PSIO 201: Exam 2

What does the skeletal system contain?

Bone, Cartilage, Ligaments, and other connective tissues

What does bone contain?

Blood CT

Blood vessels and nerves

Lymphatic vessels

Cartilage CT

CT coverings

What are the 6 functions of the skeletal system?

1.) Support

2.) Protection

3.) Leverage (assistance in movement)

4.) Mineral homeostasis (homeostasis of Ca)

5.) Triglyceride storage (in yellow bone marrow)

6.) Hemopoiesis (red and white blood cell formation, in red marrow)

What are the 6 classification of bones?

Give examples.

1.) Long bones (humerus)

2.) Short bones (carpals)

3.) Flat bones (sternum, ribs)

4.) Irregular bones (vertebrae)

5.) Sesamoid bones (patella)

6.) Sutural (cranial bones)

*7.) Pneumatized bones (shock absorption, hollow)

What are the endosteum and periosteum important for?

Bone growth and remodeling

What is the periosteum?

Covers outer surface of bone

Continuous with tendons and CT of joints

Attached to bone matrix via perforating fibers

2 layers: Outer fibrous and Inner osteogenic layer

What is the endosteum?

Coats inner surface of bone (marrow cavity, trabeculae of spongy bone, and canals of compact bone)

Contains osteogenic cells

What is the anatomy of a short bone?

Spongy bone located inside, compact bone located outside

What is the anatomy of a flat bone?

Contains compact bone, spongy bone, periosteum, and endosteum

What are osteogenic cells?

Bone stem cells

Formed from mesenchyme (embryonic CT)

Differentiate into osteoblasts

Found in periosteum and endosteum

Only one daughter cells of osteogenic cells will differentiate into osteoblasts

What are osteoblasts?

Cells that build bone (bone formation)

Synthesize organic components (collagen fibers) of matrix

Initiate calcification: take calcium from blood and deposit it within matrix by exocytosis (starts process by hardening bones)

Immature bone cells

What are osteocytes?

Mature bone cells

Involved in maintenance of bone tissue

Sense bone micro damage and mechanical forces on bone, send signals needed for repair

What are osteoclasts?

Break down bone for bone resorption (remove bone in order to repair)

Release proteolytic enzymes and acids to degrade collagen and release minerals to blood

Derived from myeloid stem cells (not from osteogenic cells)

What is the Sealing Zone of osteoclasts?

Special proteins that bind osteoclasts to the bone

What is the Ruffled Border of an osteoclast?

Proton pumps that can release proteolytic enzymes and acid (allows for secretion)

Side that is in contact with bone

What is the goal of bone remodeling?

1.) To achieve strength for loading (support any stress bone encounters)

2.) Lightness for mobility (keep bone light)

Happens through strategically depositing bone where it is needed for strength, and removing bone where it is not to avoid bulk.

-Achieve skeleton’s peak strength during growth

-Maintain bone strength by removing damaged bone during adulthood

What is bone able to do?

1.) Detect location and magnitude of damage (osteocyte)

2.) Remove damage (osteoclast)

3.) Replace it with new bone (osteoblasts)

4.) Restore bone’s material composition, microarchitecture, and macro architecture

What are the organic components of Bone ECM?

1.) Ground Substance: glycosaminoglycans (GAG)

• Glycoproteins (polysaccharide + protein)

• GAGs are negatively charged (trap water)

• Examples: Chondroitin sulfate, hyaluronic acid

2.) Collagen fibers: fibrous protein arranged in a helical form (Type I Collagen)

• Very resistant to pulling forces

• Provides flexibility and a framework for deposition of calcium

What are the inorganic components of Bone ECM?

1.) Water:

• Attracted to ground substance

• Makes up 25% of ECM

2.) Hydroxyapatite:

• Forms mineral plates that fill up spaces within collagen fibers

What does collagen do for bone?

Provide flexibility

Apply proteolytic enzymes (denature protein), removes collagen from bone, and bone become brittle/ crumbly

What do minerals do for bone?

Provides firmness

Soak bone in vinegar, remove minerals from bone, bone becomes rubbery/ flexible

What is rickets?

