2. 2.
Skeletal System
Learning Objectives:
At the end of the discussion the students must be able to:
• Enumerate the major roles of skeletal system and its parts,
• Explain the process of bone formation, remodelling, repair and
aging; and
• Acclaim the roles of skeletal system to human survival.
Topic Outline:
I. Function of Skeletal System
a. Bones
b. Cartilages
c. Tendons and Ligaments
d. Joints
II. General Features of Bone
a. Parts of Bone
b. Bone Cells
c. Bone Surface Markings
d. Bone Ossification, Remodelling and Repair
e. Types of Bones
III. General Consideration of Bone Anatomy
Skeletal System: Jaycris C. Agnes 3SED-SC
3. 3.
a. Division of Human Skeleton
IV. Bone and Calcium Homeostasis
V. Articulation
VI. Effects of Aging on the Skeletal System
I. Function of the Skeletal System
A. Bones
Mechanical
• Protection — bones can serve to protect internal organs, such as the skull protecting
the brain or the ribs protecting the heart and lungs.
• Structure — bones provide a frame to keep the body supported.
• Movement — bones, skeletal muscles, tendons, ligaments and joints function together to
generate and transfer forces so that individual body parts or the whole body can be
manipulated in three-dimensional space. The interaction between bone and muscle is studied
in biomechanics.
• Sound transduction — bones are important in the mechanical aspect of overshadowed hearing.
Synthetic
• Blood production — the marrow, located within the medullary cavity of long bones and
interstices of cancellous bone, produces blood cells in a process called hematopoiesis.
Metabolic
Skeletal System: Jaycris C. Agnes 3SED-SC
4. 4.
• Mineral storage — bones act as reserves of minerals important for the body, most
notably calcium and phosphorus.
• Growth factor storage — mineralized bone matrix stores important growth factors such
as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins and
others.
• Fat storage — the yellow bone marrow acts as a storage reserve of fatty acids.
• Acid-base balance — bone buffers the blood against excessive pH changes by absorbing or
releasing alkaline salts.
• Detoxification — bone tissues can also store heavy metals and other foreign elements, removing
them from the blood and reducing their effects on other tissues. These can later be gradually
released for excretion.
• Endocrine organ — bone controls phosphate metabolism by releasing fibroblast growth factor –
23 (FGF-23), which acts on kidneys to reduce phosphate reabsorption. Bone cells also release a
hormone called osteocalcin, which contributes to the regulation of blood sugar (glucose) and fat
deposition. Osteocalcin increases both the insulin secretion and sensitivity, in addition to
boosting the number of insulin-producing cells and reducing stores of fat.
B. Cartilage
• Cartilage provides a model for bone growth and formation, provides a smooth cushion between
adjacent bones, and provides firm and flexible support.
C. Tendons and Ligaments
• Tendons attach muscles to bones, and ligaments attach bones to bones.
D. Joints
• Joints allow movement between bones.
II. General Features of the Bone
A. Parts of Bone
Major Parts of the Bone:
Skeletal System: Jaycris C. Agnes 3SED-SC
5. 5.Skeletal System: Jaycris C. Agnes 3SED-SC
Compact Bone
Compact bone makes up the
outer layer of all bones. Although
it looks dense and solid, It is full
of holes for nerves and blood vessels.
Spongy Bone
Spongy bone contains flat
and needlelike structures
that resist stress. Red bone
marrow may fill the open
spaces in some bones.
Central Cavity
Central cavities in long
bones usually contain
yellow bone marrow (fat).
Outer Membrane
An outer membrane
covers most of a long bone.
The inner portion of a membrane
contains cells that build up and
breakdown bone.
6. 6.
B. Bone Cells
There are several types of cells constituting the typical bone:
Osteocytes
• Mature bone cells
Osteoblasts
Skeletal System: Jaycris C. Agnes 3SED-SC
7. 7.
• Bone-forming cells
Osteoclasts
• Bone-destroying cells
• Break down bone matrix for remodeling and release of calcium
C. Bone Surface Markings
Bones have characteristic surface markings
Structural features adapted for specific functions
There are two major types of surface markings:
1) Depressions and openings
Allow the passage of blood vessels and nerves or form joints
2) Processes
Projections or outgrowths that form joints or serve as attachment
points for ligaments and tendons
Skeletal System: Jaycris C. Agnes 3SED-SC
8. 8.
D. Bone Ossification, Remodelling and Repair
Bone Ossification
The formation of bone during the fetal stage of development occurs by two
processes: Intramembranous ossification and endochondral ossification.
Intramembranous ossification
Skeletal System: Jaycris C. Agnes 3SED-SC
9. 9.
