Osteoblasts, Osteocytes, Osteoclasts, and Bone Health

Flashcards covering the functions and roles of osteoblasts, osteocytes, osteoclasts, and bone health concepts.

What is the primary function of osteoblasts?

Bone formation.

What substances do osteoblasts secrete to form the bone matrix?

Collagen and ground substances (glycoproteins and proteoglycans).

Are osteoblasts involved in bone formation or resorption?

Bone formation.

What happens to osteoblasts after they become embedded in the matrix?

They differentiate into osteocytes.

What do osteoblasts eventually become once trapped in the bone matrix?

Osteocytes.

Do osteoblasts have a role in calcium regulation in the blood?

Yes, indirectly through bone formation.

What is the role of osteocytes in bone tissue?

Maintenance of bone tissue and mineral content.

Where are osteocytes located within the bone structure?

In lacunae.

How do osteocytes receive nutrients?

Through canaliculi that connect to blood vessels.

Do osteocytes actively build or break down bone?

No, they maintain bone but don’t actively build or resorb it.

What structure connects osteocytes to each other and to blood vessels?

Canaliculi.

What is the significance of the lacunae in which osteocytes reside?

They protect osteocytes and serve as communication/nutrient exchange centers.

What is the main function of osteoclasts?

Bone resorption.

Are osteoclasts multinucleated or single-nucleated cells?

Multinucleated.

What is the name of the shallow pits where osteoclasts are found?

Howship’s lacunae.

What do osteoclasts secrete to break down bone matrix?

Acids and enzymes (like collagenase).

What is another term for bone formation?

Osteogenesis.

When does osteogenesis begin?

Before birth.

What is the name of the process by which the bone matrix is formed?

Ossification.

What two minerals are primarily involved in the hardening of bone?

Calcium and phosphorus.

What is the name of the mineral crystal formed during ossification?

Hydroxyapatite.

What role does collagen play in bone structure?

It gives bone its resilience.

What is bone remodeling and how often does the entire skeleton renew itself?

Bone remodeling is the process of resorption and formation of bone; the skeleton completely renews every 10 years.

What happens to bones when someone is on prolonged bed rest or physically inactive?

Bones lose calcium, become osteopenic, weak, and fracture easily.

What hormone is released when blood calcium levels are low?

Parathyroid hormone (PTH).

How does calcitonin affect bone resorption?

It inhibits bone resorption and promotes calcium deposition in bone.

Stage I: Hematoma Formation

1. How long does it occur?

2. What is being released or formed?

3. What cells are activated in this stage?

4. What process starts due to cytokines?

Stage I: Hematoma Formation

1. How long does it occur?
→ Within the first 1 to 2 days after fracture.

2. What is being released or formed?
→ Hematoma forms; cytokines and growth factors are released; granulation tissue starts to form.

3. What cells are activated in this stage?
→ Fibroblasts, inflammatory cells, and platelets.

4. What process starts due to cytokines?
→ Angiogenesis (new blood vessel formation).

Stage II: Inflammatory Phase

1. How long does it occur?

2. What is being released or formed?

3. Which cells are active?

4. Is the fracture site strong at this point?

Stage II: Inflammatory Phase

1. How long does it occur?
→ Starts soon after Stage I and lasts up to 2–3 weeks.

2. What is being released or formed?
→ Fibrocartilaginous soft callus bridge.

3. Which cells are active?
→ Fibroblasts and osteoblasts.

4. Is the fracture site strong at this point?
→ No, not strong enough for weight bearing.

Stage III: Reparative Phase

1. How long does it occur?

2. What is being released or formed?

3. What is the condition of the fracture site?

4. Can a cast be removed during this phase?

Stage III: Reparative Phase

1. How long does it occur?
→ Begins during the 3rd or 4th week and continues until a firm bony union is formed.

2. What is being released or formed?
→ Mature bone (Wooven Bone; Hard Callus; Spongy Bone) replaces soft callus; osteoclasts reabsorb excess callus.

3. What is the condition of the fracture site?
→ Feels immovable and aligned on x-ray.

4. Can a cast be removed during this phase?
→ Yes, if a firm union is confirmed.

Stage IV: Remodeling

1. How long does it occur?

2. What is being released or formed?

3. What remains after healing?

4. What factors affect the duration of remodeling?

Stage IV: Remodeling

1. How long does it occur?
→ Can take months to years.

2. What is being released or formed?
→ Necrotic bone is removed; compact bone replaces spongy bone.

3. What remains after healing?
→ A thickened area may remain at the fracture site.

4. What factors affect the duration of remodeling?
→ Bone function, stress on bone, and extent of damage.

What imaging method is used to monitor bone healing progress?

Serial x-rays

What factors influence the rate of fracture healing?

-Type of bone fractured

-Blood supply

-Condition of fragments

-Immobility

-Age

-General health

Why is adequate immobilization important in bone healing?

To allow ossification and bone formation as confirmed by x-ray

What is the junction of two or more bones called?

Joint

What covers the ends of articulating bones in a movable joint?

Hyaline cartilage

What structure surrounds the articulating bones?

Joint capsule

What lines the joint capsule and what does it secrete?

Synovium; it secretes synovial fluid

What binds articulating bones together?

Ligaments

What connects muscle to bone?

Tendons

What provides joint stability?

Ligaments and tendons

Can ligaments stretch indefinitely?

No, they can tear if overstretched

What is a sac filled with synovial fluid?

