SKELETAL SYSTEM Flashcards
Summarize the functions of the skeletal system.
Framework for body - structure and support
Movement at joints
Protects internal organs (brain, heart, lungs, GI tract)
Produce blood cells - red & white cells produced within red bone marrow from hematopoietic stem cells
Store triglycerides - adipocytes stored in yellow bone marrow in medullary cavity
Store & release minerals - calcium and phosphate stored in extracellular matrix
Distinguish the axial and appendicular skeletons.
Axial
- 80 bones
- head and trunk
- encloses and protects body cavities
Appendicular
- 126 bones
- upper and lower limbs
- supports movement and locomotion
Distinguish compact and spongy bone.
Compact bone - external dense layer
Spongy bone - internal porous layer (surrounded by compact bone)
Medullary cavity - hollow space (surrounded by spongy bone
Categories of bones: Long
Found in limbs; Length > width
Upper
- clavicle
- radius
- ulna
- metacarpals
- phalanges
Lower
- femur
- tibia
- fibula
- metatarsals
- phalanges
Parts
- epiphyses: ends of bones
- diaphysis: shaft of bone (with medullary cavity)
- metaphases: in between
Categories of bones: Short
Found in wrists and ankles; length = width
Carpals in hands, tarsals in feet
Layer of compact bones surrounding spongy bone
Categories of bones: Sesamoid
Develop in tendons (with friction) found in knee and in front of thigh
Patella in quadriceps femoris tendon
Pisiform in flexor carpi ulnaris tendon
Categories of bones: Flat
Thin bones that protect body cavities
Including:
Bones of calvaria (skull cap)
Scapulae
Ribs
Sternum
Pelvic girdle
Two plates of compact bone surrounding inner layer of spongy bone
Categories of bones: Irregular
Shapes that do not fall into other categories
Including
- bones of the face
- vertebrae
- sacrum
Which types of bones make up the axial skeleton? Appendicular?
Axial - Flat (skull, ribs, sternum) and irregular (sacrum, vertebrae)
Appendicular - Long, short, sesamoid
Describe the basic development and functions of the cells in bone tissue.
- Osteoprogenitor cells - stem cells of bones; divide into osteoblasts
- Osteoblast - build up bone; secrete organic bone matrix and begin process of calcification (hydroxyapatite)
- Osteocytes - osteoblasts become trapped in mineralized extracellular matrix then transition into osteocytes, which are mature cells that maintain bone and detect forces
- Osteoclast - formed by fusion of monocytes (large blood cells from bone marrow); multinuclei; release enzymes and acids to break down bone at *ruffled border (deeply folded plasma membrane)
Describe the contents of the extracellular matrix of bone tissue.
Extracellular matrix/ bone matrix
Inorganic
- 55% bone minerals
- calcium phosphate and calcium hydroxide create hydroxyapatite (hardness of bones) called calcification
Organic
- 30% unmineralized
- made up of collagen fibers (flexibility of bone), ground substance and 15% water
Explain the tensile strength of bone in relation to the extracellular matrix.
Only bone minerals - hard and fragile
Only organic matrix - too flexible
Both - hard bone with tensile strength
Distinguish the periosteum and endosteum.
Periosteum (associated w/ compact bone)
- connective tissue layer
- external fibrous
Endosteum (associated w/ spongy bone)
- connective tissue layer that lines the medullary cavity
Describe the organization of bone tissue.
Spongy bone
- oriented along lines of stress
- strength in compression
- spongy/trabecular/cancellous
Compact bone
- oriented longitudinally
- strength in bending
- compact/cortical/dense
Describe the location of osteocytes within bone tissue.
Osteocytes found in between lamallae (circular plates of bone)
Trabeculae in spongy bone, osteon in compact bone
In compact bone
- layers in osteon called concentric lamellae
- space between osteons filled with broken down osteons are interstitial lamellae
- large plates that surround internal and external circumferences are circumferential lamellae
Overall, osteocytes are found between concentric lamellae, within compact bone, and within spongy bone.
