BIOL2217 9/21- 10/8

Functions of the skeletal system:

1.)

2.)

3.)

4.)

5.)

1.) support (supports the body)

2.) protection (protects internal organs)

3.) attachment for muscles (facilitates movement)

4.) energy and mineral reserves (stores and releases fat/stores and releases minerals)

5.) hemopoiesis (produces blood cells)

Bone is what kind of tissue?

Connective tissue

Cells of bone

Osteoblasts and osteoclasts

Osseous tissue (compared to cartilage, materials, nutrients?)

Denser and more durable than cartilage… organic and inorganic components (resistant to compression and tension)… highly vascular

Osteoblasts

Secrete osteoid which mineralizes later… way to remember: osteoblasts=build

Osteocytes

Osteoblasts trapped in matrix… functions: maintain matrix, repair damage, sense mechanical stretch

Osteoclasts

Break down bone matrix… function: bone remodeling… way to remember: osteoclast=consume

Extracellular matrix

Part of the skeletal structure… made up of protein fibers (collagen) and ground substance (mineralized osteoid)… combination of organic and inorganic makes bones strong and slightly flexible

Composite material > organic and inorganic components

Organic: osteoid (collagen fibers, carbs, proteins), tensile strength

Inorganic: hydroxyapatite (calcium, phosphorus, oxygen), compressive strength

Rickets/osteomalacia

Disorder of skeletal matrix

Inadequate calcification of bone ECM (usually from vitamin D deficiency)

Bones are soft and easily deformed

Osteogenesis imperfecta

Disorder of skeletal matrix

Congenital defect of collagen

Bones are brittle and easily fractured

Cortical bone

Compact form of bone… the dense outer shell

Cancellous bone

Spongy form of bone… loosely organized interior bone

Cortical bone stucture

Organized into osteons… concentric lamellae (layers) of EMC… Central canal for passage of neurovasculature… oriented parallel to direction of compressive stress

Osteon stucture

Alternating collagen fiber orientation… multidirectional stability… resistance to torsion (twisting in opposite directions)

Cancellous bone structure

Bones arranged in lattice (strong but lightweight, no osteons)… spaces sometimes filled with red bone marrow… helps absorb and transmit forces

Periosteum

Layers of dense irregular connective tissue… periosteum is external covering… highly innervated… function in growth and repair (produce osteoblasts)

Endosteum

Layers of dense irregular connective tissue… endosteum is internal lining… highly innervated… function in growth and repair (produce osteoblasts)

Long bones

Longer than wide

Support and movement

Flat bone

Thin, often curved

Protection

Irregular bones

Complex shapes

Support and protection

Short bones

Cube-like shape

Stabililty and movement

Sesamoid bones

Form in tendons

Movement

Long bone stucture

Epiphyses- enlarged ends, which have cancellous bone internally and red bone marrow… articular cartilage externally

Diaphysis- shaft, which is cortical bone with medullary cavity (yellow bone marrow)

Flat/short/irregular bones stucture

Cancellous bone surrounds by cortical bone (no medullary cavity)

Protect underlying structures, shock absorption

Ossification

Bone formation… begins around embryonic week 8…intramembranous or endochondral

Intramembranous ossification step 1 and 2

Primary ossification center forms within fetal connective tissue… osteoblasts develop and begin to secrete osteoid… mineral crystals are incorporated so osteoblasts become osteocytes

Intramembranous ossification step 3

Osteoblasts produce cancellous bone trabeculae… surrounding connective tissue becomes periosteum

Intramembranous ossification step 4

Cortical bone forms on exterior surface… produces some bones of skull, clavicles

Endochondral ossification step 1

Beings with cartilaginous model covered by perichondrium… perichhondrium starts to produce osteoblasts = becomes periosteum

Endochondral ossification step 2

Bony collar forms around shaft (early cortical bone)… enlargment of chondrocytes and calcification of EMC at primary ossification center… calcification (deposition of minerals in matrix other than osteoid)… nutrients unable to diffuse through calcified ECM = chondrocytes die

