow).
21
Q
Fibrocartilage
A
Most compressible, great tensile strength- can support a lot of weight without damage
Contain rows of chondrocytes alternating with thick collagen bands
22
Q
Where is fibrocartilage typically found
A
Examples- vertebral discs, knee, pubic symphysis (joint between pubic bones)
23
Q
Types of growth of cartilage (2)
A
- Appositional
2. Interstitial
24
Q
Appositional cartilage growth
A
laying down new cartilage on old cartilage
Cells in perichondrium deposit new matrix on top of preexisting cartilage, like stacking bricks
Occurs at surface, used for growth in width
25
Interstitial cartilage growth
growth from within
Associated with growth in length
Cells divide and secrete matrix in pre-existing cartilage
Occurs throughout tissue
26
Which 2 characteristics are used to classify bones?
1. Location (axial, appendicular)
| 2. Shape (long, short, flat, irregular)
27
Axial skeleton
makes up long axis of body- skull, vertebral column, ribs
28
Appendicular skeleton
makes up limbs of body, girdles- pectoral and pelvic girdles, arms and legs
Important for production of skeletal muscle movement
29
Long bones
Long- longer than they are wide. They don’t necessarily have to be overall long in length- you are referring to the shape of the bone instead (the bones in the fingers are also long bones). Usually column shaped
Includes almost all limb bones
30
Short bones
cube shaped (have more equal dimensions in terms of width and height). Includes wrist and ankle bones as well as sesamoid bones.
31
Sesamoid bones
bone that forms in a tendon (the kneecap). Acts like a pulley allowing the tendon to slide over surrounding surfaces and reduces stress or pulling forces on the tendon.
32
Flat bones
thin, flat, curved
| Sternum, scapulae, ribs, most cranial bones
33
Irregular bones
Vertebrae, os coxa
| Don’t fit any of the previously mentioned shape categories
34
Which 2 elements do all bones contain?
1. Compact bone
2. Spongy (trabecular) bone
These components will be found in different amounts in different places
35
Compact bone
looks smooth and solid
36
Spongy (trabecular) bone
has open spaces with needle like pieces of bone called trabeculae (located on the inside of the bone).
Space between trabeculae is filled with red or yellow marrow in living bone
37
Where are trabeculae found in the greatest concentration?
Trabeculae are found in greatest concentration along lines of stress (that part of the bone is frequently put under pressure). Prevent the bone from twisting, bending, or even breaking.
38
Structure of flat, irregular, and short bone (3)
1. Thin plate of spongy bone covered by compact bone- compact bone forms a spongy bone sandwich
2. No well defined cavities for bone marrow
3. Covered externally by bone membrane (periosteum)
39
Where is bone marrow found in flat, irregular, and short bone?
All bone marrow is found around trabeculae of spongy bone. There is no bone marrow cavity
40
4 similar features of long bones
1. Diaphysis
2. Epiphysis
3. Membranes
4. Vascularized and innervated
41
Diaphysis
bone shaft. Makes up most of the length of the long bone and is the cylinder portion
42
Characteristics of the diaphysis in long bones (3)
1. Composed of compact bone “collar” with internal medullary cavity. Helps with bearing weight loads
2. Medullary cavity filled with yellow marrow in adults
3. Very thin layer of spongy bone separates the bone marrow from compact bone
43
Epiphysis
Bone ends that form joint surfaces. Irregularly shaped because these are the locations of articulation (joint formation). Composed of compact bone externally, spongy bone internally, and they are covered in hyaline cartilage
44
What 2 membranes are found in long bones?
1. Periosteum
| 2. Endosteum
45
osteoprogenitor cells
Undifferentiated stem cells that are mitotically active (constantly reproducing)
Can remain as osteogenic cells or differentiate to form osteoblasts. They are found in the periosteum and endosteum
46
Periosteum
The membrane that covers the bone surface, except at joints. It is double layered:
outermost layer is fibrous (tougher, helps protect bone, prevents periosteum from tearing when bone bends), inner layer composed of osteoprogenitor cells
It is very well vascularized and innervated. If a bone is broken badly enough that it breaks the periosteum, the tear will contribute to the pain and bleeding experienced.
47
Endosteum
The membrane that covers the internal bone surface- trabeculae in spongy bone, canals in compact bone
Also contains osteoprogenitor cells- bone growth must occur on the inside of bone to balance out the growth occurring on the outside
48
Innervation and vascularization of bone
Nutrient artery and nutrient vein serve diaphysis (go through the periosteum into the diaphysis)
Epiphyseal artery and epiphyseal vein serve epiphysis (also go from periosteum to diaphysis)
Nerves travel with blood vessels and enter the bone at the same place, which saves space
49
Osteon
structural units of compact bone. A structural unit is the simplest part of an individual organ that can still allow the organ to be functional- can’t break down the osteon without bone losing some qualities.
