Podcast
Questions and Answers
What is the primary function of the periosteum?
What is the primary function of the periosteum?
Which structure is described as a small, rounded projection on a bone?
Which structure is described as a small, rounded projection on a bone?
Where is yellow bone marrow primarily located in long bones?
Where is yellow bone marrow primarily located in long bones?
Which term refers to a large, blunt, irregular surface on a bone?
Which term refers to a large, blunt, irregular surface on a bone?
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What distinguishes the diaphysis of a long bone?
What distinguishes the diaphysis of a long bone?
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Which type of bone is primarily composed of trabeculae?
Which type of bone is primarily composed of trabeculae?
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What purpose do Sharpey's fibers serve in the periosteum?
What purpose do Sharpey's fibers serve in the periosteum?
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What is a fossa in terms of bone anatomy?
What is a fossa in terms of bone anatomy?
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What is the main role of osteoclasts during bone resorption?
What is the main role of osteoclasts during bone resorption?
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Which of the following functions does calcium NOT support in the body?
Which of the following functions does calcium NOT support in the body?
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What is a common symptom of carpopedal spasm caused by hypocalcemia?
What is a common symptom of carpopedal spasm caused by hypocalcemia?
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What triggers the release of calcitonin in the body's hormonal mechanism?
What triggers the release of calcitonin in the body's hormonal mechanism?
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According to Wolff’s law, how does bone remodel in response to stress?
According to Wolff’s law, how does bone remodel in response to stress?
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Which type of bone fracture involves bone ends that are out of normal alignment?
Which type of bone fracture involves bone ends that are out of normal alignment?
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What describes a compound fracture?
What describes a compound fracture?
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Which statement about osteoclast activity is correct?
Which statement about osteoclast activity is correct?
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What type of fracture occurs when the bone is excessively twisted?
What type of fracture occurs when the bone is excessively twisted?
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Which type of fracture is most common in the elderly?
Which type of fracture is most common in the elderly?
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What is the first stage in the healing process of a bone fracture?
What is the first stage in the healing process of a bone fracture?
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During which phase do osteoblasts begin forming spongy bone?
During which phase do osteoblasts begin forming spongy bone?
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What typically characterizes a depressed fracture?
What typically characterizes a depressed fracture?
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How long does the healing of fractures generally take?
How long does the healing of fractures generally take?
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Which process occurs during the remodeling stage of bone healing?
Which process occurs during the remodeling stage of bone healing?
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What type of fracture is characterized by incomplete break with one side bending?
What type of fracture is characterized by incomplete break with one side bending?
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What is the purpose of the growth zone in long bone growth?
What is the purpose of the growth zone in long bone growth?
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Which hormones are primarily responsible for stimulating epiphyseal plate activity during infancy and childhood?
Which hormones are primarily responsible for stimulating epiphyseal plate activity during infancy and childhood?
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What triggers the closure of the epiphyseal plate and the end of longitudinal bone growth?
What triggers the closure of the epiphyseal plate and the end of longitudinal bone growth?
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What occurs during the transformation zone in long bone growth?
What occurs during the transformation zone in long bone growth?
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Which element is essential for the mineralization of bone?
Which element is essential for the mineralization of bone?
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What characterizes bone resorption?
What characterizes bone resorption?
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Which process involves both the deposition and resorption of bone?
Which process involves both the deposition and resorption of bone?
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What happens to the hyaline cartilage at the epiphyseal plates during ossification?
What happens to the hyaline cartilage at the epiphyseal plates during ossification?
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What condition is characterized by bones being inadequately mineralized, resulting in softened and weakened bones?
What condition is characterized by bones being inadequately mineralized, resulting in softened and weakened bones?
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Which demographic is most often affected by osteoporosis?
Which demographic is most often affected by osteoporosis?
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What is a common physical symptom of rickets in children?
What is a common physical symptom of rickets in children?
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Which condition involves excessive bone formation and breakdown, leading to a high ratio of spongy to compact bone?
Which condition involves excessive bone formation and breakdown, leading to a high ratio of spongy to compact bone?
