Student
Performance Objectives - for the lecture
1. Describe
the following functions of the skeletal system in a few, brief sentences:
support, protection, movement, hemopoiesis and mineral storage.
2. Give an example of one specific bone, by its name, in
each of the following categories: long, short, flat, irregular, and
sesamoid.
3. State the functions of collagen and apatite salts in
the structure of bone matrix.
4. Label the following parts of a typical long bone: articular
cartilage, cancellous bone, compact bone, diaphysis, endosteum, epiphyses,
epiphyseal cartilage, medullary cavity, periosteum, and marrow spaces.
5. Label the following parts of a typical flat bone: cancellous
bone, compact bone, marrow spaces, diplöe.
6. Explain the function of each of the parts of the bones
labeled in objectives 3 and 4.
7. Explain the differences and similarities of endochondral
and intramembranous ossification.
8. List the functions of each of the following cell types found
in human bones: chondroblasts, chondrocytes, osteoblasts, osteocytes,
osteoclasts, fibroblasts, fibrocytes.
9. Define: trabeculae and lamellae.
10. Explain how cancellous bone regions are transformed into compact
bone.
11. Describe the regions of bones typically transformed from cancellous
to compact.
12. Given a diagram on an Haversian system of compact bone, label these
parts: Haversian canal, lacunae, osteocytes, canaliculi, lamellae and
bone matrix.
13. Explain the effects of normal, everyday physical stresses on bone
structure and the effects of breaks.
14. Explain the role of the following nutrients in bone formation: calcium,
phosphate, vitamin D and vitamin K.
15. Explain the interplay of the following hormones in bone formation:
parathormone, calcitonin, growth hormone, thyroxine, sex hormones (estrogens
and androgens).
16. Describe how long bones grow in length including discussion of the
terms: primary ossification center and secondary ossification centers.
17. Explain how long bones and other shaped bones grow in width and
overall size.
Student
Required Bone and Bone Parts - for Laboratory Practical Examinations
(bones and bone parts will be added or removed at your laboratory instructor's
discretion).
Student Required Joints - for Laboratory Practical Examinations (joints will be added or removed at your laboratory instructor's discretion).
Lesson
Outline
A. Functions
of the Skeletal System
1. Support - as an endoskeleton,
the weight of all body parts is supported by bones. All parts of the
body attach to bone directly or indirectly through tendons, ligaments
or other fibrous connective tissue.
2. Protection - the cranium, thoracic
cage and pelvic girdle are three clear examples of bones surrounding
and protecting soft body parts.
3.
Movement - the rigid bones can move to
varying degrees depending on the type of joint articulating adjacent
bones. The skeletal muscles pull on the bones causing movements at the
joints.
4. Hemopoiesis - red marrow is
a tissue found in the spaces within cancellous bone substance. This
tissue produces the body's red blood cells and some of the white blood
cells.
http://www.bartleby.com/107/illus72.html
http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_fram11.html
5. Mineral Storage - the bones
are reservoirs for calcium, phosphates, magnesium, sodium and other
minerals.
B. Bone
Classification by Shape
1. Long bones - These are the
bones of the upper arms, the forearms, the thighs and the lower legs.
They possess a long shaft (diaphysis) that has a hollow core and is
composed of a dense type of bone called compact bone in their cylindrical
walls. The ends of the long bones (epiphyses) form some of the most
complex articulations: the shoulders, elbows, wrists, hips, knees and
ankles. http://d-mis-web.ana.bris.ac.uk/calnet/pot128/page2.htm
http://d-mis-web.ana.bris.ac.uk/calnet/musculo/page3.htm
http://www.shoppingtrolley.net/lesson1-bone-types.shtml
2.
Short bones - These are bones of the wrists, palms, fingers,
ankles, insteps and feet. These bones are solidly composed of spongy
bone and possess an outer covering of compact bone.
3. Flat bones - These are the
bones of the calvarium (upper part of the skull) and also the clavicle.
These bones' outer and inner surfaces are composed of compact bone.
