Skeletal System

Structure and Function of Bone • 1. Support—The skeleton forms a rigid framework to which

are attached the softer tissues and organs of the body. • 2. Protection—The skull, vertebral column, rib cage, and

pelvic girdle enclose and protect vital organs; sites for blood cell production are protected within the hollow centers of certain bones.

• 3. Movement—Bones act as levers when attached muscles contract, causing movement about joints.

• 4. Hemopoiesis—Red bone marrow of an adult produces white and red blood cells and platelets.

• 5. Mineral and energy storage—The matrix of bone is compose of calcium and phosphorus which can be withdrawn in small amounts if needed elsewhere in the body. Lipids stored in adipose cells of yellow bone marrow store energy.

Bones can be Compact or Spongy

• Compact bone is dense and looks smooth and homogeneous.

• Spongy bone is composed of small needlelike pieces of bone and lots of open space.

Categorization of Bones

• Long Bones: Longer than wide; Found in appendages.

• Short Bones: More or less cubical; found in confined spaces.

• Flat Bones: Protection; bones of the skull, ribs.

• Irregular Bones: Odd shaped; vertebrae, certain skull bones.

Structure determines function

• The shape of a bone is consistent with its functions. The femur, for instance, withstands great weight and pressure as it provides support for the body and attachment points form many muscles. The hollow cylindrical design provides maximum strength with minimal weight.

Types of Bones

Structure of Long Bones • The diaphysis, or shaft, makes up most of the bone’s

length and in made of compact bone. • It is covered and protected by a fibrous connective

tissue membrane, the periosteum, which is secured to the bone by hundreds perforating or Sharpey’s fibers.

• Epiphysis are the ends of long bones, consisting of a thin layer of compact bone enclosing an area filled with spongy bone. It is covered by articular cartilage, a glassy hyaline cartilage, providing a smooth slippery surface that decreases friction at joins.

• The epiphyseal line is a remant of the plates that fuse together from growing bone.

Parts of the Bone

Inside a long bone.

• The yellow marrow is the cavity of the shaft and is used for storage of fat tissue.

• Red marrow is in cavities of the spongy bone of flat bones and the epiphyses of some long bones.

Major Parts of Bone--Summary •

1. EPIPHYSIS - expanded ends of bone. ARTICULATES (forms a joint) with another bone. 2. DIAPHYSIS - shaft of the bone 3. ARTICULAR CARTILAGE - hyaline cartilage covering the ends of bones 4. PERIOSTEUM - tough membrane-like covering over entire bone, except for articular cartilage. Connects with tendons and ligaments. Forms bone tissue.

• MEDULLARY CAVITY - hollow chamber within the diaphysis connects to spaces in spongy bone. Filled with soft specialized tissue called bone marrow.

• " Red Marrow - mainly in spongy bone in adults. Produces blood cells " Yellow Marrow - fat storage. Replaces much of the red marrow in diaphysis through childhood

• ENDOSTEUM - lining of the medullary cavity

Long Bone

Compact bone through a microscope has a very complex structure.

Microscopic Structure of Bone

• - MATRIX composed of collagen and inorganic salts - OSTEOCYTES (mature bone cells) are enclosed in tiny chambers called LACUNAE and form concentric "ring" (layers) around a passageway called the HAVERSION CANAL - The osteocytes are connected by minute passages called CANALICULI (canaliculus) through which tiny "branches" or processes pass - The circular layers of matrix material and osteocytes, along with the haversian canal, forms a unit called a HAVERSIAN SYSTEM. Compact bone tissue is formed in this way - The haversian canals are interconnected by passages called VOLKMANN'S CANALS. All of these canals contain blood vessels and nerve fibers

• Mature bone cells, osteocytes, are found within the matrix in tiny cavities called lacunae. The lacunae are arranged in concentric circles called lamellae around central (Haversian) canals. Each complex consisting of central canal and matrix rings is called an osteon, or Haversian system. They run lengthwise through bony matrix, carrying blood vessels and nerves to all areas of the bone. Tiny canals, canaliculi, radiate outward to all lacunae and form a transportation system that connects all the bone cells tot the nutrient supply through the hard bone matrix. Volkmann’s canals are their communication network.

