Module 6 - Bones and Skeletal Tissue

What are the classification of bones?

Long bones
Short Bones
Sesamoid Bones
Flat Bones
Irregular Bones

What is the description of long bones?

Longer than they are wide

What is the description of short bones?

Cube shaped

What is the description of sesamoid bones?

Shaped like a sesame seed (short bone with tendon)

What is the description of flat bones?

Thin, flattened, curved

What is the description of irregular bones?

Irregular shapes that do not fit into other four categories

Where are long bones found?

Femur
Humerus

Where are short bones found?

Wrist bones
Ankle bones

Where are sesamoid bones found?

Patella

Where are flat bones found?

Skull bones
Sternum

Where are irregular bones found?

vertebrae
Some skull bones
Hip bones

What are some functions of the bone / skeletal system?

Support (framework of body)

Provides attachment points for tendons

Protects / Supports organs (brain, lungs, heart, spinal cord)

Assistance in movement

Mineral hemostasis (reservoir of minerals = calcium, phosphorus)

Blood cell production

Triglyceride storage (yellow bone marrow, adipose cells)

What is the matrix made up of?

•15% water
•30% collagen fibers
•50% crystallized mineral salts
•Calcium phosphate

What is calcification?

Deposition of calcium salts in framework formed by collagen fibers of matrix

What initiates calcification?

Bone building cells called osteoblasts

Why is collagen fibers important?

Assists in bone's flexibility

What are the types of cells present in bone tissue?

Osteoblasts

Osteocytes (most numerous)

Osteoclasts (demolition cells)

What are some characteristics of osteoblasts?

Start immature then develop into osteocytes

Bone-building cells (osteogenesis)

Synthesize extracellular matrix of bone tissue

What are some characteristics of osteocytes?

Mature osteoblasts

Exchange nutrients and wastes with the blood

Help repair damaged bone

Maintains bone tissue

What are some characteristics of osteoclasts?

Release enzymes that digest mineral components of bone matrix (resorption)

Regulate blood calcium level

What are the two bone categories?

Compact bone

Spongy bone

What are some characteristics of compact bone?

Strongest form of bone tissue

Resists stresses produced by weight and movement

Components arranged in repeating structural units called osteons (Haversian systems)

What do osteons (Haversian systems) consist of?

Central canal

Lamellae

Volkmann's canals

What do central canal contain?

Blood vessels

Nerve tissue

What do lamellae form?

Circular rings containing osteocytes

Osteocytes 'sit' in pockets called 'lacunae' (little lakes)

Interconnecting channels called canaliculi responsible for joining lacunae with each other

What do Volkmann's canals connect?

Blood / Nerve supply

What are some characteristics of spongy bone?

Lacks osteons, consist of lamellae

Lamellae arranged lattice of thin columns called trabeculae

Hemopoiesis occurs in spongy bone

Interior bone tissue is made up primarily of spongy bone

What are some characteristics of trabeculae?

Spaces b/w trabeculae make bones lighter

Support and protect red bone marrow

The trabeculae of spongy bone are oriented along lines of stress

Within each trabecula are lacunae that contain osteocytes

Osteocytes nourished from blood circulating through the trabeculae

What are the 7 long bone parts?

Diaphysis

Epiphysis

Metaphysis

Articular cartilage

Periosteum

medullary cavity

Endosteum

What are some characteristics of diaphysis?

Long shaft of bone

Mostly compact bone

What are some characteristics of epiphysis?

Enlarged ends (proximal & distal) of long bone

Covered in articular (hyaline) cartilage

What are some characteristics of metaphysis?

Part b/w diaphysis & epiphysis

Contains epiphyseal growth plate - layer of hyaline cartilage -> replaced by bone -> epiphyseal line

What are some characteristics of Articular cartilage?

'Joint cartilage' aka hyaline

Smooth, shiny surface provides movement in joints by decreasing friction

What are some characteristics of Periosteum?

Fibrous connective tissue (tough) that covers outside of bone (except at joint)

Protects, attachment point for muscles, contains blood vessels (nourish)

What are some characteristics of Medullar cavity?

Hollow center of diaphysis

Red bone marrow (infancy - blood) to yellow bone marrow (adult - fat)

What are some characteristics of Endosteum?

Thin membrane lines medullary cavity & internal spaces of spongy bone

What do periosteal arteries do?