Their interior is cancellous bone. This sandwich like arrangement of
compact-cancellous- compact bone is called diplöe. http://student.brighton.ac.uk/anatomy/flat_bones.htm
4. Irregular bones - These are
the vertebrae and many other bones of the body including several skull
bones. They are composed of cancellous bone within and covered by a
veneer of denser, harder compact bone. http://student.brighton.ac.uk/anatomy/irregular_bones.htm
5. Sesamoid bones - These are
irregularly shaped bones that form within tendons and serve to protect
and strengthen them. A good example is the patella - the bone found
within the patella tendon of the knee joint. http://student.brighton.ac.uk/anatomy/flat_bones.htm
http://student.brighton.ac.uk/anatomy/Sesamoid_Bones.htm
C. Osseus
tissue - the structure of bone as a substance
1. The origin of osseus tissue.
Our original "skeleton", which we form during the first 8
weeks of gestation, is composed of hyaline cartilage (sometimes called
cartilage models, http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_frame9.html,
slide 35) and, in our cranial area, fibrous membranes. So as an embryo,
we have a soft, pliable skeleton that has no bone substance.
2. From embryo to fetus. Eight
weeks, or 2 months, into gestation, marks an important turning point
for us in that the first bone-forming cells, osteoblasts, make
their appearance in the embryo and begin ossifying cartilage and fibrous
membranes into osseus tissue. At this time the embryo changes its name
to "fetus".
3. Osseus tissue, or bone substance,
is a combination of organic and inorganic materials.
a. Organic material:
the major organic substance of osseus tissue is collagen which
is formed in and secreted from osteoblasts into the fluid surrounding
them. The collagen polymerizes into rods that begin to surround and
enclose the osteoblasts.
b. Inorganic material:
ions of calcium and phosphates combine into a complex called apatite
salts. These salts also contain ions of magnesium, fluoride, and
sodium in lesser concentrations.
c. The apatite salts
adhere to the outer surface of the collagen rods making them more rigid.
What we call mature osseus tissue is this combination of collagen and
apatite salts.
d. The collagen
brings a tough pliability to bone; the apatite salts bring rigidity
and hardness to bone. In a healthy bone, this combination is just about
as strong as reinforced concrete.
e. Osteoblast Living
Space: The osteoblasts gradually become encased in a bony armor
that they have secreted around themselves. These living cells are immersed
in a fluid space just within the boundaries of the bone substance. This
space the osteoblasts are in is called a lacuna. http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_frame9.html,
slide 43 and 44. The fluid in each of the many lacunae is
interstitial fluid - the same fluid that is found in all capillary
beds of the body.
f. Cellular Communication:
Adjacent osteoblasts communicate with each other through fine canals
- canaliculi - filled with interstitial fluid. Nutrients, wastes,
and hormones easily pass through each canaliculus. http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_frame9.html,
slide 42.
g. Red Marrow:
If you picture the osseus tissue formed like a honeycomb, then what
is the honey? It is red marrow in those bones that accumulate this tissue.
It is yellow marrow in other bones. The main red marrow accumulating
bones are the frontal, sternum, vertebrae, ribs and iliac crests.
http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_fram11.html
4. The cells of osseus tissue. After
osteoblasts have formed bone substance and are now enclosed within it,
their metabolism changes them into bone-maintaining cells called osteocytes.
http://www.bartleby.com/107/illus76.html If
a bone breaks or additional bone substance is required, osteocytes can
change back into osteoblasts. It is just the same cell called by two
different names depending on what it is doing - synthesizing bone substance,
or maintaining it. Another named cell type in osseus tissue is the osteoclast.
http://www.bartleby.com/107/illus81.html This
cell can dissolve bone substance and is important in bone remodeling.
For example, as a long bone grows in length, the hollow space within
the bone's shaft is expanded. Osteoclasts help to dissolve osseus tissue
to widen the area of this medullary cavity. It has been observed that
osteoblasts - the bone-forming cells - can, under certain circumstances,
also dissolve bone substance the way osteoclasts do.
5. Other cells found in bones.
The outer surfaces of living bones are covered by a tightly adhering
membrane called the periosteum. This tough connective tissue
covering is formed by fibroblasts and is maintained by fibrocytes.