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Which treatment can slow bone loss in individuals with osteoporosis?
Which treatment can slow bone loss in individuals with osteoporosis?
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What is the potential effect of insufficient vitamin D in breastfeeding infants?
What is the potential effect of insufficient vitamin D in breastfeeding infants?
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Which drug is commonly used for the treatment of Paget’s disease?
Which drug is commonly used for the treatment of Paget’s disease?
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What role does mesoderm play in bone development?
What role does mesoderm play in bone development?
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What type of cartilage is most abundant and provides support and flexibility?
What type of cartilage is most abundant and provides support and flexibility?
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Which type of cartilage contains elastic fibers and is found in the external ear?
Which type of cartilage contains elastic fibers and is found in the external ear?
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Which process refers to the growth of cartilage from the perichondrium?
Which process refers to the growth of cartilage from the perichondrium?
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What is NOT a characteristic of fibrocartilage?
What is NOT a characteristic of fibrocartilage?
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Which bone classification includes the vertebrae?
Which bone classification includes the vertebrae?
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Which of the following is a function of bones?
Which of the following is a function of bones?
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What type of bone is primarily cube-shaped and found in the wrist and ankle?
What type of bone is primarily cube-shaped and found in the wrist and ankle?
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Which marking on a bone serves as a site for muscle and ligament attachment?
Which marking on a bone serves as a site for muscle and ligament attachment?
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What is the primary composition of the diaphysis in long bones?
What is the primary composition of the diaphysis in long bones?
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Which part of a long bone is responsible for the growth in length during development?
Which part of a long bone is responsible for the growth in length during development?
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What characterizes trabecular or spongy bone?
What characterizes trabecular or spongy bone?
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What type of tissue covers the internal surfaces of bone?
What type of tissue covers the internal surfaces of bone?
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Where is hematopoietic tissue found in adults?
Where is hematopoietic tissue found in adults?
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What is the function of the periosteum in bone health?
What is the function of the periosteum in bone health?
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Which of the following describes a ramus in bone structure?
Which of the following describes a ramus in bone structure?
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What best describes the texture of compact bone?
What best describes the texture of compact bone?
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What type of bone formation occurs directly from a fibrous membrane?
What type of bone formation occurs directly from a fibrous membrane?
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Which component provides bone with its hardness and resistance to compression?
Which component provides bone with its hardness and resistance to compression?
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During which stage of endochondral ossification does the cartilage begin to cavitate?
During which stage of endochondral ossification does the cartilage begin to cavitate?
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What is the role of osteoblasts in bone chemistry?
What is the role of osteoblasts in bone chemistry?
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The Haversian system is primarily associated with which type of bone?
The Haversian system is primarily associated with which type of bone?
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What initiates the formation of the bony skeleton during development?
What initiates the formation of the bony skeleton during development?
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What does the term 'lacunae' refer to in bone structure?
What does the term 'lacunae' refer to in bone structure?
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Which statement correctly describes osteoclasts?
Which statement correctly describes osteoclasts?
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What condition is characterized by inadequately mineralized bones in children, leading to deformities such as bowed legs?
What condition is characterized by inadequately mineralized bones in children, leading to deformities such as bowed legs?
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Which of the following best describes osteoporosis?
Which of the following best describes osteoporosis?
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What is a common treatment method for osteoporosis that helps to slow bone loss?
What is a common treatment method for osteoporosis that helps to slow bone loss?
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What can result from insufficient calcium or vitamin D in a breastfeeding infant?
What can result from insufficient calcium or vitamin D in a breastfeeding infant?
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Paget's disease is characterized by which of the following conditions?
Paget's disease is characterized by which of the following conditions?
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What skeletal development aspect does mesoderm contribute to?
What skeletal development aspect does mesoderm contribute to?
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What is a significant consequence of osteoporosis on physical activity?
What is a significant consequence of osteoporosis on physical activity?
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What is a primary symptom of osteomalacia?
What is a primary symptom of osteomalacia?
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What is the primary role of the growth zone in long bone growth?
