topic 5 Flashcards
Types of Bones
- Long
* Longer than they are wide
* Examples: most limb bones (this includes the small bones of fingers
and toes) - Short
* Equally long and wide (roughly cube-shaped)
* Examples: carpals of the hand and tarsals of the feet - Flat
* Thin, broad, and often curved
* Examples: skull bones, sternum, ribs - Sesamoid
* Name implies a sesame seed shape: small, flat, and oval-shaped
* Specialized bones found within tendons
* Increase muscle leverage and increase the longevity of tendons
* Example: patella (knee cap) - Irregular
* All bones that do not easily fit into the previous classifications
* Example: vertebrae
macroscopic anatomy of bone
Periosteum
Vascularized dense irregular connective
tissue covering bone except at joint surfaces
Compact bone
* Hard outer layer of bone
* Mostly concentric lamellar osteons and
interstitial lamellae.
* Strong and resistant to compression,
twisting, and shearing stress
Spongy bone
* Underneath compact bone
* Honeycomb-like (sponge-like) network of trabeculae
Endosteum
Thin, vascularized connective
the tissue lining the inner surfaces of
bone
Anatomical structure of long bones.
Diaphysis
* Long axis, or shaft
* Thick layer of compact bone (minimal spongy bone)
Epiphyses
* Rounded ends
* Spongy bone with a compact bone shell
* Covered by hyaline cartilage to reduce friction from the adjoining bones
Metaphyses
* Narrow portion between epiphysis and diaphysis
* Major site of bone growth
Epiphyseal lines
* Within the metaphyses
* Remnants of the epiphyseal plates
(growth plates)
Red Marrow
Contains hematopoietic stem cells that produce blood cells
Infants & young children have mostly red marrow to support rapid growth and increasing blood cell requirements
In the medullary cavities of flat bones, as well as in the ends of long bones
Yellow Marrow
At age five, yellow marrow begins to replace red marrow
Yellow marrow contains adipocytes
By adulthood, the amount of red marrow is usually less than yellow marrow
in the medullary cavity of the shaft of long bones
Osteocyte
maintains bone tissue
Mature osteoblasts that
maintain bone health
osteoblasts
Forms Bone Matrix
Osteogenic cell
Stem Cell develop into Osteoblasts
Osteoclasts
Resorbs Bone
Inorganic matrix
– 65% of bone weight
– Provides strength
- Mostly hydroxyapatite– calcium
phosphate crystals – Ca5(PO4)3OH - Makes bone hard and strong and extra resistant to compression
- Also find bicarbonate, potassium,
magnesium, and sodium
spongy bone
Spongy bone is made up of trabeculae - a loose meshwork of extensively branched bone tissue.
No osteons, central canals, or perforating canals
* Trabeculae do have lamellae, lacunae housing osteocytes, and
canaliculi (allow the cells to obtain oxygen and nutrients from blood vessels supplying the marrow)
Compact Bone Microscopic Anatomy
Osteons
Cylindrical structures of
multiple concentric lamellae
(4-20) surrounding a central
canal
Lamellae
* Thin rings of bone tissue
* Collagen fibers of adjacent
lamellae orient in opposite
directions to resist twisting and
bending forces in several
directions
Central canal
Passageway for nerves and blood
vessels that innervate and supply the
cells of the osteon
Perforating canals
* aka Volkmann’s canals
* Perpendicular to
central canals
* Allow blood vessels and nerves
to enter the bone & connect centrally
canals to each other
Canaliculi
* Tiny canals
* Connect lacunae to the central canal
* Provide nutrients to osteocytes
Organic matrix (osteoid)
– 35% of bone weight
– Provides flexibility
- Collagen fibers align with hydroxyapatite crystals to increase bone’s hardness
- Other proteins (proteoglycans, various bone-specific proteins, etc.); some of these trap water, keeping bone hydrated/healthy and helps resist compression
Intramembranous ossification
- Bone develops from within a fibrous membrane
- Forms facial bones, cranial bones, and clavicles
Endochondral ossification
Bone develops from a hyaline cartilage model
* Quite complex – hyaline cartilage must be broken down as ossification occurs
* Forms almost every bone below the skull (except clavicles)
Longitudinal growth
Proliferation zone: chondrocytes divide, pushing older cells toward the diaphysis.
Hypertrophic zone: as cells move
toward diaphysis, they begin to
hypertrophy and die
Calcification zone When chondrocytes die, the matrix becomes calcified by the surrounding tissues
Ossification zone
Invaded by blood vessels & bone cells
* Osteoclasts break down the
existing cartilaginous matrix
* Osteoblasts can begin to deposit
bone matrix.
Appositional growth
- Osteoblasts creating new bone at the surface
- Osteoclasts resorbing old bone lining the medullary cavity
Hormones
- Growth hormone (GH)
– Increases length of bones by stimulating chondrocytes in
the epiphyseal plate
– Increases bone density by increasing Ca2+ retention &
stimulating activity of osteoblasts - Thyroxine
– One of the two thyroid hormones
– Works with GH to by promoting osteoblast activity - Sex hormones
– Testosterone & estrogen
– Promote activity of osteoblasts
– Cause the growth spurt(s) during adolescence
– Eventually cause closure of the epiphyseal plate (convert it
to bone – now the epiphyseal line)
Bone remodeling
involves both bone creation (by
osteoblasts) and bone resorption (by osteoclasts), and is influenced by:
- Hormonal regulation of Ca2+ homeostasis
- The physical forces/demands placed upon bones (Wolff’s law)
Why Ca 2+
Wolfs Law
Bones will remodel themselves over time to become stronger and resist the loads placed on them
Bone Fracture
(1) Fracture hematoma forms
* Torn blood vessels bleed
* Blood begins to clot
* 6-8 hours after fracture clotted
blood forms the fracture hematoma
(2) Internal & external calli form
* Occurs within approx. 48 hrs
* Internal – fibrocartilaginous
* External – hyaline cartilage & bone
* Provide stability
(3) Calli replaced by trabecular bone
* Osteoclasts resorb the dead bone
* Osteogenic cells differentiate into
osteoblasts
* Calli replaced by trabecular bone
via endochondral ossification
* Occurs over several (6-8) weeks
(4) Remodeling occurs
* Healing is complete
* Compact bone replaces spongy
bone at the outer margins
* Remodeling in response to usage
will return bone to its typical
structure (over several months)
Osteoporosis
Most frequently
encountered bone
disease
* Healthy bone has
a balance between
osteoblast and
osteoclast
activities
* With osteoporosis,
balance tips
toward osteoclasts
and bone
Weakened bones cannot adequately
support weight nor resist breakage!
* Stooped posture & loss of vertical height
* Increased susceptibility to fracture of:
– Hips
– Forearms
– Wrists
– Vertebrae
Pagets Diseases
- Problem with bone remodeling
- Excessive bone resorption followed
increased bone formation - Results in enlarged and deformed bones
- Bones can weaken, resulting in bone pain,
arthritis, deformities, and fractures - Idiopathic – possibly viral or inherited
