3_Bones and Skeletal Tissue (ch 6) Flashcards
Marieb Chapter 6
What are the 7 functions of bones?
1) Support (for body and soft organs)
2) Protection (for brain, spinal cord, and vital organs)
3) Movement (levers for muscle action)
4) Mineral and growth factor storage (Calcium and phosphorus, and growth factors reservoir)
5) Blood cell formation (hematopoiesis) in red marrow cavities of certain bones
6) Triglyceride (fat) storage (yellow marrow)(Energy source)
7) Hormone production
(osteocalcin which regulates bone formation
Protects against obesity, glucose intolerance)
What hormone produced by bone regulates bone formation
and protects against obesity and glucose intolerance
Osteocalcin
What is hematopoiesis
Blood cell formation
Why are bones categorized as organs?
Because they contain different types of tissues
bone (osseous) tissue, nervous tissue, cartilage, fibrous connective tissue, muscle and epithelial cells in its blood vessels
How many levels of structure do bones have?
3:
Gross anatomy
Microscopic
Chemical
Name the two bone textures
Compact and spongy bone
What are the characteristics of compact bone?
Dense outer layer; smooth and solid
What are the characteristics of Spongy (cancellous or trabecular) bone?
Honeycomb of flat pieces of bone deep to compact called trabeculae
What is the structure of short, irregular and flat bones? (e.g. skull)
**Thin plates of spongy bone covered by compact bone
**Plates sandwiched between connective tissue membranes
**Periosteum (outer layer) and endosteum
**No shaft or epiphyses
**Bone marrow throughout spongy bone; no marrow cavity
**Hyaline cartilage covers articular surfaces
What is the structure of typical long bones? (e.g.humerus)
1) Diaphysis
*Tubular shaft forms long axis;
*Compact bone surrounds medullary cavity)
2) Epiphyses
*Bone ends
*External compact bone; internal spongy bone
*Articular cartilage covers articular surfaces
*Between is epiphyseal line
Remnant of childhood bone growth at epiphyseal plate
What membrane covers bones?
Periosteum
Where would you find periosteum membrane? and what are its characteristics?
*White, double-layered membrane
*Covers external surfaces except joint surfaces
*Outer fibrous layer of dense irregular connective tissue
Note: Sharpey’s fibers secure to bone matrix
*Osteogenic layer abuts bone
Note: Contains primitive stem cells – osteogenic cells
*Many nerve fibers and blood vessels
*Anchoring points for tendons and ligaments
Where would you find the endosperm membrane?
Delicate connective tissue membrane covering internal bone surface
Covers trabeculae of spongy bone
Lines canals that pass through compact bone
Contains osteogenic cells that can differentiate into other bone cells
What is red marrow?
Hematopoietic Tissue in Bones
Where is red marrow found?
*Found within trabecular cavities of spongy bone and diploë of flat bones (e.g., Sternum)
*In medullary cavities and spongy bone of newborns
*Adult long bones have little red marrow [Heads of femur and humerus only]
*Red marrow in diploë and some irregular bones is most active
*Yellow marrow can convert to red, if necessary
What five major cell types are found in bones?
Osteogenic cells
Osteoblasts
Osteocytes
Bone lining cells
Osteoclasts
What are osteogenic cells?
Also called osteoprogenitor cells - STEM CELLS
Mitotically active stem cells in periosteum and endosteum
When stimulated differentiate into osteoblasts or bone lining cells [some persist as osteogenic cells]
What are osteoblasts?
Matrix-synthesizing cell responsible for BONE GROWTH
Secrete unmineralized bone matrix or osteoid [Includes collagen and calcium-binding proteins][Collagen = 90% of bone protein]
Actively mitotic
What protein makes up 90% of bone protein?
collagen
What are Osteocytes?
MATURE bone cells in lacunae
Monitor and maintain bone matrix
Act as stress or strain sensors
Respond to and communicate mechanical stimuli to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur
What are osteoclasts?