What is the primary role of the growth zone in long bone growth?
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Which hormones are responsible for the initial increase in epiphyseal plate activity during puberty?
Which hormones are responsible for the initial increase in epiphyseal plate activity during puberty?
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What occurs during the transformation zone of long bone growth?
What occurs during the transformation zone of long bone growth?
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What role do osteoblasts play in bone remodeling?
What role do osteoblasts play in bone remodeling?
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Which components are required for bone deposition?
Which components are required for bone deposition?
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What is primarily involved in the process of bone resorption?
What is primarily involved in the process of bone resorption?
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What remains in the epiphyseal plates after ossification?
What remains in the epiphyseal plates after ossification?
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What does alkaline phosphatase contribute to in bone health?
What does alkaline phosphatase contribute to in bone health?
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Study Notes
Bone Markings
- Erosity: Rounded projection
- Crest: Narrow, prominent ridge of bone
- Trochanter: Large, blunt, irregular surface
- Line: Narrow ridge of bone
- Tubercle: Small rounded projection
- Epicondyle: Raised area above a condyle
- Spine: Sharp, slender projection
- Process: Any bony prominence
- Head: Bony expansion carried on a narrow neck
- Facet: Smooth, nearly flat articular surface
- Condyle: Rounded articular projection
- Ramus: Armlike bar of bone
- Meatus: Canal-like passage
- Sinus: Cavity within bone
- Fossa: Shallow basin-like depression
- Groove: Furrow
- Fissure: Narrow, slit-like opening
- Foramen: Round or oval opening through bone
Bone Texture
- Compact bone: Dense outer layer
- Spongy bone: Honeycomb of trabeculae filled with yellow bone marrow
Structure of Long Bones
-
Diaphysis: Tubular shaft that forms the axis of long bones
- Composed of compact bone that surrounds the medullary cavity
- Contains yellow bone marrow (fat)
-
Epiphyses: Expanded ends of long bones
- Exterior is compact bone, and the interior is spongy bone
- Joint surface is covered with articular (hyaline) cartilage
- Epiphyseal line separates the diaphysis from the epiphyses
Bone Membranes
-
Periosteum: Double-layered protective membrane
- Outer fibrous layer is dense regular connective tissue
- Inner osteogenic layer is composed of osteoblasts and osteoclasts
- Richly supplied with nerve fibers, blood, and lymphatic vessels
- Secured to underlying bone by Sharpey's fibers
- Endosteum: Delicate membrane covering internal surfaces of bone
Structure of Short, Irregular, and Flat Bones
- Thin plates of periosteum-covered compact bones on the outside with endosteum-covered spongy bone (diploe) on the inside
- Have no diaphysis or epiphysis
- Contain bone marrow between the trabeculae
Hematopoietic Tissue (Red Marrow)
- Infants: Found in the medullary cavity and all areas of spongy bone
- Adults: Found in the diploe of flat bones, and the head of the femur and humerus
Bone Development
- Intramembranous Ossification: Bone develops directly from mesenchymal tissue
-
Endochondral Ossification: Bone develops from hyaline cartilage
- Formation of the bony collar
- Cavitation of the cartilage
- Invasion of the internal cavities by the periosteal bud, and spongy bone formation
- Formation of the medullary cavity, appearance of secondary ossification centers in the epiphyses
- Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates
Postnatal Bone Growth
-
Growth in length of long bones:
- Cartilage on the epiphyseal plate closest to the epiphysis is relatively inactive
- Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth
- Cells of the epiphyseal plate proximal to the resting cartilage form three functionally different zones: growth, transformation, and osteogenic
Functional Zones in Long Bone Growth
- Growth zone: Cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis
- Transformation zone: Older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate
- Osteogenic zone: New bone formation occurs
