Bone Tissue Ch. 6 Flashcards
Different Tissues in and on Bone
- Dominated by bone connective tissue
- Contain cartilage on articular surfaces
- Contain nervous tissue and blood connective tissue
- Contain epithelial tissue lining blood vessels
Cartilage
- firm & flexible connective tissue
- resilient tissue that springs back to original shape
- no or few blood vessels/nerves
- matrix contains up to 80% water (yet it is firm)
- comes from chondrocytes
- cell type is chondrocyte
- chondroblasts are found in growing cartilage
Two growths of cartilage are
- appositional growth
- interstitial growth
Appositional growth
- perichodrium (look it up in latin terms) is membrane of fibrous connective tissue that surrounds the external surface of cartilage
- chondroblasts in surrounding perichondrium produce new cartilage
Interstitial growth
- chonodroblasts produce matrix
- chondrocytes (mature chondroblasts) lie in lacunae, divide & secrete new matrix
- Lacuna is a small depression or cavity in bone and/or cartilage that contains a cell
- interstitial growth of cartilage stops when the skeleton stops growing
3 types of Cartilage
- Hyaline Cartilage
- Elastic Cartilage
- Fibrocartilage
Hyaline Cartilage Histology & function
- rich in collagen fibers with glassy appearance
- imperceptible collagen fiber (hyaline=glassy)
- Amorphous but firm matrix
- most abundant cartilage
- supports and reinforces
- resilient, flexible, cushion
- resists repetitive compressive stress
Hyaline Cartilage location
- embryonic/fetal skeleton
- articular cartilage at ends of adjoining bones of moveable joints
- costal cartilage of ribs; attachments of ribs to sternum
- nose
- respiratory tubular structures in neck and thorax including, trachea, bronchi
- in the end of long bones
Fibrocartilage histology & function
- matrix similar but less firm than hyaline cartilage
- not that glassy
- thick collagen fibers predominate
- resists strong compression (pushing pressures) & strong tension (pulling pressures)
- tensile strength & ability to absorb compressive shock
Fibrocartilage locations
- public symphysis (the area in a woman’s body that opens up for birth)
- knew joints
- articular discs of some joints, e.g., menisci in knees
- annulus fibrosis portion of the discs in between vertebrae
Elastic cartilage histology & function
- Similar to hyaline cartilage
- More elastic fibers in matrix than hyaline cartilage
- Contains many elastic fibers in addition to collagen fibers
- Allows great flexibility
- Able to tolerate repeated bending (i.e. ear)
- Maintains shape of structure
Elastic Cartilage location
•External ear pinnae •Epiglottis
Function of Bones
- Support—provides hard framework
- Movement—attachment site for ligaments and muscle tendons; skeletal muscles use bones as levers
- Protection—of underlying organs
- Blood-cell formation—bone contains red marrow
- Fat storage—in yellow marrow in middle of bone
- Mineral storage—reservoir for important minerals e.g., phosphorus and calcium
- Energy metabolism—osteoblasts secrete osteocalcin which stimulates pancreas to produce more insulin and induces fat cells to become more insulin sensitive
Bone Tissue
MAKE SURE TO ADD THE LOCATION AND FUNCTION FROM SLIDE
•Organic components: cells, fibers, and ground substance
•Inorganic components: mineral salts that deposit in bony matrix
•Ground substance calcified with inorganic salts
•Calcified matrix contains many collagen fibers
•Well vascularized
-osteocytes live within lacuna
Composition of bone
- 35%—organic components (especially collagen)
* 65%—inorganic components (hard crystals)
Organic components of Bone Tissue
- Makes up 35% of bone
- Rich in collagen fibers which provide tensile strength and flexibility to resist twisting & pulling
- Tensile strength is the force required to pull something until it breaks
Inorganic components of Bone Tissue
- Makes up 65% of bone
- Inorganic hydroxyapatites, mineral salts e.g., calcium phosphate
- Mineral salt crystals pack tightly in and around the collagen fibrils of the extracellular matrix to give bone its exceptional hardness to resist compression
Bone cells which produce or maintain bone
MAKE INTO SEPERATE FLASH CARDS
