Week 2: Skeletal System Flashcards
What are skeletal structures?
- The axial skeleton: Portion of the skeleton located along the midline of the body
- The appendicular skeleton: All other bones of the skeleton (names such because they are appendages of the axial skeleton)
- Upper and lower limbs (includes girdles)
- Pectoral and pelvic girdles
- Arm, forearm and hand
Thigh, leg and foot
Landmark that forms joint: Condyle
Large rounded knobs at the end of a bone that forms articulations with other bones e.g. lateral condyle of the femur
Landmark that forms joints: Facet
Smooth, flat (maybe slightly concave or convex) articular surface e.g. Superior articular facet of the vertebra
Landmark that forms joints: Head
Usually rounded articular surface supported on the neck. The epiphysis of a long bone e.g. head of the humerus
Landmarks for connective tissue attachment points: Crests
Prominent raised edged of bone or elongated projections e.g. iliac crest of the hip
Landmarks for connective tissue attachment points: Epicondyle
a roughened projection that sits above a condyle e.g. lateral epicondyle of the femur
Landmarks for connective tissue attachment points: Line (linea)
A long narrow ridge or border (less prominent than a crest) e.g. linea aspera of femur
Landmarks for connective tissue attachment points: Process
A bulging bony outgrowth of a larger bone e.g. mastoid process of the temporal bone
Landmarks for connective tissue attachment points: Protuberance
Similar to processes, they are either a swelling, bulging or protruding part of a bone e.g. mental protuberance of the mandible
Landmarks for connective tissue attachment points: Spinous process
A sharp slender projection e.g. spinous process of the vertebra
Landmarks for connective tissue attachment points: Trochanter
A very large irregularly shaped projection e.g. only present on the femur e.g. greater and lesser trochanters
Landmarks for connective tissue attachment points: Tubercle
Variably sized, rounded projections e.g. grater tubercle of the humerus
Landmarks for connective tissue attachment points: Tuberosity
Similar to tubercle but often with a rough surface e.g. maxillary tuberosity
Openings/depressions allowing passage of soft tissue or formation of joints: Fissure
A narrow slit between adjacent parts of bones e.g. superior orbital fissure of the sphenoid bone
Openings/depressions allowing passage of soft tissue or formation of joints: Foramen
An opening or hole in the bone e.g. mental foramen of the mandible
Openings/depressions allowing passage of soft tissue or formation of joints: Fossa
A broad and shallow depression in the bone e.g. temporal fossa
Openings/depressions allowing passage of soft tissue or formation of joints: Meatus
A tubelike channel extending into the bone e.g. external auditory meatus of the temporal bone (ear canal)
Openings/depressions allowing passage of soft tissue or formation of joints: Notch
An indentation at the edge of a structure e.g. scapular notch
Openings/depressions allowing passage of soft tissue or formation of joints: Sulcus
A furrow along a bone surface e.g. intertubercular sulcus of the humerus
Bone Formation: Ossification
- The formation and remodeling of bone tissue
- Begins during early embryonic development
- Finishes at the end of life
Both methods involve the replacement of pre-existing connective tissue wit bone
What are the two types of bone ossification?
Intramembranous ossification: Bones form in embryonic tissue membranes. e.g. flat bones of the skull, many bones of the face, mandible and medical clavicle
Endochondral ossification: Bones form in embryonic hyaline cartilage. e.g. all other bones that are not mentioned above
What are the bone cells?
- Osteogenic cell: Stem cell that develops into an osteoblast
- Osteoblast: Produces organic components of bone matrix (proteins, collagen) e.g. lays down new bone
- Osteoclast: Resorbs (removes) bone
Osteocyte: Maintains bone matrix
Intramembranous ossification: Steps 1 and 2
Step 1. Development of the ossification center
- At the site of bone development, and in response to specific chemical messages, mesenchymal cells (stem cells that form connective tissue) cluster together
- Mesenchymal cells differentiate: Osteogenic cells > Osteoblasts
Osteoblasts secrete bone matrix until they are surrounded by it
Step 2: Ossification
- Osteoblasts become trapped in bone matrix > Osteocytes
- Osteocytes sit in lacunae (small cavities)
Calcium and other minerals are deposited and bone matrix hardens (calcifies)
Intramembranous ossification: Step 3 and 4
Step 3: Formation of trabeculae
- Blood vessels grow into the area to provide nutrients and delivery of osteoclasts
- Osteoclasts resorb bone and cause the formation of trabeculae (spongey appearance)
Connective tissue associated with blood vessels differentiates into red bone marrow
Step 4: Development of periosteum (hard layer outside a bone)
- Continued bone remodeling forms typical bony product
- Thin layer of compact bone replaces surface layers of trabecular/spongey bone
Mesenchyme condenses at the periphery and develops into the periosteum
What is Intramembranous ossification?