50
What is the function of an osteon?
Function- helps the bone to withstand pressure and stress. Allows the bone to bend/twist without breaking
51
Osteon structure
A single osteon is composed of several layers (lamella) packed closely together- the walls of one lamella with be in contact with the other in a concentric manner. It contains collagen fibers and bone salts are located in between the fibers of each osteon
52
What direction do collagen fibers run in the osteon, and why?
Collagen fibers in matrix run in one direction for a single lamella
Fibers always run in opposite directions in adjacent lamella
Functionally, this is important- if all fibers ran in the same direction, they could slide past one another and twist much more easily, causing the osteons to snap and break. You don’t want the bone to have too much flexibility. The orientation of the fibers prevents easy twisting.
53
Haversion canal
Canals run through the center of each osteon. The haversion (central) canal contains nerves and blood vessels (artery and vein)
54
Perforating canals
connect nerve/blood supply of marrow cavity to central canal, which connects the haversian canal to the marrow cavity. Allows the marrow cavity to be supplied with blood and nervous fibers.
55
Interstitial lamellae
incomplete lamellae found in between complete osteons
Fill gaps between osteons- osteons are circular and there are no corners, so there will be spaces in between- you don’t want air pockets in bone. They don't form perfect circles
56
Circumferential lamellae
found just deep to periosteum and form a complete layer.
They extend completely around the circumference of diaphysis (outermost lamellae of compact bone), and resist twisting of long bone, as well as bundle the osteons together
57
Which 2 lamellae are not found within an osteon?
Interstitial and circumferential lamellae
58
Hematopoietic Tissue
This tissue (red bone marrow) is used to make RBCs, WBCs, and platelets
59
Where is bone marrow found in flat or irregular bones?
The marrow is found between trabeculae (these bones don’t have a medullary cavity)
60
Where is bone marrow found in long bones?
marrow found in marrow cavity of diaphysis
61
In what regions is bone marrow found in infants?
found in spongy bone, marrow cavities of all diaphyses in the long bones (pretty much found everywhere). This is because infants will grow and require many more blood cells.
62
In what regions is bone marrow found in adults?
found around trabeculae of bones of skull, ribs, hips, sternum, clavicles, scapula, vertebrae, heads of femur and humerus. Adults don’t require large amounts of bone marrow as they have stopped growing.
63
What is most red bone marrow converted to in adults?
Red marrow is converted to yellow marrow. However, if an individual has a disease that results in low amounts of a blood cell (like severe anemia), the yellow bone marrow can convert to red bone marrow and make cells (only happens when absolutely necessary).
64
Yellow bone marrow
Contains more fat and less blood supply than red marrow. It can be converted back to red marrow
65
What types of diseases can require a bone marrow transplant?
Leukemia (“white blood”)- cancer where a person is producing a massive amount of abnormal WBCs. These cells do not carry out their defensive function.
Other diseases can also require BMTs, including sickle cell anemia and autoimmune diseases
If a person’s marrow stem cells are damaged, a marrow transplant can be used to replace them
66
What are the 2 types of bone marrow transplant?
Autologous or allogeneic
67
Autologous bone marrow transplant
an individual is donating to themselves. This would require the disease to be caught early enough that you still have healthy bone marrow somewhere. Can be extracted from the hip bone or sternum and be stored until treatment for the disease is over.
This is very advantageous- the immune system will not reject your own bone marrow
68
Allogeneic bone marrow transplant
must receive donated bone marrow. This happens if the disease progressed very quickly.
There are disadvantages- about 70% of these patients don’t have a match in their immediate family members and must rely on other donors. There is also a rejection risk
69
What types of cells are found in bone?
1. Osteoprogenitor cells
2. Osteoblasts
3. Osteocytes
4. Bone lining cells
5. Osteoclasts
70
Osteoblasts
immature bone forming cells (responsible for bone growth). Secrete osteoid that forms hard bone tissue- they will only secrete matrix until they are surrounded. Then, they will mature to form an osteocyte. The activity of the cell depends on its shape
71
Osteoid
Unmineralized bone matrix that is secreted by the osteoblasts
72
Cube shaped osteoblasts function
active, responsible for secreting matrix
73
Flattened/squamous osteoblasts function
still an osteoblast, just inactive
74
Osteocytes
mature bone cell. They monitor and maintain bone matrix
Osteocytes often have several slender projections- extend through the matrix and make immediate contact with neighboring bone cells (osteoblasts/osteoclasts). This allows these cells to communicate.