Microscopic structure of the bone

Bone Formation

• Bone Development and Growth:

• There are two types of bone based on the way the bones form • 1. INTRAMEMBRANOUS BONES = broad, flat bones of the skull. These bones form from membrane-like sheets of

connective tissue • 2. ENDOCHONDRAL BONES = all other bones. • Bones first form as hyaline cartilage. The cartilage then gradually changes into bone tissue - a process called

OSSIFICATION, which begins near the middle of the diaphysis in an area called the PRIMARY OSSIFICATION CENTER. Later the bone begins to ossify in the epiphysis - these areas are called the SECONDARY OSSIFICATION CENTERS.

• As long as growth is occurring, a "band" of cartilage (called an epiphyseal disk, growth plate) remains between the diaphysis and the epiphysis.

• Bones increase in length as these cartilage cells continue to reproduce and ossify • Cartilage cells form cells called OSTEOBLASTS. These cells produce bone matrix and once the cell is enclosed in

bone matrix it is considered to be a mature bone cell and called an OSTEOCYTE • Growth in thickness of bone occurs as osteoblasts from beneath the periosteum produce bone matrix and build

compact bone just underneath the periosteum • Bone tissue is constantly being replaced as special cells called OSTEOCLASTS dissolve bone tissue from within the

medullary cavity - a process called RESORPTION. At the same time new bone tissue is being added to the outside of the bone.

3 Types of Joints

• 3 Basic Types of Joints (articulations): • 1. SYNARTHROTIC - immoveable joint, such as bones in the skull,

these junctions are called SUTURES. - Fibrous Joints • 2. AMPHIARTHROTIC - slightly moveable joint, vertebrae -

Cartilaginous Joints • 3. DIARTHROTIC - freely moveable joint, such as shoulders, hips,

knees, elbows, wrists, fingers… --these joints are enclosed within a fibrous capsule which contains a lubricating fluid called SYNOVIAL fluid. These are called SYNOVIAL JOINTS.

• Ball & Socket Hinge Pivot Saddle

Bones of the Skull

• 1. Frontal - anterior portion above eyes 2. Parietal - one on each side of the skull, just behind frontal bone 3. Occipital - forms the back of the skull and base of the cranium 4. Temporal - forms parts of the sides and base of cranium 5. Sphenoid - wedged between several other bones in anterior portion of the cranium 6. Maxilla - forms upper jaws 7. Mandible - lower jaws, only moveable bone of the skull

Sutures • 1. Coronal - between frontal and parietal bones

2. Lambdoidal - between occipital and parietal bones 3. Squamosal - between temporal and parietal bones 4. Sagittal - between parietal bones

• Fontanels - "soft spots" of an infant's skull: - anterior fontanel, posterior fontanel, sphenoid fontanel, mastoid fontanel

• Foramen Magnum - Large opening through the underside of the skull, spinal cord enters skull

Cranial and Facial Bones

Label:

The Rest of the Bones

• Ribs - Thoracic Cage, 12 pairs - True Ribs - first seven pairs, attach directly to STERNUM by costal cartilage (Vertebralsternal) - False Ribs - last five pairs (Vertebralchondral) - Floating ribs - last two pairs (Vertebral)

• Pectoral Girdle: Shoulder. Two clavicles • (collar bones) and two scapula (shoulder blade) • Arms: Upper arm - humerus. Lower arm - radius and ulna.

Wrist - 8 small bones called carpals Fingers - Metacarpals, Phalanges

• Pelvic Girdle: Hips. Two large bones called COXAL BONES • Legs: Upper leg (thigh) - FEMUR. Lower leg - tibia & fibula.

Ankle and Upper foot - 7 bones called TARSALS, Largest is the heel bone called the CALCANEOUS Toes - Metatarsals, Phalanges

The Bones for “Chunk #1”

Wrist Bones

Ankle Bones

What About Broken Bones? • A complete fracture (or closed) is when the bone has broken into

two pieces. • A greenstick fracture is when the bone cracks on one side only, not

all the way through. • A single fracture is when the bone is broken in one place. • A comminuted (say: kah-muh-noot-ed) fracture is when the bone is

broken into more than two pieces or crushed • A bowing fracture, which only happens in kids, is when the bone

bends but doesn't break • An open fracture is when the bone is sticking through the skin.