Long Bone Growth and Remodeling
- Growth in length: Cartilage continually grows and is replaced by bone
- Remodeling: Bone is resorbed and added by appositional growth
Hormonal Regulation of Bone Growth During Youth
- Infancy and childhood: Epiphyseal plate activity is stimulated by growth hormone
-
Puberty: Testosterone and estrogens
- Initially promote adolescents growth spurts
- Cause masculinization and feminization of specific parts of the skeleton
- Later induce epiphyseal plate closure, ending longitudinal bone growth
Bone Remodeling
- Remodeling units: Adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces
Bone Deposition
- Occurs where bone is injured or added strength is needed
- Requires a diet rich in protein, calcium, phosphorus, magnesium, and manganese
- Alkaline phosphatase is essential for mineralization
- Sites of new matrix deposition are revealed by the:
- Osteoid seam: unmineralized band of bone matrix
- Calcification front: abrupt transition zone between the osteoid seam and the older mineralized bone
Bone Resorption
- Accomplished by osteoclasts
- Resorption bays: grooves by osteoclasts as they break down bone matrix
- Resorption involves osteoclast secretion of:
- Lysosomal enzymes that digest organic matrix
- Acids that convert calcium salts into soluble forms
- Dissolved matrix is transcytosed across the osteoclast's cell where it is secreted into the interstitial fluid and then into the blood
Importance of Ionic Calcium in the Body
- Calcium is necessary for:
- Transmission of nerve impulses
- Muscle contraction
- Blood coagulation
- Secretion by glands and nerve cells
- Cell division
Carpopedal Spasm
- Hypocalcemia causing overexcitability of the nervous system and muscle spasm of hands and feet
Control of Remodeling
- Two control loops regulate bone remodeling:
- Hormonal mechanism maintains calcium homeostasis in the blood
- Mechanical and gravitational forces acting on the skeleton
Hormonal Mechanism
- Rising blood Ca2+ levels trigger the thyroid to release calcitonin
- Calcitonin stimulates calcium salt deposit in bone
- Falling blood Ca2+ levels signal the parathyroid glands to release PTH
- PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood
Calcitriol Synthesis & Action
- Calcitriol (active form of vitamin D) increases blood Ca2+ levels:
- Stimulates intestinal Ca2+ absorption
- Enhances osteoclast activity
- Promotes reabsorption of Ca2+ by the kidneys
Response to Mechanical Stress
- Wolff's law: A bone grows or remodels in response to the forces or demands placed upon it
- Observations supporting Wolff's law include:
- Long bones are thickest midway along the shaft (where bending stress is greatest)
- Curved bones are thickest where they are most likely to buckle
- Trabeculae form along lines of stress
- Large, bony projections occur when heavy, active muscles attach
Bone Fractures (Breaks)
- Classified by:
- Position of the bone ends after fracture
- Completeness of the break
- Orientation of the bone to the long axis
- Whether or not the bone ends penetrate the skin
Types of Bone Fractures
- Nondisplaced: Bone ends retain their normal position
- Displaced: Bone ends are out of normal alignment
- Complete: Bone is broken all the way through
- Incomplete: Bone is not broken all the way through
- Linear: The fracture is parallel to the long axis of the bone
- Transverse: The fracture is perpendicular to the long axis of the bone
- Compound (open): Bone ends penetrate the skin
- Simple (closed): Bone ends do not penetrate the skin
Common Types of Fractures
- Comminuted: Bone fragments into three or more pieces; common in the elderly
- Spiral: Ragged break when bone is excessively twisted; common sports injury
- Depressed: Broken bone portion pressed inward; typical skull fracture
- Compression: Bone is crushed; common in porous bones
- Epiphyseal: Epiphysis separates from diaphysis along epiphyseal lines; occurs where cartilage cells are dying
- Greenstick: Incomplete fracture where one side of the bone breaks and the other side bends; common in children
Stages in the Healing of a Bone Fracture
-
Hematoma formation:
- Torn blood vessels hemorrhage
- A mass of clotted blood (hematoma) forms at the fracture site
- Site becomes swollen, painful, and inflamed
-
Fibrocartilaginous callus formation:
- Granulation tissue (soft callus) forms a few days after the fracture
- Capillaries grow into the tissue and phagocytic cells begin cleaning debris
- Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone
- Fibroblasts secrete collagen fibers that connect broken bone ends
- Osteoblasts begin forming spongy bone
- Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies
-
Bony callus formation:
- New bone trabeculae appear in the fibrocartilaginous callus
- Fibrocartilaginous callus converts into a bony (hard) callus
- Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later
-
Bone remodeling:
- Excess material on the bone shaft exterior and in the medullary canal is removed
- Compact bone is laid down to reconstruct shaft walls
Healing of Fractures
- Normally healing takes 8-12 weeks (longer in the elderly)
- Stages of healing:
- Fracture hematoma
- Granulation tissue
- Callus formation
- Remodeling
Homeostatic Imbalances
-
Osteomalacia: Bones are inadequately mineralized causing softened, weakened bones
- Main symptom is pain when weight is put on the affected bone
- Caused by insufficient calcium in the diet, or by vitamin D deficiency
-
Rickets (in Children): Bones of children are inadequately mineralized causing softened, weakened bones
- Bowed legs and deformities of the pelvis, skull, and rib cage are common
- Caused by insufficient calcium in the diet, or by vitamin D deficiency
-
Osteoporosis: Group of diseases in which bone reabsorption outpaces bone deposition
- Spongy bone of the spine is most vulnerable
- Occurs most often in postmenopausal women
- Bones become so fragile that sneezing or stepping off a curb can cause fractures
- Treatment:
- Calcium and vitamin D supplements
- Increased weight-bearing exercise
- Hormone (estrogen) replacement therapy (HRT)
- Natural progesterone cream
- Statins
Isolated Cases of Rickets
- Rickets have been essentially eliminated in the US
- Only isolated cases appear
- Example: Infants of breastfeeding mothers deficient in vitamin D will also be Vitamin D deficient and develop rickets
Paget's Disease
- Characterized by excessive bone formation and breakdown
- Pagetic bone with an excessively high ratio of woven (spongy) to compact bone is formed
- Pagetic bone, along with reduced mineralization, causes spotty weakening of bone
- Osteoclast activity wanes, but osteoblast activity continues to work
- Usually localized in the spine, pelvis, femur, and skull
- Unknown cause (possibly viral)
- Treatment includes the drugs Didronate and Fosamax (also calcitonin by inhalation)
Development Aspects of Bones
- Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton
- The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be determined
Skeletal Cartilage
- Contains no blood vessels or nerves
- Surrounded by the perichondrium, a dense irregular connective tissue that restricts outward expansion
- Three types of cartilage: hyaline, elastic, and fibrocartilage
Hyaline Cartilage
- Provides support, flexibility, and resilience
- Most abundant skeletal cartilage
- Found in:
- Articular cartilage: covers the ends of long bones
- Costal cartilage: connects ribs to the sternum
- Respiratory cartilage: makes up the larynx and reinforces air passages
- Nasal cartilage: supports the nose
Elastic Cartilage
- Similar to hyaline cartilage but contains elastic fibers
- Found in the external ear and epiglottis
Fibrocartilage
- Highly compressed with great tensile strength
- Contains collagen fibers
- Found in the menisci of the knee and intervertebral discs
Growth of Cartilage
- Appositional growth: cells in the perichondrium secrete matrix against the external face of existing cartilage
- Interstitial growth: lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within
- Calcification of cartilage occurs during normal bone growth and during old age
Classification of Bones
- Axial skeleton: bones of the skull, vertebral column, and rib cage
- Appendicular skeleton: bones of the upper and lower limbs, shoulder, and hip
- Long bones: longer than they are wide (e.g., humerus)
- Short bones: cube-shaped bones of the wrist and ankle, bones that form within tendons (e.g., patella)
- Flat bones: thin, flattened, and slightly curved (e.g., sternum, most skull bones)
- Irregular bones: complicated shapes (e.g., vertebrae, hip bones)
Function of Bones
- Support: forms the framework that supports the body and cradles soft organs
- Protection: provides protective cases for the brain, spinal cord, and vital organs
- Movement: provides levers for muscles