•Osteogenic cells—stem cells that differentiate into osteoblasts
•Osteoblasts—actively produce and secrete bone matrix (osteoid) that contains ground matrix & collagen fibrils
•Within a week of osteoid
secretion, inorganic
calcium salts crystallize
within osteoid
•Osteocytes—mature bone cells in lacunae that maintain bone matrix
•Osteoclasts—responsible for bone resorption
Classification of Bone Shapes
- Long bones: longer than wide; a shaft plus two ends; common in extremities
- Short bones: roughly cube-shaped; in wrist and ankle; sesamoid bones are a special type of short bone which are sesame seed shaped and include kneecaps
- Flat bones: thin and flattened, usually curved; includes ribs, sternum, scapula and some cranial bones
- Irregular bones: various shapes, do not fit into other categories; include vertebrae and hip bones
Gross Anatomy of Bones
- Compact bone has dense outer layer of bone
- Spongy bone (also called trabecular bone) has internal three-dimensional network of bone with small needle-like or flat pieces called trabeculae; open spaces in between trabeculae are filled with red bone marrow (mainly hematopoietic cells) and/or yellow bone marrow (mainly adipose cells)
Typical Long Bone Structure
- Diaphysis: “shaft”long axis of a bone
- Epiphysis: ends of a bone with joint surfaces typically covered with a thin layer of hyaline cartilage called articular cartilage
- Epiphyseal line runs in between the diaphysis and epiphysis in adults and is the remnant of the epiphyseal plate (this is where the growth plate use to be)
- Blood vessels: unlike cartilage, bones are well vascularized
- Medullary cavity: the center of the diaphysis has no spongy bone and is filled with yellow bone marrow
- Membranes: periosteum surrounds bone and endosteum lines medullary cavity and inner surface of osteons
Periosteum & Perforating Fibers
- Periosteum:connective tissue membrane which covers the external surface of the bone, except the ends of the epiphyses which are covered with articular cartilage
- Two layers of periosteum
- Deep inner periosteum layer abuts the outer surface of the compact bone; this deep layer is osteogenic and forms osteoblasts and osteoclasts
- Superficial outer periosteum layer of dense irregular connective tissuewhich resists tension placed on the bone
- Perforating fibers (Sharpey’s fibers) secure periosteum to the underlining bone with thick bundles of collagen that run from periosteum into bone matrix
- Periosteum provides insertion points for tendons and ligaments with dense concentrations of perforating fibers at these insertion sites
Endosteum
SLIDE 46
- Lines medullary cavity
- Thin connective tissue membrane layer which lines internal bone surfaces including trabeculae of spongy bone and inner surface of central canals of osteons (long cylindrical structures which run along long axis of bone)
- Endosteum is osteogenic and contains both osteoblasts and osteoclasts
Osteons of compact bones
•Contains passage ways for blood vessels, lymph vessels, and nerves
•*Osteons* (Haversian System): long cylindrical structures oriented parallel to the long axis of the bone
•Function in support
•Structurally has transverse
cross-section of individual
osteons resemble tree
rings
•Group of concentric tubesOsteons contain
LEARN WHAT A LACUNA IS
•Lamellae •Central canal •Perforating (Volksmann’s) canals •Canaliculi -lacuna (which contains osteocyte)
Osteons of Compact Bones
- Each osteon is a group of concentric tubes
- Each concentric tube is a lamella with a layer of bone matrix in which the collagen fibers and mineral crystals align and run in a single direction
- The fibers and crystals of adjacent lamella run roughly perpendicular
- This alternating pattern is optimal for withstanding torsion (twisting) stresses and inhibiting crack propagation and fracture development
Central Canal/Haversian System
- Canal which runs through each osteon
- Central canal is lined with the osteogenic endosteum layer
- Lamella are added to the inner surface of the osteon which decreases the diameter of the inner canal
- Perforating (Volkmann’s) canals lie at right angles to the central canals and central marrow cavity and connect the blood and nerve supply of the periosteum to these areas