Endochondral ossification step 3

Osteoclasts penetrate bony collar… break down calcified cartilage to form primary medullary cavity (only in long bones)… osteoblasts, blood vessels, and bone marrow enter… bony collar expands… secondary ossificetions center develop at epiphyses

Endochondral ossification step 4

Cartilaginous model enlarges… bony collar and primary medullary cavity expands… calcification of secondary ossification centers… osteoblasts secrete osteoid over calcified cartilage to form cancellous trabeculae… developmental stage of bone at birth… continues to develop postnatally

Endochondral ossification step 5

Bone ossification continues during early childhood… articular cartilage (hyaline cartilage retained on epiphyses)… epiphyseal plate (site of continued bone growth) which is present through early childhood and body growth

Endochondral ossification step 6

Epiphysial fusion marks end of skeletal growth… bone completely ossified… only articular cartilage remains (caps to form joints)

Note: only long bones have a medullary cavity

Note: only long bones have a medullary cavity

Primary bone

Immature… produced by osteoblasts very quickly…benefit: quick, good for initial skeletal element or bridging a fracture site… cons: haphazardly built, little inorganic (mineralization) matrix, irregularly arranged collagen fibers… eventually reabsorbed and replaced by secondary bone

Secondary bone

Mature bone… produced much slower than primary… fully formed osteons… parallel collagen orientation… higher percentage of inorganic material (mineralization) = stronger

Bone marrow

Type of tissue/organ… two different types (red and yellow)

Red bone marrow

Hematopoietic tissue… children have it in every bone, adults have it in the head and trunk…

Yellow bone marrow

Fat storage… replaces red bone marrow of children as we age… adults have it in the limbs

Longitudinal bone growth

Occurs at epiphyseal plate condrocytes divide and mature (push epiphysis away from diaphysis)… cartilage matrix ossifies and is replaced with bone… rates of growth and ossification balance during childhood (continues as long as proliferative zone is active)

Zones: zone of reserve cartilage (inactive chondrocytes)… zone of proliferation (rapid cell division)… zone of hypertrophy (chondrocytes increase in size)… zone of calcification (dead chondrocytes, calcified matrix)… zone of ossification (osteoblasts ossify calcified cartilage)

Zones of longitudinal bone growth

Zone of reserve cartilage (inactive chondrocytes)… zone of proliferation (rapid cell division)… zone of hypertrophy (chondrocytes increase in size)… zone of calcification (dead chondrocytes, calcified matrix)… zone of ossification (osteoblasts ossify calcified cartilage)

Epiphyseal plate closure

Proliferation rate slows near end of adolescence… cartilaginous tissue overtaken by ossification… epiphyseal plate ossifies entirely = fusion/closure which is the end of longitudinal growth

Achondroplasia

Failure of cartilage growth in epiphyseal plate (results of spontaneous mutation)… long bones stop growing in childhood… disproportionately short limbs

Appositional growth

Occurs at periosteal surface… periosteal osteoblasts secrete new matrix (new cortical bone develops superficially)… osteoclasts erode medullary cavity (bone widens but remains proportional)… can continue after cessation of longitudinal growth (due to additional force/muscle activity or response to increase in body weight, in addition to other reasons)

Hormonal regulation of bone growth

Growth hormone increases chondrocyte cell division at epiphyseal plate, increases activity os osteogenic cells, and stimulates osteoblasts in periosteum… growth hormone is responsible for development in adolesense… testosterone increases appositional growth and increases chondrocyte cell divison… estorigen inhibits osteoclast activity and accelerates epiphyseal closure

Growth hormone impact on bone growth

Increases chondrocyte cell division at epiphyseal plate

Increases activity os osteogenic cells

Stimulates osteoblasts in periosteum

Growth hormone is responsible for development in adolescence

Testosterone impact on bone growth

Increases appositional growth

Increases chondrocyte cell divison

Estrogen impact on bone growth

Inhibits osteoclast activity

Accelerates epiphyseal closure

Which is an adult, a or b?

