Skeletal System: Bones and Joints

Topics: Bone, Skeletal system, Bone marrow Pages: 25 (4014 words) Published: August 24, 2013
Chapter 6
The Skeletal System: Bones and Joints
* A born baby has about 276 bones while an adult has 206 bones, this is because as you grow some bones join together in a single bone. * Bones are 20% of your weight.
* The Skeletal System consist of:
* Bones
* Cartilages
* Tendons
* Ligaments
* Joints
* Functions of the skeletal system
-bones perform various anatomic (mechanical) & physiologic function. They: 1. Stabilize, provide shape & support the body
2. Protect internal tissues & organs
3. Allows body movements
4. Stores minerals & fats
-hydroxyapatite-calcium phosphate crystals
5. Site of blood cell production
Blood supply
* Blood reaches the bones through three paths:
* Haversian canals- minute channels that lie parallel to the axis of the bone, that are passages for arterioles. * Volkmann’s canals- contain vessels that connect to the outer bone * Vessels in the bone ends & within the marrow

Types of Bones according to shape:
1. Long Bone
-longer than they are wide
-most of the upper & lower limbs are long bones except the wrist & ankle. 2. Short Bones
-approximately as broad as they are long
-mostly spongy
Ex. Bones of the wrist & ankle
3. Flat Bones
-relatively thin, flattened shape
Ex. *certain skull bones
4. Irregular Bones
-include the vertebrae & facial bones
-with shapes that do not fit readily into the other 3 categories Parts of the Long Bone:
1. Diaphysis- shaft
2. Epiphysis- end of long bones
3. Articular cartilage- covers the epiphyses
4. Epiphyseal plate/growth plate
-made up of cartilage in between the epiphyses & diaphysis
-site of growth in bone length
5. Epiphyseal line
-replaces the epiphyseal plate when growth ceases
-bone that replaces the cartilage of each epiphyseal plate
Medullary Cavity
* cavity within the bone (diaphysis)
* contains the marrow
Marrow- soft tissue within the cavity
a. Yellow marrow
* Mainly fat
b. Red marrow
* Consist of blood forming cells
* Is the only site of blood formation in an adult
* Children’s bones:
* More red marrow than adults
* As a person ages, red marrow is mostly replaced by yellow marrow * In adults, red marrow is confined to the bones in the central axis of the body & in the most proximal epiphyses of the limbs Layers of a Bone: (cross-sectional)

1. Periosteum
* Outermost layer
* Surrounds the diaphysis
* Contains blood vessels, nerves & osteoblasts
2. Bone Substance- made up of matriz & cells.
3. Endosteum
* Innermost layer
* Thin connective tissue membrane
* Lines the medullary cavity
Note: both periosteum & endosteum contains osteoblasts
Histologic Structures:
A. Lamellae
* Thin sheets of extracellular matrix which forms the bones * Contains osteocytes(mature bone cells) located between the lamellae

B. Lacunae
* Spaces that contains the osteocytes found between the lamellae C. Canaliculi (tiny canals)
* Channels between adjacent central canal
* Connects on osteocyte to another osteocyte
* Nutrition & Communication
2 Major Types of Bones According to Histological Feature:
1. Compact Bone
* Mostly solid matrix and cells
2. Cancellous Bone
* Consist of lacy network of bone with many small, marrow filled spaces

1. Compact/Cortical Bone
* Forms the diaphysis of long bones & the thinner surfaces of short, flat & irregular bones. * Consists of layers of calcified solid matrix containing spaces occupied by osteocytes (bone cells); * Tightly packed; smooth

* Osteocytes
* Bone cells located in the lacunae
* Lamellae (bone layers)
* Arranged/organized into concentric rings around central canals (haversian canals) * Haversian canals
* Contains the blood vessels that run parallel to the long axis of the bone....
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