Inorganic component deficiency

Calcium deficiency due to lack of Vitamin D (allows gut to absorb calcium from diet)

Leads to flexible bones (bowed legs)

What is scurvy?

Organic component deficiency

Problem with collagen synthesis due to Vitamin C deficiency

Leads to brittle bones that can fracture easily

What is spongy bone?

Location: Epiphyses of long bones, surrounding marrow cavities, flat, short, and irregular bones

Functions: Withstands forced from many directions, trabeculae arranged along lines of stress, lightense the skeleton, contains red marrow for hemopoiesis, irregular lattice of thin plates called trabeculae

What is compact bone?

Organization: Solid network of bone organized in concentric ring structure called osteons.

Location: External layer of all bones, diaphysis of long bones

Function: Gives long bones ability to withstand forced along longitudinal axis (can only withstand in certain direction)

Where is the bone of an infant particularly soft (bone formation incomplete)?

Fontanels (soft spots on skull)

Epiphyses of long bones (made of cartilage in infants)

Epiphyseal (growth) plates (stays as cartilage until end of puberty)

What are the bones of a fetus composed of?

Loose CT: Mesenchyme

Hyaline cartilage

What is ossification?

The replacement of connective tissue by bone

• Begins during the second month of development

• Continues for many years after birth

What are the two types of ossification?

Intramembranous ossification: “Within membrane”

• Mesenchyme (starting tissue) to bone

Endochondral ossification: “Inside cartilage”

• Mesenchyme to cartilage to bone (cartilage intermediate)

What bones are formed by intramembranous ossification?

1.) Cranial bones (frontal, parietal, occipital, temporal, sphenoid, ethmoid)

2.) Most facial bones

3.) Sternum

4.) Clavicle

All the REST are ENDOCHONDRAL OSSIFICATION

What is heterotropic bone formation?

Happens with sesamoid bones (forms within ligaments/ tendons to give more support to join)

Abnormal stresses can stimulate bone formation in areas where bone is not normally found

What are the steps of intramembranous ossification?

1.) Development of ossification center

• Mesenchymal cells differentiate into osteogenic cells then osteoblasts

• Osteoblasts secrete bone matrix

2.) Calcification

• Osteoblasts deposit calcium into the matrix

• Osteoblasts differentiate into osteocytes

3.) Formation of trabeculae (spongy bone)

4.) Development of periosteum

• Remodeling of spongy bone to compact bone

What is calcification?

The deposition of calcium into matrix

• Important step in ossification but NOT ossification

What are the steps of endochondral ossification?

1.) Development of cartilage model

2.) Growth of cartilage model

3.) Osteoblasts create a primary ossification center (bone replaces cartilage)

• Blood vessels penetrate model and stimulate differentiation of osteogenic cells into osteoblasts

• Osteoblasts form bone on the outer surface of the model

4.) Osteoclasts create a marrow cavity

• Spongy bone is remodeled into compact bone

5.) Around birth, secondary ossification center form in epiphyses.

6.) Spongy replaces most of the cartilage at the epiphyses (except for the epiphyseal plate and articular cartilage)

What 2 processes happen at the epiphyseal plate?

1.) Interstitial growth of cartilage (hyaline cartilage must grow for bone to grow)

2.) Endochondral ossification

What is the interstitial growth of cartilage?

Cartilage growing from within at the epiphyseal side of the epiphyseal plate (grows at side closet to epiphysis)

What are the steps of the interstitial growth of cartilage?

1.) Mesenchymal cells differentiate into chondroblasts

2.) Chondroblasts build matrix and differentiate into chondrocytes

3.) Chondrocytes divide and spread apart (mitosis)

4.) Cartilage tissue grows from within

When does the epiphyseal plate close?

At the end of adolescence (18 for women, and 21 for men)

Epiphyseal cartilage cells stop dividing and are replaced by bone

Epiphyseal line forms

Interstitial growth cannot occur after the epiphyseal plate closes

What is appositional growth and what does it generate?

Growth in width

Periosteal osteogenic cells differentiate into osteoblasts

Periosteal osteoblasts build bone on outer surface of bone

Endosteal osteoclasts increase the diameter of the marrow cavity

• Bone diameter, cortical width, and medullary cavity size increases.

