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Intramembranous Ossification is responsible for formation of for:
- Bone healing
- Growth of flat bones (i.e. skulls, carpals, tarsals)
- Thickening of long bones
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What are the steps of osteoblasts in intramembranous ossification?
- Osteoblasts secrete organic matrix (osteoid)
- Osteoblasts then directly mineralize the matrix with hydroxyapatite crystals
- Once surrounded by calcified matrix, osteoblasts become osteocytes
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Osteoblasts are formed by differentiation of cells of the:
Periosteum and endosteum or bone marrow stem cells (mesenchyme)
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What function do chondrocytes perform?
Produce cartilage and calcify the matrix
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Where do osteoblasts deposit bone matrix (osteoid)?
Over the pre-existing cartilage matrix
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Function of osteoblasts/osteocytes
Remove remnants of cartilage matrix resulting in typical bone matrix
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Endochostral ossification is responsible for
- Growth of long bones
- Bone healing
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Area of normal hyaline cartilage and chondrocytes
Resting zone
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Area of intestine mitosis (proliferation) of chondrocytes
Proliferative zone
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What happens in the Hypertrophic Zone?
- Area of chondrocyte hypertrophy due to glycogen uptake
- Cartilage ECM is partially resorbed
- Remnants appear as septa of matrix material between hypertrophic chondrocytes
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What happens in the Calcified cartilage zone?
- Thin septa of cartilage matrix become calicified
- Chondrocytes in this zone die after matrix calcification
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The Ossification zone is in charge of being
- The osteoprogenitor cells from the bone marrow are delivered to the calcified cartilage
- -Osteoprogenitor cells differentiate into osteoblasts
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Osteoblasts deposit bone matrix over calcified cartilage matrix
Ossification
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Following ossification, the _____ cartilage is resorbed, leaving a calcified bone matrix, which is ______ bone tissue
old; "true"
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Overall, the thickness of the _________ _______ does not change as that rate of bone production and cartilage growth are equal at opposite ends.
Epiphyseal plate
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Endochondral ossification during fetal development is a ______ process
similar
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Bone under goes ________ remodeling througout life.
Constant
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Bone remodeling is dependent on ________ placed on bones
stresses (forces)
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Stresses placed on bones affect:
Deposition and resorption
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State Wolff's Law
Every change in form and function of bone, or in its function alone, is followed by certain, definite changes in its internal architecture and external form.
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Describe the process of how bones are repaired from a fracture
- Damaged blood vessels produce a localized clot
- Clot material is later removed by macrophages
- Periosteum and Endosteum repond with intense proliferation of cells
- Periosteal/endosteal fibroblasts differentiate into chondroblasts and hyaline cartilage model = soft callus
- Mesenchyme cells differentiate into osteoblasts and form osteoid
- Endochondral and intramembranous ossification occur to form primary (woven) bone = hard callus
- Hard callus is replaced by lamellar bone
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Healing Time Table
- Soft callous - 2 wks
- Hard callous - 4 wks
- Lamellar bone - 6 wks
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Does stress affect healing bone?
Yes. Healing bone is influenced by stresses placed upon it during the healing process
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How does inactivity affect bones?
- Inactivity or decreased loading of bone results in reduced osteoblast activity but does not affect osteoclast activity
- Overall result is increased degradation of bone and increase in serum CA++ levels
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What 3 qualities of bone change with increased loading?
- Hypertrophy of bone
- ↑ bone mass/density
- ↑ load to failure (strength)
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Repetitive loading on bone creates:
microscopic deformities
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What aides the bone healing process?
Rest
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What causes stress fratures?
Stress fractures result when loading outpaces bone repair/remodeling
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What is Osteopenia?
- Reuction in bone mineral density below normal levels, results in decreased bone strength
- (Often a precursor to the development of osteoporosis)
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What causes Osteopenia?
Inactivity, aging, low intake of vitamin D and calcium, and smoking
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What is the definition of Osteoporosis?