Bone formation within the embryonic tissue membranes
What is endochondral ossification?
- Bone formation within the cartilage model: Long bone example
- Forming in a cartilage model
- Children still have a lot of bones made of cartilage when born, as they are not hard yet
A lot don’t turn hard until years and years old, and bones aren’t fully bone until around 30 (depends on individual)
Endochondral ossification: Step 1 and 2
Step 1: Development of cartilage model
- Mesenchymal cells respond to specific chemical messages and group together in the shape of the future bone
- Mesenchymal cells differentiate > chondroblasts (cartilage-forming cells)
Chondroblasts secrete cartilage matrix, producing a cartilage model made of hyaline cartilage
Step 2: Growth of the cartilage model
- Chondroblasts become buried within the cartilage> chondrocytes
- Cartilage model grows: Growth in length by continual cell division of chondrocytes and matrix secretion (interstitial growth). Growth in width due to deposition of matrix on the external surface (appositional growth)
- Osteogenic cells within the perichondrium differentiate > osteoblasts
Osteoblasts lay down superficial bone to form edges of diaphysis
Endochondral ossification: Step 3 and 4
Step 3: Development of the primary ossification center
- A nutrient artery penetrates cartilage at diaphysis
- Osteoblasts enter alongside blood vessels to produce spongy bone template within cartilage model diaphysis (primary ossification center)
Bone growth increases and spreads towards both ends of the cartilage model
Step 4: Remodeling of the primary ossification center/development of the medullary cavity
- Osteoclasts enter via blood vessel and remove the spongey bone template (formation of the medullary cavity)
- Osteoblasts lay down new bone to form cortical/compact bone) at the diaphysis
Cartilage and bone continues to grow increasing the size of the model
Endochondral ossification: Step 5
Step 5: Development of the secondary ossification centers
- Blood vessels penetrate the cartilage at the epiphyses (heads)
Osteoblasts follow and lay down spongey bone (secondary ossification centers, unlike primary, spongey bone remains in epiphyses (not remodeled into a cavity))
Endochondral ossification: Step 6
Step 6: Formation of epiphyseal growth plate
- Epiphysis is remodeled to form spongey (trabecular) bone (contains bone marrow)
- The line dividing the epiphysis and the metaphysis remains as cartilage until adulthood (specific age varies depending on bone)
- While the line is still cartilages = epiphyseal growth plate
- Cartilage of the growth plate continues to lengthen the long bone (interstitial growth)
- When the line ossifies at adulthood = epiphyseal line
- Cartilage on the very ends of the epiphysis remains as cartilage and forms the articular surface
- Only fully mature bone at 18-21
- Before then most people still have growth plates
- If not growth plate/chondroblasts, it is all fused to bone (no cartilage) so no more growth occurs
Ends of epiphyses, articular/hyaline remains cartilage and cartilage surface
What happens if a child breaks their growth plate
If a child fractures their growth plate, bone formation is different to bone remodeling/repair, so if the epiphyseal line is broken, then it will be replaced with new bone rather than cartilage, and bone can’t grow. Therefore, if the epiphyseal line is broken in the leg, their leg stops growing and will be shorter than the other.
Bone remodeling: overview
- Process of bone cells removing old bone and replacing with new bone continuously
- In normal circumstances osteoclasts remove bone at the same rate that osteoblasts form new bone (balance)
- Disruption of this balance can lead to bone pathology e.g. osteoporosis
Bone remodeling process?
- Osteoclasts attach to the endosteum or periosteum forming a seal at the edges
- Osteoclasts release lysosomal enzymes and various acids into the sealed pocket
- The acids dissolve the bone minerals while the lysosomal enzymes break down the organic components
- Bone resorption (loss) results
- Following osteoclastic activity, osteoblasts move in the area
- Osteoblasts deposits minerals and collagen fibers (components of bone extracellular matrix)
Bone formation (growth) results
Factors effecting bone remodeling:
- If osteoblasts are more active = more bone formation
- If osteoclasts are not active = less bone resorption
- If osteoclasts are more active = more bone loss
If osteoblasts are not active = less bone formation
How does Nutrition affect bone remodeling?
- There are large amounts of phosphorus and calcium stored in bones and these minerals are required fort bone growth and remodeling
- Several vitamins are involved in bone remodeling as well
- Vitamin A: stimulates osteoblast activity and therefore influences bone deposition
- Vitamin D: Increases the absorption of calcium and therefore influences bone deposition
- Vitamin C: required for collaged synthesis (collage is a major component of bone ECM)
- Vitamin B12 and Vitamin K: are required for the synthesis of bone proteins
Dietary intake of relevant vitamins and minerals are therefore important for bone remodeling
How do hormones impact bone remodeling?
