Class 8 - Bone Tissue Flashcards
What the skeletal system is comprised of (3)
- Bones
- Cartilages
- Ligaments - Hold bones together at joints
Tendons are NOT part of this system, but attach muscle to bone.
Functions of the skeleton (7)
- Support
- Protection
- Movement
- Electrolyte balance - Calcium and phosphate levels
- Acid-base balance - buffers blood against pH changes by altering phosphate and carbonate salt levels
- Blood formation - red bone marrow produces
- Hormone secretion - affect action of insulin and moderate stress response
Mineralization/calcification
Crystallization process in which calcium, phosphate, and other ions are taken from blood and deposited on bone.
Osteoblasts produce collagen fibers which spiral length of osteon and become encrusted with minerals
First few crystals act as seed crystals that attract more ions.
What individual bones each consist of (6)
Each is an organ with:
1. Bone tissue
2. Bone marrow
3. Cartilage
4. Adipose tissue
5. Nervous tissue
6. Fibrous connective tissue
Flat bones (5)
Thin, curved plates; protect soft organs.
Includes:
1. Parietal bones of skull
2. sternum
3. scapula
4. ribs
5. hip bones
Long bones (9)
Longer than wide; rigid levers acted upon by muscles; crucial for movement
Includes:
1. Humerus
2. radius
3. ulna
4. femur
5. tibia
6. fibula
7. metacarpals
8. metatarsals
9. phalanges
Short bones (2)
Approximately equal in length and width
Includes: bones of wrist and ankle
Irregular bones (2)
Elaborate shapes
Includes: Vertebrae, some skull bones
Compact bone
3/4 of skeleton by weight
Dense outer shell of bone, encloses marrow cavity.
Spongy bone
1/4 of skeleton (by weight)
Loosely organized bone tissue found in center of ends and shafts of long bones and in middle of others.
Covered by compact bone
Diaphysis
Shaft of bone that provides leverage
Epiphysis
Enlarged end of a long bone. Strengthens joints and anchors ligaments and tendons.
Epiphyseal line
Remnant of childhood growth zone (epiphyseal plate)
Articular cartilage
Layer of hyaline cartilage that covers joint surface; allows joints to move more freely
Nutrient foramina
Minute holes in bone surface that allow blood vessels to penetrate
Periosteum + perforating fibers
External sheath covering most of bone.
Has an outer fibrous layer of collagen and inner osteogenic layer of bone-forming cells
Perforating fibers: penetrate underlying bone matrix
Endosteum
Thin layer of reticular connective tissue lining the marrow cavity and all internal bone surfaces
Flat bone structure
Sandwich-like; inner and outer tables of compact bone enclosing layer of spongy between (called diploe in cranium)
Four types of bone cells
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Osteogenic cells + locations
Stem cells found in endosteum and inner layer of periosteum.
Arise from embryonic mesenchyme; multiply continuously and give rise to osteoblasts.
Osteoblasts + 2 locations
Bone-forming cells in endosteum and inner layer of periosteum.
Perform osteogenesis— synthesize soft organic matter of matrix and promote its mineralization
Stress stimulates osteogenic cells to multiply rapidly and increase number of osteoblasts which reinforce bone
Osteocytes + how they communicate
Former osteoblasts that have become trapped in the matrix they deposited. Some reabsorb bone matrix while others deposit it.
Have cytoplasmic processes which reach into canaliculi and contact neighboring cells’ processes; gap junctions allow for passage of substances
Act as strain sensors— when stressed produce biochemical signals that regulate bone remodeling (hormone osteocalcin)
Lacunae and canaliculi
Lacunae - Tiny cavities where osteocytes reside
Canaliculi - Little channels that connect lacunae
Osteoclasts + formation
Perform osteolysis, the breakdown of bone as part of bone remodeling.
Often reside in reabsorption bays etched into bone surface
Develop from same bone marrow stem cells that give rise to red blood cells, unlike other bone cells
Form from fusion of several stem cells; have multiple nuclei each.
Infoldings imcrease surface area, form ruffled border
Composition of osseous tissue matrix (2)
1/3 organic matter - synthesized by osteoblasts. Collagen and carbohydrate-protein complexes.
2/3 inorganic matter - mineral component; 85% hydroxyapatite (calcium salt), 10% calcium carbonate, 5% inorganic ions
Combination forms a COMPOSITE material that provides flexibility and strength
Why bone matrix is a composite material
Combination of organic (collagen) and inorganic matter (minerals) creates combination of FLEXIBILITY and STRENGTH.
—Protein portion gives some flexibility since collagen have sacrificial bonds that dissipate shock under load (osteogenesis imperfecta = defect in collagen)
—Mineral portion allows bone to support body weight without sagging. (Rickets = disease of mineral deficiency causing soft bones)
Histology of compact bone (5)
- Concentric lamellae
a. Circumferential lamellae - encircle inner-outer region
b. Interstitial lamellae - fill irregular regions between osteons.
- Central canal
- Perforating canals - connect central canals
- Collagen corkscrews - Down each lamella to enhance bone strength
- Cement line - prevents spread of microfractures
Bone marrow + 2 types
Soft tissue occupying marrow cavities of long bones and small spaces of spongy bone
- Red
- Yellow
Red bone marrow (myeloid tissue)
Contains multiple tissues that produce blood cells.
In nearly every bone of a child but only in some of adults’.
Yellow bone marrow
Fatty marrow that does not produce blood. Found in adults.
Can transform back to red marrow in event of chronic anemia (requires making of more blood cells)
Ossification/ osteogenesis + 2 methods
Both begin in embryonic mesenchyme.
- Intramembranous ossification
- Endochondrial ossification
Intramembranous ossification
Produces flat bones of skull, most of clavicle, and part of mandible.
Bone develops from osteoid tissue, which calcifies and entraps osteocytes.
Also important in lifelong thickening and remodeling of long bones
Endochondral ossification
Bone develops from hyaline cartilage model; produces most bones of body
Bone elongation
Epiphyseal plate serves as growth zone.
Metaphysis: Transitional zone on each side where cartilage is replaced by bone. Structure corresponds to steps of cartilage replacement
Describe bone elongation process
Chondrocyte multiplication in zone 2 and hypertrophy in zone 3 push zone of reserve cartilage toward ends of bone, causing elongation
Cartilage growth from within = interstitial growth
Bones changes which occur by late teens/early twenties (3)
- Primary and secondary marrow cavities unite into one
- Junction fills with spongy bone
- Site of original epiphyseal plate becomes epiphyseal line
Achondroplastic vs pituitary dwarfism
Achondroplastic - long bones stop growing in childhood; normal torso, short limbs.
Pituitary - lack of growth hormone; normal proportions, short stature
Term for bone widening and thickening + 3 steps
Appositional growth - deposition of new tissue at bone surface. Occurs by Intramembranous ossification at bone surface.
- Osteoblasts of inner layer of periosteum deposit osteoid tissue, become trapped as tissue calcifies.
- Lay down matrix layers parallel to surface, forming circumferential lamellae.
- Osteoclasts of endosteum enlarge marrow cavity
Bone remodeling
- 3 causes, Wolff’s law of bone
Bone continually remodels, replacing 10% of skeleton per year. Collaborative action of osteoblasts and osteoclasts.
- Repairs microfractures
- releases minerals into blood
- reshapes bones in response to disuse
Wolff’s law — architecture of bone determined by mechanical stress placed on it. Grow larger in response to stress
Ossification vs osteolysis
Ossification - Laying down of new bone material by osteoblasts
Osteolysis - Active resorption of bone matrix by osteoclasts. Raises blood calcium levels.