B

Skeletal remodeling: function

Reshape bone during growth

Reshape bone in response to use

Repair damage

Release minerals in blood

Skeletal remodeling occurs where

Occurs on periosteal and endosteal surfaces

Skeletal remodeling: deposition

Osteoblasts secrete osteoid (collagen fibers arranged in a spiral pattern along osteon), mineralization occurs (calcium and phosphate crystalize on collagen fibers as hydroxyapatite)

Skeletal remodeling: rebsorption

Osteoclasts dissolve bone and return minerals to blood… secrete H+ ions and enzymes

Regulation of remodeling: calcium homeostasis

Needed for neuron signaling, muscle contraction, blood clotting… balance between intake, excretion, and exchanges between skeleton and blood… regulated by calcitriol, calcitonin, and parathyroid hormone

Calcitriol

The active form of vitamin D… produced by actions of skin, liver, and kidney (initiated by UV radiation)… Raises blood calcium levels (which promotes calcium absorption in small intestine, increases calcium resorption for skeleton, reduces calcium excetion in kidneys)

Calcitonin

Secreted by thyroid in response to hypercalcemia… it inhibits osteoclasts and stimulates osteoblasts

Parathyroid hormone (PTH)

Secreted by parathyroid glands in response to hypocalcemia… stimulates osetoclast activity, inhibits osteoblast activity… reduces calcium excretion in kidneys… promotes calcitriol synthesis

Regulation of remodeling: mechanical stress

Stress: force/area

More bone deposition in areas under high stress (monitored by osteocytes)

Wolff’s law: bones remodel in response to habitual demands… compact bone is thickest in diaphysis… large projections occur where heavy, active muscles attach… exercise increases bone formation

Wolff’s law

Bones remodel in response to habitual demands… compact bone is thickest in diaphysis… large projections occur where heavy, active muscles attach… exercise increases bone formation

Orthodontic braces

Wires place tension on the teeth, alveolar bone is resorbed in response to increased pressure (allows teeth to shift)… additional bone deposited to fill in spaces

Fractures

Two types: stress fractures and pathological fractures

Stress: caused by abnormal trauma to a bone

Pathological: break in bone weakened by disease

Healing of fractures: step 1

Inflammatory response

Blood clot formation (clot invaded by blood vessels, fibroblasts, macrophages, osteoclasts, osteoblasts, chondrocytes) and those invasions produce granulation tissue

Healing of fractures: step 2

Soft callus formation

Fibroblasts secrete collagen, chondrocytes produce fibrocartilage

Healing of fractures: step 3

Hard callus formation

Osteoblasts produce bony collar around fracture… takes 4-6 weeks

Healing of fractures: step 4

Remodeling

Osteoclasts remove bon fragments, osteoblasts lay down cancellous bone, continued ossification produces cortical bone

Effects of aging

Children and adolescents: deposition>resorption (greatest period of bone growth, attainment of peak bone mass)

Young adults: deposition=resorption

Older adults: deposition<resorption (bone mass, mineralization, and healing ability decrease)

Osteoporosis

Excessive resorption leads to severe loss of bone density… cancellous bone of spine and femur are the most vulnerable (vertebral and hip fractures are common)… related to decline in estrogen production (postmenopausal women have greatest risk, occasionally in younger females with very low body fat)… Other risk factors = race, smoking, diabetes, nutritional deficit, activity level

Osteoporosis treatment and prevention

Treatments= estrogen replacement therapy (which increase risk of heart disease, stoke, breast cancer), medications, weight bearing exercise, nutritional supplements

Preventative behaviors= calcium-rich diet and weight bearing exercise increase peak bone mass… reduced consumption of alcohol and carbonated drinks

Axial skeleton

Skull, hyoid, vertebra, ribs/sternum

Appendicular skeleton

Clavicle, scupula, upper limb, os coxae, lower limb

Cranial bone function

Protect brain

Attachment sites for head/neck muscles

Facial bone function

Form the framework of face, hold the teeth, and anchor muscles of the face

Cranial bones (6)

