Chapter 7 - A+P
Interstitial Bone Growth: Describe zone 4
- 2-3 layers of chondrocytes in an opaque matrix - Minerals deposit in between the columns of chondrocytes - The calcification destroys the chondrocytes
What are the risk factors of osteoporosis?
- Age - Gender (female) - Diet - Sedentary life-style (don't move around much, bedridden)
What helps to lose bone mass?
- Bedridden - Breaking a bone (immobilized limb; cast) - Going to outer space
What is the first step of bone remodeling?
- Bone Resorption (breakdown of bone tissue) - Osteoclasts - Osteoclasts develop within a remodeling site
What is the third step of bone remodeling?
- Bone deposition (bone formation) - Osteoprogenitor cells turn into osteoblasts
Storage of minerals & energy reserve (bone)
- Bone stores and releases the body's mineral reserves of calcium and phosphate - Energy reserves are stored as lipids in yellow bone marrow
What are the hormones released when blood calcium levels are high?
- Calcitonin
What are the hormones released when blood calcium levels are low?
- Calcitriol (active form of vitamin D) - Parathyroid hormone (PTH)
Interstitial Bone Growth: Describe zone 3
- Chondrocytes cease dividing and hypertrophy - Chondrocytes start resorbing cartilage matrix (which thins lacuna walls)
Interstitial Bone Growth: Describe zone 2
- Chondrocytes undergo rapid mitotic cell division and enlarge - Align in longitudinal columns of flattened lacuna parallel to diaphysis
Long Bone regions
- Distal epiphysis - Metaphysis - Diaphysis (shaft) - Metaphysis (again) - Proximal epiphysis - Epiphyseal line (plate) - Medullary cavity
What is in the periosteum (surrounds bone)?
- Fibrous layer - Cellular layer - Perforating fibers
Interstitial Growth
- Growth in length - Dependent on growth of cartilage within the epiphyseal plate "I" in interstitial is tall and skinny to grow in length
Appositional Growth
- Growth in width - Occurs within the periosteum "A" in appositional is round and wide because of growth in width
What does the skeletal system consist of?
- bone - cartilage - ligaments - tendons - articulation structures
Parathyroid hormone and calcitriol effectors (usually an organ system)
1) Bone - PTH & calcitriol increase osteoclast activity 2) Kidneys - PTH & calcitriol decrease calcium excreted in urine 3) Small intestine - Calcitriol increases calcium absorption from small intestines
What are the two types of bone growth?
1. Interstitial growth 2. Appositional growth
How much of the human skeleton is replaced annually?
20%
Yellow Bone Marrow is made up of
Adipose tissue - "Adi has yellow skin"
Yellow Bone Marrow is most common in...
Adults • Red marrow remains only portions of axial skeleton & proximal epiphyses of humerus and femur
How do hormones interact with bone growth?
Alter rates of osteoblast and/or osteoclast activity
What are the two types of ossification?
Intramembranous ossification and endochondral ossification
What is interstitial bone growth dependent on?
Is dependent on the growth of the cartilage within the epiphyseal plate (has zones)
Metaphysis
Junction between diaphysis & epiphysis
Epiphyseal plate
Layer of hyaline cartilage permitting lengthwise growth during childhood
What bones are formed during endochondral ossification?
Long bones of upper and lower limbs, vertebrae, ossa coxae, ends of the clavicle
Parathyroid hormone and calcitriol stimulus
Low blood calcium
In short, flat, and irregular bones... there is no...
Medullary cavity!
What model is used during intramembranous ossification?
Mesenchyme
Endochondral Ossification nemonic
Most Classes Bring Dreadful Exams Before Easter Model develops Cartilage calcifies Bone collar forms Diaphysis ossification Epiphysis ossification Bone replaces cartilage Epiphyseal plate ossifies
What type of bone (compact or spongy) is formed first during endochondral ossification?
Compact
In short, flat, and irregular bones... the exterior is made of...
Compact bone
Mechanical stress: - _____ communicate to osteoblasts.
Osteocytes
Mechanical stress: - Stress is detected by _____ and is the process of _____.
Osteocytes; mechanosensation
What bones are formed during intramembranous ossification?
Flat bones of the skull, some facial bones, central region of the clavicle
Are the external circumferential lamellae parallel or antiparallel to the surface and expand diameter?