75
How do osteocytes maintain the bone matrix?
If the osteocyte is monitoring and decides the matrix is too thin, it will send a message to the osteoblast to stimulate it to create more matrix. In contrast, if the bone becomes too dense, the osteocyte can tell the osteoblast to stop or can tell the osteoclast to begin breaking down the bone. They respond to both mechanical stress/stimuli and calcium levels as well
76
Bone lining cells
Maintain a matrix at the bone surface. These cells have a very specific location, unlike the osteocyte.
77
Osteoclasts
Bone degrading cells, multinucleate. Has a ruffled side of the cell that contacts bone directly. The ruffled edge increases the surface area, meaning the bone can be broken down faster
78
Which enzyme breaks down bone tissue?
collagenase breaks down bone tissue (released by ruffled side of the osteoclast)
79
Osteoclast functions (2)
1. Maintains, repairs, and remodels bones
Breaks down old tissue- don’t want the bone to be too dense. The bone will need to be remodeled after going through stress so it can continue to withstand stress.
Bones bearing more weight must be remodeled so they will be thicker
2. Important function in blood calcium homeostasis.
Osteoclasts will be stimulated to break down bone and get calcium to be released to the blood
80
What are the organic components of bone? (2)
Cells and osteoid
81
Sacrificial bonds
in or between collagen molecules stretch and break easily when pressure is put on bone without damaging the bone. They make the bone more flexible
82
Inorganic component of bone
Mineral salts
83
Mineral salts
mostly calcium phosphate packed around collagen fibers. This is what gives bone its hardness and makes it slow to degrade/break down. This is why the bones are the last to break down after death.
84
Which homeostatic imbalances are caused by deficient deposition of mineral salts in the bone?
Osteomalacia (adults) and rickets (children). Mineral salts are deposited in bone in much lesser amounts- bone is weak/soft
Caused by insufficient calcium in diet, low vitamin D (lack of exposure to sunlight)
85
Osteomalacia
only occurs in adults- calcium salts are not deposited to the tissue, so the bone bends really easily and pushes on the nerves, causing pain. This can be reversed with normal calcium intake
86
Rickets
only occurs in children but tends to be more severe as children are still growing. Can result in permanent bone deformities
Can cause skull deformities (dents), misshapen pelvis due to weight of the body and visceral organs, rib cage can be deformed (problematic, it's very important for breathing).
87
What are the 2 types of bone ossification
endochondral and intramembranous
88
Endochondral ossification
Formation of ossified bone by replacement of cartilage- this type of ossification occurs in most bones below the skull. Hyaline cartilage is used as a “blueprint” to form ossified bone. As an ossified bone is laid down, hyaline cartilage is broken down/replaced
89
Endochondral ossification steps (5)
1. formation of a bone collar (week 9 in embryonic development)
2. cavity formation in diaphysis center
3. formation of spongy bone (month 3)
4. formation of medullary (marrow) cavity, elongation of diaphysis
5. Secondary ossification begins in epiphyses (childhood to adolescence)
90
Intramembranous ossification
formation of bone from a fibrous membrane. Forms the cranial bones of the skull and clavicles (flat bones)
91
Intramembranous ossification steps (4)
1. mesenchymal cells differentiate into osteoblasts
2. matrix is secreted by the osteoblasts, then calcified
3. formation of periosteum and immature spongy bone
4. compact bone replaces some spongy bone, red marrow develops
92
Interstitial bone growth
Causes growth in length of the bone. If our body is growing, so are our bones
93
Where does interstitial growth occur?
The epiphyseal plate
94
Epiphyseal plate
Cartilage plate that is found between the epiphysis and diaphysis of a bone. Bone formation chases cartilage growth- cartilage is used as a blueprint
95
What zones does interstitial growth involve? (4)
1. Proliferation zone
2. Hypertrophic zone
3. Calcification zone
4. Ossification zone
96
Does interstitial growth occur in the epiphyses as well?
This process must also occur in the epiphyses because they are articulation points- don't want to have large diaphyses and very small/weak joints. They consist of mostly the same steps and it occurs at the time time, however, the epiphyses do not have medullary cavities
97
How does bone growth change by the end of adolescence?
Chondrocytes divide less often- new cartilage between diaphysis and epiphysis is not produced
Bone formation still continues- epiphyseal plates eventually close
98
What happens when the epiphyseal plate closes?
Epiphyseal plate closure is complete when the bone of the diaphysis and bone of epiphysis meet and fuse
The ossification zone catches up to and overtakes the mostly dead proliferation zone
At this point, the epiphysis is not being pushed away from the diaphysis any longer
99
Appositional bone growth
Causes an increase in the width of the bone. This occurs at the same time as bone lengthening, just underneath the periosteum.