Appositional growth generates new osteons.

How are osteons added to the periosteal side of the bone?

1.) Ridges in periosteum create groove for periosteal blood vessel.

2.) Periosteal ridges fuse, forming an endosteum-lined tunnel.

3.) Osteoblasts in endosteum build new concentric lamellae inward toward center of tunnel, forming new osteon.

4.) Bone grows outward as osteoblasts in periosteum build new circumferential lamallae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

What is acting together in Appositional Growth?

Osteoblasts and osteoclasts woking together in medullary cavity.

• Osteoclasts acting first, osteoblasts going in to build bone

What is a fracture?

A break in the continuity of bone rendering it structurally incompetent.

What are the classification of fractures?

1.) Traumatic: normal bone experiencing abnormal force (i.e car accident)

2.) Pathologic: abnormal bone experiencing normal forces (i.e. results from having a disease).

What are the steps of fracture repair?

1.) Formation of fracture hematoma (about 6 to 8 hours)

• Nearby bone cells die which leads to swelling and inflammation.

• Phagocytes and osteoclasts remove damaged tissue (3 to 4 weeks)

2a.) Fibrocartilage callus formation (3 weeks)

• Blood vessels grow into hematoma

• Mesenchymal cells in periosteum differentiate into fibroblasts, chondroblasts and osteogenic cells

• Chondroblasts produce fibrocartilage; fibroblasts produce collagen

2b.) Bony callus formation (endochondral ossification; 3-4 months)

• Osteogenic cells differentiate into osteoblasts

• Osteoblasts produce spongy bone

3.) Bone remodeling (up to 6 to 9 months)

What are the treatments for bone fractures?

Immobilization: prevent movement using a splint, cast, or brace

Reduction: repositioning bones (followed by immobilization)

• Closed reduction: the manipulation of bones without surgery

• Open reduction: the surgical use of rods, plates, pins, etc. to position bones and bone fragments correctly for proper bone healing

What are the 3 factors that influence bone?

1.) Dietary

2.) Hormones

3.) Exercise

What are the minerals that influence bone?

Calcium and phosphorus

( also magnesium, fluoride, and manganese)

What are the vitamins that influence bone?

Vitamin A: stimulate activity of osteoblasts

Vitamin C: needed for collagen synthesis

Vitamin D: Stimulates calcium absorption in GI tract

Vitamin K, B12: needed for synthesis of bone proteins

Why is calcium homeostasis important?

1.) Membrane excitability: action potential relies on calcium concentration

2.) Blood clotting: need to properly clot in response to injury

3.) Intracellular activity: carry signals as a part of cascade

How is the blood calcium level regulated?

Control calcium entry into and exit from blood:

1.) Bone storage

2.) Kidney excretion: getting rid of calcium in urine (dec. of calcium of urine, inc. blood calcium level, inc. calcium of urine, dec. blood calcium level)

3.) Intestinal absorption

Which hormones influence bone and are involved in calcium homeostasis?

Calcitriol (Active form of Vitamin D)

Calcitonin

Parathyroid Hormone (PTH)

• Travel through blood and have effects on different target tissues (hormones are signaling molecules with receptor molecules)

How much calcium do you need per day?

1000 mg of calcium per day

Which hormones that influence bone act on osteoclasts?

Calcitonin and Parathyroid hormones

Which hormones that influence bone act on osteoblasts?

Growth hormones and estrogen/ testosterone (sex hormones)

What does growth hormone (somatotropin) do?

Simulates cell growth and protein synthesis (collagen)

Stimulates secretion of insulin-like growth factors (IGFs) then stimulates osteoblast activity then stimulates bone formation

Example: HGH

What are the skeletal disorders associated with growth hormones?

1.) Pituitary dwarfism: children with low levels of GH results in slow epiphyseal growth (short stature)

• Signals not being sent to actively grow

2.) Pituitary gigantism: hyper secretion of GH in childhood results in accelerated epiphyseal growth (tall stature)

• Too much growth hormone being secreted while epiphyseal plate is still open

*Both happening before puberty

3.) Acromegaly: hyper secretion of GH after puberty results in appositional growth (thickening of bones) in the skull, hands, and feet as well as overgrowth of cartilage

• Epiphyseal plates of long bones already closed

What do estrogen and testosterone do?