Parallel
Parathyroid hormone and calcitriol receptor
Parathyroid glands (everyone has about 4) - Detect low blood calcium
Parathyroid hormone and calcitriol control center
Parathyroid glands (release parathyroid hormone) - Parathyroid hormone (PTH) and calcitriol would both be present in the blood
What stimulates the synthesis of calcitriol?
Parathyroid hormone (PTH)
Zone 2 is known as...
Proliferating cartilage (dividing cells; producing new cells)
Periosteum
Protective sheath surrounds all but areas covered by articular cartilage (ends)
What type of enzyme digests osteoids?
Proteolytic enzymes "Proteo, like osteo"
What dissolve hydroxyapatite crystals?
H+ "H+ for hydroxyapatite"
Red Bone Marrow function
Hemopoiesis
Calcitonin stimulus
High blood calcium
Medullary cavity
Hollow space within shaft
What model is used during endochondral ossification?
Hyaline Cartilage
What deposits around collagen in step three of bone remodeling?
Hydroxyapatite crystals
Zone 3 is known as...
Hypertrophic cartilage "Chondrocytes stop proliferating and start breaking down the cartilage matrix, chondrocytes become mature cells"
Endosteum
Incomplete layer of cells covering internal surface of medullary cavity
Zone 1 is known as...
Resting cartilage "It's chillin' there, resembling healthy hyaline cartilage nearest to the epiphysis"
Red Bone Marrow is made up of
Reticular connective tissue, immature blood cells, and fat
What do reversal cells do during the second step of bone remodeling?
Reversal cells prepare the surface for subsequent bone formation - Remove debris and undigested collagen fibers - Secrete chemical signals that recruit osteoprogenitor cells (for step 3 of bone remodeling)
Zone 2 location
Second closest to the epiphysis
What type of bone (compact or spongy) is formed first during intramembranous ossification?
Spongy
In short, flat, and irregular bones... the interior is made of...
Spongy bone
Where does ossification begin during endochondral ossification?
The bone collar and then within the future diaphysis (primary ossification center)
What is bone remodeling dependent on?
The coordinated activity of osteoblasts, osteocytes, and osteoclasts
Appositional Bone Growth occurs within...
The periosteum
Diaphysis
The shaft
Intramembranous Ossification
Thickened regions of mesenchyme - Bone growth within a membrane (mesechyme)
Calcitonin receptor
Thyroid gland
Calcitonin control center
Thyroid gland (release calcitonin)
Where does ossification begin during intramembranous ossification?
Within thickened regions of mesenchyme (ossification centers)
Which zone is closest to the epiphysis?
Zone 1
Which zone is closest to the diaphysis?
Zone 5
Parathyroid hormone
increases blood calcium levels by encouraging bone resorption by osteoclasts
Calcitonin
promotes calcium deposition in bone and inhibits osteoclast activity
Osteoporosis
• A disease of bone remodeling characterized by decreased bone mass • Vulnerability to fracture
Hydroxyapatite crystals are made of...
• Calcium phosphate • Calcium hydroxide • Incorporate other salts and ions - Resists compressional forces
Osteoid is made of...
• Collagen fibers • Ground substance of glycosaminoglycans, proteoglycans & glycoproteins - Resists torsion and tensile forces
Compact Bone (dense cortical)
• Dense, rigid connective tissue • White, smooth, solid • Withstands mechanical stress • 80% of total bone mass - Osteon
Skeletal system
• Dynamic, living tissue • Interacts with all other body systems • Continually rebuilds, remodels
Bone Remodeling
• Dynamic, ongoing process that renews and reshapes bone throughout our lifetime • New bone tissue replaces old bone tissue
Irregular bone
• Elaborate, sometimes complex shape • E.g. Ossa coxae, ethmoid bone
Hyaline cartilage locations
• Fetal skeleton • Costal cartilage • Articular cartilage • Epiphyseal plate
What is the periosteum made up of?
• Fibrous layer: dense irregular CT; protection, anchoring site • Cellular layer: osteoprogenitor cells, osteoblasts, osteoclasts • Perforating fibers: collagen fibers anchoring periosteum to bone
Intramembranous Ossification produces what bones?
• Flat bones of the skull • Some facial bones • Mandible • Central part of clavicle - Bones superior to the clavicle are bones that go through intramembranous ossification (not including vertabre)
Ossification (osteogenesis)
• Formation & development of bone connective tissue • Begins in the embryo (8th - 12th week) • Continues through adolescence
What are some inorganic components of the extracellular matrix of bone?