- Human growth hormone (hGH) and insulin-like Growth Factors (IGF) are important for bone growth during childhood
- They stimulate osteoblasts, promote synthesis of proteins for new bone and promote cell division in periosteum and at the epiphyseal plate
- Sex hormones (estrogen and testosterone) are important for growth spurts at puberty
- They stimulate osteoblasts and stimulate synthesis of bone ECM
Insulin and thyroid hormone (T3 and T4) both influence an increase in bone deposition across the lifespan
How does age and mortality impact bone remodeling?
- Bones stop lengthening when sex hormones stop influencing interstitial growth from epiphyseal growth plate (after puberty)
- Cells become less active as we age and it takes more energy to create new bone than it does to remove it
- Increase in mineral loss (especially calcium) with increasing age leads to weakening of the bone
- Loss of estrogen at menopause slows osteoblast activity and increases osteoclast activity > post-menopausal osteoporosis
- Use it or lose it, especially in the elderly > mechanical force/stress encourages bone deposition, no mechanical stress = increased bone loss
What do bones and cartilage do?
Support, movement, protection, blood cell production, triglyceride storage, mineral homeostasis
Overview on bones:
- Adults - 206 bones
- Children - have more, fuse as they develop
- Axial: Cranial bones and spine: 80
- Appendicular: Bones in limbs and pelvic, pectoral and shoulder girdle: 126 bones
5 types:
What are long bones?
Longer than they are wide: Humerus, radius, upper arm, ulna, femur, thig, tibia, tibia, phalanges
What are short bones?
Equal in length and width, cube shaped: Tarsal, ankle, carpal, wrist, thin external layer of compact bone but mostly spongey bone
What are flat bones?
Thin, spongey enclose by two plates of hard bone almost parallel: Cranial, ribs, sternum, Capula
What are irregular bones?
Complex shape: Pelvic, some facial, vertebrae, heel bone, vary in composition of compact and spongey
What are sesamoid bones?
Some tendons with friction and physical stress, wear and tear. Sesame seed shaped, patella/ knee cap, only a few millimeters, palms and soles of feet, some are not completely ossified
Diaphysis and Metaphysis:
- Diaphysis: Shaft, slightly curved for stress of weight baring and prevent fracture
Metaphysis: in between Diaphysis and Epiphysis, growing bone, contains growth plate
Epiphyseal line, Articular cartilages and Periosteum:
- Structure replacing the epiphyseal plate is the epiphyseal line
- Articular cartilages: End of bone to bone, assists with shock absorption and friction
Periosteum covers the bones that is not covered by articular cartilage, tough connective tissue, inner and outer layer, protects bone, nourishes, assist in repair, attaches to bone
- Articular cartilages: End of bone to bone, assists with shock absorption and friction
Medullary, Endosteum:
- Medullary: Hollow, diaphysis, contains marrow and blood vessels in adults, minimized weight of bone
- Endosteum: thin membrane composed of a single layer of bone forming cells, lie sin medullar, involved in bone remodeling
What do synovial joints do?
- Joint/synovial cavity between articulating bones
- Allows movement
- Bones articulating surfaces at the synovial joint are covered in hyaline cartilage/articular cartilage
- Provides smooth slippery surface, but does not bine surfaces together, reduces friction, allows for shock absorption
- Sleeve structure around synovial joint: joint capsule
- Inner synovial membrane: areolar connective tissue, elastic fibers
Outer fibrous membrane: thickened continuation of the periosteum, and is collagen rich dense connective tissue
Intra and extra scapular ligaments:
- Intracapsular ligaments: in joint space, separate to fluid e.g. anterior and posterior cruciate ligaments
Extracapsular ligaments: outside joint capsule e.g. medial, lateral ligaments of knee
Menisci, Labrum, intervertebral discs:
- Menisci: discs in some synovial joints such as knee, wrist and jaw. Crescent shaped pads of fibro cartilage between joint surfaces and attached to joint capsules, improves articulation of bony surfaces, weight distribution, distribution of synovial fluid, shock absorptions
- Labrum: shoulder, hip, deepens joint socket increasing contact area between articulating surfaces
Intervertebral discs: sit between vertebrae, outer fibrous ring, nucleus polyposis, elastic substance in the anulus fibrosis, thin layer of cartilage. Allow movements of spine, form strong joints, vertical shock, discs compress during the day
- Labrum: shoulder, hip, deepens joint socket increasing contact area between articulating surfaces
Plane joints:
- Biaxial or triaxial
- Allows movements in two axes
- Allows for gliding, or back and forth or side to side
Found in-between carpals, intertarsal between tarsals in ankle, sternoclavicular, sternocostal, vertebrae costal joints
Pivot Joint:
- Uniaxial, one axis
- Rotation only around its longitudinal axis
- Permits head to turn from side to side
Ulna joint, palms to turn anteriorly and posteriorly
Hinge joint:
- Uniaxial movement
- Flexion, extension
Knee, elbow, ankle and interphalangeal joints (fingers and toes)
- Flexion, extension
Condyloid joint:
- Biaxial movement
- Flexion, extension, abduction, adduction
- Limited circumduction (not isolated movement)
- Radiocarpal joint at wrist, ‘
Saddle joint:
- Biaxial
- Allow movement in two directions
- Flexion, extension, abduction, adduction
- Limited circumduction
Metacarpal, carpus
Ball and Socket joint:
- Triaxial movement
- Three axes
- Flexion, extension, abduction adduction, rotation
- Shoulder, hip joint
Bone resorption:
osteoclasts remove collagen fibers and minerals from bone tissue. Attach to endosteum or periosteum forming a seal at edges, put enzymes into pocket created, acids dissolve bone minerals. Minerals From ECM and bone proteins pass through osteoclast into the interstitial fluid and into the capillaries
Bone Deposition:
Osteoblasts provide collagen fibers and minerals. Bone ECM
What is bone remodeling influence by?