- Mineral storage: reservoir for minerals, especially calcium and phosphorus
- Blood cell formation (hematopoiesis): occurs within the marrow cavities of bones
Bone Markings
- Bulges, depressions, and holes serve as:
- Sites of attachment for muscles, ligaments, and tendons
- Joint surfaces
- Conduits for blood vessels and nerves
Muscle and Ligament Attachment
- Tuberosity: rounded projection
- Crest: narrow, prominent ridge of bone
- Trochanter: large, blunt, irregular surface
- Line: narrow ridge of bone
- Tubercle: small rounded projection
- Epicondyle: raised area above a condyle
- Spine: sharp, slender projection
- Process: any bony prominence
- Head: bony expansion carried on a narrow neck
- Facet: smooth, nearly flat articular surface
- Condyle: rounded articular projection
- Ramus: armlike bar of bone
Passages and Cavities
- Meatus: canal-like passageway
- Sinus: cavity within bone
- Fossa: shallow basin-like depression
- Groove: furrow
- Fissure: narrow, slit-like opening
- Foramen: round or oval opening through bone
Bone Texture
- Compact bone: dense outer layer
- Spongy bone: honeycomb of trabeculae filled with yellow bone marrow
Structure of Long Bones
- Long bones consist of a diaphysis and epiphysis
-
Diaphysis:
- Tubular shaft that forms the axis of long bones
- Composed of compact bone that surrounds the medullary cavity
- Yellow bone marrow (fat) is contained in the medullary cavity
-
Epiphyses:
- Expanded ends of long bones
- Exterior is compact bone, and the interior is spongy bone
- Joint surface is covered with articular (hyaline) cartilage
- Epiphyseal line separates the diaphysis from the epiphyses
Bone Membranes
-
Periosteum: double-layered protective membrane
- Outer fibrous layer is dense regular connective tissue
- Inner osteogenic layer is composed of osteoblasts and osteoclasts
- Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina
- Secured to underlying bone by Sharpey's fibers
- Endosteum: delicate membrane covering internal surfaces of bone
Structure of Short, Irregular, and Flat Bones
- Thin plates of periosteum-covered compact bones on the outside with endosteum-covered spongy bone (diploe) on the inside
- Have no diaphysis or epiphysis
- Contain bone marrow between the trabeculae
Hematopoietic Tissue (Red Marrow)
- In infants: found in the medullary cavity and all areas of spongy bone
- In adults: found in the diploe of flat bones, and the head of the femur and humerus
Compact Bone
-
Haversian system (osteon): the structural unit of compact bone
- Lamellae: weight-bearing, column-like matrix tubes composed mainly of collagen
- Haversian (central) canal: central channel containing blood vessels and nerves
- Volkmann's canals: channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal
- Osteocytes: mature bone cells
- Lacunae: small cavities in bone that contain osteocytes
- Canaliculi: hairlike canals that connect lacunae to each other and the central canal
Chemical Composition of Bone: Organic
- Osteoblasts: bone-forming cells
- Osteocytes: mature bone cells
- Osteoclasts: larger cells that resorb or break down bone matrix
- Osteoid: unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen
Chemical Composition of Bone: Inorganic
- Hydroxyapatites (mineral salts): 65% of bone by mass, mainly calcium phosphates, responsible for bone hardness and resistance to compression
Bone Development
-
Osteogenesis (ossification): process of bone tissue formation, leading to:
- Formation of the bony skeleton in embryos
- Bone growth until early adulthood
- Bone thickness, remodeling, and repair
Formation of the Bony Skeleton
- Begins at week 8 of embryo development
- Intramembranous ossification: bone develops from a fibrous membrane
- Endochondral ossification: bone forms by replacing hyaline cartilage
Intramembranous Ossification
- Formation of most flat bones of the skull and clavicles
- Fibrous connective tissue membranes are formed by mesenchymal cells
Stages of Intramembranous Ossification
- An ossification center appears in the fibrous connective tissue membrane
- Bone matrix is secreted within the fibrous membrane
- Woven bone and periosteum form
- Bone collar of compact bone forms and red marrow appears
Endochondral Ossification
- Begins in the second month of development
- Uses hyaline cartilage "bones" as models for bone construction
- Requires breakdown of hyaline cartilage prior to ossification
Stages of Endochondral Ossification
