Chapter 6 Review - Bone Flashcards
Bone Function
1 Support 2 Protection 3 Movement 4 Mineral Storage/Homeostasis 5 Hemopoiesis 6 Triglyceride Storage
Support
structural framework for the body.
Protection
protects vital organs & tissues.
Movement
tendons insert into bone & produce movement at joints.
Mineral Storage/Homeostasis
Stores & releases minerals into blood.
Hemopoiesis
Red Bone Marrow produces all the blood elements.
Triglyceride Storage
Yellow marrow of diaphysis stores & releases fat.
Gross Anatomy
206 bones in the body characterized by their shape.
Bone Shape
Long Bones Flat Bones Sutural Bones (wormian) Irregular Bones Short Bones Sesamoid Bones
Long Bones
slender bones of arms, legs, hands, fingers, feet, toes, etc.
Diaphysis, Epiphysis, Metaphysis
Diaphysis
cylindrical shaft of compact bone with a central yellow marrow containing fat. Made up of osteons running in a parallel direction.
Epiphysis
tips of long bone made of spongy (cancellous) bone w/ osteons. Spongy bones are made of struts of bone called trabeculae and the space between is red marrow which functions in hemopoeisis.
Metaphysis
is the region which joins the epiphysis to the diaphysis and contains the growth plate (epiphyseal plate) in growing bone.
Articular Cartilage
tips of epiphysis which articulates with other bones will contain hyaline cartilage:
- Shock absorption
- Reduce friction during movement.
Periosteum
Outermost layer covering the whole bone (except at articulations which have a perichondrium covering articular cartilage). It serves as site of attachment for tendons & ligaments where they are reinforced to the bone by Sharpey’s fibers. Made of two layers:
- Outer layer
- Inner layer
Endosteum
incomplete cellular layer lining the medullary cavities (red & yellow) and participates in bone growth, repair & remodeling
- Osteogenic progenitor cells are present to replace bone
- Osteoclasts present in endosteum spaces to breakdown bone.
Shock Absorption
displacing the weight load over larger surface.
Periosteum Inner Layer
- cellular layer w/osteogenic progenitors to form osteoblasts.
Periosteum Outer Layer
- dense irregular CT
Flat Bones
thin parallel surfaces of roof of skull, scapula, ribs, coxa bone, etc.
Sutural Bones (Wormian)
small flat irregular shaped bones between flat bones of skull (fit like jigsaw puzzle).
Irregular bones
have complex shape as with vertebrae.
Short bones
short boxy bones seen in carpal & tarsals of wrist & ankle.
Sesamoid bones
flat irregular bones which develop in tendons (eg- patella)
Surface Markings
appear on surface owing to physical demands of a given region:
- Rough irregular raised surfaces
- Depressions (fossa) & Grooves (sulcus)
- Tunnels (foramen or canal)
Rough irregular raised surfaces
point of attachment for tendons or ligaments seen as tuberosity, trochanter or tubercle.
Depressions and Grooves
indicates site for nerves or blood vessels.
Depressions
fossa
Grooves
sulcus
Tunnels
foramen or canal
- serves as passageway for nerves or blood vessels.
Histology of Bone
Bone is either compact or spongy. It is largely a calcified matrix with a relatively small number of cells.
Matrix of Bone
50% crystallized mineral salts, 25% collagen & 25% water.
- Collagen
- Hydroxyapatite
- Ossification
Collagen
the fibrous protein that provides the framework for bone.
Hydroxyapatite
crystal from calcium phosphate & calcium hydroxide.
Ossification
process by which minerals crystallize to harden the matrix.
Cells of Bone
Four cells in bone:
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Osteoprogenitor cells
mitotically mesenchymal stem cells which differentiate into osteoblasts. Important for growth & repair.
Osteoblasts
responsible for osteogenesis by synthesizing both osteoid matrix & collagen. After laying down osteoid material, they mature into osteocytes.
Osteocytes
are the mature bone cells that sit in lacunae and communicate via canaliculi to help maintain bone metabolism by exchanging nutrients & wastes.
Osteoclasts
multinucleated macrophage formed from about 50 monocytes and releases both acid & lysosomal enzymes to perform bone resorption. Osteoclasts sit in spaces w/in endosteum
Compact Bone
accounts for about 80% of bone, very strong to handle compression:
- Osteon (Haversian System)
- Circumferential lamellae
- Lacunae: region between lamellae which house osteocytes.
- Canaliculi
- Perforating Canals (canals of Volkmann)
Osteon (Haversian System)
the functional unit of compact bone consisting of repetitive concentric lamellae of bone tissue w/central canal w/a blood vessel.
Circumferential lamellae
Outer most layer of compact bone under periosteum.
Canaliculi
little canals through which osteocytes send cytoplasmic extensions to communicate with other osteocytes (w/gap junctions) and the blood supply.
