Chapter 6 Bones and bones tissue Flashcards
INTRODUCTION TO BONES AS ORGANS
Skeletal system
Includes:
–Bones, joints, and associated supporting tissue
Bones
Main organs of skeletal system:
Like any organ, composed of more than osseous tissue
Also dense regular, irregular collagenous connective tissue and bone marrow
Functions skeletal system
- Protection
- Mineral storage and acid-base homeostasis
- Blood cell formation
- Fat storage
- Movement
- Support
Protection
Certain bones (skull, sternum (breastbone), ribs, and pelvis) protect underlying organs
Mineral storage and acid–base homeostasis
Bone is most important storehouse for calcium, phosphorus, and magnesium salts
-minerals are also present in blood as electrolytes, acids, and bases
-critical for electrolyte and acid–base maintenance
Blood cell formation
Bones house red bone marrow – specialized connective tissue involved in formation of blood cells (hematopoiesis)
Fat storage
Bones also contain yellow bone marrow; made up of fat cells (adipocytes); store triglycerides; fatty acids from breakdown of triglycerides can be used as fuel by cells
Movement
Bones serve as sites for attachment of most skeletal muscles; when muscles contract, they pull on bones; generates movement at joint
Support
Skeleton supports weight of body; provides its structural framework
Bone Structure
Can be organized into 5 classes despite diversity of bone appearance; all 206 bones fit into categories based on shape:
- Long bones
- Short bones
- Flat bones
- Irregular bones
- Sesamoid bones
Long bones
Named for overall shape; not actual size (some are quite small); longer than they are wide; include most bones in arms and legs
Short Bones
Also named for shape rather than size; roughly cube-shaped or about as long as they are wide.
-wrist or carpals
-ankle or tarsals
Flat bones
Thin and broad bones; include ribs, pelvis, sternum (breastbone), and most skull bones
Irregular bones
Include vertebrae and certain skull bones; do not fit into other classes because of irregular shapes
Sesamoid bones
Specialized bones located within tendons
-usually small, flat, and oval-shaped
-give tendons mechanical advantage
-give muscles better leverage
Ex: patella (kneecap)
Structure of long bones: Periosteum
– membrane composed of dense irregular collagenous connective tissue
-rich with blood vessels and nerves
-surrounds outer surface of long bone
Structure of long bones: Perforating Fibers
(Sharpey’s fibers)
– made of collagen;
– anchors periosteum firmly to underlying bone surface by penetrating deep into bone matrix
Structure of long bones: Diaphysis
– shaft of long bone
-each end is epiphysis; covered with thin layer of hyaline cartilage (articular cartilage) found within joints (articulations) between bones
Structure of long bones: Medullary cavity
(marrow cavity) within diaphysis contains either red or yellow bone marrow, depending on bone and age of individual
Structure of long bones: Compact bone
– one of two bone textures; hard, dense outer region; allows bone to resist linear compression and twisting forces among other stresses
Structure of long bones: Spongy bone
(cancellous bone)
– second bone texture; inside cortical bone; honeycomb-like framework of bony struts; allows long bones to resist forces from many directions; provides cavity for bone marrow
Structure of long bone , endosteum
–Thin membrane that cover bony struts of spongy bone and all inner surfaces of bone
- contain different populations of bone cells involved in maintenance of bone homeostasis
Structure of long bones: Epiphyseal lines
– separate both proximal and distal epiphyses from diaphysis
-remnant of epiphyseal plates (growth plates)
- line of hyaline cartilage found in developing bones of children
Structure of short, flat, irregular, and sesamoid bones:
Do not have diaphyses, epiphyses, medullary cavities, epiphyseal lines, or epiphyseal plates:
–Covered by periosteum, with associated perforating fibers, blood vessels, and nerves
–Internal structure – two outer layers of thin compact bone with middle layer of spongy bone (diploë) and associated bone marrow
–Some flat and irregular bones of skull contain hollow, air-filled spaces (sinuses), which reduce bone weight
Blood and nerve supply to bone
–Blood supply to short, flat, irregular, and sesamoid bones is provided mostly by vessels in periosteum that penetrate bone
–Long bones get third of their blood supply from periosteum; mostly supplies compact bone
Red bone marrow
loose connective tissue; supports islands of blood-forming hematopoietic cells
–Amount of red marrow decreases with age
–Red marrow in adult is only in pelvis, proximal femur and humerus, vertebrae, ribs, sternum, clavicles, scapulae, and some bones of skull
–Children need more red marrow to assist in growth and development
Yellow bone marrow
Triglycerides, blood vessels, and adipocytes
MICROSCOPIC STRUCTURE OF BONE TISSUE
Bone or Osseous tissue
Primary tissue found in bone; composed mostly of extracellular matrix with a small population of cells scattered throughout
Extracellular matrix of bones
–Inorganic matrix – minerals make up about 65% of bone’s total weight
–Organic matrix – makes up remaining 35%; consists of collagen fibers and usual ECM components
Inorganic Matrix
Predominantly calcium salts; bone stores around 85% of total calcium ions as well as large amount of phosphorus:
–Calcium and phosphorus salts exist as large molecules of hydroxyapatite crystal
–Crystalline structure makes bone one of hardest substances in body; strong and resistant to compression
–Allows bone to be both protective and supportive
–Bicarbonate, potassium, magnesium, and sodium are also in inorganic matrix
Organic Matrix
Known as osteoid; consists of protein fibers, proteoglycans, glycosaminoglycans, glycoproteins, and bone-specific proteins
–Collagen – predominant protein fiber; forms cross-links with one another; helps bone resist torsion (twisting) and tensile (pulling or stretching) forces
–Collagen fibers align themselves with hydroxyapatite crystals; enhances hardness of bone
–Glycosaminoglycans and proteoglycans create an osmotic gradient; draw water into osteoid; help tissue resist compression
–Glycoproteins in osteoid bind different components of osteoid and inorganic matrix together
Bone Cells
Responsible for bone’s dynamic nature:
–Osteoblasts
–Osteocytes
–Osteoclasts
Osteoblasts
Metabolically active bone cells in periosteum and endosteum:
–Osteogenic cells – flattened cells; differentiate into osteoblasts when stimulated by specific chemical signals
–Osteoblasts – bone-building cells; perform bone deposition
–Bone deposition –osteoblasts secrete organic matrix materials; assist in formation of inorganic matrix
Osteocytes
-Osteoblasts eventually surround themselves with matrix in small cavities (lacunae); become osteocytes that no longer actively synthesize bone matrix
–No longer metabolically active except for maintaining bone extracellular matrix
–Appear to have ability to recruit osteoblasts to build up or reinforce bone under tension
Osteoclasts
–Responsible for bone resorption; cell secretes hydrogen ions and enzymes; break down bone matrix
–Completely different overall cell structure than other two cell types; large multinucleated cells; resemble jellyfish; derived from fusion of cells from bone marrow
–Eventually located in shallow depressions on internal and external surfaces of bone
Osteoclasts cont.
–Hydrogen ions dissolve components of inorganic matrix; enzymes break down organic matrix
Structure of compact bone
Continuously subjected to great deal of stress; tends to strain or deform objects like bone; must be able to withstand these forces or suffer damage:
–Compact bone cross section resembles forest of tightly packed trees; each tree is a unit called Osteon or Haversian system
–Rings of each tree are made up of thin layers of bone called Lamellae