Osteoblasts at periosteum secrete bone matrix, osteoclasts at the endosteum break down bone tissue- don’t want the bones to become too thick
Osteoblast activity is greater than osteoclast activity to allow for grow in width
100
Which hormone increases activity at the epiphyseal plate?
Growth hormone
101
Growth hormone
controls (increases) activity at the epiphyseal plate- cartilage cells divide faster or divide more, increasing bone length
The amount of each hormone you produce is mostly genetically determined. Growth hormone is released by the anterior pituitary gland
102
Hypersecretion of growth hormone results in
gigantism. This can cause many health problems for the individual.
Can cause mobility problems- tall people are heavier which puts stress on joints- they will wear down over time
Circulation problems- they have very long arms and legs. The heart will work harder than it should to get blood to the fingers and toes, causing heart problems at some point in their life
103
Hyposecretion of growth hormone results in
dwarfism. This could be the result of an issue with the anterior pituitary gland or the part of the brain that controls it
Bones won’t grow much before the epiphyseal plate closes
104
How do estrogens affect bone growth?
Cause growth spurt at puberty
In high levels they will induce epiphyseal plate closure- people who produce more estrogens will close their epiphyseal plate early, at around 18. Once the epiphyseal plate closes, you are stuck at your current height.
Cause feminization of certain parts of the female skeleton- the hip bones are set wider/farther apart to allow for childbirth
105
How does testosterone affect bone growth?
These hormones do not cause epiphyseal plates to close. Individuals with more testosterone will stop growing later, at around age 21
Cause masculinization of certain parts of the male skeleton. For example, the mandible is usually thicker- reduces the likelihood of breakage
106
Bone deposition and resorption
New bone tissue is continuously laid down, old bone tissue resorbed by the body
This occurs throughout your life. You get a new skeleton every 7-10 years, the slowest rate of replacement for any organ system
Prevents the bone from being too thick/too thin and ensures that the bones undergoing the most weight won’t break
107
What is the importance of bone deposition and resorption? (2)
1. Maintenance of Ca2+ homeostasis
2. Bone health- mechanical/gravitational forces acting on bone tissue drive remodeling- strengthens bone exactly where it is needed
108
Why is maintenance of calcium homeostasis important?
Ca2+ is essential for maintaining the resting membrane potential of all cells. Without Ca2+, nerves do not fire and muscle does not contract. This is controlled hormonally.
109
What 3 factors control bone deposition and resorption?
1. Parathyroid hormone
2. Calcitonin
3. Mechanical stress
110
Parathyroid hormone negative feedback mechanism
PTH is released in response to decreasing calcium blood levels. This stimulates the osteoclasts begin to resorb bone tissue. Other cell types (osteoblasts) produce proteins to increase the number of osteoclasts produced to speed up the process. This calcium is freely released to the blood
Once blood Ca+ returns to normal, PTH is no longer released
111
PTH only responds to
PTH only responds to and cares about the blood calcium level- does not care about breaking down too much bone- blood calcium homeostasis will be maintained no matter what
112
Calcitonin
A hormone that affects calcium homeostasis, but to a much lesser extent than PTH
Doesn’t have much effect on bone remodeling, other functions are unclear. If injected into a person’s body in high amounts, it will decrease blood calcium levels (opposite effect of PTH)
113
Wolff's law
Bones are strongest where they are subject to high pressure. Bending a bone on one side increases the tension on the other.
For example, the head of the femur articulates with the ox coxa. Your body weight pushes down on the ox coxa, but also the head of the femur. Therefore, there is compression on the inner part of the femur. The bone is being pressed together on that side, but the other side is being stretched apart and experiences tension. This creates stress, but the bone will not bend because the strongest part of the femur is at the point of the most stress (midway down the diaphysis)
114
Where are bones strongest?
where they are subject to high pressure (Wolff’s Law), or where they are most likely to break
115
What must happen for bone repair to begin?
Bone must be reduced for repair to begin- the ends of the broken bone must be put back in line with each other. This can be very painful.
The bone must also be immobilized (usually with a cast) to ensure the bone ends will be kept together
116
What determines the amount of pain and healing time associated with a broken bone?
It depends on the bone that is broken (if the bone is large/weight bearing, repair time increases)
117
Bone repair steps (4)
1. A hematoma forms
2. Fibrocartilaginous callus forms
3. Bony callus forms
4. Bone remodeling occurs
118
Why do people who have had broken bones go to physical therapy?
therapists will put a lot of stress on the broken bone (they are basically applying Wolf’s Law so the bone will be stronger). If no stress is applied to the bone, it will be the same as before.