Also, cartilage is found at several locations on and in bone and the
cartilage-forming cells are called chondroblasts; the cartilage-maintaining
cells are called chondrocytes: http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_frame9.html
- slide 33.
a. Cartilage on bone
surfaces is at freely movable joints. This hyaline or articular
cartilage is only a few millimeters thick but cushions the joints
and helps to make joint motions smooth and frictionless (working with
the lubricating gel - synovial fluid).
b. Cartilage in bones
occurs in all individuals still growing in height. The interior growing
regions of the long bones of the arms and legs are regions composed
of hyaline cartilage. The cartilage disappears and is replaced by osseus
tissue when growth in height for that individual has ended.
D. Types
of Osseus Tissue
1. Cancellous bone substance - This is
the type of tissue described in formation in the above section. Pictured
as a honeycomb, the osseus tissue is hard and possesses internal marrow
spaces that are filled with either red or yellow marrow.
a. Cancellous bone formation
results from the ossification of either cartilage models of bone,
or by the ossification of fibrous membranes.
(1).
Endochondral ossification - this is the conversion of cartilage
models found in the early embryo into bone. Formation occurs as described
above, part C.
http://en.wikipedia.org/wiki/Endochondral_ossification
http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_fram10.html
(2).
Intramembranous ossification - this is the conversion of the
fibrous membranes composing the bones of the upper part of the skull,
the calvarium, and the clavicle, into bone. Formation occurs as described
above, part C.
2. Compact
bone substance - This harder and more dense type of bone substance
forms at the surface of all bones to give them resistance to potentially
being damaged, and is also found composing the walls of the shafts (diaphyses)
of the long bones. http://www.lumen.luc.edu/lumen/MedEd/Histo/frames/h_frame9.html,
slides 40-42. The
formation of compact bone follows the following steps:
a. Picture the honeycomb
pattern of cancellous bone and imagine the osteocytes in the bone substance
surrounding the marrow cavities.
b. Imagine some of these
osteocytes, now called osteoblasts because they are ready to lay down
new bone substance, moving into the marrow cavities and laying down
new bone substance. As they do this they reduce the size of the marrow
cavity. Since they are coming into the marrow cavity from the edges,
the cavity gets smaller.
A
way to understand what is happening is to imagine a group of 100 children
holding hands in a large circle. The children stop holding hands and
75 of them take 1 step forward deeper into the circle, moving toward
the center. Then 50 take another step forward moving even deeper toward
the circle's center. This continues until the once large circle now
is filled with children forming smaller circles (concentric circles)
all the way to the theoretical center of the original large circle.
Eventually there is only a small space at the circle's center that has
no children in it. The children are arranged in circular layers around
the circle's tiny center.
c. The marrow cavity
is reduced in size gradually as each wave of bone migration inward converts
the marrow space into bone substance. Each new layer of bone that forms
is called a lamella.
d. As the osteocytes
migrate inward, lamella by lamella, the cells on the periphery maintain
contact with those migrating inward through canaliculi. http://www.mc.vanderbilt.edu/histology/powerpoint/2003//Ossification_files/frame.htm,
canaliculi. The inwardly migrating cells also maintain contact
with each other through canaliculi.
e. At the end of the
process, what used to be a honeycomb pattern of bone substance and marrow
spaces is now bone substance in layers (lamellae) encircling small central
regions that are still marrow spaces and which are now called Haversian
canals. The entire structure of the Haversian canal surrounded by
the concentric lamellae populated with interconnected bone cells (osteocytes)
is called a Haversian System. Each system looks something like
a bull's-eye target although Haversian systems are not generally perfectly
circular. http://student.brighton.ac.uk/anatomy/flat_bones.htm
E. The
Structure of Bones
1. The long bones of growing
children possess the following structures:
a. Diaphysis
- the bone shaft - hollow with walls made of compact bone substance.
b. Epiphyses
- the ends of the bone, composed of cancellous bone substance with compact
bone as a veneer on the surface except where there is articular cartilage.
c. Epiphyseal growth
discs - the growing regions composed of hyaline cartilage inside
bones at the region between the diaphysis and each epiphysis.
d. Medullary cavity
- the hollow region free of bone substance in the center of the diaphysis.
e. Endosteum
- the tissue lining the medullary cavity.
f. Articular cartilage
- the hyaline cartilage covering the surface of the bones at the
joints.
g. Periosteum - the
fibrous connective tissue covering the bone's outer surface, except
where there is articular cartilage.
h. Nutrient foramen
- blood vessels and nerves can enter the bone through this opening.
