Chapter 6 Flashcards
Hyaline cartilage
- Provide support with flexibility and resilience
- Most abundant; made of collagen fibers
- Includes: Articular cartilages (at ends of bones), Costal cartilages (connect ribs to sternum), Respiratory cartilages (larynx and respiratory passageways), Nasal Cartilages (support external nose)
Elastic cartilage
- Resemble hyaline cartilages, but contain more elastic fibers
- Able to stand up to repeated bending
- Ear and epiglottis
Fibrocartilage
- Highly compressible with great tensile strength
- Parallel rows of chondrocytes alternating with thick collagen fibers
- Menisci of the knee and discs between vertebrae
Explain how cartilage grows
- Appositional growth: New matrix secreted from the perichondrium against the external face of the existing cartilage tissue
- Interstitial growth: Chondrocytes in lacunae divide and secrete new matrix, expanding cartilage from within
Axial skeleton
Forms the long axis of the body
-Bones of skull, vertebral column, and rib cage
Appendicular skeleton
Consists of the bones of the upper and lower limbs and the girdles (shoulder and hip bones)
Long bones
- Longer than they are wide
- Shaft plus two expanded ends
- All limb bones expect the patella, wrist, and ankle are long bones
Short bones
- Roughly cube shaped
- Wrist and ankle
- Sesamoid bones: special type of short bone formed in a tendon (patella)
Flat bone
- Thin, flattened, and usually a bit curved
- Sternum, scapulae, ribs, most skull bones
Irregular bones
- Complicated shapes that fit none of the other classes
- Vertebrae and hip bones
Functions of bones
- Support: framework, cradle organs
- Protection: surround important features
- Movement: skeletal muscles use bones as levels to move body
- Mineral and growth factor storage: reservoir for minerals, stores important growth factors
- Blood cell formation: (hematopoiesis) occurs in red marrow of certain bones
- Hormone production: osteoclacin
Gross anatomy of a flat bone
- Thin plates of spongy bone covered by compact bone
- Covered outside by periosteum and inside by endosteum
- No shaft of epiphyses
- Bone marrow, but no marrow cavity
- Covered by hyaline cartilage where they form moveable joints
Gross anatomy of a long bone
- Diaphysis (shaft): long axis of bone, collar of compact bone, medullary cavity, and yellow marrow cavity
- Epiphyses (bone ends): outer shell of compact bone, interior contains spongy bone; articular (hyaline) cartilage covers joint surface; epiphyseal line (remnant of epiphyseal plate which lengthens the bone) or metaphysis
- Membranes:
- Periosteum covers the external surface of the entire bone except joint surfaces–outer fibrous layer (dense irregular connective tissue) and inner osteogenic layer (primitive stem cells)–richly supplied with nerve fibers and blood vessels–perforating (Sharpey’s) fibers secure periosteum to bone
- Endosteum covers internal bone surfaces–trabeculae of spongy and canals of compact bone
Red marrow
Typically found in trabecular cavities of spongy bone in long bones and diploe of flat bones–red marrow cavities
Yellow marrow
Found in the medullary cavity, can convert to red blood cells
Function of bone markings
Serve as sites of muscle, ligament, and tendon attachment, as joint surfaces, or as conduits for blood vessels and nerves
Histology of compact bone
- Osteon (Haversian system): structural unit of compact bone, group of hollow tubes of bone matrix; each matrix tube is a called a lamella and contains collagen fibers
- Canals and canaliculi: Central or Haversian canal runs through the core of each osteon; Perforating Volksmann’s canals connect blood and nerve supply of medullary cavity to central canals; Osteocytes in lacunae; Canaliculi connect lacunae to each other and the central canal
- Interstitial and Circumferential lamellae: interstitial lie between intact osteons and incomplete lamellae, fill gaps or remnant of osteons; circumferential resist twisting of long bone
Histology of spongy bone
Trabeculae with irregularly arranged lamellae and osteocytes interconnected by canaliculi; no osteons are present
Chemical composition of bone
Organic components: bone cells and osteoid (ground substance and collagen fibers)
Inorganic components: mineral salts, which account for hardness and resistance to compression
Osteogenic cells
- Mitotically active stem cells found in the periosteum and endosteum
- Can differentiate into other cells
Osteoblasts
- Bone forming cells that secrete the bone matrix
- Actively mitotic
- Includes collagen and calcium-binding proteins to make up osteoid
- Play a role in matrix calcification
Osteocytes
- Mature bone cells in lacunae
- Monitor and maintain bone matrix, act as stress or strain sensors, and respond to mechanical stimuli
Bone lining cells
- Flat cells found on bone surfaces where bone remodeling is not going on
- Help maintain matrix
- External surface: periosteal cells
- Internal surface: endosteal cells
Osteoclasts
- Giant, multinucleate cells located at sites of bone resorption
- Located in resorption bay with ruffled border, which increase surface area for enzymatically degrading the bones
Intramembranous ossification
- Develops from fibrous membrane and the bone is called a membrane bone
1. Ossification centers appear in the fibrous connective tissue membrane
2. Osteoid secreted within the fibrous membrane and calcifies
3. Woven bone and periosteum form
4. Lamellar bone replaces woven bone and red marrow appears
Endochondral ossification
- Develops by replacing hyaline cartilage and the resulting bone is called a cartilage, or endochondral, bone
1. Bone collar forms around the diaphysis of the hyaline cartilage model
2. Cartilage in the center of the diaphysis calcifies and then develops cavities
3. The periosteal bud invades the internal cavities and spongy bone forms
4. The diaphysis elongates and a medullary cavity forms
5. Epiphyses ossify
Process of long bone growth
- Occurs at the epiphyseal plate
- Side facing epiphysis contains resting cartilage cells
- Area proximal to the resting cartilage is arranged in four zones: proliferation, hypertrophic, calcification, and ossification (region of earliest stage of growth to region where bone is replacing cartilage)
Remodeling functions of osteoblasts
In bone deposit, the osteoid seam marks areas of new matrix deposits by osteoblasts
Remodeling functions of osteocytes
Packets of adjacent osteoblasts and osteoclasts called remodeling units coordinate bone remodeling
Remodeling functions of osteoclasts
In bone resorption, they move along a bone surface, digging depressions or grooves as they break down the bone matrix
How do hormones and physical stress regulate bone remodeling?
Hormones: parathyriod hormone (PTH), when levels of calcium decline, PTH stimulates osteoclasts to resorb bone and release calcium into blood
Mechanical stress: bone grows or remodels in response to the demands placed on it
Steps of fracture repair
- Hematoma forms
- Fibrocartilaginous callus forms
- Bony callus forms
- Bone remodeling occurs
Osteoporosis
Refers to a group of diseases in which bone resorption outpaces bone deposit, sex hormones help maintain health and normal density of the skeleton; can be treated with calcium, vitamin D supplements, exercise, and hormone replacement therapy
Osteomalacia
Includes a number of disorders in which the bones are poorly mineralized; osteiod produced, but calcium slats are not adequately deposited
-Rickets is the analogous disease in children
Paget’s disease
Characterized by excessive and haphazard bone deposit and resorption; bone is hastily made and has a abnormally high ration of spongy to compact bone
Development of bone throughout life
- At birth: well ossified bones except epiphyses
- After birth: secondary ossification centers develop
- Bone formation exceeds bone resorption in children and adolescents
- Young adults: nearly all bones ossified, skeletal growth ceases, formation and resorption are in balance
- Old age: resorption predominates