• Hydroxyapatite crystals • Calcium phosphate • Calcium hydroxide • Incorporate other salts and ions
Fibrocartilage locations
• Intervertebral discs (of spine) • Pubic symphysis • Menisci of knee
Osteoclasts
• Large, multinuclear phagocytic cells • Located within/near pit on surface of bone called resorption lacuna
Short bone
• Length equals width • Includes sesamoid bones • E.g. Carpals
Spongy Bone (cancellous trabecular)
• Located internal to compact bone • Porous • Store bone marrow, distribute stress • 20% of total bone mass - Trabeculae - Spaces filled with marrow
Long bone
• Longer than wide • E.g. Femur, ulna
Osteocytes
• Mature bone cells • No bone forming ability - in lacunae
Calcium helps with...
• Muscle contraction • Blood clotting • Neurotransmitter release
Phosphate helps with...
• Nucleotides (e.g. ATP) • Phospholipids
Calcification
• Osteoblasts secrete semisolid osteoid • Hydroxyapatite crystals deposit around collagen fibers - Requires vitamin D & A
During the first step of bone remodeling, what do osteoclasts form?
• Osteoclasts form a resorption lacunae and breakdown the matrix - H+ dissolves hydroxyapatite crystals - Proteolytic enzymes digest osteoid
What are some organic components of the extracellular matrix of bone?
• Osteoid • Collagen fibers • Ground substance of glycosaminoglycans, proteoglycans & glycoproteins
Osteoclast functions
• Perform bone resorption • Secrete hydrogen ions to dissolve inorganic matrix • Secrete proteolytic enzymes to digest the organic matrix
Estrogen
• Primary sex hormone regulating bone remodeling in both women and men
Bone Resorption (breakdown of bone tissue) Osteoclasts secrete:
• Proteolytic enzymes that digest organic components • Hydrochloric acid to dissolve inorganic components
Interstitial Bone Growth: - How does bone growth in length stop?
• Rate of epiphyseal cartilage production slows • Rate of osteoblast activity accelerates • Epiphyseal plate narrows/disappears, leaving an epiphyseal line (looks like a white scar)
Support and protection (bone)
• Structural framework • Protects delicate organs: Examples: • Rib Cage - heart, lungs • Cranial bones - brain • Vertebrae - spinal cord • Pelvis - reproductive, urinary organs
Flat bone
• Thin, possibly curved surface • E.g. Frontal bone of skull, rib bones
Interstitial Bone Growth: - Where does the bone actually grow in length?
• Zone 2: chondrocytes undergo mitosis • Zone 3: chondrocytes hypertrophy
Interstitial Bone Growth: Describe zone 5
- Lacuna walls breakdown, forming longitudinal channels - Capillaries & osteoprogenitor cells from medullary cavity invade these spaces - New bone matrix is deposited on remaining calcified cartilage matrix
Trabeculae
- Latticework of thin plates - Parallel lamellae
Osteocyte functions
- Mechanosensation - Orchestrate bone remodeling "Cyte-ation sensation and orchestration"
Endochondral Ossification produces...
- Most of the bones of the skeleton • Upper & lower limbs • Pelvis • Vertebrae • Ends of clavicle - All bones inferior to the clavicle are developed by endochondral ossification
Interstitial Bone Growth: Describe zone 1
- Nearest to the epiphysis (secures it to the epiphyseal plate) - Small chondrocytes - Resembles mature, healthy hyaline cartilage
What is in the endosteum?
- Osteoclast - Osteoblast - Osteoprogenitor cell
Osteoblasts
- Perform bone deposition: secrete osteoid & regulate mineralization • Cuboidal shape with abundant rough ER & Golgi • Become "trapped" in the bone matrix and differentiate into osteocytes
What is the second step of bone remodeling?
- Reversal (these cells come in and clean up the area like a zamboni) - Reversal cells
Osteoprogenitor cells
- Stem cells • Divide to generate 1 stem cell and 1 "committed cell" (an osteoblast)
What is the fourth step of bone remodeling?
- Termination - Osteoblasts turn into osteocytes
What are the steps in activating calcitriol?
