Bone Tissue Flashcards
Bones
hard, dense connective tissue that forms the adult skeleton (Bones are dynamic and complex organs)
Skeletal system
composed of bones and cartilage which grows, repairs, and renews itself.
(206 bones that compose the adult skeleton)
The function of the skeletal system:
- supports the body: provide a scaffold to support the body and its weight
- facilitates movement: points of attachment for muscles to move the body and its parts
- protects internal organs: Skull protects the brain, rib cage protects heart and lungs, the spine protects vertebrae
- produces blood cells: Red marrow is involved in hematopoiesis (production of red blood cells, white blood cells, and platelets)
- stores and releases minerals and fat: a reservoir for calcium, and phosphorus which can be released into the blood. Yellow marrow contains adipose tissue and stores triglycerides
General Structure of Bone Tissue
Structure: a small number of cells in a matrix of collagen fibers embedded with inorganic salt crystals (hydroxyapatite made from calcium phosphate and calcium carbonate, magnesium hydroxide, fluoride, sulfate)
Strong and flexible: hardness and strength from hydroxyapatite crystals and flexibility from collagen fibers
Periosteum: connective tissue membrane that covers the outer surfaces of bones, except at joints
Endosteum: connective tissue membrane that covers the inner surfaces of bones, eg the medullary cavity
Compact bone is dense so that it can withstand compressive forces, while spongy (cancellous) bone has open spaces and supports shifts in weight distribution.
Blood vessels
Blood vessels (arteries and veins) in bone
Function: provide nourishment and remove waste
Pathway in spongy bone and medullary cavity: travel from periosteum to spongy bone and penetrates via nutrient foramen (small openings in the diaphysis) to reach medullary cavities
Pathway in compact bone: via central and perforating canals
Nerves in bone
Function: to sense pain and regulate bone growth and blood supply to the bone. Nerves tended to be concentrated in metabolically active sites of bone
Pathway: follow the same paths as blood vessels into bone
Types of Bone Cells
Osteogenic cells (Stem cells)
Osteoblasts
Osteocytes (most common)
Osteoclasts (multinucleated)
Osteogenic cells (Stem cells)
Description: high mitotic index, undifferentiated cells which differentiates and develops into osteoblasts
Location: Deep layers of the periosteum and the marrow
Osteoblasts
Description: Forms bone matrix by synthesizing and secreting the collagen matrix and calcium salts
Location: Growing portions of bone, including periosteum and endosteum
Osteocytes (most common)
Osteocytes (most common)
Description: mature cells which maintain the mineral concentration of matrix
Location: Entrapped in lacunae within the calcified matrix
Osteoclasts (multinucleated)
Description: Resorbs bone: breaks down old, injured or unneeded bone and releases calcium into the blood
Location: Bone surfaces and at sites of old, injured, or unneeded bone
Common features of bone
Organization of bone tissue
Lamellae: concentric rings of calcified matrix.
Waterways
Lacunae: Spaces surrounded by calcified matrix which contain fluid & osteocytes
Canaliculi: ultra-small canals radiating in all directions from the lacunae throughout bone matrix. The fluid in the lacunae is continuous with fluid in canaliculi, allowing osteocytes to communicate with each other and to transport nutrients & wastes
In compact bone, canaliculi connect with the canaliculi of other lacunae and eventually with the central canal
Compact Bone
Arrangement: cylindrical osteons which are denser and stronger than spongy bone to provide support and protection
Location: under periosteum and in diaphysis of long bones
Function: provide strength and flexibility
Spongy (cancellous) Bone
Arrangement: Osteocytes and lacunae form a lattice-like network (trabeculae) which are formed along lines of stress to provide strength to the bone
Location: various areas
Function: lighten bone for easier movement. Houses red marrow which is involved in hematopoiesis
Unique features of Compact Bone
Lamellae: concentric rings of calcified matrix.
Concentric lamellae: forms osteons
Interstitial lamellae: occurs between osteons
Circumferential lamella: occurs around the perimeter of compact bones
Osteon (Haversian system): microscopic structural unit of compact bone composed of concentric lamellae
Canals: pathways for blood & lymphatic vessels, nerves to penetrate compact bone
Central (Haversian) canal: center of each osteon
Perforating (Volkmann’s) canal: right angles to central canal and extends to periosteum and endosteum
Canaliculi: ultra-small canals containing osteocytes trapped in solid matrix. Canaliculi connect with the canaliculi of other lacunae and eventually with the central canal.