Describe the location of blood cell production.
BONE MARROW
- found within hollow portions of bone such as extensive spongy bone or within medullary cavity
Red bone barrow
- supports blood cell formation and filters out old blood cells
- * red & white blood cells produced within red bone marrow from hematopoietic stem cells
- typically ends of bones (spongy)
Yellow bone marrow
- supports vasculature within the medullary cavity
- fat cells & storage
Describe the major pathways of neurovasculature within a bone.
Nutrient vasculature within medullary cavity (big veins)
Periosteal vasculature remains superficial and supplies external surfaces of bones (small veins)
Each individual osteon supplied by capillaries within the central canal
Communicative branches run perpendicular through interosteonic canals (communicate between osteons and connect sources of blood.
Innervation - sensory nerves reach all aspects of bone by following blood vessels
* BUT only periosteum receives SOMATIC info (localized info; pain info)
Describe typical bone formation during embryonic development.
A mesenchymal (embryonic connective tissue) skeleton is formed by week 6 of development
At birth:
- joints remain between flat bones of skull that will later ossify
- bones forming thru intramembranous ossification are ossified
- diaphyses of long bones are ossified and have developed a medullary cavity
Describe intramembranous ossification and identify the bones that form from this process.
Bone formation within Mesenchyme (most direct way of bone formation)
- Differentiation of osteoprogenitor cells
- Turn into osteoblasts due to blood supply, which build bone and initiate calcification
- Osteoblasts become trapped and turn into osteocytes
- Osteoclasts remove parts of bone and result in internal spaces around trobeculae of spongy bone
- Periosteum forms (both outer protective fibrous layer and inner cellular layer); dormant osteoprogenitor cells lie deep in periosteum
Bones formed:
- most bones of the skull (facial bones and flat bones of calvaria)
- Majority of the clavicle
Describe endochondral ossification and identify the bones that form from this process.
First cartilage model forms within mesenchyme, then bone forms within cartilage model
- Chondroblasts replace mesenchymal model with hyaline cartilage, which then grows in length and width
- Blood vessels bring osteoprogenital cells which transition into osteoblasts, which initiate calcification (bone collar/periosteal collar is formed at diaphysis)
- Formation of bone collar leads to formation of primary ossification center made by osteoblasts
- Osteoclasts enter to remove debris and begin formation of trobeculae and intermedullary cavity
- Blood vessels infiltrate epiphyses at secondary ossification center (spongy bone forms)
- Interstitial growth
- Eventually epiphyseal plates are replaced by bone and called epiphyseal lines (growth in length stops)
- Hyaline cartilage remains on ends of bones as articular cartilage (periosteum attaches everywhere but where hyaline cartilage is)
Bones formed:
- base of the skull (sphenoid, occipital, and ethmoid)
- most bones of the body
Differentiate interstitial and appositional growth.
Interstitial growth
- growth in bone length
- occurs through endochondral ossification at epiphyseal plates (growth plate)
- adds bone on diaphysis side
Appositional growth
- growth in bone width (due to pull of skeletal muscles)
- occurs on surface of bone or superficial to medullary cavity (near periosteum)
Define bone remodeling. Which type of bone typically remodels at a faster rate?
Old bone replaced by new bone
5-10% of bone remodeled per year
Spongy bone (20% per year) remodels faster than compact bone (4% per year)
Resorption - osteoclasts break down bone matrix and release minerals into blood
Deposition - osteoblasts lay down new bone; addition of minerals and collagen
Cells involved in remodeling - osteoprogenitors, osteoblasts, and osteoclasts (distributed in periosteum, endosteum, and intersteonic canals); osteocytes recruit either osteoblasts (build new area) or osteoclasts (remove weak area)
Describe the minerals stored in high quantities in bone.
Bone contains 99% of calcium and 85% of phosphorus in the body
Explain why minerals would be released from bone.
Bone contains minerals such as calcium and phosphate. Resorption is how these minerals are freed into the blood.