*cells that destroy bone
*Derived from hematopoietic stem cells that become macrophages
*Giant, multinucleate cells for bone resorption
*When active rest in resorption bay and have ruffled border
[Ruffled border increases surface area for enzyme degradation of bone and seals off area from surrounding matrix]
What are bone-lining cells?
Flat cells on bone surfaces believed to help maintain matrix
On external bone surface called periosteal cells
Lining internal surfaces called endosteal cells
What are the characteristics of Compact Bone?
*aka lamellar bone
*Osteon or haversian system
[Structural unit of compact bone]
*Elongated cylinder parallel to long axis of bone
*Hollow tubes of bone matrix called lamellae [Collagen fibers in adjacent rings run in different directions;
Withstands stress – resist twisting]
What is the structural unit of compact bone?
Osteon or haversian system
Note: Canals and canaliculi
Central (haversian) canal runs through core of osteon
Contains blood vessels and nerve fibers
Perforating (volkmann’s) canals
Canals lined with endosteum at right angles to central canal
Connect blood vessels and nerves of periosteum, medullary cavity, and central canal
Where do you find canaliculi in compact bone?
in compact bones; these hairlike canals connect lacunae to each other and central canal
What is ossification (osteogenesis)?
*Process of bone tissue formation
*Formation of bony skeleton
Begins in 2nd month of development
*Postnatal bone growth
until early adulthood
*Lifelong Bone remodeling and repair
How are canaliculi formed in compact bone?
Osteoblasts secreting bone matrix maintain contact with each other and osteocytes via cell projections with gap junctions
When matrix hardens and cells are trapped the canaliculi form
Allow communication
Permit nutrients and wastes to be relayed from one osteocyte to another throughout osteon
What are lamellae in compact bone?
**Interstitial lamellae
[Incomplete lamellae not part of complete osteon
Fill gaps between forming osteons
Remnants of osteons cut by bone remodeling]
**Circumferential lamellae
[Just deep to periosteum
Superficial to endosteum
Extend around entire surface of diaphysis
Resist twisting of long bone]
Name two types of lamellae in compact bone.
*Interstitial lamellae
*circumferential lamellae
What are the characteristics of spongy bone?
Appears poorly organized
Trabeculae [Align along lines of stress to help resist it][No osteons]
[Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi
Capillaries in endosteum supply nutrients]
What is osteoid?
1/3 of organic bone matrix is secreted by osteoblasts
Made of ground substance (proteoglycans and glycoproteins)
Collagen fibers
Contributes to structure; provides tensile strength and flexibility
What are the organic components of bone?
Include cells and matrix: Osteogenic cells, osteoblasts, osteocytes, bone- lining cells, and osteoclasts, as well as osteoid
What makes bones resilient?
sacrificial BONDS in or between COLLAGEN molecules stretch and break easily on impact to dissipate energy and prevent fracture. If no additional trauma, bonds re-form
What are the Inorganic components of bone?
Hydroxyapatites (mineral salts)
*65% of bone by mass
*Mainly of tiny calcium phosphate crystals in and around collagen fibers
*Responsible for hardness and resistance to compression
Why do bones last long after death?
because of their mineral composition
What are growth arrest lines on bones?
Reveal information about ancient people
These horizontal lines on bones can reveal information about ancient people such as proof of illness - when bones stop growing so nutrients can help fight disease
Compare and contrast the strength of bone vs. steel
Half as strong as steel in resisting COMPRESSION
As strong as steel in resisting TENSION
Identify two types of ossification
Endochondral ossification
Intramembranous ossification
What is endochondral ossification?
Bone forms by replacing hyaline cartilage
Bones called cartilage (endochondral) bones
Forms most of skeleton
What is intramembranous ossification?
Bone develops from fibrous membrane
Bones called membrane bones
Forms flat bones, e.g. clavicles and cranial bones
How do bones grow after birth?
