Skeletal System
The human hand has 27 bones; your face has
14!
You have 206 bones but were born with 300.
The longest bone in your body? Your thigh bone,
the femur -- it's about 1/4 of your height. The
smallest is the stirrup bone in the ear which can
measure 1/10 of an inch.
Did you know that humans and giraffes have the
same number of bones in their necks? Giraffe
neck vertebrae are just much, much longer!
You have over 230 moveable and semimoveable joints in your body.
Skeletal System
Functions:
Support – hold the body up
Protection – protects vital organs from
damage – heart, lungs, brain
Movement – through the joints
Mineral Storage – is a reservoir for calcium
Blood cell production – red and white blood
cells are produced in the bone marrow
Energy Storage – the yellow marrow in
adult bones is fat storage
Types of Bones
Long Bones
Needed to support the weight of the trunk & for
locomotion
Mostly the bones of the limbs
Has a main shaft that is cylindrical with two ends
The wall of the shaft is made of thick compact
bone and only a small amount of spongy bone
on the inside
At the ends there is more spongy bone with a
thin layer of compact bone
Examples: femur, tibia, fibula, metatarsals,
humerus, radius, ulna, metacarpals, phalanges,
clavicles
Long Bones
Flat Bones:
Strong, light, & flat
Used for protection
Two thin layers of compact bone
surrounding spongy bone
(amounts of spongy bone vary
In adulthood, produces most
of the RBC’s
Examples: ribs, sternum
scapula, cranium, ~pelvis
Short Bones:
Strength and compaction
but not much motion
Small bones tied together
by ligaments
Spongy throughout with
a very thin compact layer
at the surface
Examples: carpals, tarsals
(Wrist and ankle bones)
Irregular Bones
Cannot be groups with
any other group
Examples: Vertebrae,
pubis,
Ischium,
Patella,
Hyoid,
Ear
bones
Epiphyseal Line
Articular Cartilage
Spongy Bone
Epiphysis
Medullary cavity
↓
Periosteum
↑
Yellow Marrow
Compact Bone
Bone Parts
Epiphysis – ends of bone (contains spongy bone
and early in life makes RBC’s)
Epiphyseal Plate – cartilage plate where bones grow
Epiphyseal Line – when bone fusion occurs (no more
cartilage) and growth is finished
Articular Cartilage – covering bone ends
Diaphysis – bone shaft
Medullary Cavity – center of bone containing some
spongy bone and in adulthood is filled with fat
(yellow marrow)
Periosteum – fibrous connective tissue covering
over the bone
Parts of the Bone
Bone Histology
Bone Histology
Bone Histology
Haversian Canal (central canal) – run
longitudinally to bone tissue – carry blood
vessels
Volkmann Canal – run perpendicular to
bone tissue and carry blood vessels
Osteocyte – bone cells surrounding
Haversian canals in concentric circles
Lacunae – spaces in the matrix that the
bone cells live in
Bone Histology Continued
Canaliculi – tiny canals through the matrix
connecting each lacunae to the main
blood vessels in the Haversian and
Volkmann canals
Lamellae – concentric circles of matrix
formed by the bone cells
Osteon – whole bone unit including the
Haversian canal, the lamallae and
osteocytes that go with that canal
Histology
Bone Histology
Bone Cells
Osteoprogenitors – stem cells that create all of
the other bone cells. Found in the inner layer of
the periosteum.
Osteoblasts – the bone cells that are actively
creating the matrix – located also on the inner
face of the periosteum.
Osteocytes – mature bone cells that are fully
embedded in matrix and just maintain the matrix.
Osteoclasts – specialized white blood cells that
live in the bone and chew up the bone matrix
and return the protein and calcium to the blood.
Matrix – collagen protein hardened with calcium
phosphate and calcium carbonate.
Bone Remodeling
What is it?
Constant break down and rebuilding of bone
Bone resorption – breaking down bone
Caused by action of osteoclasts
Bone deposition – building of bone
Cause by the action of osteoblasts
Bone Turnover
Purposes of Bone Remodeling:
Turn old bone into new bone
Turn spongy bone into compact bone
Increase the diameter of the bone
(resorbed on inside, built on outside
(matrix secreted by osteoblasts on
periosteum side)
Repair broken bones
Regulation of Bone Dynamics
Weight bearing exercise (mechanical
stress) causes more bone deposition than
resorption
Availability of aa to form the collagen
protein of the matrix
Availability of Minerals (lack of minerals,
especially calcium, will cause bone to be
broken down)
Regulation of Turnover Continued
Vitamins – lack of vitamins will be negative for
bone construction
Vitamin C – necessary for collagen synthesis – so needed to
make and maintain the matrix
Vitamin D – necessary to absorb calcium from blood
Hormones – control balance of bone
resorption/deposition
Estrogen and Testosterone – positive for bone depostion
Insulin – needed for bone deposition
Calcitonin (Thyroid) – positive for bone depostion when blood
calcium is high
Parathyroid Hormone – speeds bone resorption when blood
calcium is low
Osteoclast –
multinucleated,
modified WBC –
“eating bone”
Osteoporosis
Epidemiology – statistics of a disease –
study of a disease in a population
Lifetime risk of breaking a hip, radius, or
spine is 40%
500,000 hospital stays, 83,000 nursing
home stays / year
$5-10 billion/yr cost in US
½ with hip breaks never walk again, ¼
stay in rest homes until death
Osteoporosis is increasing because we
have a large aging population
Bone Turnover - Causes of Osteoporosis
Loss of bone mass after menopause or low peak
bone mass or both
Imbalance of bone resorption and formation
Negative calcium balance – not enough calcium
intake, not enough vitamin D, calcium leeching
Loss of hormone - inhibits osteoclasts and may
signal osteoblasts (takes 100-150 osteoblasts to
form bone destroyed by 1 osteoclast)
Lack of exercise
Low peak bone mass
Higher PTH – activates osteoclasts
Risk Factors – make a person
more likely to get a condition
Being female – men have 30-50% greater bone
mass
Asian
Thin
Late menarchy
Early menopause (doubles the risk of heart
disease and osteoporosis)
Heavy drinking and smoking
Inactivity
Peak Bone Mass Determined By:
Genetics
collagen gene mutation (makes up 80% of bone)
causes bone fragility
Vitamin D receptor – polymorphic
Estrogen Receptor
Bone geometry
Gender
Ethnic origin
African Americans have best bone density >
Caucasians > Asians
Peak Bone Mass Determined By:
Nutrition
Calcium intake
Vitamin D intake
Protein intake
Hormones
Estrogen
Testosterone
PTH
Peak Bone Mass Determined By:
Weight bearing exercise
Other environmental factors
Tobacco use
Alcohol use
Hormone Replacement Therapy
Pros
Increased bone density
Increase in collagen –
younger skin
Decrease menopausal
symptoms like hot flashes
and vaginal dryness
May improve mood
Cons
Increase risk of heart
attack
Increased risk of breast,
ovarian, and uterine
cancer
May increase risk of
blood clots in legs and
lungs
Effects are temporary
Can’t be taken if have
blood clots, migraines,
fibroids, endometriosis
Side effects – bloating,
headaches, mood swings