 Functions
of the skeletal system
 __________________ (support for body,
attachment for soft tissues)
 Storage of _______________ (calcium and
phosphate)

Calcium most abundant mineral in body (~2–4
lb)

98% stored in bones
Blood ____________ production (all
formed elements of blood)
 Protection (delicate tissues and organs
surrounded by bone)
 ____________________ (act as levers with
skeletal muscles to move body)

 Six
1.
categories based on shape
____________ bones


2.
Sutural bones (Wormian bones)


3.
Thin, roughly parallel surfaces
Examples: cranial bones, sternum
Irregular bones formed between cranial bones
Number, size, and shape vary
___________ bones


Relatively long and slender
Examples: various bones of the limbs

Six categories based on shape (continued)
Irregular bones

Complex shapes

Examples: vertebrae, bones of pelvis, facial bones
5. _______________ bones

Small, flat, and somewhat shaped like sesame seed

Develop in tendons of knee, hands, and feet
4.

6.
Individual variation in location and number
Short bones

Small and boxy

Examples: bones of the wrist (carpals) and ankles
(tarsals)
 Bones

are important mineral reservoirs
Mostly _____________________________ but
other ions as well
 Calcium




Most abundant mineral in body
1–2 kg (2–4 lb)
~__________% deposited in skeleton
Variety of physiological functions


Concentration variation greater than 30–35% affects
neuron and muscle function
Normal daily fluctuations are <10%

Levels controlled by activities of:



Intestines
 Absorb calcium and phosphate under hormonal control
Bones
 Remodeling by osteoblasts and osteoclasts
Kidneys
 Calcium and phosphate loss in urine under hormonal control
 As
a calcium reserve, skeleton has primary role in
calcium _________________________
 Has direct effect on shape and length of bones


Release of calcium into blood weakens bones
Deposit of calcium salts strengthens bones
 Factors


that increase blood calcium levels
____________________ hormone
Responses



Bones: stimulates osteoclasts to release calcium
Intestines: enhances calcitriol effects and increases
calcium absorption
Kidneys: increase release of hormone calcitriol,
which causes calcium reabsorption in kidneys
 Factors

that decrease blood calcium levels
___________________

Responses
 Bone: decrease osteoclast activity
 Intestines: decreased absorption with decreasing
PTH and calcitriol
 Kidneys: inhibits calcitriol release and calcium
reabsorption
 Long

bone features
______________________ (expanded ends)



Consist largely of _________________ bone
(trabecular bone)
 Network of struts and plates
 Resists forces from various directions and directs
body weight to diaphysis and joints
Outer covering of ______________________ bone
 Strong, organized bone
Articular _________________________
 Covers portions of epiphysis that form articulations
 Avascular and receives resources from synovial fluid
 Long


bone features (continued)
_____________________________ (connects
epiphysis to shaft)
______________________ (shaft)

