Week 4- Skeletal System Flashcards
Types of Bones
Compact and Spongy
Compact Bone
-Rigid
-appears white, smooth, and solid
-80% total bone mass
Spongy Bone
-internal to compact
-porous
-20% total bone mass
Function of Bone
1) Support and Protection
2) Levers for Movement
3) Storage of Minerals and Energy Reserves
Support and Protection
-Provide structural support and serves as framework for entire body
-Protects tissues/organs from injury/trauma
Levers for Movement
-Serve as attachment sites for skeletal muscles, soft tissues, and some organs
-Muscles attached to bone contract and exert pull on skeleton, which functions as a system of levers
-Can alter direction and magnitude of forces generated by skeletal muscles (powerful vs precise)
Storage of Minerals and Energy Reserves
-Most of body’s calcium and phosphate are stored within and released from bone
-When calcium or phosphate is needed, some bone gets broken down and minerals are released into blood
-Potential energy in lipid form stored in yellow bone marrow sometimes
Calcium
Essential for muscle contraction, blood clotting, and release of neurotransmitters from nerve cells
Phosphate
-Structural component of ATP, other nucleotides, and phospholipids
-Important component of plasma membrane
Hematopoiesis
-Process of blood cell production
-Occurs in red bone marrow(contains stem cells that form blood cells and platelets)
Classes of Bones
1) Long Bones
2) Short Bones
3) Flat Bones
4) Irregular bones
Long Bones
-greater in length than width
-bones have elongated, cylindrical shaft (diaphysis)
-most common bone shape
-found in upper and lower limbs
-examples: metatarsals, femur, tibia, fibula
Short Bones
-length nearly equal to width
-Ex: carpals and tarsals
-Sesamoid bones: small sesame shaped bones along tendons of some muscles (ex: patella)
Flat Bones
-Flat, thin surfaces that may be slightly curved
-Provide extensive surface areas for muscle attachment and protect underlying soft tissues
-Form roof of skull, scapulae, sternum, and ribs
Irregular Bones
-Elaborate, sometimes complex shapes
-Vertebrae, ossa coxae, and several skull bones (ethmoid, sphenoid, and maxilla)
Regions of Long Bones
-Diaphysis
-Epiphysis
-Metaphysis
Diaphysis
-elongated, cylindrical shaft
-provides leverage and support
-composed of compact bone and spongy bones extends internally from compact in form of spicules(thin needlelike structures)
Medullary Cavity
-Hollow, cylindrical space within diaphysis
-contains bone marrow
Epiphysis
-expanded, knobby region at ends of each bone
-composed of outer, thin layer of compact bone and inner, more extensive region of spongy bone
-spongy bone resists stress that is applied from many directions
Proximal epiphysis
End closest to trunk
Distal epiphysis
End furthest from trunk
Articular cartilage
-Thin layer of hyaline cartilage covers joint surfaces of epiphysis
-Helps reduce friction and absorb shock in moveable joints
Metaphysis
-Region where bone widens and transfers forces between diaphysis and epiphysis
-Thin layer of hyaline cartilage provides for continued lengthwise growth
-contains epiphyseal plate in growing bones
Coverings and Linings of Long Bones
-Periosteum
-Endosteum
Periosteum
-Tough sheath that covers outer surface of bone except for areas cover by articular cartilage
-Responsible for width growth
-anchored to bone by numerous collagen fibers(perforating fibers) which run perpendicular to diaphysis
Layers of Periosteum
-Outer, fibrous layer
-Inner, cellular layer
Fibrous Layer
-made of dense irregular connective tissue
-protects bone from surrounding structures, anchors blood vessels/nerves to surface of bones, and serves as attachment site for tendons and ligaments
Cellular layer
-includes osteoprogenitor cells, osteoblasts, and osteoclasts
-osteoprogenitor cells and osteoblasts produce circumferential layers of bone matrix
Endosteum
-Very thin layer of connective tissue containing osteoprogenitor cells, osteoblasts, and osteoclasts