Supply periosteum and outer part of compact bone with blood

What do epiphyseal veins do?

Carry blood away from long bones

Which bone part is richer in nerves?

Periosteum is rich in sensory nerves sensitive to tearing or tension

What is ossification?

Process of bone formation

What are the 4 situations in which bone formation occurs?

Formation of bone in an embryo

Growth of bones until adulthood

Remodeling of bone

Repair of fractures

What are the two patterns of bone formation?

Intramembranous ossification

Endochondral ossification

What is Intramembranous ossification?

Flat bones of skull and mandible are formed

"Soft spots" that help fetal skull pass through birth canal later become ossified, forming skull

What is Endochondral ossification

Replacement of cartilage by bone

Most bones formed in this way, including long bones

What are some characteristics of bone remodeling?

Bone forms before birth and continually renews itself

Ongoing replacement of old bone tissue by new bone tissue

Old bone is continually destroyed and new bone is formed in its place throughout an individual's life

What are the characteristics of bone growth during childhood?

Growth in Length and in thickness at the outer surface

Growth of cartilage on the epiphyseal plate

GH stimulate growth

Estrogen & testosterone cause plate to seal

Replacement of cartilage by bone tissue in epiphyseal plate

Late teens is when plate completely ossifies (end of growth)

What could happen if balance does not exist between osteoclasts / osteoblasts?

If too much new tissue is formed, the bones become abnormally thick and heavy

Excessive loss of calcium weakens the bones, as occurs in osteoporosis

May become too flexible, as in rickets and osteomalacia

What is osteoporosis?

Condition where bone resorption outpaces bone deposition (brittleness)

May be due to depletion of calcium from the body

What are the different types of fractures?

Complete

Incomplete

Open (compound)

Close (simple)

Transverse

Comminuted

Impacted

What is a complete fracture?

Across entire section of bone

What is a incomplete fracture?

Almost across entire section of bone (pieces of bone partially joined aka Greenstick)

What is a open fracture?

Bone protrudes through skin

What is a closed fracture?

Bone does not protrudes through skin

What is a transverse fracture?

Broken at right angles to long axis

What is a comminuted fracture?

Crushed into pieces

What is a impacted fracture?

Forcefully driven into interior of other bone

What are the steps of bone repair?

Formation of fracture hematoma

Fibrocartilaginous callus formation

Bony callus formation

Bone remodeling

Describe Formation of fracture hematoma

Blood leaks from the torn ends of blood vessels and a clotted mass of blood forms around the site of the fracture

Describe Fibrocartilaginous callus formation

Fibroblasts invade the fracture site and produce collagen fibers which bridge the broken ends of the bone

Describe Bony callus formation

Osteoblasts begin to produce spongy bone trabeculae joining portions of the original bone fragments

Describe Bone remodeling

Compact bone replaces spongy bone

How are levels of calcium maintained?

By controlling the rates of calcium resorption from bone into blood

And of calcium deposition from blood into bone

Which important elements depend on calcium?

Nerve / muscle cells to function

Blood clotting

Enzymes as a cofactor

What helps elevate blood calcium levels?

Parathyroid hormone (PTH)

How does parathyroid hormone (PTH) regulate calcium?

Increases the number and activity of osteoclasts

Acts on the kidneys to decrease loss of Ca2+ in the urine

Stimulates formation of calcitriol

What does calcitriol do?

Promotes absorption of calcium from foods in the gastrointestinal tract

What helps decrease blood calcium levels?

Calcitonin (CT), secreted by thyroid gland

What does calcitonin do?

Inhibits activity of osteoclasts.

CT promotes bone formation and decreases blood Ca2+ level.

What are the changes bone tissues go through in response to mechanical stress?

Under stress - bone tissue is stronger through deposition of mineral salts / production of collagen fibers by osteoblasts.

Unstressed bones - diminish because of loss of bone minerals / decreased numbers of collagen fibers.

What is the main mechanical stresses on bone?

Pull of skeletal muscles

Pull of gravity.

What are the two effects of aging on bone tissue

Loss of bone mass

Brittleness

What are some consequences of loss of bone mass?

Results from the loss of calcium from bone matrix

The loss of calcium from bones is one of the symptoms in osteoporosis

What are some consequences of brittleness?

Results from a decreased rate of protein synthesis

Collagen fibers give bone its tensile strength

The loss of tensile strength causes the bones to become very brittle and susceptible to fracture