Contains medullary cavity (marrow cavity)
 Filled with marrow


Red bone marrow (red blood cell production)
Yellow bone marrow (adipose storage)
Coronal sections through a right femur, showing the boundaries of a long bone’s major
regions, plus the bone’s internal organization and how it distributes the forces applied
to the bone
The epiphysis
(e-PIF-i-sis) is an
expanded area
found at each end
of the bone.
The metaphysis
(me-TAF-i-sis; meta,
between) is a narrow
zone that connects
the epiphysis to the
shaft of the bone.
The diaphysis
(shaft) is long and
tubular.
Metaphysis
Epiphysis
The epiphysis consists
largely of spongy bone,
also called trabecular
bone. Spongy bone
consists of an open network
of struts and plates that
resembles latticework with
a thin covering, or cortex, of
compact bone.
The wall of the diaphysis
consists of a layer of
compact bone.
The medullary cavity
(medulla, innermost part), or
marrow cavity, is a space
within the hollow shaft. In
Compression
life, it is filled with bone
on medial
marrow, a highly vascular
side of shaft
tissue. Red bone marrow
is highly vascular and
involved in the production
of blood cells. Yellow
bone marrow is adipose
tissue important in the
storage of energy reserves.
Body weight
(applied force)
Tension
on lateral
side of
shaft
A longitudinal section of the humerus, showing the extensive
|network of blood vessels in long bones
Epiphyseal artery
and vein
The metaphyseal artery (red) and
metaphyseal vein (blue) carry blood to
and from the area of the metaphysis and to
the epiphysis through epiphyseal arteries
and veins.
Metaphysis
Most bones have only one
nutrient artery (shown in
red) and one nutrient vein
(shown in blue), but a few
bones, including the femur,
have more than one of each.
Periosteum
A nutrient foramen is a
tunnel that penetrates the
diaphysis and provides
access for the nutrient artery
and/or vein. Branches of
these large vessels supply
the osteons of the
surrounding compact bone
before entering and
supplying the tissues of the
medullary cavity.
Medullary
cavity
Metaphyseal
artery and vein
An articular cartilage covers portions of
the epiphysis that articulate with other
bones. The cartilage is avascular, and it
relies primarily on diffusion from the
synovial fluid to obtain oxygen and
nutrients and eliminate wastes.
Compact
bone
Metaphysis
 Bone


vasculature
Growth and maintenance requires extensive
_______________________ supply
Vascular features


Nutrient artery/vein (commonly one each/bone)
 Nutrient __________________(tunnel providing
access to marrow cavity)
 Also supplies osteons of compact bone with blood
Metaphyseal artery/vein
 Carry blood to/from metaphysis
 Connects to epiphyseal arteries/veins
 _____________________



features
Smaller blood vessels (supply superficial osteons)
Lymphatic vessels (collect lymph from bone and
osteons)
____________________ nerves (innervate
diaphysis, medullary cavity, and epiphyses)
 Four
1.
bone cell types
__________________________ (osteo-,
bone + cyte, cell)




Mature bone cells that cannot divide
Most numerous bone cell type
Maintain protein and mineral content of adjacent
matrix

Dissolve matrix to release minerals

Rebuild matrix to deposit mineral crystals
Occupy ____________________(pocket)

Separated by layers of matrix (lamellae)

Connected with canaliculi
2.
______________________ (blast,
precursor)


Produce new bony matrix (osteogenesis or
ossification)

Begins with release of proteins and other
organic components to produce unmineralized
matrix (= osteoid)

Then assists in depositing calcium salts to
convert osteoid to bone
Become osteocytes once surrounded by bony
matrix
The structures of osteocytes and osteoblasts within a
long bone
The layers of matrix
are called lamellae
(lah-MEL-lē; singular,
lamella, a thin plate).
Osteocytes account for most
of the cell population in bone.
Each osteocyte occupies a
lacuna, a pocket sandwiched
between layers of matrix.
Osteocytes cannot divide,
and a lacuna never contains
more than one osteocyte.
Osteoblast
Osteoid
Narrow passageways
called canaliculi
penetrate the lamellae,
radiating through the
matrix and connecting
lacunae to one another
and to various blood
vessels that supply
nutrients.
3.
_________________________ cells
(progenitor, ancestor)



Mesenchymal (stem) cells that produce cells that
differentiate into osteoblasts
Important in fracture repair
Locations

Inner lining of periosteum

Lining endosteum in medullary cavity

Lining passageways containing blood vessels
4.
______________________ (clast, to break)



Remove and remodel bone matrix
Giant cells with ______________+ nuclei

Derived from same stem cells as macrophages
Release acids and proteolytic enzymes to dissolve
matrix and release stored minerals

= Osteolysis (lysis, loosening)
The structures of osteocytes and osteoblasts
within a long bone
Endosteum
Osteoprogenitor cell
Osteoclast
 Bone