- Formation of a bone collar
- Cavitation of the hyaline cartilage
- Invasion of internal cavities by the periosteal bud, and spongy bone formation
- Formation of the medullary cavity, appearance of secondary ossification centers in the epiphyses
- Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates
Postnatal Bone Growth
-
Growth in length of long bones:
- Cartilage on the epiphyseal plate closest to the epiphysis is relatively inactive
- Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth
- Cells of the epiphyseal plate proximal to the resting cartilage form three functionally different zones: growth, transformation, and osteogenic
Functional Zones in Long Bone Growth
- Growth zone: cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis
- Transformation zone: older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate
- Osteogenic zone: new bone formation occurs
Long Bone Growth and Remodeling
- Growth in length: cartilage continually grows and is replaced by bone
- Remodeling: bone is resorbed and added by appositional growth
Hormonal Regulation of Bone Growth during Youth
- During infancy and childhood: epiphyseal plate activity is stimulated by growth hormone
-
During puberty: testosterone and estrogens:
- Initially promote adolescent growth spurts
- Cause masculinization and feminization of specific parts of the skeleton
- Later induce epiphyseal plate closure, ending longitudinal bone growth
Bone Remodeling
- Remodeling units: adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces
Bone Deposition
- Occurs where bone is injured or added strength is needed
- Requires a diet rich in protein, vitamins C, A, and D, and calcium, phosphorus, magnesium, and manganese
- Alkaline phosphatase is essential for mineralization
- Sites of new matrix deposition are revealed by the:
- Osteoid seam: unmineralized band of bone matrix
- Calcification front: abrupt transition zone between the osteoid seam and the older mineralized bone
Bone Resorption
- Accomplished by osteoclasts
- Resorption bays: grooves made by osteoclasts as they resorb bone
Homeostatic Imbalances
-
Osteomalacia:
- Bones are inadequately mineralized, causing softened, weakened bones (osteoid without minerals)
- Main symptom is pain when weight is put on the affected bone
- Caused by insufficient calcium in the diet or vitamin D deficiency
-
Rickets (in children):
- Bones of children are inadequately mineralized, causing softened, weakened bones
- Bowed legs and deformities of the pelvis, skull, and rib cage are common
- Caused by insufficient calcium in the diet or vitamin D deficiency
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Osteoporosis:
- Group of diseases in which bone resorption outpaces bone deposition
- Spongy bone of the spine is most vulnerable
- Occurs most often in postmenopausal women
- Bones become so fragile that sneezing or stepping off a curb can cause fractures
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Treatment:
- Calcium and vitamin D supplements
- Increased weight-bearing exercise
- Hormone (estrogen) replacement therapy (HRT) slows bone loss
- Natural progesterone cream prompts new bone growth
- Statins increase bone mineral density
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Treatment:
Isolated Cases of Rickets
- Rickets have been essentially eliminated in the US
- Only isolated cases appear (e.g., infants of breastfeeding mothers deficient in vitamin D)
Paget's Disease
- Characterized by excessive bone formation and breakdown
- Pagetic bone with an excessively high ratio of woven (spongy) to compact bone is formed
- Pagetic bone, along with reduced mineralization, causes spotty weakening of bone
- Osteoclast activity wanes, but osteoblast activity continues to work (can get irregular bone thickenings)
- Usually localized in the spine, pelvis, femur, and skull
- Unknown cause (possibly viral)
- Treatment includes drugs Didronate and Fosamax (also calcitonin by inhalation)
Development Aspects of Bones
- Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton
- The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be estimated
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Description
Test your knowledge on various bone markings, textures, and the structure of long bones. This quiz covers terms like erosity, crest, trochanter, and distinguishes between compact and spongy bone. Perfect for anatomy students and enthusiasts.