Both stimulate osteoblast activity (bone formation)

Levels increase at puberty

• Bone growth/ growth spurts (surge in estrogen/ testosterone increase massively)

• Eventually cause closure of the epiphyseal plates because osteoblast/ osteoclast activity is slightly greater than chondrocyte activity

Levels decrease with older age

What are the effects of the exercise of exercise on bone?

Bone will change in response to the stresses it encounters:

1.) Muscle pulling on bone results in joint reaction forces

2.) Impact results in ground reaction forces

Sir Isaac Newton: “For every force, there is an equal and opposite force”.

What is spongy bone like compared to compact bone?

More metabolically active: can respond to changes in mechanical loading more readily

Where are the sites of fracture mostly located and what do they all have in common?

Hip, wrist, and spine

All have high spongy bone content

What is the goal of exercise and what are its roles?

Goal: reach the fracture threshold later in life

1.) Exercise early in life- increase peak bone mass

2.) Exercise later in life- prevent bone loss

3.) Fall prevention- exercise promotes better balance and coordination

• Improved strength

• Improved balance and coordination

Why do astronauts need to exercise in space?

Osteoclasts act more because osteocytes are not sensing stress in microgravity (bone still needs to be remodeled)

Astronauts exercise for at least 2 hours each day in space to prevent bone and muscle loss (loose average of 1-2% of their BMD each month)

What happens when you exercise?

Force applied to bone is sensed by osteocytes then proliferation of osteocytes begins, bone formation is greater than bone resorption in response to exercise.

What is osteoporosis?

Porous bones (reduced bone mass), increase risk of fractures

The proportion of collagen and minerals is normal but there is a decrease in mass

Osteoclasts more active than osteoblasts

Silent disease: no symptoms unless a fracture occurs, cannot diagnose using blood tests

What causes reduced bone mass?

Any factor that stimulates bone resorption or inhibits bone formation (or both)

Osteoclast activity > osteoblast activity

What is osteomalacia?

Decreased mineralization of newly formed bone matrix at sites of bone remodeling as a consequence of Ca2+ deficiency (due to Vitamin D deficiency) associated with achy bone pain

What is osteogenesis imperfecta?

Congenital disorder that affects production of Type I collagen due to genetic mutation

Brittle bones that fracture easily, often in childhood or adolescence

Pain associated with fracture

What is an articulation?

A point of contact between:

1.) Bones (elbow)

2.) Bones and cartilage (epiphyseal plates)

3.) Bones and teeth

What is arthrology?

The study of joints

What is kinesiology?

the study of body motion

The more stable a joint is ….

The less mobility it affords the body

The less stable a joint is ….

The more mobility it affords the body

What are the two types of arthritis caused by synovial joints?

Osteoarthritis: degenerative

• “Wear and tear” arthritis (one joint affected on one side of the body)

Rheumatoid arthritis: inflammatory

• Body attacks Type 2 collagen (sees it as foreign), causes inflammation and pain on both sides

What kind of joint is the shoulder?

Diarthrosis- freely movable

Ball and socket joint

Tri-axial joint (more prone to injury)

What kind of joint is the knee?

Diarthrosis- freely movable

Hinge joint

Mono-axial joint

Medial and lateral menisci cushion the joint

How many ligaments stabilize the knee joint?

7: 2 intracapsular ligaments, 5 extracapsular ligaments

What are the 5 extracapsular ligaments?

1.) Fibular Collateral ligament: stabilizes lateral side of knee

2.) Tibial Collateral ligament: stabilizes medial capsular of ligametns

3.) Patellar ligament: stabilizes anterior side of knee

4.) Oblique Popliteal ligament: stabilize popliteal side of ligament

5.) Arcuate Popliteal ligament: stabilizes popliteal side of ligament

What are the 2 intracapsular ligaments?

1.) Anterior cruciate ligament: prevents anterior sliding of tibia on femur

2.) Posterior cruciate ligament: prevents posterior sliding on tibia and femur