Collagen fibers account for ~1/3 bone weight


_________________
Provide _________________
Calcium phosphate (Ca3(PO4)2) accounts for ~2/3
bone weight

Interacts with calcium hydroxide (Ca(OH)2) to form
crystals of hydroxyapatite (Ca10(PO4)6(OH)2) salts
 Incorporates other salts (calcium carbonate, CaCO3)
and ions (Na, Mg2, F)
 Provides _______________________
 _________________

bone
Functional unit is _________________



Organized concentric lamellae around a central canal
 Osteocytes (in lacunae) lie between lamellae
 Central canal contains small blood vessels
Canaliculi connect lacunae with each other and
central canal
Strong along its length
The structure of compact bone, as shown in
the shaft of a long bone
Capillary and venule
Central canal
Concentric lamellae
Canaliculi radiating
through the lamellae
interconnect the lacunae
of the osteons with one
another and with the
central canal.
Endosteum
Central canal
Periosteum
Circumferential
lamellae
Osteon
Vein
Compact bone
LM x 375
The osteocytes occupy lacunae that lie
between the lamellae. In preparing this
micrograph, a small piece of bone was
ground down until it was thin enough to
transmit light. In this process, the lacunae
and canaliculi are filled with bone dust, and
thus appear black.
Artery
Interstitial
lamellae
Central canal
Perforating canal

Typical long bone organization
Periosteum (outermost layer)
 Compact bone (outer bone tissue layer)
 ___________________________ lamellae
(circum-, around + ferre, to bear)
 Outer and inner surfaces of compact bone layer
 Interstitial lamellae
 Fill spaces between osteons
 _______________________________
 Contain central canals (parallel to bone surface)
 Connected by perforating canals (perpendicular)
 Spongy bone (innermost layer)

 _______________________


bone
Located where bones not heavily stressed or in
many directions
Lamellae form struts and plates (trabeculae)
creating an open network


_______________________ weight of skeleton
No blood vessels in matrix
 Nutrients reach osteons through
___________________________________ open to
trabeculae surfaces
The structure of spongy bone, as shown in the head of the femur
Trabeculae of
spongy bone
Canaliculi
opening on
surface
Endosteum
Lamellae
 _____________________

Increases bone diameter of existing bones


bone growth
Does not form original bones
Osteoprogenitor cells differentiate into
osteoblasts that ____________ bone matrix
under periosteum


Adds successive _____________________ of
circumferential lamellae
Trapped _____________________ become osteocytes
Deeper lamellae recycled and replaced by
osteons
 Osteoclasts remove matrix at inner surface to
enlarge medullary cavity

Increase in bone diameter resulting from appositional growth
Additional circumferential
lamellae are deposited, and
the bone continues to
increase in diameter.
Periosteum
Enlargement of the medullary cavity with increased bone diameter
resulting from appositional growth
Bone matrix is removed
by osteoclasts
Infant
Child
Bone deposited by
superficial osteoblasts
Young adult
Adult
 _________________

Two layers
1.
2.

_________________________ outer layer
_____________________________ inner layer
Functions
1.
2.
3.
________________ bone from surrounding tissues
Route for blood and nervous supply
Actively participate in bone growth and
_____________________
 ____________________


fibers
Created by osteoblasts in periosteum cellular
layer
Strongly connect tendons, ligaments, and joint
capsules to bone through periosteum
Structure of the periosteum
Circumferential
lamellae
Fibrous layer
of periosteum
Cellular layer
of periosteum
Canaliculi
Osteocyte
in lacuna
Perforating
fibers

__________________




Incomplete cellular layer lining medullary
cavity
Covers spongy bone and lines central canals
Consists of simple layer of osteoprogenitor
cells
Where incomplete, osteoclasts and osteoblasts
remodel matrix
Structure of the endosteum
Endosteum
Osteoclast
Circumferential lamella
Osteocyte
Osteoprogenitor
cell
Osteoid
Osteoblast


