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Chapter Seven - Bone Tissue
Bone Tissue
75
Anatomy
Undergraduate 4
02/27/2013

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Term
What are the two types of cartilage in a growing bone, and where are they?
Definition
Hyaline cartilage covering the surface of the bone where joints articulate

Episeal line
Term
Where are red and yellow marrow found in adults?
Definition
Yellow - in the center of the bone

Red (Adults) - in the head of the femur and humerus, ribs, skull, sternum (remainder of axial skeleton)
Term
True or false: Kids have red marrow in most of their bones
Definition
True
Term
Are mature bones metabolically active?
Definition
Yes - they maintain their own growth and remodeling
Term
Endostheum
Definition
thin layer of connective tissue that lines outside of bone; source of bone stem cells (unspecialized base cells)
Term
Why isn't your entire body made of Compact Bone?
Definition
weight - compact bone is very heavy
Term
Benefits of spongy bone
Definition
adds strength without adding weight

space for blood cells to form
Term
Osteogenic cells
Definition
stem cells found in endosteum, periosteum, and central canals
Term
Osteocytes
Definition
Former osteoblasts that have become TRAPPED IN THE MATRIX
Term
Lacunae
Definition
Tiny cavities where osteocytes reside
Term
Canaliculi
Definition
little channel that connect lacunae
Term
What do we mean when we say bone is a "composite"?
Definition
Made of multiple structural materials - a CERAMIC and a POLYMER (think of composite bats - both light and strong)
Term
What gives bones their flexibility?
Definition
collagen
Term
What is Rickets?
Definition
lack of calcium salts that cause the bones to become soft
Term
Osteogenesis Imperfecta
Definition
Brittle bone disease (lack of collagen, or lower proportion of collagen to salts)
Term
Three types of Osseous Tissue
Definition
Compact Bone
Spongy Bone
Marrow
Term
Concentric Lamellae
Definition
Like onion circles; layers of matrix
Term
Osteon
Definition
Area that includes the concentric lamellae and the Haversian Ccanal
Term
Spongy bone consists of
Definition
trabeculae (thin plates of bone)

Spaces filled with red marrow
Term
HOw are trabeculae laid out?
Definition
In the orientation that will best support the bone based on the places pressure will be applied (lines of stress)
Term
What are the main methods of bone growth
Definition
Intramembranous Ossification - produces flat bone