INTERSTITIAL (longitudinal) growth
Increase in length of long bones
APPOSITIONAL growth
Increase in bone thickness
How do long bones grow interstitially?
Near end of adolescence chondroblasts divide less often
Epiphyseal plate thins then is replaced by bone
Epiphyseal plate closure:
*Bone lengthening ceases –Requires presence of cartilage
*Bone of epiphysis and diaphysis fuses
*Females – about 18 years
*Males – about 21 years
How do long bones grow appositionally?
*Allows lengthening bone to widen
*Occurs throughout life
*Osteoblasts beneath periosteum secrete bone matrix on external bone
*Osteoclasts remove bone on endosteal surface
*Usually more building up than breaking down – Thicker, stronger bone but not too heavy
How do bones maintain homeostasis?
Recycle 5-7% of bone mass each week
Spongy bone replaced ~ every 3-4 years
Compact bone replaced ~ every 10 years
What regulates the continuous remodeling of bones?
Negative feedback hormonal loop for Ca2+ homeostasis
Controls blood Ca2+ levels; Not bone integrity
Responses to mechanical and gravitational forces
What are the most common causes of fractures in youth?
trauma
What are the most common causes of fractures in old age?
result of weakness from bone thinning
What the 3 either/or fracture classifications?
1) Position of bone ends after fracture
2) Completeness of break
3) Whether skin is penetrated
What is the difference between displaced and non displaced fractures?
whether bone ends retain normal position or are out of normal alignment
What is the difference between complete and incomplete fractures?
whether the bone is broken all the way through or not
What is the difference between open (compound) and closed (simple) fractures?
whether the skin is or is not penetrated
Describe a comminuted fracture
bone fragments into 3 or more pieces. common in elderly people
Describe a compression fracture
bone is crushed. common in porous bones (e.g. osteoporotic bones) subjected to extreme trauma, as in a fall
Describe a spiral fracture
ragged break occurs when excessive twisting forces are applied to a bone; common in sports
Describe an epiphyseal fracture
epiphysis separates from the diaphysis along the epiphyseal plate.
tends to occur where cartilage cells are dying and calcification of the matrix is occurring
Describe a depressed fracture
broken bone portion is pressed inward (typical of skull fracture)
Describe a greenstick fracture
bone breaks incompletely, like a green twig. Only one side of the shaft breaks; the other side bends.
Common in children whose bones have relatively more organic matrix and are more flexible than those of adults.
Name the 4 stages in the healing of a bone fracture
1) hematoma forms
2) fibrocartilaginous callus forms (internal callus of fibrous tissue and cartilage)
3) bony callus forms (bony callus of spongy bone)
4) bone remodeling occurs
When treating a fracture, what is reduction?
realignment of broken bone ends
What is the difference between a closed reduction and open reduction treatment of a fracture?
Closed reduction – physician manipulates to correct position
Open reduction – surgical pins or wires secure ends
How is a fracture immobilized during treatment?
by cast or traction for healing
Depends on break severity, bone broken, and age of patient
what two treatment modalities are used in fractures?
1) reduction
2) immobilization
Describe the 4 steps in intramembranous ossification.
1) ossification centers appear in the fibrous connective tissue membrane
2) osteoid is secreted within the fibrous membrane and calcifies
3) woven bone and periosteum form
4) lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears
Where do you find hyaline cartilage and what is its function?
Hyaline cartilage is lubricated cartilage that remains only in the epiphyseal plates and articular cartilages.
Support, flexibility, and resilience
Collagen fibers only; most abundant type
Articular, costal, respiratory, nasal cartilage
Flat bones consist of a layer of spongy bone sandwiched between 2 thin layers of compact bone.
A
The structure of the long bone of the arm.
The structure of a long bone (humerus).
The structure of a long bone - humerus.
types of bone cells
Microscopic anatomy of compact bone
Intramembranous Ossification
Long Bone Growth vs Remodeling
Stages in the healing of a bone fracture