Initial bone formation in embryo begins
with ______________________
Replaced by bone through endochondral
(endo-, inside + chondros, cartilage)
_______________________________


Uses cartilage as small model
Bone grows in diameter and length

Diameter growth involves appositional bone
deposition

Steps of endochondral ossification
1.
In shaft, _______________________ enlarge
and matrix ossifies

2.
3.
Chrondrocytes die, leaving cavities within
cartilage
___________________ vessels grow around
cartilage edge and osteoblasts form to create
a superficial layer of bone
Blood vessels penetrate central region

Allow entering fibroblasts to change into
osteoblasts
 Spongy bone produced
(_______________________________
ossification center) and spreads toward
bone ends
4.
_____________________ cavity created as
cartilage replaced by osseous tissue

5.
6.
Bone grows in length and diameter
__________________ ossification centers
form as capillaries and osteoblasts migrate
into epiphyses
Epiphyses fill with __________________ bone

Only articular cartilage (on epiphyses) and
epiphyseal cartilage (in metaphysis) remain
The process of endochondral ossification
Hyaline cartilage
Articular cartilage
Epiphysis
Enlarging
chondrocytes within
calcifying matrix
Metaphysis
Epiphysis
Medullary
cavity
Blood
vessel
Diaphysis
Primary
ossification
center
Medullary
cavity
Epiphyseal
cartilage
Periosteum
Compact
bone
Spongy
bone
Formation of an epiphyseal
cartilage between epiphysis
and diaphysis
Metaphysis
Secondary
ossification
center
Hyaline cartilage
Formation of superficial
layer of bone
Diaphysis
Superficial
bone
Bone
formation
Enlargement of
chondrocytes
Spongy
bone
Production of spongy bone at
a primary ossification center
Further growth in length
and diameter
Formation of secondary
ossification centers
7.
Bone grows in _________________ at
epiphyseal cartilage



Chondrocytes actively produce more cartilage on
epiphysis side
Osteoblasts _____________________ replace
cartilage with bone on shaft side
As long as both processes are equally active, bone
lengthening continues
 At puberty, hormones increase bone growth
and epiphyseal cartilage is replaced

Leaves
_____________________________________
________________in adults

Steps of intramembranous ossification

_____________________________ cells
secrete osteoid matrix


Differentiate into osteoblasts
Osteoid matrix becomes mineralized

Forms _________________________________
Bone grows out in small struts
(____________________________)
 Osteoblasts become trapped and mature
into osteocytes



Mesenchymal cells produce more osteoblasts
Blood vessels enter and become trapped
in developing bone

Further membranous bone development





__________________ bone formed initially
Remodeling around blood vessels forms
osteons of compact bone
Periosteum forms, lined with osteoblasts
Begins at approximately ____________ week
of embryonic development
Examples:




Roofing bones of skull
Lower jaw
Collarbone
Sesamoid bones such as patella
16 weeks of development
10 weeks of development
Flat bones
of the skull
Intramembranous
ossification centers
that produce the
roofing bones of
the skull
Primary
ossification
centers of the
long bones of
the lower limb
Future
hip bone
Long bones
of the limbs
The extent of intramembranous and
endochondrial ossification occurring between
10 and 16 weeks of development
 Endocrine
and metabolic problems can affect
the skeletal system
Reduction in
_______________
hormone leads to
reduced epiphyseal
cartilage activity
and short bones
Epiphyseal cartilage grows unusually slowly
_______________
syndrome
Excessive
cartilage
formation
at
epiphyseal
cartilage
_______________
Overproductio
n of
growth
hormone
before
puberty
Gene
mutation
that causes
bone
deposition
around
skeletal
muscles
Growth hormone levels rise
after epiphyseal plates
close
Bones get thicker
Especially those in face,
jaw, and hands
 Joint

Cht 8
 Movement

8.3-8.4
 Labs

Pages 19-27