Parietal, occipital, frontal, temporal, sphenoid, and ethmoid (others: occipital condyles and foramen magnum)

Sutures

Immobile joints, filled with dense connective tissue… wide and flexible during infancy (easier passage through birth canal and allows for brain growth)… interdigitate (get closer) as cranial bones grow… fuse over time

Major sutures (4)

Coronal, sagittal, squamous, and lambdoid

Vertebral column (numbers and sections)

26 total= 7 cervical, 12 thoracic, 5 lumbar, 5 sacral (fused into 1), 4 coccyx (fused into 1)

Vertebral column functions

Protect spinal cord, support body axis, attachment points for ribs and muscles of back and neck

Basic vertebral anatomy

Articular processes/facets (superior and inferior), vertebra arch, vertebral body, vertebral foramen, transverse process, spinous process

Spinous and transverse process function

Muscle and ligament attachment sites

Cervical vertebra

C1-C7, top two different (atlas which has no body and a large superior articular facet and axis which has a dens)

All cervical vertebrae are distinguishable because they have transverse foramina (which transmit vertebral arteries)

Atlas (C1)

No body, superior articular facet articulates with occipital condyle, atlano-occipital joint allows for head flextion and extension

Axis (C2)

Modified body (dens), atlas-axis joint allows heat L/R rotation

Thoracic vertebrae

T1-12, has costal facets (which articulate with ribs)

Lumbar vertebrae

L1-5, large bodies and lack of other structures

Intervertebral discs

Fibrocartilage with gel-like center, join vertebrae into column, allow for mobility, and cushion/absorb force

Ribs

12 pairs

1-7=true ribs that attach to sternum by costal cartilages

8-10=false ribs that attach to sternum via shared cartilage

11 and 12=floating ribs

All are attached to the thoracic cage

Thoracic cage

Protects underlying organs and attachment site for respiratory muscles

Rib structure

Body/shaft: main portion

Head and tubercles: articular surfaces

Angle: most lateral point

Costal groove: channel for neurovasculature

Clavicle

Provides muscle attachment, braces scapula and arms (only point of attachment between upper limb and axial skeleton), only intramembranous long bone

Pectoral girdle: scapula

Acromion articulates with clavicle, glenoid fossa articulates with humerus, other fossae: muscle attachment sites

Humerus

Articulations: proximal (scapula) distal (radius, ulna)

Fossae: articulate with ulna

Tubercles/tuberosities: muscle attachment

Ulna and radius

Ulna: olecranon forms majority of elbow

Radius: head allows for rotation

Styloid processes: ligament attachment sites

Interosseous membrane: Dense connective tissues and allows rotation while maintaining spatial relationships

Os coxae

AKA innominate bones

Formed from fusion of ilium, ischium (ischial tuberosity: hold weight while sitting), pubis (pubic symphysis: anterior articulation via interpubic disc)

Acetabulum: articular site for femur and composed of all three bone

Pelvic sexual dimorphism

90° or less space in pelvic girdle=male

100° or more=female

Femur

Articulation: proximal (acetabulum) distal (tibia and patella)

Large trochanters and epicondyles=muscle attachments

Fractures most frquently at neck

Patella

Largest sesamoid bone

Cartilaginous at birth (ossifies at age 3-6)

Anchored to rectus femoris proximally and tibia distally

Tibia and fibula

Tibia: receives and transmits body weight, flat anterior surface→shin, articulations (proximal: femur, patella, fibula… distal: talus, fibula)

Fibula: stabilizes ankle, articulations (proximal: tibia… distal: tibia, talus)

Interosseous membrane

Carpals

Allow wrist to be very flexible and mobile

Pisiform: sesamoid bone, develops by age 12

Scaphoid most frequently fractured (FOOSH)

Tarsals

Calcaneus→heel (attachment for achilles tendon)

Talus: articulates with tibia and fibula

Calcaneus and talus bears most of weight