Perforating Canals (canals of Volkmann)
vessels that enter the bone perpendicular to the diaphysis surface to reach osteon vessels and yellow marrow.
Spongy (cancellous) Bone
less dense (lighter) than compact bone composed of struts of bone called trabeculae which handles stress in many directions.
Trabeculae
is osseous tissue of spongy bone which is arranged in struts to handle stress in many directions. Covered with an incomplete layer of endosteum.
Red Bone Marrow
fills the space between trabecula containing reticular CT with hemopoietic tissue to synthesize blood elements.
Lacunae & canaliculi
have same role as in compact tissue.
Bone Growth
begins during fetal development & extends through adolescence. Growth is by one of two methods: Endochondral or Intramembranous.
Intramembranous Ossification
development of bone directly from embryonic CT, and is associated with flat bones such as skull, mandible & clavical often called dermal ossification
- Ossification centers
- Ossification
- Trabeculae formation
- Red Bone Marrow
- Periosteum
- Outer Compact Bone
Ossification centers IO
Intramembranous Ossification - ONE
mesenchymal cells differentiate into osteoblasts and ossification occurs in fetal (flat) bones.
Ossification IO
Intramembranous Ossification - TWO
Once osteoblast secrete a matrix in which salts crystallize.
Trabeculae formation IO
Intramembranous Ossification - THREE
ossification proceeds as struts or plates of bone which fuse and separate leading to the formation of spongy bone.
Red Bone Marrow IO
Intramembranous Ossification - FOUR
Red Bone Marrow: blood vessels proliferate into spaces between trabeculae and then develop into red bone marrow.
Periosteum IO
Intramembranous Ossification - FIVE
In the last stages of endochondral development, mesenchyme condenses in the periphery forming a periosteum with an inner cellular layer (osteogenic progenitor cells) and fibrous outer layer (dense irregular CT).
Outer Compact Bone IO
Intramembranous Ossification - SIX
is then formed from periosteum leaving the spongy bone sandwiched by outer compact bone with osteons.
Endochondral Ossification
more common in which the bone forms from hyaline cartilage, and then becomes replaced by osteoid tissue:
Cartilage model EO
Endochondral Ossification - ONE
mesenchyme differentiates into chondroblasts creating fetal bones composed of hyaline cartilage. This bone has both interstitial (lengthen) & appositional (widening) growth
Cartilage Model grows EO
Endochondral Ossification - TWO
after chondroblasts lay down a collagen matrix, they mature to chondrocytes which receive nutrients through diffusion, and larger older cells in center of shaft start to die, as boney collar begins to develop externally.
Boney Collar EO
Endochondral Ossification - THREE
a nutrient artery converts perichondrium into a periosteum which begins to lay down a boney collar allowing blood vessels to invade cartilage.
Primary ossifications sites EO
Endochondral Ossification - FOUR
In fetus, invading nutrient artery brings mesenchymal cells that become osteoblasts replacing old dying chondrocytes in the center of the shaft, thus producing spongy bone within diaphysis (epiphysis remains cartilage).
Medullary Cavity EO
Endochondral Ossification - FIVE
Osteoclasts then hollow out the center of the diaphyseal shaft.
Secondary ossification sites EO
Endochondral Ossification - SIX
Around the time of birth, an epiphyseal artery will convert perichondrium to a periosteum and allow blood vessel in to the epiphysis ossifying the cartilage from the inside outward. Trabeculae remains along with red bone marrow (not a hollow marrow).
Articular cartilage EO
Endochondral Ossification - SEVEN
hyaline cartilage remains on ends of epiphysis where bone articulates with another. This region is covered w/perichondrium not periosteum.
Epiphyseal (Metaphyseal) plate EO
Endochondral Ossification - EIGHT
Regions that remains hyaline cartilage and undergoes interstitial growth until closes when entirely replaced by osteoid matrix
Zone of Resting Cartilage
EO. superior layer of chondrocytes closest to the epiphysis.
Zone of Proliferation
EO. next layer which contains mitotically active chondrocytes.
Zone of Hypertrophic Cartilage
EO. lower layer with enlarging maturing chondrocytes moving closer to the diaphysis.
Zone of Calcified Cartilage
EO. lowest layer abutting boney diaphysis and contains large dead chondrocytes in calcified matrix and becomes replaced by advancing osteoblasts from the primary ossification site.
Epiphyseal line
Endochondral Ossification - NINE
shortly after puberty, osteoblast activity overtakes chondrocyte proliferation and the growth plate closes halting interstitial growth.