2. The long bones of adults who are no
longer growing possess all the parts of the long bone above
except that the epiphyseal growth discs are gone. They are replaced
by an epiphyseal line which is made of bone substance. All interior
cartilage areas of the bone are now ossified.
3. Flat bone structure was discussed
previously and is referred to as diplöe.
4. Short and Irregular bone structure
consists of a core of cancellous bone and a covering veneer of compact
bone.
F. The
Growth of Bones
http://www.mc.vanderbilt.edu/histology/powerpoint/2003//Ossification_files/frame.htm,
review the series.
1. During gestation, the initial
laying down of bone substance in the bone models made of cartilage occurs
at primary ossification centers located at the center of the
shaft of each long bone, and which are roughly in the center of other
types of bones. The process involves many cell types and is a marvel
of cellular interactions.
2. Growth of long bones in length.
a. Remember that at
the beginning of the growth of a long bone, the bone is made out of
cartilage and is a tiny model of the bone.
b. Osteoblasts enter
the bone at the center of the diaphysis and begin ossifying the central
region. This is the primary ossification center.
c. The osteoblasts migrate
from the center of the long bone, in both directions, toward the bone's
ends - the epiphyses. As the osteoblasts migrate they ossify each successive
area they encounter: regions formerly made of cartilage are turned into
bone.
d. As the osteoblasts
migrate toward the epiphyses, chondroblasts composing the cartilage
areas not yet ossified lay down new cartilage in the direction of the
bone's ends, and the bone grows in length.
e. By the time
a baby is born, ossification has been going on for 30 weeks: from the
8th week of gestation through the end of week 38 when the baby is full
term and ready to be born. In this period of time the diaphyses of the
long bones have been ossified but the epiphyses are unossified.
f. By age 2, secondary
ossification centers have appeared in the centers of the epiphyses
of the long bones and the epiphyses completely ossify thereafter.
g. As long as the child
is still growing in height, a region of cartilage remains between the
diaphyses and each epiphysis - the epiphyseal growth plate (or
disc). It is here that cartilage growth toward the epiphyses elongates
the bone, followed by ossification of non-growth plate cartilage regions.
Growth is not uniform: spurts in growth occur based on factors including
the next item - sex hormones.
h. Cartilage growth in the
plates is stimulated by sex hormones - girls' estrogens secreted
during the several years prior to and during puberty stimulate
plate growth and therefore bone elongation. Girl's growth in early teen
is often rapid. Boy's androgens (mainly testosterone) also stimulate
plate growth and bone elongation, and androgen influence lasts
longer than estrogen influence. The result is that female growth in
height in the early teen years is generally followed by complete ossification
of the epiphyseal growth plate and cessation of growth in height. Male
growth in height continues through late teen years, until the growth
plate is ossified, as in the female. A completely ossified epiphyseal
plate is called an epiphyseal line. Its presence indicates that
further growth in length is not possible.
3. Growth of long bones in width.
a. Bones thicken as they get
longer through growth in width. Osteoblasts under the periosteum lay
down new bone substance, thickening the bone, as growth in length occurs.
b. Bone growth in width can
occur even after bone lengthening is no longer possible since bone growth
in width is now dependent on regions of cartilage. Bones can thicken
in response to exercise against gravity (walking, running, skiing, weight
training) at any age.
4. Role of Osteoclasts in bone growth.
a. As long bones grow in length
and width, the medullary cavity is maintained mostly free of bone substance.
The medullary cavity contains either red or yellow marrow. The
hollow medullary cavity contributes to bones' lightness.
b. Osteoclasts dissolve bone
within the medullary cavity keeping it hollow in proportion to the bone's
overall length and width.
