lec4 anatomy

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Anatomy Dr.Israa H. Mohsen
Lecture 4
BONES & BONE TISSUE
The 206 bones in the adult human body are actually dynamic living tissue. Bone constantly breaks down and rebuilds itself, not just during the growth phases of childhood, but throughout the life span. Bone is filled with blood vessels, nerves, and living cells; in addition, its interaction with other body systems is necessary not only for movement, but also for life itself.
Bone fulfills multiple roles in the body, including:
? Shape , Support , Protection ,Movement ,Blood production
? Electrolyte balance: Bones store and release minerals such as calcium and phosphorus—necessary ingredients for a variety of chemical reactions throughout the body.
? Acid-base balance: Bone absorbs and releases alkaline salts to help maintain a stable pH.
FAST FAC
Classification of Bones
Bones perform a variety of functions. It’s those functions that dictate the bone’s shape. This variety in the shape of bones lends itself to a classification system.
1. Long bones
As the name suggests, these bones have a very long axis and are longer than they are wide. Examples include the femur of the thigh and the humerus of the arm. Long bones work like levers to move limbs.
2. Short bones
About as broad as they are long, these tend to be shaped like cubes. Examples include the carpal bones of the wrist and the tarsal bones of the ankle.
3. Flat bones
These thin, flat, often curved bones protect organs, such as the bones of the skull, the ribs, and the breastbone (sternum). Others, such as the shoulder blades (scapulae), provide a large surface area for the attachment of muscles.
4. Irregular bones
Often clustered in groups, these bones come in various sizes and shapes. Examples include the vertebrae and facial bones. Sesamoid bones are small bones embedded in tendons. The kneecap is an example of a sesamoid bone
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Flat bones
Long bones
Irregular bones
The tiniest bone in the body is
3 mm long and is found in the
ear.
Short bones
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Parts of a Long Bone
Long bones consist of several key structures:
1. The head of each end of a long bone is the epiphysis. The bulbous
structure of the epiphysis strengthens the joint; it also allows an
expanded area for the attachment of tendons and ligaments.
2. Covering the surface of the epiphysis is a thin layer of hyaline cartilage
called articular cartilage. This cartilage, along with a lubricating fluid
secreted between bones, eases the movement of the bone
3. The central shaft-like portion of the bone is called the diaphysis. Thick,
compact bone makes up this hollow cylinder, giving the bone the
strength it needs to support a large amount of weight.
4. A dense fibrous membrane called the periosteum covers the diaphysis.
Periosteum weave together with the fibers of tendons. (Tendons attach
muscle to bone.)This arrangement ensures a strong connection between
muscle and bone.
5. • In children, the medullary cavity is filled with blood cell-producing
red bone marrow. In adults, most of this marrow has turned to yellow
marrow, which is rich in fat..
epiphysis.
articular cartilage.
Medullary cavity.
red bone marrow.
yellow marrow,
diaphysis.
periosteum
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NOTE :
In growing children, a layer of cartilage, called the epiphyseal plate or growth plate, separates the epiphysis from the diaphysis at each end of a long bone. Once growth stops, the plate is replaced by an epiphyseal line.
Types of Bone Tissue
Not all bone, or osseous tissue, has the same characteristics:
? Some osseous tissue is light and porous; this is spongy, or cancellous, bone. Spongy bone is found in the ends of long bones and in the middle of most other bones; it is always surrounded by the more durable compact bone.
? Other osseous tissue—called compact bone—is dense and solid. Its density offers strength, which is why it forms the shafts of long bones and the outer surfaces of other bones.
Bone Marrow
Bone marrow is a type of soft tissue that fills the medullary cavity of long bones as well as the spaces of spongy bone. There are two types of bone marrow:
1. Red bone marrow: This is the bone marrow charged with producing red blood cells. Nearly all of a child’s bones contain red bone marrow.
2. Yellow bone marrow: Over time, red marrow is gradually replaced with fatty yellow marrow. Because its marrow cells are saturated with fat, yellow marrow no longer produces blood cells. However, in cases of severe, chronic blood loss or anemia, yellow marrow can change back into red marrow.
NOTE: In an adult, red bone marrow can be found only in the ribs, sternum, vertebrae, skull, pelvis, and the upper parts of both the humerus (arm) and femur (thigh). All other bones contain yellow marrow.
Skeletal system
While most adults have 206 bones, of these bones 80 comprise the upright, central supporting axis of the body, which includes the skull, rib cage, and vertebral column. This is the axial skeleton.
The other 126 bones make up the bones of the limbs and the pelvic and shoulder area. This is the appendicular skeleton.
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Cranium and Suture Lines
The cranium is the bony structure housing the brain. It consists of eight cranial
bones which join together at immovable joints called sutures.
The coronal suture
The lambdoidal suture
The squamous suture
Parietal bones (2 bones): Join
together at the top of the head to
form the top and sides of the
cranial cavity
Occipital bone (1 bone): Forms
the rear of the skull
Temporal bones (2 bones): also contain
the structures of the inner and middle ear,
including the:
• External auditory meatus (an opening
into the ear)
• Mastoid process (aprominent lump
behind the ear)
• Zygomatic arch (cheekbone)
• Styloid process (an attachment point for
several neck muscles)
Sphenoid bone (1 bone): Forms a
key part of the cranial floor as well as
the floor and side walls of the orbits
Ethmoid bone (1 bone): Contributes to
the walls of the orbits, the roof and walls
of the nasal cavity, and the nasal septum
Frontal bone
(1 bone):
Forms the
forehead and
the roof of the
eye sockets
(orbits)
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Facial Bones
The 14 bones of the face perform several functions. They support the teeth, provide an
attachment point for the muscles used in chewing and for facial expression, form part
of the nasal and orbital cavities, and also give each face its unique characteristics.
Maxillae (2 bones)
(singular: maxilla)
Zygomatic bones
(2 bones)
Mandible (1 bone)
Vomer (1 bone
Inferior nasal
conchae (2 bones)
Nasal bones (2
bones
Lacrimal bones
(2 bones)
Palatine bones
(2 bones)
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Bones Associated with the Skull
Several other bones are associated with the skull but not considered a part of the skull.
These include the three bones of the middle ear. Called auditory ossicles, these bones
are named the malleus (hammer), incus (anvil), and stapes (stirrup).
Hyoid Bone
Another bone associated with the skull is the hyoid bone: a U-shaped bone that sits
between the chin and the larynx. The hyoid bone—which is the only bone that doesn’t
articulate with any other bone—serves as an attachment point for muscles that control
the tongue, mandible, and larynx.
Sinuses
The skull contains several cavities, which include the paranasal sinuses. The four
pairs of sinuses—which are named for the bones in which they reside—open into the
internal nose. Filled with air, they lighten the skull and act as resonators for sound
production. The frontal, maxillary, and ethmoid sinuses have well-defined shapes.
The sphenoid sinuses are more like sinus cells, having a honeycombed shape.
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The Infant Skull
An infant’s skull varies from that of an adult in two key ways:
1. The suture lines in the skull have not yet fused. Because the suture lines haven’t fused, the bones of the skull can shift and overlap, molding the head so the infant can pass through the birth canal. The un-fused suture lines also allow for the rapid brain growth that occurs during infancy.
2. The infant’s skull contains fontanels. The areas between the un-fused bones, which are covered by fibrous membranes, are called fontanels. Soft to the touch, it’s possible to palpate pulsations in these areas. Over time, the fontanels shrink and usually close completely by age two years.