1. The Skeletal System Part 1
Chapter 5

2. Functions of The Skeletal System :
Support - Provides an internal framework that supports and anchors all soft organs.
Protects organs by enclosure; for example – the skull protects the brain, the vertebrae surrounds the spinal cord, and the rib cage helps protect the vital organs of the thorax
Movement – skeletal muscles attached to bone by tendons, use the bones as levers to move the body and its parts.
Storage – fat is stored in the internal cavities of the bones. Bone also serves as a store house for minerals, the most important being calcium and phosphorus.
Blood cell formation – also called hematopoiesis occurs within the marrow cavities of the bone.

3. Subdivisions of the Skeleton
The adult skeleton is composed of 206 bones.
The skeleton is sub-divided into
two (2) divisions:
Axial – the bones that form the longitudinal axis of the body. It has 80 bones.
Appendicular – the bones of the limbs and girdles. It has 126 bones.
In addition to the bones the skeletal system includes joints, cartilage, tendons and ligaments.

5. Classification of Bones
There are two (2) basic types of osseous (or bone) tissue:
Compact bone – dense and looks smooth and homogeneous
Spongy bone – composed of small needle-like pieces of bone and lots of empty spaces.

6. Short – cubed shaped containing mostly spongy bone.
Bones are classified into four (4) groups according to shape:
Long – longer shape than wider consisting of mostly compact bone; usually have a head at both ends.
Examples: all bones of the limbs except wrist and ankle bones are long bones.
Short – cubed shaped containing mostly spongy bone.
Examples: bones of the wrist and ankles, most known is the patella or knee cap.
Flat – thin, flattened and usually curved; they have two thin layers of compact bone sandwiching a layer of spongy bone.
Examples: most bones of the skull, the ribs, and the sternum (breastbone).
Irregular – bones that do not fit into one of the previous groups. Examples: vertebrae (makes up spinal column) and the hip bones.

8. Structure of a Long Bone
Diaphysis (shaft) – makes up most of the bone’s length; it is composed of compact bone.
Periosteum is a fibrous connective tissue membrane that covers and protects the diaphysis.
Epiphyses are the ends of the long bones. They consists of a thin layer of compact bone enclosing an area filled with spongy bone.
Articular cartilage covers the exterior of the epiphyses.

9. The cavity of the shaft is primarily a storage area for adipose (fat) tissue. In adults, it is called the yellow marrow (or medullary) cavity.
In infants this area forms red blood cells and red marrow is found there.
In adults the red marrow is confined to the cavities of the spongy bone of flat bones and the epiphyses of some long bones.

10. Bone Markings
Bone markings reveal where muscles, tendons and ligament where attached and where blood vessels and nerves passed.

11. There are 2 categories of bone markings: Projections or processes which grow out of the bone surface. They are the site of muscle & ligament attachment; and also they are the sites that help form joints. Depressions or cavities which are indentations or openings in the bone allowing blood vessels and nerve fibers to pass

12. Projections that are the sites of muscle and ligament attachment:
Tuberosity – large rounded projection
Crest – narrow prominent ridge
Line – narrow ridge of bone less prominent than a crest

13. Trochanter – large, blunt, irregularly shaped process *
Tubercle – small rounded projection or process
Epicondyle – raised area on or above a condyle
Spine – sharp, slender, often pointed projection
Process – any bony prominence
*(only found on the femur)

14. Projections that help form joints: Head – bony expansion carried on a narrow neck Condyle – rounded articular projection Ramus – arm like bar of bone
All terms beginning with “T” are projections; terms beginning with “F” (except facet) are depressions.

15. Depressions and openings allowing blood vessels and nerve fibers to pass:
Meatus – canal-like passageway
Sinus – cavity within bone filled with air and lined with mucous membrane
Fossa – shallow basin like depression in bone
Fissure – narrow, slit like opening
Foramen – round or oval opening through a bone

17. Microscopic Anatomy of Bone
Compact bone tissue appears to be very dense, but through a microscope, it is actually riddled with passageways carrying nerves, and blood vessels, which provide the living bone cells with nutrients and a route for waste disposal.