Endochondral Ossification - comes from chondroctyes (cells in cartilage)
Term
Mesenchyme
Definition
gelatinous embryonic connective tissue derived from mesoderm
Term
What type of cells does the Mesenchyme give rise to?
Definition
osteogenic cells
Term
What percentage of our bone remodels per year?
Definition
10%
Term
Why does bone have to remodel itself?
Definition
to repair microfractures, release minerals into blood, reshape bones in response to use and disuse
Term
Wolff's Law of Bone
Definition
bone remodels due to mechanical stress that is placed on it (how braces work - Maxilla is remodeled as tension is placed on teeth)
Term
What is appositional growth
Definition
Bones widen throughout life due to the stress placed on them over time
Term
What happens in achondroplastic dwarfism?
Definition
Long bones stop growing in childhood - this is why the torso is normal but limbs are short
Term
What happens in Pituitary Dwarfism?
Definition
This is from lack of growth hormone - proportions will be normal - all bones stop growing as opposed to just the long bones
Term
What serves as a calcium reservoir for the body?
Definition
Bone
Term
Why is destroying calcium homeostasis a problem?
Definition
disrupts the function of other organ systems, especially NERVOUS and MUSCULAR
Term
Mineral Deposition
Definition
crystallization process in which calcium phosphate and other ions are taken from the blood plasma and deposited in bone tissue
Term
Minderal Resorption
Definition
dissolving bone (releases minerals into the blood)
Term
Calcium regulation is linked to which other mineral?
Definition
Phosphate
Term
What processes need calcium?
Definition
neuron communication, muscle contraction, blood clotting, and exocytosis
Term
Hypocalcemia
Definition
Blood calcium is LOW
Term
What components of the body require phosphate?
Definition
DNA, RNA, ATP, phospholipids, and pH buffers
Term
Why does the body deposit minerals in the skeleton
Definition
to retain them for withdrawl when they are needed later, like a mineral savings account
Term
Which hormones regulate calcium homeostasis?
Definition
Calcitriol, Calcitonin, and Parathyroid
Term
What organs are necessary in the production of Calcitriol?
Definition
skin, liver, and kidneys
Term
What is the process of Calcitriol creation?
Definition
The keratinocytes of the epidermis use UV to convert a steroid (7 dehydrocholesterol) to previtamin D3.
The liver adds a hydroxyl group to make Calcidiol.
Kidneys add another hydroxyl group to make Calcitriol
Term
How does Calcitriol behave?
Definition
as a hormone that raises blood calcium concentration
Term
What functions does Calcitriol perform?
Definition
increases calcium absorption by the small intestine
Increases calcium resorption from the skeleton
Promotes kidney reabsorption of CA ions so there is less loss in urine
Term
What is Calcitonin?
Definition
secreted by C cells (clear cells) of the thyroid gland when calcium concentration rises too high
Term
What function do C cells (clear cells) of the thyroid have in calcium regulation
Definition
C cells release Calcitonin
Term
What do osteoclasts do?
Definition
Break down bone
Term
Why does Calcitonin inhibit osteoclasts?
Definition
Because calcium levels in the blood are too high. Osteoclasts break down bone to release calcium, so they need to be STOPPED when levels are high
Term
What does Calcitriol do to blood calcium?
Definition
Raises it!!
Term
What do osteoblasts do?
Definition
generate bone
Term
Why does Calcitonin need to stimulate osteoblasts?
Definition
Calcitonin is used when calcium levels are too high. It stimulates osteoblasts to help grow bone in which to deposit extra calcium
Term
Where can Calcitriol access calcium?
Definition
intestines, kidneys, bones
Term
Parathyroid hormone
Definition
secreted by the parathyroid glands which adhere to the posterior surface of the thyroid gland; raises blood calcium
Term
How does PTH affect osteoblasts?
Definition
inhibits them
Term
How does PTH affect osteoclasts?
Definition
stimulates
Term
HOw does PTH affect the kidneys
Definition
promotes calcium reabsorption by the kidneys - instead of losing calcium in the urine, PTH encourages the kidneys to reabsorb Ca to maintain levels
Term
HOw does PTH affect calcitriol?
Definition
promotes the final step of calcitriol synthesis by the kidneys, enhancing calcium-raising effect of the calcitriol
Term
Which has a stronger affect on bone growth: estrogen or testosterone?
Definition
estrogen!
Term
How do Anabolic steroids stop growth?
Definition
epiphyseal plate closes prematurely
Term
Orthopedics
Definition
deals with the prevention and correction of injuries and disorders of bones, joints, and muscles
Term
What is a stress fracture?
Definition
break caused by abnormal trauma to a bone (falls, athletics, military combat)
Term
What is a pathological fracture?
Definition
break in a bone weakened by some other disease (bone cancer, osteoporosis)
Term
How are fractures classified?
Definition
by structural characteristics
Term
What are the structural characteristics of bone fractures?
Definition
Nondisplaced (crack but bone not shifted), displaced, Comminuted, Greenstick (breaks in one place and splinters on the opposite side - like breaking a twig)
Term
How does a broken bone heal?
Definition
blood rushes to the area
deposition of collagen, forms a soft callous to glue the fracture temporarily
spongy bone begins depositing on collagen fibers
compact bone remodels along the outside (often leads to calcium deposits on the outside of the fracture)
Term
Types of treatment for fractures
Definition
Closed Reduction
Open reduction
Cast
Traction
Electrical Stimulation
Term
Why is breaking the femur especially dangerous?
Definition
strong muscles of the thigh can pull the bones on top of each other; this movement can penetrate the femoral artery
Term
What is the most common bone disease?
Definition
Osteoporosis
Term
What is Osteoporosis
Definition
bone loses mass and becomes brittle due to loss of organic matrix and minerals
Term
What type of bone does osteoporosis mainly affect?
Definition
spongy bone
Term
Why does osteoporosis affect spongy bone most?
Definition
because this bone is the most metabolically active
Term
Why is the widow's hump (kyphosis - caused by osteoporosis) a problem?
Definition
it can cause breathing problems along with mobility problems
Term
HOw does estrogen affect bone density?
Definition
inhibits resorption by osteoclasts
Term
What do drugs like Fosomax and Actonel do?
Definition
destroy osteoclasts to treat osteoporosis
Term
What dietary components help prevent osteoporosis?
Definition
calcium and vitamin D
Term
Why is exercise important for prevention of osteoporosis?
Definition
bones develop according to use
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