Classification of bones by shape
- long: Cylinder-like shape, longer than it is wide
Function: Leverage: move when muscle contract
Example: Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges - Short: Cube-like: equal in length, width, & thickness
Function: Provide stability, support, limited motion
Example: Carpals, tarsals - Flat: Thin and curved
Function: Protect internal organs
Example: Sternum, ribs, scapulae, cranial bones - Irregular: Complex shape
Function: Protect internal organs
Example: Vertebrae, facial bones - Sesamoid: Small & round; embedded in tendons
Function: Protect tendons from compressive forces
Example: Patellae
Gross Anatomy of a Long Bone
Parts of a long bone:
Diaphysis: long tubular shaft located between the proximal and distal ends
Epiphyses: Points of connection of tendons and ligaments to bones, wider section at each end filled with spongy bone and red marrow
Metaphysis: Located between diaphysis and epiphyses, contains epiphyseal plate (for growth) or epiphyseal line (in adults)
Medullary cavity: hollow region in the diaphysis filled with yellow marrow
Bone Coverings:
Endosteum: delicate membranous lining in medullary cavity for growth, repair, remodeling
Periosteum: fibrous membrane covering outer surface of the bone (except for at the joints) which contain blood vessels, nerves, and lymphatic vessels to nourish compact bone
Articular cartilage: thin layer of cartilage at joints that reduces friction and acts as a shock absorber
Gross Anatomy of a flat bone
Structure: middle layer of diploë (spongy bone), lined on either side by a layer of compact bone.
Function: three layers work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.
ossification (Bone Formation and Development)
Bone formation (osteogenesis) and development (ossification) starts at week 6 or 7 of embryonic life
Intramembranous ossification
bone development from fibrous membranes
Process: bone develops directly from sheets of mesenchymal (undifferentiated) connective tissue in embryonic skeleton and continues until adult size is reached
Bones formed via this process: facial bones, most cranial bones, clavicle (collarbone)
Endochondral ossification (most common):
bone development from hyaline cartilage
Process: hyaline cartilage acts as a template for bone to build on
Bones formed via this process: Bones at base of skull and long bones
Intramembranous Ossification process
- Mesenchymal cells differentiate into specialized cells, eg capillaries, osteogenic cells and osteoblasts. Early osteoblasts are clustered in an ossification center.
- Osteoblasts secrete osteoid (uncalcified matrix) that quickly calcifies with mineral salt, trapping osteoblasts. Osteoblasts transform into osteocytes. Osteogenic cells continue to differentiate into new osteoblasts.
- Osteoid near capillaries forms a trabecular matrix. Periosteum develops from superficial osteoblasts in spongy bone to create protective compact bone.
- Blood vessels within spongy (trabecular) bone develop into red marrow
Endochondral Ossification process
- Mesenchymal cells differentiate into chondrocytes: template for bones is formed, outer layer forms perichondrium
- Chondrocytes in center get bigger and secrete calcified matrix → inhibits nutrient transport → chondrocytes die and disintegrate → spaces created → spaces enlarge & combine to form medullary cavity.
- Spaces are enlarged by penetrating capillaries → becomes primary ossification center. Capillaries transport osteogenic cells → develop into osteoblasts → periosteal collar of compact bone formed around the diaphysis → perichondrium transformed to periosteum.
- Chondrocytes and cartilage continue to grow at future epiphyses → bone lengthens while replacing cartilage in diaphyses
- After birth, process continues to form secondary ossification centers at epiphyseal regions → continued longitudinal growth of bones
- A fully formed fetal skeleton is left with cartilage only at joint surface (articular cartilage) and between the diaphysis and epiphysis (epiphyseal plate)
Appositional growth (modeling)
growth in diameter
can continue even after longitudinal growth ceases
Osteoclasts resorb old bone lining the medullary cavity, while osteoblasts produce new bone tissue beneath the periosteum via intramembranous ossification to increase the diameter of diaphysis and medullary cavity
