Bio 150- Skeletal System Flashcards
Components of theskeletal system
- Bones
- Cartilage: Mainly hyaline cartilage
- Tendons: Connect muscles to bones
- Ligaments: Connect bone to bone
Functions of the skeletal system
- Support: framework to support body
- Protection: think – skull, vertebrae, ribcage…
- Movement: (with skeletal muscles) act as levers to move body (walk, breathe, etc)
- Storage: minerals (calcium, phosphate)- Related to electrolyte and acid-base balance
- Blood cell production: in the marrow cavity of certain bones
Bone anatomy: shapes (6)
- Long: Longer than they are wide
- Short: Cube-shaped
- Flat: Thin, flattened, parallel surfaces, often curved
- Sutural bones: Found in the sutures
- Sesamoid bones: Found deep inside tendons
- Irregular: Don’t fit in the other categories
Parts of a long bone (4)
-Diaphysis : Collar of compact bone, medullary cavity (marrow cavity) in middle
-Epiphysis: The “ends” of long bones- Compact bone, with spongy bone inside
-Epiphyseal line: Between epiphysis and diaphysis
Remnant of epiphyseal plate
-Epiphyseal plate: Disc of hyaline cartilage- During childhood, it grows to lengthen the bone
Layers of a long bone (2)
Periosteum
Endosteum
Periosteum
- Covers external surface of bone
- 2 layers (outer = dense irregular CT, inner = various cells…)
- Anchored to bone tissue by perforating (Sharpey’s) fibers
- Lots of blood vessels, nerve fibers, lymphatic vessels
Endosteum
- Lines the inner surfaces of bone (even the canals, etc)
- Much thinner than periosteum
- An incomplete, cellular layer
Parts of a long bone (2 types of bone)
-Compact (Haversian) bone
Outer layer, dense, strong
-Spongy (cancellous) bone
In epiphyses, and near marrow cavity
Honeycomb-like
Articular cartilages
- Covers joint surface of the epiphyses
- Hyaline cartilage
- Cushions, absorbs stress between adjoining bone ends
Marrow cavity (aka “medullary cavity”)
- In the diaphysis of long bone
- Most bone marrow is here
2 types of Bone marrow
-Red marrow:
Hemopoeitic tissue (blood forming)
Present in basically all marrow cavities of infants
In adults, only present in spongy bone in head of femur + humerus, plus some flat bones (e.g., sternum), and irregular bones (e.g., hip bones)
-Yellow marrow:
Fat (think… why?)
Normally fills marrow cavities in diaphysis of adult long bone
Spongy bone
- Honeycomb like
- Trabeculae are aligned along lines of stress
- Each trabecula is only a few cells thick, so easy for nutrients to diffuse to the osteocytes
Microstructure of compact bone
-Haversian system/ Osteon
-3 types of layers (lamellae):
Concentric lamellae make up each osteon (to help resist twisting)
Interstitial lamellae
Circumferential lamellae
-2 Canals
Haversian (central) canal
Volkmann’s (perforating) canals
-Osteocytes in lacunae: Lacunae connected by canaliculi
compact bone 3 types of layers (lamellae)
- Concentric lamellae make up each osteon (to help resist twisting)
- Interstitial lamellae
- Circumferential lamellae
compact bone 2 canals:
- Haversian (central) canal
- Volkmann’s (perforating) canals
compact bone Osteocytes in
lacunae
Lacunae connected by
canaliculi
Mineral salts
- Mainly calcium phosphates (mostly hydroxyapatite crystals)
- Tight packed crystals in the ECM
- Makes bone hard, able to resist compression
Collagen fibers
Allows bone to be flexible, and able to resist tension
Osteoblasts:
- Bone-forming cells
- Develop from osteogenic cells
- Make up endosteum and part of periosteum
Osteocytes:
- Mature bone cells. Found in lacunae. Maintain bone matrix. Also monitor need for bone remodeling.
- Develop from osteoblasts (that get trapped in matrix)
Osteoclasts:
- Bone-dissolving cells. Large. Different origin.
- Make up endosteum and part of periosteum
bone cells make up bone tissue. Bone tissue plus other tissues (e.g., blood, nerves…) make up a bone, therefore a bone is a(n)
organ
Bone formation and growth
- Intramembranous ossification
- Endochondral ossification
Ossification:
- the formation of bone
- Involves calcification
Calcification:
-the deposition of calcium salts within a tissue
-Calcification occurs DURING ossification!
(Other tissues could become calcified too…)
Two different ways that bones can be formed:
-Intramembranous ossification
-Endochondral ossification
Basic differences between these?
- In intramembranous ossification, the mesenchyme (embryonic tissue) differentiates into bone tissue directly
- Endochondral ossification involves the formation of cartilage first. The cartilage is then transformed into bone tissue.
Both intramembranous and endochondral ossification:
What do they have in common?
- Start out as mesenchyme
- Osteoblasts are the first “bone cells”, and begin to form the matrix (which will become ossified)
- Little spicules of bone form first. They are thickened and form trabeculae of spongy bone. This spongy bone can then be remodelled to form compact bone.
Intramembranous ossification
- Trabeculae are formed (as already described)
- Cancellous bone is formed, and red marrow develops in the spaces.
- Surrounding cells form periosteum.
- Can then be remodelled to form compact bone with cancellous bone center
- Bones formed: most skull bones, part of the mandible, part of the clavicles
Endochondral ossification
- Cartilage model is formed (hyaline cartilage)
- Chondrocytes die out, osteoblasts develop… form a bone collar on the surface
- Chondrocytes enlarge, matrix gets calcified, chondrocytes die
- Blood vessels move in…
- Osteoblasts form bone on the calcified cartilage…
- Bones formed: base of skull, part of mandible, part of clavicles, and most other bones!
Elongation of long bone
- Bones must grow by appositional growth (not interstitial growth)
- Long bones: growth in length occurs at epiphyseal plate
- Interstitial growth of cartilage, then appositional growth on surface of the cartilage
Elongation of long bone: 5 regions/zones:
1: Zone of reserve cartilage
2: Zone of cell proliferation
3: Zone of cell hypertrophy
4: Zone of calcification
(5: Zone of bone deposition)
New bone is formed on the
diaphyseal side of the plate: more cartilage grows on the epiphyseal side (increase in length!)
Bone remodeling and repair
- Bone is not a “dead”, fixed tissue!
- 5-7% of your bone mass is recycled every week
- Building up of new tissue (osteoblasts), and breaking down (osteoclasts)
Gross Skeleton- 2 divisions:
Axial skeleton
Appendicular skeleton
