Download Bone Physiology PPT

Bone Tissue
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Bone is made up of several
different tissues working
together: bone, cartilage,
dense connective tissue,
epithelium, various blood
forming tissues, adipose tissue,
and nervous tissue
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Each individual bone is an organ
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The bones, along with their
cartilages, make up the
skeletal system
Functions of Bone
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Supporting & protecting soft
tissues
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Attachment site for muscles
making movement possible
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Storage of minerals, especially
calcium & phosphate (mineral
homeostasis)
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Blood cell production occurs in
red bone marrow (hemopoiesis &
EPO)
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Energy storage in yellow bone
marrow
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Gives pirates something to put on
their flags
Anatomy of a
Long Bone
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Diaphysis = shaft (compact
bone)
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Epiphysis = one end of a
long bone (spongy bone)
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Metaphyses are the areas
between the epiphysis and
diaphysis and include the
epiphyseal plate in growing
bones
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Articular cartilage over
joint surfaces acts as
friction reducer & shock
absorber
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Medullary cavity = marrow
cavity
Anatomy of a
Long Bone
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Endosteum = lining of
marrow cavity
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Periosteum = tough
membrane covering bone
but not the cartilage
 Fibrous layer = dense
irregular connective
tissue
 Osteogenic layer = bone
cells & blood vessels
that nourish or help
with repairs
Anatomy of a
Flat Bone
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Internal and external
surfaces formed of
compact bone
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Middle layer is spongy bone
and red bone marrow
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Fractures may break the
compact bone layer but
leave the spongy bone
relatively unharmed
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Bone is a type of connective
tissue as seen by widely
spaced cells separated by
matrix
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Matrix of 25% water, 25%
collagen fibers & 50%
crystalized mineral salts
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~85% hydroxyapatite, a
crystalized calcium
phosphate salt
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Mineral salts are deposited in
a framework of collagen
fibers, a process known as
mineralization or calcification
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Hardness of bone depends on
mineral salts, flexibility
depends on collagen fibers
(“like fiberglass”)
General Histology of Bone
Bone Cells
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Osteogenic Cells: Undifferentiated cells
 can divide to replace themselves & can become osteoblasts
 found in inner layer of periosteum and endosteum
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Osteoblasts: Form matrix & collagen fibers but can’t divide
Osteocytes: Mature cells that no longer secrete matrix, now trapped
in the matrix they secreted
Osteoclasts: Huge cells from ~50 fused monocytes (WBC)
 function in bone resorption at surfaces such as endosteum
Compact
or Dense
Bone
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Looks like solid hard layer of bone
Makes up the shaft of long bones and the external layer of all bones
Resists stresses produced by weight and movement
Compact or Dense Bone
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Compact bone is arranged in
units called osteons or
Haversian systems
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Osteons contain blood vessels,
lymphatic vessels, nerves, and
osteocytes along with the
calcified matrix
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Osteons are aligned in the same
direction along lines of stress,
which can slowly change as the
stresses on the bone change
Histology of Compact Bone
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Osteon is concentric rings
(lamellae) of calcified
matrix surrounding a
vertically oriented blood
vessel
Osteocytes are found in
spaces called lacunae
Osteocytes communicate
through canaliculi filled
with extracellular fluid
that connect one cell to
the next cell
Interstitial lamellae
represent older osteons
that have been partially
removed during tissue
remodeling
Structure and Histology of Spongy Bone
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No Osteons
Generally does NOT contain osteons
Latticework of thin plates of bone called trabeculae oriented along lines of stress
Provides strength with little weight
Spaces in between struts of trabeculae are filled with red marrow where red blood
cells develop
Central canals not needed because no osteocyte is far from the marrow
Found in epiphyses of long bones and inside flat bones such as the hipbones, sternum,
sides of skull, and ribs
Blood and Nerve Supply of Bone
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Periosteal arteries
 Supply periosteum
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Nutrient arteries
 Enter through nutrient
foramina
 Supply compact bone of
diaphysis & red marrow
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Metaphyseal & epiphyseal
arteries
 Supply red marrow &
bone tissue of epiphyses
Bone Formation
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All embryonic connective tissue begins as mesenchyme
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Bone formation is termed osteogenesis or ossification and begins when
mesenchymal cells provide the template for subsequent ossification
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Two types of ossification occur
 Intramembranous ossification is the formation of bone directly from or within
fibrous connective tissue membranes
 Flat bones of the skull
 Thin layers of compact bone with spongy bone in the middle
 Endochondrial ossification is the formation of bone from hyaline cartilage
models, forming most of the bones in the body
 Two growth centers: primary & secondary
 Two types of growth: interstitial & appositional
Intramembranous Bone Formation
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Mesenchyme condenses into sheets
Osteoblasts secrete matrix & become osteocytes, periosteum forms
Trabeculae form, creating spongy bone
Calcification converts surfaces to compact bone
Endochondral Bone Formation
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Cartilage model forms
Formation of periosteum and the primary ossification center in the diaphysis
Vascular invasion, formation of medullary cavity
Formation of secondary ossification center in epiphysis
Epiphyseal plate forms, bone grows in length from this plate
Epiphyseal plate closes to form epiphyseal line, bone stops growing