Canaliculi
- Osteocytes (mature bone cells) are spider shaped and their bodies occupy small cavities in the solid matrix called lacunae and their “legs”occupy thin tubes called canaliculi
- Canaliculi connect neighboring lacunae to one another and to capillaries for nutrient supply
- Within the canaliculi, the extensions of the neighboring osteocytes touch and form gap junctions for nutrient exchange
Lamellae outside of osteons
- Interstitial lamellae: groups of incomplete lamellae which lie between osteons; these are remains of old osteons cut through by bone remodeling
- Circumferential lamellae: extends around the entire circumference of the diaphysis
Microscopic Structure of Spongy Bone
- Less complex than compact bone
- Trabeculae are too small to contain osteons or its own blood vessels
- Trabeculae contain several layers of lamellae and osteocytes
- Osteocytes receive nutrients from capillaries in the endosteum surrounding the trabeculae via connections through the canaliculi
Ossification(osteogenesis): bone-tissue formation
•Membrane bones (e.g. cranial bones, clavicles)—form directly from mesenchyme through intramembranous ossification without first being modeled in cartilage
this doesn’t start off with cartilage
•Endochondrial bones—develop initially from hyaline cartilage which is replaced by bonethrough a process called endochondral ossification
this starts off with cartilage first
Intramembranous ossification
•Ossification center appears in fibrous connective tissue membrane where mesenchymal cells differentiate into ostoblasts
•Osteoblasts secrete osteoid (bone matrix) within fibrous matrix which calcifies; “trapped”osteoblasts become osteocytes
•Woven bone (network of trabeculae) and periosteum form (have blood vessels running through it)
•Compact lamellar bone replaces woven bone just deep to periosteum and red marrow appears in spongy bone (diploe)
-spongy bone is rich red blood cells
Structure of Short, Irregular, & Flat Bones
•Flat bones, short bones, and irregular bones
–Have no diaphysis
–Hard dense compact outer layer of bone
–Diploë: internal spongy
bone with trabeculae flat
bones
–No deep marrow
(medullary) cavity is presentEndochondrial Ossification
- All bones except some bones e.g., some skull bones and clavicles
- Bones are modeled in hyaline cartilage
- Begins forming late in the second month of embryonic development
- Continues forming until early adulthood
Stages of endochondral ossification
- Week 9 gestation: bone collar forms around hyaline cartilage
- Cartilage in center of diaphysis calcifies and forms cavities
- Month 3 gestation: periosteal bud with blood vessel invades internal cavities and spongy bone begins to form
- Birth: secondary ossification center forms in epiphyses
- Childhood to adolescence: epiphyses ossify, hyaline cartilage only remains in epiphyseal plates and articular cartilages
Anatomy of Epiphyseal Growth Areas in Growing Bones
- Hyaline cartilage is organized for quick, efficient growth
- Cartilage cells form stacks with rapidly dividing chondroblasts just inside of the epiphyseal plate (in direction of diaphysis)
- Pushes the epiphysis away from the diaphysis (causing growth)
- Lengthens entire long bone
Epiphyseal plate
- Resting zone: cells nearest the epiphysis that are relatively small and inactive•Columns of stacked cartilage cells are inside the resting zone (in direction of diaphysis)
- Proliferation zone is made up of chondroblasts at the top of the stack which divide quickly which pushes the epiphysis away from the diaphysis causing the bone to elongate
- Hypertrophic zone: older chondrocytes have enlarged in size (hypertrophied) and are positioned deep in the stack •Calcification zone: The older hypertrophied chondrocytes signal the surrounding cartilage matrix to calcify and produce a calcification zone
- Ossification zone: new bone formation
Postnatal Childhood and Adolescent Growth of Endochondrial Bones
- Bones lengthen entirely by growth from the epiphyseal plates
- Cartilage is replaced with bone tissue in diaphysis side as quickly as it grows
- Whole bone lengthens