-covers all internal surfaces of bone within medullary cavity
-active during bone growth, repair, and remodeling
Anatomy of other bone classes
-external surface= compact bone covered by periosteum
-interior= spongy bone
-no medullary cavity
-in flat bones of skull
Blood Supply and Innervation
-bone is highly vascularized, especially regions with spongy bone
-blood vessels enter from periosteum
-nerves accompany blood vessels through nutrient foramen and innervate bone, periosteum, endosteum, and marrow cavity
-mainly sensory nerves
Nutrient Foramen
Small opening/hole through which 1 nutrient artery enters and 1 nutrient vein exits
Bone Marrow
-Soft connective tissue of bone
-2 types: Red and yellow
Red Bone Marrow
-contains reticular connective tissue, developing blood cells, and adipocytes
-primary function is hematopoiesis
-in children, it’s widely distributed and located in spongy bone of most bones and medullary cavity of long bones
-in adults, in select bones of axial skeletons (flat bones of skull, vertebrae, ribs, sternum, and ossa coxae) and in proximal epiphyses of each humerus and femur
Yellow Bone Marrow
-Within medullary cavity of long bones and inner core of epiphyses there is a decrease in developing blood cells and increase in adipocytes
-fatty appearing substance
-severe anemia may cause yellow to turn to red to produce RBCs
Cells in Bone
-Osteoprogenitor cells
-Osteoblasts
-Osteocytes
-Osteoclasts
Osteoprogenitor cells
-stem cells derived from mesenchyme
-when they divide, produce stem cell and committed cell (matures to osteoblast)
-in periosteum and endosteum
Osteoblasts
-form new bone
-synthesize and secrete initial semisolid bone matrix called osteoid (later calcifies)
-as a result of mineral deposition, osteoblasts become trapped and mature into osteocytes
Osteocytes
-mature cells that lost ability to form bone
-maintain matrix and detect mechanical stress
Osteoclasts
-large multinuclear phagocytic cells
-involved in breaking down bone in process called bone resorption
Composition of Bone Matrix
Organic and Inorganic component
Organic Component
-Osteoid
-collagen and semisolid ground substance of proteoglycans and glycoproteins
-gives bone tensile strength by resisting stretch/twisting
Inorganic Component
-Calcium and phosphate
-provide bone with rigidity/inflexibility
Bone Formation
-begins with osteoblasts secreting osteoid
-calcification occurs subsequently with osteoid deposition
-requires many substances (vitamin D, vitamin C, calcium, and phosphate)
Bone Resorption
-bone matrix is destroyed by osteoclasts
-occurs when blood calcium levels are low
Compact Bone Anatomy
-composed of osteons (small cylindrical structures)
Osteons
-basic functional and structural unit of bone
-parallel to diaphysis
-looks like bulls-eye
Components of Osteon
-Central canal
-Concentric lamellae
-Osteocytes
-Lacunae
-Canaliculi
-Perforating Canals
-Circumferential lamellae
-Interstitial lamellae
Central canal
-Cylindrical channel that lies in center and runs parallel
-Contains blood vessels/nerves
Concentric lamellae
-rings that surround central canal
-forms bulk of osteon
-# present varies among osteons
-contains collagen fibers oriented at angle perpendicular to previous and following
Osteocytes
-Mature bone cells between adjacent concentric lamellae
-Maintain bone matrix
Lacunae
Small spaces that house an osteocyte
Canaliculi
-channels that extend from each lacuna, through lamellae, and connect to other lacunae and central canal
-house osteocyte cytoplasmic projections that permit intercellular contact/communication
-nutrients, minerals, gases, and wastes are transported within passageways, allowing their exchange between osteocytes and blood vessels within central canal
Perforating Canals
-resemble central canals (contain blood vessels and nerves)
-run perpendicular to central canals and help connect multiple canals within different osteons