Appositional growth
Endochondral Ossification - TEN
- is a widening of the bone that occurs from periosteum
a. Osteogenic progenitor cells of periosteum differentiate into osteoblasts which secrete boney matrix. Differentiation is greatest around periosteal blood vessels resulting in boney ridges.
b. Tunnel is formed around blood vessels and ridges merge on each side.
c. Osteons: as bone is laid down around the blood vessel creating concentric lamellae proceeding inward. Older layers are further away from blood vessel.
d. Circumferential lamellae from directly from osteogenic layer under the periosteum. Osteons and circumferential lamellae are part of appositional growth.
Dynamics of Bone
bone remodels throughout life with osteoblasts building new bone and osteoclasts causing bone resorption. Bones reshape according to the applied stress.
Nutritional effects
Influence growth & maintenance:
- Calcium & Phosphorus: needed for matrix
- Vit. D3: required for synthesis of Calcitriol
- Vit C: required for enzymatic reactions in collagen formation.
Hormone Effects
Influence growth & maintenance:
Calcitriol
Growth Hormone & Thyroid Hormone
Sex hormones
Calcitriol
hormone synthesized in kidney and stimulated Calcium absorption from the gut.
Growth Hormone & Thyroid Hormone
both increase chondrocyte activity (of growth plate) & osteoblast activity.
Sex hormones
stimulates osteoblastic activity so that it eventually out-paces chondrocyte activity and closes the growth plate.
Mineral Reservoir
Bone serves as a calcium reservoir:
Parathyroid hormone
Calcitonin
Skeletal System as a Calcium Reserve
thus maintaining calcium homeostasis. Calcium ions play a major role in nerve and muscle activity.
Low calcium levels (35% drop)
will result in hyper-excitable neurons with convulsions.
High calcium levels (30% rise)
can make neurons and cardiac muscles unresponsive.
Parathyroid hormone released when… (and its effects)
is released in response to low blood calcium and serves to raise the blood calcium level at the expense of calcium loss from bone
- Stimulates osteoclast activity and enhances recycling of minerals by osteocytes.
- Increases the rate of intestinal absorption of calcium ions from the gut by working synergistically with Calcitriol.
- Decrease the rate of calcium excretion by the kidneys.
Calcitonin released when… (and its effects)
is released in response to high blood calcium and serves to lower the blood calcium level by storing more calcium in bone:
Inhibiting Osteoclast activity such that osteoblastic activity dominates.
Increasing the rate of calcium excretion by the kidneys.
Fracture
of bone can heal completely because it is so metabolically active. Some of the more common fractures are characterized as:
- Stress fracture
- Closed (simple) fracture
- Open (compound) fractures
- Comminuted fracture
- Greenstick fracture
- Impacted fracture
- Pott’s fracture
- Colles’ fracture
Colles’ fracture
fracture of the distal radius (lateral forearm) in which the distal end (attached to the wrist) is displaced posteriorly.
Pott’s fracture
is a fracture of the distal fibula of the lateral leg which seriously injures the tibia’s articulation with the ankle.
Impacted fracture
one end of the bone is driven into the interior or the other end of the bone.
Greenstick fracture
a partial fracture in which one end breaks and the other bends. This is seen in young children in which the bones are like a live branch and do not completely snap.
Comminuted fracture
in which the ends of the fracture splinter leaving bone fragment between the fractured ends.
Open fractures
(Compound) where the broken ends protrude through the skin.
Closed fracture
(Simple) is a break that does not break the skin.
Stress fracture
is a series of microscopic fissures in the bone without any evidence of injuries to other tissues.
Fracture Healing
Fracture Healing occurs in stages:
- Fracture Hematoma
- Fibrocartilaginous callus
- Boney callus
- Bone remodeling
Fracture Hematoma
FRACTURE HEALING - ONE
develops from broken blood vessels which bleed into the injured site w/in 6 -8 hrs. As normal circulation is interrupted, nearby bone cells die and swelling an inflammation ensues. Phagocytes move into the site to remove the debris over the next several weeks.
Fibrocartilaginous callus
FRACTURE HEALING - TWO
formation occurs over the next 3 weeks. During this time, fibroblasts from the periosteum invade the injured site and produce collagen and cartilage to bridge the injured site and serve as a platform for bone repair.
Boney Callus
FRACTURE HEALING - THREE
starts to form 3-4 wks when osteogenic bone cells (from well-vascularized regions) in the periphery of the fracture site differentiate into osteoblasts and gradually replace the Fibrocartilage callus with spongy bone (moving from the periphery inward). The boney callus lasts about 3 – 4 months.
Bone Remodelling
FRACTURE HEALING - FOUR
occurs in the final stages in which bone takes on a more normal appearance. Osteoclasts reabsorb all the dead fragments, and osteoblasts of the periosteum replace spongy bone with compact bone.
Aging and Demineralization
With aging, osteoclastic resorption out-paces osteoblastic activity (which is normally protected by sex hormones), resulting in osteopenia (demineralization) or osteoporosis (pathological demineralization).