Defined as decrease in bone density and decrease in overall volume of bone
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How is Osteopenia classified?
1 to 2.5 standard deviations from the norm
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How is Osteoporosis classified?
Greater than 2.5 standard deviations from normal BMD
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How many Americans have osteoporsis?
10 million (80% females)
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Name some risk factors for Osteoporosis
- Female
- Older age
- Small frame
- Caucasian, Asian, Hispanic
- Menopause
- Inactivity
- Poor diet (Low Vit D % calc; excess protein, sodium, caffeine)
- Smoking, alcohol abuse
- Steroid medications
- Anorexia, RA, GI pathology
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What percent of the body's calcium is stored in bone?
99%
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Calcium levels are controlled by what system?
endocrine system
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What are 3 regulators in calcium metabolism?
- -Parathyroid hormone
- -Calcitonin
- -Vitamin D
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How is Hypercalcemia determined?
- >10.5 mg/dL of blood
- Causes mild to severe proximal weakness in extremities
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How is Hypocalcemia determined?
- <8.5 mg/dL of blood
- neurmosucular excitability and muscular tetany (especially UE flexion)
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What is secreted in response to low levels of Ca++ in the plasma?
Parathyroid Hormone
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PTH promotes what action in the bone?
Osteoclast resorption and liberation of Ca++ into the blood
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Where does PTH bind?
- Osteoblasts
- -Osteoblasts stop producing bone
- -Osteoblasts secrete an osteoclast-stimulating factor
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Where else does PTH act to affect calcium levels?
- Enhances calcium absorption from intestines
- Decreasese calcium excretion by kidneys
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The thyroid gland synthesizes what hormone in response to elevated levels of Ca++ in the blood?
Calcitonin
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What is the function of Calcitonin?
- Inhibits matrix resorption by osteoclasts
- Inhibits new osteoclast formation
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What vital bone cell does Calcitonin NOT interact with?
Osteoblasts
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What is essential for intestinal absorption of Ca++ and PO4- from the kidney?
Vitamin D
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Vitamin D is necessary for active reabsorption of Ca++ and PO4- from what organ?
The kidney
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What stimulates the formation of Vitamin D?
UV light
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What processes inative Vitamin D? What activates it?
liver; kidneys
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4 characteristics of Diarthrodial Joint
- Capsule
- Outer fibrous layer
- Inner synovial layer (synovial membrane)
- Joint cavity
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Define synovial fluid
Viscous, colorless & transparent fluid formed from a dialysate of plasma
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The outer fibrous layer is comprised of what 3 things
- Dense irregular CT
- Continuation of periosteum
- Continuation with tendons and ligaments
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Functions of Joint Capsule
- Nourishment (Direct vascular supply)
- Innervation (Mechanoreceptors, Free nerve endings, GVA/GVE to vasculature)
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Cell types of synovium
- F cells - Synthesize large amounts of hyaluronic acid that is secreted into the synovial fluid
- M cells - Differentiated blood monocyte that serves as phagocytic cell of synovial membrane
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Functions of the synovium
- Nourishment
- -Highly vascularized
- -No neural innervation
- Produces synovial fluid for waste/nutrient exchange
- Synovial fluid to improve frictionless motion
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Main constituents on Synovial Fluid
- Hyaluronic acid
- Water
- Electrolyte composition similar to plasma
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Function of Synovial Fluid
- Delivers O2 to articular cartilage
- Medium for removal of waste products
- Reduces friction on articular surfaces
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What are syndesmosis?
- When bones are united by dense connective tissue
- -ex. interosseus ligament between radius and ulna
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What are Synchondrosis?
- Bones are united by hyaline cartilage
- -ex. epiphyseal plates, sternocostal joints
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What is Symphysis?
- Bones united by fibrocartilage. Type of Synchondrosis
- -ex. pubic symphysis and IV disks
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What are syntosis?
- Bones are united by bony tissue that has replaced normal synarthroses
- -Ex. cranial sutures in adults, epiphyseal plates upon maturity
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