Intramembranous ossification mainly occurs during formation of the flat bones of the skull but also the
mandible, maxilla, and clavicles; the bone is formed from connective tissue such as mesenchyme tissue
rather than from cartilage. The steps in intramembranous ossification are:
1. Development of ossification center
2. Calcification
3. Formation of trabeculae
4. Development of periosteum
Endochondral ossification
Endochondral ossification, on the other hand, occurs in long bones and most of the rest of the bones in
the body; it involves an initial hyaline cartilage that continues to grow. The steps in endochondral
ossification are:
1. Development of cartilage model
2. Growth of cartilage model
3. Development of the primary ossification center
4. Development of the secondary ossification center
5. Formation of articular cartilage and epiphyseal plate
Remodelling
Skeletal System: Jaycris C. Agnes 3SED-SC
10. 10.
Bone remodelling consists of removal of existing bone by osteoclasts and deposition of new
bone by osteoblasts.
Repair
During bone repair, cells move into the damaged area and form a callus, which is replaced by
bone.
E. Types of Bone
Long Bones
Skeletal System: Jaycris C. Agnes 3SED-SC
11. 11.
• Greater length than width and are slightly curved for
strength
• Femur, tibia, fibula, humerus, ulna, radius, phalanges
Short bones
• Cube-shaped and are nearly equal in length and
width
• Carpal, tarsal
Flat bones
• Thin and composed of two nearly parallel plates
of compact bone tissue enclosing a layer of
spongy bone tissue
• Cranial, sternum, ribs, scapulae
Irregular bones
• Complex shapes and cannot be grouped into any
of the previous categories
• Vertebrae, hip bones, some facial bones,
calcaneus
Sesamoid bones
• Protect tendons from excessive wear and tear
• Patellae, foot, hand
III. General Consideration of Bone Anatomy
A. Division of Human Skeleton
• The human skeleton consists of 206 named bones
• Bones of the skeleton are grouped into two principal divisions:
Axial skeleton
Consists of the bones that lie around the longitudinal axis of the human body
Skull bones, auditory ossicles (ear bones), hyoid bone, ribs, sternum
(breastbone), and bones of the vertebral column
Appendicular skeleton
Consists of the bones of the upper and lower limbs (extremities), plus the
bones forming the girdles that connect the limbs to the axial skeleton
Skeletal System: Jaycris C. Agnes 3SED-SC
14. 14.
IV. Bone and Calcium Homeostasis
1. Osteoclasts remove calcium from bone, causing blood calcium levels to increase.
2. Osteoblasts deposit calcium into bone, causing blood calcium levels to decrease.
3. Parathyroid hormones increases bone breakdown, whereas calcitonin decreases bone
breakdown.
V. Articulations
An articulation, or joint, is a place where two bones come together.
A. Kinds of Joint based on movement:
Synarthrosis - non movable joints
Amphiarthrosis - slightly movable joints
Diarthrosis - freely movable joints
B. Kinds of Joint based on structural connection:
Skeletal System: Jaycris C. Agnes 3SED-SC
15. 15.
Fibrous Joints - consist of two bones that are united by fibrous tissue and that are
united by fibrous tissue and that exhibit little or no movement.
Sutures are fibrous joints between the bones of skull.
Syndesmoses are fibrous joints in which the bones are separated by some distance and
are held together by ligaments. An example is the fibrous membrane connecting most of
the distal parts of the radius and ulna.
Gomphoses consist of pegs fitted into sockets and held in place by ligaments. The joint
between a tooth and its sockets is a gomphosis.
Cartilaginous Joints - unite two bones by means of cartilage. Only slight movement can
occur at these joints
.
Examples are the cartilage in the epiphyseal plates of growing long bones and the
cartilages between the ribs and the sternum.
Synovial Joints - are freely
movable joints that contain
synovial fluid in cavity
surrounding the ends of
articulating bones.
Skeletal System: Jaycris C. Agnes 3SED-SC
16. 16.
• Kinds of Synovial Joints:
Skeletal System: Jaycris C. Agnes 3SED-SC
17. 17.
C. Types of Movement
Skeletal System: Jaycris C. Agnes 3SED-SC
19. 19.
VI. Effects of Aging on the Skeletal System and Joints
1. Bone matrix becomes more brittle and decreases in total amount during aging.
2. Joints lose articular cartilage and become less flexible.
______________________________________________________________________________
Submitted to
Ms. Jaydee S.M. de Leon
Anatomy and Physiology Professor
Bibliography:
• en.wikipedia.org/Bone%20-%20Wikipedia,%20the%20free
%20encyclopedia.htm
• en.wikipedia.org/Human%20skeleton%20-%20Wikipedia,%20the%20free
%20encyclopedia.htm
• John Wiley & Sons, Inc.
Skeletal System: Jaycris C. Agnes 3SED-SC
20. 20.
• Starr, Cecie. (2008) Human Biology 7th
Edition. Thomson Learning.
• Bryan H. Derrickson; Tortora, Gerard J. (2005). Principles of
anatomy and physiology. New York: Wiley
• Seeleys et al, Essentials of Anatomy and Physiology. 6th
edition
Skeletal System: Jaycris C. Agnes 3SED-SC