- Upon exposure to UV radiation: 1. Keratinocytes synthesize Vitamin D3 (cholecalciferol) - Or dietary intake of vitamin D3: 2. Vitamin D3 is converted to calcidiol in the liver - Parathyroid hormone (PTH) increases the rate of step 3 (final step) 3. And converted to calcitriol in the kidney
What helps to build/retain bone mass?
- Weight-lifting - Walking - Running
Steps of endochondral ossification
1) Fetal hyaline cartilage model develops 2) Cartilage calcifies & periosteal bone collar forms 3) Primary ossification center forms in diaphysis 4) Secondary ossification centers form in epiphysis 5) Bone replaces almost all cartilage 6) Epiphyseal plates ossify to form epiphyseal line
What are the 4 bone classifications?
1) Long 2) Short 3) Flat 4) Irregular
What two factors influence bone remodeling?
1) Mechanical stress 2) Hormones
Bone remodeling is influenced by what two factors?
1) Mechanical stress (like exercise) 2) Hormones
Steps of intramembranous ossification
1) Ossification center forms within thickened mesenchyme 2) Osteoid undergoes calcification 3) Immature woven bone (primary bone) and surrounding periosteum forms 4) Lamellar bone (secondary bone) replaces woven bone, forming compact and spongy bone
What are the main types of bone cells?
1) Osteoprogenitor cells (develop into osteoblasts) 2) Osteoblasts (differentiate into osteocytes) 3) Osteocytes 4) Osteoclasts PBYL "People Buy Youthful Lotions"
What are the general functions of bone?
1) Support & protection 2) Movement (as levers) 3) Hemopoiesis (hematopoiesis) 4) Storage of minerals & energy reserve
Red Bone Marrow is most common in...
Children • Spongy bone of most bones • Medullary cavity of long bones
Osteon
Basic structural/functional unit
What will happen to bone after baking it?
Becomes dry and brittle.
What will happen to bone after soaking it in acid?
Becomes soft.
Endochondral Ossification
Begins with hyaline cartilage model
Bone remodeling plays a critical role regulating _____.
Blood calcium
Parathyroid hormone and calcitriol homeostasis restored
Blood calcium levels rise
Hemopoiesis (hematopoiesis) (bone)
Blood cell production (red bone marrow)
Movement (as levers) (bone)
Bones are attachment sites for skeletal muscles, as well as some soft tissues and organs.
Zone 4 is known as...
Calcified cartilage (like empty graves) "The matrix is calcified and the chondrocytes die"
What cells are included in the endosteum?
Cells include osteoprogenitors, osteoblasts, osteoclasts
How could this hormone (estrogen) contribute to the development of osteoporosis?
Decrease osteoblast activity with age during menopause (decrease in estrogen levels).
What does heat do to bone?
Destroy the organic matrix; Denature collagen protein fibers (like collagen in hot bone broth).
What do osteoprogenitor cells differentiate into after returning to the remodel site in step three of bone remodeling?
Differentiate into osteoblasts
What does acid do to bone?
Dissolve the inorganic matrix; Breakdown hydroxyapatite and mineral salts.
When does bone growth begin?
During embryological development
What is mesenchyme
Embryonic connective tissue
Yellow Bone Marrow function
Energy reserve
What is an example of a hormone that interacts with bone growth?
Estrogen
What is the primary mechanism of estrogen?
Estrogen stimulates osteoblast activity
Epiphysis
Expanded end (proximal & distal)
Osteoblasts in inner cellular layer deposit matrix in these layers...
External circumferential lamellae
The parathyroid hormone and calcitriol process is negative or positive feedback?
Negative (like most processes)
Nutrient foramen
Opening through which blood vessels and nerves enter and exit
The extracellular matrix is made out of an organic and an inorganic component. What is the organic component and what is the inorganic component?
Organic: osteoid Inorganic: hydroxyapatite crystals
Zone 5 is known as...
Ossification "Cartilage is replaced by bone"
Mechanical stress: - What bone cell accelerates the synthesis of osteoid & mineralization?
Osteoblasts
What bone cell secretes osteoid and mineralization-promoting substances in step three of bone remodeling?
Osteoblasts
______ become "trapped" in the mineralized matrix and mature into ______.
Osteoblasts; osteocytes
Calcitonin effector
Osteoclasts (decreases activity)
How is the medullary cavity expanded during appositional bone growth?
Osteoclasts along the medullary cavity resorb matrix to expand the medullary cavity