-form channels for vascular/innervation connection among osteons
Circumferential lamellae
- External circumferential lamellae: rings of bone internal to periosteum
-Internal circumferential lamellae: external to endosteum
-extend circumference of bone
Interstitial lamellae
-Components of compact bone between osteons or leftover parts of osteons that have been partially reabsorbed
-incomplete and no central canal
Spongy Bone Anatomy
-no osteons
-open lattice of narrow rods and plates of bones called trabeculae
-bone marrow fills in between trabeculae
-contains parallel lamellae composed of bone matrix
-between adjacent lamellae are osteocytes resting in lacunae with many canaliculi radiating from lacunae
-nutrients reach osteocytes by diffusion through cytoplasmic processes of osteocytes, which extend within canaliculi that opens into surface of trabeculae
Trabeculae
-meshwork of crisscrossing bars and plates of small bone pieces
-provides resistance to stress applied in many directions by distributing stress throughout entire framework
Cartilage Growth
Interstitial Growth: increase in length
Appositional Growth: increase in width
-interstitial growth decreases as cartilage matures because cartilage becomes semirigid and isn’t able to expand
-later growth primarily appositional
-growth only occurs after injury but is limited due to lack of blood vessels
Steps in Interstitial Growth
1) Chondrocytes housed within lacunae are stimulated to undergo mitotic cell division
2) Following Cell Division, 2 cells occupy single lacuna (now called chondroblasts)
3) As chondroblasts begin to synthesize and secrete new cartilage matrix, they are pushed apart (each cell now resides in its own lacuna and called a chondrocyte)
4) Cartilage continues to grow in internal regions as chondrocytes continue to produce more matrix
Steps in Appositional Growth
1) Undifferentiated stem cells at internal edge if perichondrium begin to divide
2) -New undifferentiated stem cells and committed cells that differentiate into chondroblasts form -chondroblasts at periphery edge of old cartilage begin to produce/secrete new cartilage matrix)
3) -Chondroblasts push apart and become chondrocytes with each occupying its own lacuna
-Cartilage continues to grow at periphery as chondrocytes continue to produce matrix
Ossification
-formation/development of bone
-begins in embryo and continues into childhood/adolescence
2 Types: Intermembranous and Endochondral
Intermembranous Ossification
-happens in mesenchyme
-produces flat bone of skull, some facial bones, mandible, and central part of clavicle
-begins when mesenchyme becomes thickened and condensed with dense supply of capillaries
Steps of Intermembranous Ossification
1) Ossification centers form within thickened regions of mesenchyme beginning at 8th week of development (# ossification centers increases as # of osteoblasts increase)
2) Osteoid undergoes calcification
3) Woven bone and its surrounding periosteum form
4) Lamellar bone replaces woven bone as compact and spongy bone form
Woven bone
Immature and not well organized
Endochondral Ossification
Produces bones of skeleton (upper and lower limbs, pelvis, vertebrae, and ends of clavicle)
Steps of Endochondral Ossification
1) Fetal hyaline cartilage model develops
2) Cartilage calcifies and periosteal bone collar forms
3) Primary ossification center forms in diaphysis
4) Secondary ossification center forms in epiphyses
5) Bone replaces almost all cartilage, except articular cartilage and epiphyseal cartilage
6) Lengthwise growth continues until epiphyseal plate ossifies and forms epiphyseal line
Bone Growth
Interstitial Growth and Appositional Growth
Interstitial Growth
Dependent upon growth of cartilage within epiphyseal plate
Zones of Epiphyseal Plate
1) Zone of Resting Cartilage (closest to epiphysis)
2) Zone of Proliferating Cartilage
3) Zone of Hypertrophic Cartilage
4) Zone of Calcified Cartilage
5) Zone of Ossification (closest to diaphysis)
