Chapter 6 Flashcards
(124 cards)
Skeletal System
Components include:
- Bones of the skeleton
- Cartilages, joints, ligaments, connective tissue that stabilize or connect bones
Functions of the Skeletal System
- Support
-Provides structural support for the entire body
-Bones provide attachments for soft tissues and organs - Storage of minerals and lipids
-Mineral reserves for calcium and phosphorus ions held in calcium salts in bone
-Yellow bone marrow stores lipids for energy reserves - Blood cell production
-Red blood cells, white blood cells, and other blood elements produced in the red bone marrow - Protection
-Soft tissues and organs are surrounded by skeletal structures
Examples:
-The skull encloses the brain
-The ribs protect the heart and lungs - Leverage
-Bones function as levers
-Change size and direction of force generated by skeletal muscles
-Result is body movement
Bone or osseous tissue
-Supporting connective tissue containing cells in a matrix
-Cells are called osteocytes
Matrix contains:
-Calcium salts in the form of calcium phosphate, Ca3(PO4)2
-Accounts for almost 2/3 of the weight of bone
Extracellular protein fibers
-About 1/3 of bone weight comes primarily from collagen fibers
Classifying bones by shape
- Bones of the skeleton are categorized into four general shapes
1. Long bones - Longer than they are wide
2. Short bones - About as wide as they are long
3. Flat bones - Thin and relatively broad
4. Irregular bones - Complex shapes that don’t fit another category
Features of a Long Bone
- The diaphysis is the central shaft
- Surrounds a marrow cavity, or medullary cavity, in the center filled with bone marrow
- The epiphyses are the expanded portions at each end
- Covered with articular cartilage
- Articulate with an adjacent bone at a joint
Types of Bone Tissue in a Long Bone
- Compact bone, or dense bone
- Relatively solid
- Forms the wall of the diaphysis
- Spongy bone, or cancellous bone
- Interlacing network of bony rods separated by spaces
- Fills the epiphyses
- Lines the marrow cavity
Coverings of a Long Bone
- Outer surface covered by periosteum
- Inner cellular layer
- Outer fibrous layer
- Isolates bone from surrounding tissue
- Forms attachments with fibers of tendons and ligaments
- Inner surfaces and spongy bone of marrow cavity covered by endosteum
- Functions during bone growth and repair
Microscopic Features of Bone
- Bone cells are called osteocytes
- Located in pockets called lacunae
- Found between sheets of calcified matrix called lamellae
- Canaliculi are small channels
- Contain cytoplasmic extensions of the osteocytes
- Radiate through the matrix
- Connect the lacunae to blood vessels for nutrient and waste exchange
Histology of Compact Bone
- Basic functional unit is the osteon, or Haversian system
- Osteocytes arranged in concentric layers (lamellae)
- Layers surround a central canal, or -Haversian canal
- Central canals run parallel to surface of bone and contain blood vessels
Perforating canals
Link blood vessels of central canal with blood vessels of periosteum and marrow cavity
Characteristics of Compact Bone
- Covers all bone surfaces except inside joint capsules
- Articular cartilage protects opposing bone surfaces here
- Parallel arrangement of osteons resists stress in specific direction
- Withstands forces applied on either end of a long bone
- Cannot tolerate moderate stress applied to the side of the shaft
Structural Features of Spongy Bone
- Has no osteons
- Lamellae form rods or plates called trabeculae
- Still contains osteocytes, lacunae, and canaliculi
- Contains red bone marrow
- Found in spaces between trabeculae
Functional Features of Spongy Bone
Found in:
-Locations not heavily stressed
-Locations with stresses arriving from many different directions
Example: epiphyses of long bones where stresses transferred across joints
-Much lighter than compact bone
-Reduces weight of the skeleton
-Easier for muscles to move bones
Osteoblasts
Produce new bone through a process called ossification
Osteocytes
- Most abundant cells in bone
- Mature cells that maintain bone structure by recycling calcium salts
Osteoclasts
- Secrete acid and enzymes that dissolve the matrix
- Process releases minerals through osteolysis, or resorption
Bone Formation
-Embryonic development of bone
-Begins at week 6 as a cartilaginous formation
-Replaced with bone, a process called ossification
Two types
1. Intramembranous ossification
2. Endochondral ossification
Calcification occurs during ossification
-Can also occur in other tissues besides bone
Intramembranous Ossification
- Occurs during fetal development
- Bone develops within sheets of connective tissue
- Begins in an ossification center
- Osteoblasts differentiate from connective tissue stem cells and form new bone matrix
- Bone matrix formation extends outward
- Osteoblasts surrounded by matrix change into osteocytes
- Blood vessels grow into area and are trapped within developing bone
- Bone remodeling produces osteons of compact bone
- Flat bones of skull formed in this manner
Endochondral Ossification
-Process of formation for most bones of the skeleton
-Begins with hyaline cartilage models
-Cartilage replaced by true bone in five steps
Steps 1–3 of Endochondral Ossification
1. Chondrocytes enlarge and surrounding matrix begins to calcify
-Chondrocytes die from lack of nutrients
Calcification of matrix slows diffusion
2. Bone formation starts at the shaft surface
-Blood vessels grow around edges
-Cells of perichondrium differentiate into osteoblasts
-Osteoblasts produce bone matrix around shaft surface
3. Blood vessels invade inner region of cartilage
-Migrating fibroblasts differentiate into osteoblasts
-New osteoblasts form spongy bone in center of shaft at the primary ossification center
-Bone develops toward each end filling shaft with spongy bone
4. Osteoclasts begin to break down spongy bone in center of bone
-Forms marrow cavity
-Epiphyseal cartilages, or epiphyseal plates, on the ends of the bone continue to enlarge
-Increases length of the bone
5. Centers of the epiphyses begin to calcify
-Secondary ossification centers form as blood vessels and osteoblasts enter
-Epiphyses fill with spongy bone
-Thin layer of original cartilage covers joint surfaces as the articular cartilage Bone of shaft and epiphysis separated by epiphyseal
Epiphyseal Line
- At puberty, bone growth accelerates due to increased sex hormone production
- Osteoblasts produce bone faster than the epiphyseal cartilage can expand
- Epiphyseal cartilages get narrower until disappear
- Called epiphyseal closure
- X-rays of adult bones show former location of epiphyseal cartilage as epiphyseal line
Appositional Growth
- Growth in diameter of bones occurs along with growth in length
- Process of growing in diameter is appositional growth
- Periosteum cells develop into osteoblasts
- Produce more matrix on the outer surface of the bone
- Osteoclasts erode the inner surface
- Marrow cavity enlarges as a result
Timing of Epiphyseal Closure
- Varies from bone to bone
- Digits close early
- Arm, leg, and pelvis bones close later
- Varies from person to person
- Different timing in males versus females
- Mostly due to differences in sex hormones
- Later closure in males
Requirements for Bone Growth (Mineral Supply)
- Calcium salts (calcium and phosphate)
- Absorbed from mother’s bloodstream during prenatal development
Requirements for Bone Growth (Vitamin D3)
- Plays role in calcium metabolism
- Liver and kidney process into calcitriol that stimulates calcium and phosphate absorption
- Manufactured by epidermal cells exposed to UV radiation
- Also obtained from dietary supplements
- Deficiency leads to softening of bones
- Condition called osteomalacia in adults and rickets in children