- Remodeling is influenced by: Minerals (phosphorus, calcium, magnesium, manganese, fluoride. Vitamins (A, B12, C, D, K). Hormones (insulin like growth factors, insulin, thyroid hormones, human growth hormones)
- In children, more bone deposition than loss, which results in bone growth
- Sex hormones create growth spurt during puberty: antigen’s, estrogens, these increase osteoblast activity and synthesis of bone ECM
Bone stop lengthening when sex hormones (estrogens) stop growth at the epiphyseal or growth plate, hence why growth in females ends before males
What is de-mineralization?
Loss of minerals (8% of bone mass each decade for women)=, for men = 3% each decade after 60
What is brittleness?
Susceptible to fractures, decrease rate of protein synthesis as we age, causes lack of bone density and frailness
Can lead to loss of teeth, height, pain
What are the two criteria for structural classification of joints?
- Presence or absence of a space between articulating bones
The type of connective tissue that binds the bone together
With respect to bone formation, match the (A) type of ossification, with (B) its correct description.
(A) Endochondral ossification (B) Bone formation within the cartilage model
Given that only the diaphyses of Jack’s bones are visible, what stage of bone formation does this suggest he has reached?
Primary ossification
What classification does the wrist joint belong to?
Synovial joint
What bones predominantly make up the wrist joint?
Carpals and radius
What specific kind of joint is the wrist joint?
Condyloid
Regarding normal bone remodelling, which option is correct with respect to (A) the cell type, and (B) its corresponding function?
(A) Osteoblasts (B) Deposit minerals and collagen fibres (components of bone ECM)
What are the 3 types of structural joints?
What are the 6 types of synovial joints?
What re the 6 types of synovial joints?
- Hinge, pivot, ball and socket, saddle, condyloid, plane
What are the three types of structural classification of joints?
- Cartilaginous
- Fibrous
Synovial
Degree of congruency in hip and shoulder joints?
Hip joint is more congruent than shoulder prioritizing stability for weight baring, while the shoulder favors mobility and range of motion
Degree of congruency in comparing knee and elbow joint?
The elbow has a higher degree of congruency than the knee prioritizing stability for controlled movement, while the knee with moderate congruency balances stability and flexibility to accommodate weight baring and range of motion
What is joint congruence
A congruent joint is where the bone ends fit well
An incongruent joint is where the bone ends do not fit well
What happens if bones fit well/don’t fit well together
Bone ends fit well together
Joint more stable
Not as reliant on other structures
Less likely to slip (dislocate)
Bone ends don’t fit well together
Joint less stable
Need other structures to hold the joint in place
Ligaments, muscles/tendons
Hip joint
Classification of joints?
Synarthorsis: Immobile or limited mobility (fibrous joints)
Amphiarthrosis: Small about of mobility (cartilaginous joints)
Diarthrosis: Freely moving (synovial joints)
Movement at:
Fibrous joints
Cartilaginous joints
Synovial joints
Movement at fibrous joints:
Depends on the length of fibers uniting the bones
Generally little to no movement
Movement: some to none
Types:
Primary = synchondrosis
Secondary = symphysis
Synovial joints
Definition
A joint which has:
- Hyaline cartilage covering bone ends
- A joint cavity containing synovial fluid
- A synovial membrane
- A fibrous capsule
Synovial joints
5, Reinforced by ligaments
6. Have rich blood and nerve supply
Primary and secondary cartilaginous joints
Primary cartilaginous joint
Bones joined by hyaline cartilage
Can be temporary
Epiphyseal plate of developing bones
Can be permanent
Where costal cartilage of the first rib joins the manubrium (= 1st sternocostaljoint)
Secondary cartilaginous joints
Articular surfaces covered by hyaline cartilage and joined by fibrocartilage
Strong joints – limited movement
Pubic symphysis
Manubriosternal joint
Anterior intervertebral joints