Bone Growth in Length
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Epiphyseal plate or cartilage growth plate
 Cartilage cells are produced by mitosis on
epiphyseal side of plate
 Cartilage cells are destroyed and replaced
by bone on diaphyseal side of plate
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Between ages 18 to 25, epiphyseal plates close
 Cartilage cells stop dividing and bone
replaces the cartilage, forming the
epiphyseal line
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Growth in length stops at age ~25
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Zone of reserve cartilage
 Anchors growth plate to bone
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Zone of cell proliferation
 Rapid cell division (stacked
coins)
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Zone of cell hypertrophy
 Mitosis stops, cells enlarge
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Zone of calcification
 Cartilage matrix calcifies
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Zone of bone deposition
 Osteoclasts break down
lacunae
 Osteoblasts & capillaries move
in to create bone over
calcified cartilage
Zones of Growth in
Epiphyseal Plate
Bone Growth in Thickness
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Only by
appositional
growth at the
bone’s surface
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Periosteal cells
differentiate into
osteoblasts and
form bony ridges
and then a tunnel
around periosteal
blood vessel
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Concentric
lamellae fill in the
tunnel to form an
osteon
Factors Affecting Bone Growth
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Nutrition
 Adequate levels of minerals and vitamins
 Calcium and phosphorus for bone growth
 Vitamin C for collagen formation
 Vitamin K and Vitamin B12 for protein synthesis
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Sufficient levels of specific hormones
 During childhood need insulinlike growth factor (IGF)
 Promotes cell division at epiphyseal plate
 Human growth hormone (hGH), thyroid hormones, & insulin
 Sex steroids at puberty
 Estrogen and testosterone, stimulate sudden growth and modifications of
the skeleton to create the male and female forms
Testosterone
Hormonal Abnormalities in Bone Growth
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Oversecretion of hGH during childhood produces giantism
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Oversecretion of hGH during adulthood results in acromegaly
 From the Greek akros = high and megalos = large
 Individuals with acromegaly have unusually large facial features, large
hands, large feet, and wide tooth spacing
 Usually caused by a benign tumor of the pituitary gland
 Today acromegaly can be treated with drugs or surgery
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Undersecretion of hGH or thyroid hormone during childhood produces short
stature
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Both men or women that lack estrogen receptors on cells grow taller than
normal
 estrogen is responsible for closure of growth plate
Hormonal Abnormalities in Bone Growth
• Worked as a journalist
 The Brute Man
 Jungle Captive
 House of Horrors
 The Creeper
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Rondo Hatton (1894 - 1946)
Suffered from acromegaly
“Star” of “fright films” of the 1930’s & 1940’s
Immortalized by the Rondo Hatton Classic
Horror Awards
• Originally given a bit part in
a movie because of his looks
• Inducted into his HS
football team’s Hall of Fame
Hormonal Abnormalities in Bone Growth
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Richard Kiel (1939 -)
“Jaws” in James Bond
films
Also in Happy Gilmore
& other films
Hormonal Abnormalities in Bone Growth
Mineral Homeostasis
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Bone is a storehouse for calcium
and phosphate
Phosphate is important in many
physiological processes
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Needed for ATP
Component of DNA, RNA
Forms phospholipid bilayer
The body’s pH buffering system
Calcium is one of the most important regulatory elements in the body
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Needed for muscle contraction
Needed for release of neurotransmitter from synaptic end bulbs
Excess blood calcium is hypercalcemia (muscle weakness)
Insufficient blood calcium is hypocalcemia (muscle spasms)
Mineral Homeostasis
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Calcitriol is a form of Vitamin D produced by the skin, liver, & kidney
 Raises blood calcium by promoting absorption in small intestine & from bones
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Calcitonin is secreted by the thyroid gland
 Lowers blood calcium by stimulating osteoblasts & inhibiting osteoclasts
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Parathyroid hormone (PTH) is secreted by the parathyroid glands
 Raises blood calcium by stimulating osteoclasts & promoting resorption
Mineral Homeostasis
• Hypercalcemia is excess Ca2+ in the blood
• Hypocalcemia is insufficient Ca2+ in the blood
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Regulation of blood calcium provides a good demonstration of negative
feedback loops
Bone Fractures
Repair of a Fracture
1) Formation of fracture hematoma
 Damaged blood vessels produce clot in 6-8 hours, bone cells die
 Inflammation brings in phagocytic cells for clean-up duty
 New capillaries grow into damaged area
2) Formation of fibrocartilagenous callus
 Fibroblasts invade the fracture site & lay down collagen fibers
 Chondroblasts produce fibrocartilage to span the broken ends of the bone
Repair of a Fracture
3) Formation of bony callus
 Osteoblasts secrete spongy bone that joins 2 broken ends of bone
 Lasts 3-4 months
4) Bone remodeling
 Compact bone replaces the spongy bone in the bony callus
 Surface is remodeled back to normal shape
Exercise And Bone Tissue
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Within limits, bone has the ability to alter its strength in response to
mechanical stress by increasing deposition of mineral salts and production
of collagen fibers (Wolff’s Law)
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Removal of mechanical stress leads to weakening of bone through
demineralization (loss of bone minerals) and collagen reduction
 Reduced activity while in a cast
 Astronauts in weightless environment
 Bedridden person
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Weight-bearing activities, such as walking or
moderate weightlifting, help build and retain
bone mass
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Decreased bone mass resulting in porous
bones
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Those at risk
 White, thin, menopausal females
 Athletes who are not menstruating due to
decreased body fat & decreased estrogen
levels
 People allergic to milk or with eating
disorders whose intake of calcium is too low
 Smoking, drinking, & family history increase
risk
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Prevention or decrease in severity
 Adequate diet, weight-bearing exercise, &
estrogen replacement therapy (for
menopausal women)
 Behavior when young may be most important
factor
Osteoporosis