18. Mature bone cells are called osteocytes
Mature bone cells are called osteocytes. They are found in tiny cavities inside the matrix called lacunae.
The lacunae are arranged in concentric circles called lamellae around central (Haversian) canals
Each complex consisting of central canal and lacunae is called an oseton (or Haversian system).

20. Bone is one of the hardest materials in the body.
It is relatively light in weight.
It has a remarkable ability to resist tension and other forces acting on it.

21. The calcium salts deposited in the matrix give bone its hardness.
The organic parts (especially the collagen fibers) provide for the bone’s flexibility and strength.
The skeleton is formed of 2 of the strongest and most supportive tissues in the body – cartilage and bone.

22. Bone Formation & growth
In embryos, the skeleton is primarily made of hyaline cartilage.
In the young child, most of the cartilage has been replaced by bone. Cartilage only remains in isolated areas such as the bridge of the nose, parts of the ribs, and the joints.
Most bones develop using hyaline cartilage as their “models”.

23. By birth or shortly thereafter, the cartilage has been converted to bone except for two(2) regions – the articular cartilage (that cover the bones ends) and epiphyseal plates.
The articular cartilage persists for life, reducing friction at joint surfaces.

24. The epiphyseal plates of the long bones allow the bone to grow longitudinally during childhood.
Growing bones must also widen as they lengthen. The process by which the bone increases in diameter is called appositional growth.

25. Long bone growth is controlled by hormones (during puberty the sex hormone is the controlling factor).It ends in adolescence, when the epiphyseal plates are completely converted to bone.
As the body increases in size and weight, bone remodeling is necessary so that bones keep the normal proportions and strength during long bone growth.

26. Bones are remodeled continually in response to changes in two factors: calcium levels in the blood and the pull of gravity and muscles on the skeleton.

27. Normal movement and exercise puts a good form of stress on bones.
The stress of muscle pull and gravity acting on the skeleton determines where the bone matrix is to be broken down or formed so that the skeleton can remain as strong and vital as possible.
The bones of bedridden or physically inactive people tend to lose mass and atrophy because they are no longer subjected to stress.

28. Rickets is a disease in children where the bones fail to calcify.
As a result, the bones soften and a definite bowing of the weight bearing bones of the legs occur.
Rickets is usually due to a lack of calcium in the diet or lack of vitamin D, which is needed to absorb calcium into the bloodstream.
Milk, bread and other foods are fortified with vitamin D.
An active form of vitamin D is synthesized by skin cells when exposed to sunlight.

30. Bone fractures Fractures or breaks happen throughout life.
A fracture where the bone breaks cleanly, but does not penetrate the skin is called closed (or simple).
A fracture where the broken bone ends penetrate through the skin, is called open (or compound).

31. Common Types of Fractures
Comminuted - bone is broken into fragments ; usually seen in older people with brittle bones
Compression – bone is crushed; typical in osteoporotic bones.
Depressed – broken bone portion is pressed inward; typical of skull fractures
Impacted – broken bone ends are forced into each other; usually happens when one attempts to break a fall.
Spiral – break occurs when excessive twisting forces are applied to a bone; common sports fracture.
Greenstick – incomplete break; common in children where bones are more flexible.

33. Bone fracture repair
A bone fracture is treated by reduction, which is the realignment of the broken bone ends
In closed reduction, a doctor realigns the bone ends.
In an open reduction, surgery is required to align and secure bone ends with pins/screws or wires.

34. Bone fracture repair
The repair of bone fractures involves 4 major events:
A hematoma is formed. Blood vessels are ruptured when bone breaks
The break is splinted by a fibrocartilage callus. New capillaries grow into clotted blood (hematoma). Connective tissue cells of various types form a mass of repair tissue- the fibrocartilage callus. It acts like a splint for the broken bone and closes the gap.
The bony callus is formed. Osteoblasts and osteoclasts migrate into the area and multiple. The fibrocartilage callus is replaced by one made of spongey bone which is called the bony callus.
The osteoclasts remove excess bony tissue, restoring new bone tissue like the original.
Bone remodeling occurs. The bony callus is remodeled in response to the mechanical stresses placed on it so that it forms a strong permanent patch at fracture site.