5. Bone growth after injury.
If a bone is fractured,
connective tissue, known as a callus, grows around and into the
broken region. Phagocytic
cells within the callus absorb and digest the damaged tissue and osteoclasts
dissolve broken bone fragments. Osteoblasts restore bone to the region
over a period of 8-12 weeks. After healing, the formerly broken region
may be stronger than it was prior to the break, in a healthy person.
6. Bone remodeling throughout life.
Bones are continually maintained
throughout life through the combined actions of the osteoblasts and
the osteoclasts. These cells work under genetic control and are influenced
by nutrition, hormones and drugs.
a. Role of Hormones
in Bone Growth: In children, growth hormone from
the pituitary gland, parathormone from the parathyroid glands,
and calcitonin and thyroxine from the thyroid gland contribute
to bone growth and have an influence on the skeletal system's final
size and degree of hardness. During and after puberty, the sex
hormones, as indicated earlier, contribute to the growth of bone. Changes
in sex hormone concentration after menopause in women and in older age
groups in men can result in bone weakening due to loss of bone's protein
matrix. In the disease osteoporosis, merely taking calcium supplements
may have little effect on the progression of bone deterioration: reduced
hormonal levels combined with as yet poorly identified genetic factors
reduce the ability of bones to bind calcium that may be present either
from food or supplements. For this reason, some doctors recommend hormone
replacement therapy, although this practice may make women more prone
to cardiovascular disease and other problems.
b. Role of Dietary factors in Bone
Growth : Sun exposure and vitamin D synthesis along with dietary
intake of protein, and minerals (mostly calcium and phosphates) contributes
to bone strength. Osteomalacia is a condition of adults in which
the bones are weakened based on dietary deficiency of vitamin D and/or
calcium and phosphates. This condition is reversible based on improvements
in the diet and/or better sun exposure in the case of vitamin D deficiency.
Rickets is a disease of children in which the bones are weakened
and sometimes deformed based on poor dietary practices of the mother
during gestation and often poor diet during childhood.
Biomedical
Terminology:
Define
each term.
Apatite salts
Articular cartilage
Canaliculi
Cancellous bone
Collagen
Compact bone
Diploe
Endochondral ossification
Endosteum
Epiphyseal line
Epiphyseal plate
Epiphysis
Haversian canal
Haversian system
Hemopoiesis
Hemopoietic tissue
Intramembranous ossification
Lacunae
Lamellae
Medullary cavity
Osteoblast
Osteoclast
Osteomalacia
Osteoporosis
Periosteum
Primary ossification center
Red marrow
Rickets
Secondary ossification center
Trabeculae
Yellow marrow
Skeletal
System Problems
1. Choose one of the problems described below.
2. Prepare your solution as a word document.
3. Send it to your professor as an email attachment. You will
receive an email response.
Problem
#1: A woman of 50 years begins experiencing symptoms that her
physician tells her are the beginning of menopause. The physician suggests
she consider taking estrogen replacement therapy (ERT) to relieve these
symptoms and to prevent, or slow down, bone demineralization over time.
Utilize the Internet or other sources to research the pros and cons
of estrogen replacement therapy.
Your report should include
1. A definition
of menopause and a description of menopausal symptoms.
2. An explanation
of ERT.
3. The benefits
of ERT.
4. The potential
side-effects of ERT, both short and long-term.
5. Your
decision, based on your research, whether or not the lady should consider
ERT as an option in her life.
Problem
#2: A man of 48 years experiences chronic low-back pain based,
in part, on a history of running and football injuries. The physician
suggests non-steroidal anti-inflammatory drugs for immediate pain releif.
Utilize the Internet to answer the following questions:
1. List and describe
possible causes of low-back pain.
2. What is a non-steroidal
anti-inflammatory drug? Give 5 specific examples listing both generic
and brand names.
3. From the 5
drug examples you have chose, choose one and list its possible side
effects.
4. List and decribe
3 alternatives to drug therapy for releif of chronic low-back pain.
5. If you were
the individual experiencing this pain, what treatment(s) would you pursue
to obtain relief, based on your research.
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