- Epiphyseal plate maintains constant thickness during growth of diaphysis
Postnatal Growth of Endochondrial Bones
•*Growing bones widen as they lengthen*
–*Osteoblasts*—add bone
tissue to the external
surface along the diaphysis
–Osteoclasts—remove
bone from the internal
surface along the diaphysis
as remodeling takes place
with increase in diameter
•*Appositional growth*—growth of a bone by addition of bone tissue to its surfaceHormone Regulation of Bone Growth
•Growth hormone—produced by the pituitary gland–Stimulates epiphyseal plates
•Thyroid hormone—ensures that the skeleton retains proper proportions
•Steroid hormones(estrogen and testosterone)
–Promote bone growth
–Later induce closure of
epiphyseal plates
At end of adolescence, long bone growth ends
- Chondroblasts divide less often and then stop dividing
- Epiphyseal plates become thinner
- Cartilage stops growing and is replaced by bone tissue
- Long bones stop lengthening when the bone of the diaphysis and epiphysis fuse and epiphyseal plates close
- People can no longer grow in height once their epiphyseal plates have closed
Bone Remodeling: bone is a dynamic tissue
- 500 mg of calcium may enter or leave the adult skeleton each day
- Cancellous (spongy) bone of the skeleton is replaced every 3–4 years in most bones
- Compact bone is replaced every 10 years in most bones
Bone deposition and resorption
•Occurs at periosteal (periosteum) and endosteal
(endosteum) surfaces
•In adults, this occurs primarily at the endosteal surface
Bone Remodeling
- Bone deposition/formation—accomplished by osteoblasts
- Bone resorption—accomplished by osteoclasts
- Maintains normal levels of Ca+ and PO43-in body fluids
- Bone is remodeled in response to mechanical stress it experiences
Osteoclast: A Bone-Degrading Cell
•A giant cell with many nuclei •Derived from hematopoietic stem cells -resorption bone •Crawls along bone surfaces •Breaks down bone tissue -Secretes concentrated HCl –Releases lysosomal enzymes –May also phagocytize collagen and dead osteocytes
Bone design & stress
- Superficial surfaces of bones reflect stresses on them
- Bones are subjected to stresses as weight bears down on them and as muscles pull on them
- Bending compresses bone on one side and stretches bone (subjects it to tension) on the other side
- The trabeculae of spongy bones align along lines of stress in an organized pattern to provide structural support
Bone design and stress
•Bone design and stress
–Anatomy of a bone reflects stresses
–Compression and tension greatest at external surfaces
Phases of healing of simple fracture
- Hematoma formation: blood vessels break in periosteum and inside bone
- Fibrocartilaginous callus formation: within a few days new blood vessels from the periosteum and endosteum grow into the clot filling it with fibrous granulation tissue called soft (fibrocartilaginous) callus
- Bony callus formation: Within a week, trabeculae bone begin to form in bony callus
- Bone remodeling: Over many months the bone callus is remodeled
Types of fractures
- Comminuted: 3 or more bone fragments
- Compression: bone crushed e.g., a crushed vertebra
- Spiral: caused by twisting force
- Epiphyseal: epiphysis separates from diaphysis •Depressed: fractured bone depressed inward
- Greenstick: only one side of long bone fractures
Osteoporosis
- Characterized by low bone mass
- Bone resorption outpaces bone deposition
- Increased ratio of osteoclasts to osteoblasts activity
- Compact bone becomes thinner and less dense and spongy bone has fewer trabeculae
- Occurs most often in women after menopause
Disorders of Bones
•Osteomalacia (“soft bones”)
–bones are inadequately
mineralized
•Rickets
–Children with inadequate
intakes of vitamin D can
develop inadequately
mineralized bones
–Bones are “soft”which can
cause the child to have
bowed legs and cranial
bone deformitiesThe Skeleton Throughout Life
- Skeleton grows until the age of 18–21 years
- In children and adolescents, bone formation exceeds rate of bone resorption
- In young adults, bone formation and bone resorption are in balance
- In old age, bone resorption exceeds rate of bone formation
- Bone mass declines with age after young adulthood