Appositional Growth
-occurs within periosteum
-bone increases in width
-osteoblasts in periosteum produce and deposit bone matrix in external circumferential lamellae
-continues throughout lifetime
Bone Remodeling
Constant dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone (bone resorption)
Mechanical Stress
Weight bearing movement or exercise
Hormones That Promote Growth and Repair
-Growth hormone
-Thyroid hormone
-Calcitonin
-Sex hormones (estrogen and testosterone)
-Parathyroid hormone
-Calcitriol
Growth Hormone
Stimulates liver to make IGF, which causes cartilage proliferation at epiphyseal plate resulting in bone elongation
Thyroid Hormone
Stimulates bone growth by stimulating metabolic rate of osteoblasts
Calcitonin
Promotes calcium deposition in bone and inhibits osteoclast activity
Sex hormones (estrogen and testosterone)
Stimulate osteoblasts and promotes epiphyseal plate growth and closure
Parathyroid hormone
Increases blood calcium levels by encouraging bone resorption by osteoclasts
Calcitriol
Stimulates absorption of calcium ions from small intestine into blood, which may cause net decrease in calcium loss from bone
Hormones That Inhibit Growth or Increase Resorption
-Glucocorticoids
-Serotonin
Glucocorticoids
-Increases bone loss
-In kids, can impair growth if there’s chronically high levels
Serotonin
Inhibits osteoprogenitor cells from differentiating into osteoblasts when there’s chronically high levels
Regulating Blood Calcium Levels
-Calcium required for physiologic processes (muscle contractions, exocytosis of molecules from cells, stimulation of heart by pacemaker cells, blood clotting, ect)
-Calcium levels regulated by calcitriol, parathyroid hormone, and calcitonin
Conversion of Vitamin D into Calcitriol
1) UV light converts molecule in keratinocytes to vitamin D3 (cholecalciferol), which is released into blood
2) D3 circulates and when passes through liver, enzymes convert D3 to calcidiol
3) Calcidiol circulates and when passes through kidney, converted to calcitriol by enzymes
Calcitriol
-active form of vitamin D3
-stimulates absorption of Ca2+ from small intestine to blood
Parathyroid hormone
Released in response to low blood calcium levels
Interaction of PTH and Calcitriol With Bone
Acts synergistically to increase release of calcium from bone in blood by increasing osteoclast activity
Interaction of PTH and Calcitriol With Kidneys
Acts synergistically to stimulate kidneys to excrete less calcium in urine
Interaction of Calcitriol With Small Intestine
Increase absorption of calcium from small intestine into blood
Calcitonin
Aids in regulating calcium levels but less than PTH and calcitriol
Avulsion
Complete severing of body part (usually toe/finger)
Colles
-Fracture of distal end of lateral forearm bone (radius)
-aka dinner fork deformity
Comminuted
Bone is splintered into several small pieces between main parts
Complete
Bone broken into 2 or more pieces
Compound
Broken ends of bone protrude through skin
Compression
Bone is squashed
Depressed
Broken part forms a concavity (skull fracture)
Displaced
Fractured part out of anatomic alignment
Epiphyseal
Epiphysis separated from diaphysis at epiphyseal plate
Greenstick
Partial fracture (one side breaks, other is bent)
Hairline
Fine crack in which sections remain aligned
Impacted
One fragmented bone firmly driven into other
Incomplete
Partial (extends only partway across bone)
Linear
Fracture parallel to long axis of bone
Oblique
Diagonal fracture at angle
Pathologic
Weakening of bone caused by disease process
Pott
Fracture at distal ends of tibia and fibula
Simple
Bone does not break skin
Spiral
-Fracture spirals around axis of long bone
-Results from twisting stress
Stress
Thin fractures due to repeated stressful impact like running
Transverse
At right angle to long axis of bone
Steps of Fracture Repair
1) Fracture hematoma forms
2) Fibrocartilaginous (soft) callus forms
3) Hard (bony) callus forms
4) Bone is remodeled