Bursa

What cushion movement of tendons, ligaments, and bones?

Bursa

Where can bursae be found?

Elbow, shoulder, hip, and knee

What type of contraction when muscle length stays the same, but tension increases?

Give an example.

Isometric contraction
Example: Pushing against a wall

What type of contraction when muscle shortens, but tension stays the same?

Give an example.

Isotonic contraction

Example: Flexing the forearm

What kind of contractions occur during walking?

Both isotonic (leg shortens) and isometric (leg pushes against floor)

What is the main energy source for muscle cells?

ATP (adenosine triphosphate)

How is ATP produced during low activity?

Oxidation of glucose (aerobic metabolism)

What happens during strenuous activity?

Glucose is converted to lactic acid (anaerobic metabolism)

What causes muscle fatigue?

Glycogen depletion and lactic acid buildup

What happens to unused energy from ATP?

It’s released as heat

Which type of contraction releases more heat?

Isometric contraction

What kind of muscle activity is mainly for heat generation?

Shivering

What is the primary function of red marrow?

The primary function of red marrow is to produce blood cells, including red blood cells, white blood cells, and platelets.

Where is red marrow typically found in adults?

In adults, red marrow is typically found in the flat bones (such as the sternum, ribs, and pelvis) and in the ends of long bones (such as the femur and humerus). It is also found in the vertebrae.

Can red marrow be found in all bones throughout life?

No, red marrow is gradually replaced by yellow marrow in long bones as a person ages. It remains in flat bones and the ends of long bones in adults.

What is the primary function of yellow marrow?

The primary function of yellow marrow is to store fat, which serves as an energy reserve.

Where is yellow marrow mainly found in adults?

Yellow marrow is mainly found in the shafts of long bones, such as the femur, tibia, and humerus.

Can yellow marrow transform into red marrow?

Yes, yellow marrow can convert back into red marrow, particularly in response to conditions that require increased blood cell production, such as anemia.

Can yellow marrow become a factor in bone healing complications after fractures?

Yellow marrow fat can be released into the bloodstream after a fracture (especially if the bone is fractured severely), which may contribute to fat embolism syndrome.

Can fat from yellow marrow contribute to stroke?

Yes, fat released from yellow marrow in fat embolism syndrome can travel through the bloodstream and potentially lodge in small blood vessels in the brain, leading to a blockage. This can result in stroke-like symptoms, such as paralysis, confusion, and speech difficulties.

Can yellow marrow contribute to a myocardial infarction (heart attack)?

If fat embolism syndrome is severe enough, fat particles from yellow marrow can travel through the bloodstream and reach the coronary arteries, where they may cause an obstruction, leading to myocardial infarction.

What is the term for the continuous, passive contraction of muscles that helps maintain posture?

Muscle tone

What term describes a muscle that lacks tone and is limp?

Flaccid

When a person is asleep, what happens to the muscle tone?

Decreased muscle tone

What happens to muscle tone when a person is anxious?

Increased muscle tone

What term describes a muscle with excessive tone and resistance to movement?

Spastic

What is the muscle called that is primarily responsible for causing a particular movement?

What are the muscles called that assist the prime mover in producing movement?

What term describes muscles that cause movement opposite to the prime mover?

What must an antagonist do to allow the prime mover to produce motion?

Prime mover

Synergists

Antagonists

Relax

What is the term for the enlargement of muscles due to repeated maximum tension, such as in weightlifting?

What happens to muscles when they are immobilized for long periods or decrease in muscle size due to disuse or aging?

Hypertrophy

Atrophy

What type of exercise can help decrease the effects of immobility on muscles during bed rest or casting?

Isometric exercise

What two nutrients are essential to protect against skeletal demineralization?

Calcium and Vitamin D

During which life stages should calcium intake be increased?

Adolescence and middle years

How many glasses of vitamin D–enriched milk are recommended daily?

Three

What is the recommended daily calcium intake for men aged 50 to 70 years?

1000 mg

What is the recommended daily calcium intake for women aged 51+ and men 71+?

1200 mg

Which type of milk is recommended?

Skimmed vitamin D–enriched milk

Vitamin D Intake in:

• Young Adults

• 50 and above

600 IU

800-1,000 IU

What complications does Vitamin D deficiency cause?

Bone mineralization deficit

Deformity

Fracture

Which hormone increases calcium and phosphate absorption from the gut to support bone mineralization?

Calcitriol

Which hormone increases blood calcium levels by stimulating osteoclasts and bone resorption?

Parathyroid hormone (PTH)

Which hormone lowers blood calcium levels by inhibiting osteoclast activity?

Calcitonin

Which hormone, when chronically elevated, inhibits bone formation and increases bone resorption?

Glucocorticoids, such as cortisol.

Which hormone stimulates bone growth but can cause bone loss if present in excess?

Thyroid Hormone

Which hormone promotes bone growth by stimulating IGF-1 and increasing osteoblast activity?

Growth Hormone

Which hormone inhibits bone resorption and supports osteoblast survival, especially important in women?

Estrogen

Which hormone promotes bone formation and helps maintain bone density, partly by converting to estrogen in bone?

Testosterone

What diagnostic test is used to determine bone density, texture, erosion, and bone relationship changes?

X-ray

What imaging test is best for assessing tumors, soft tissue injuries, and complex fractures not visible on x-rays?

Computed Tomography (CT)

What test uses magnetic fields and radio waves to view torn ligaments, cartilage, and herniated discs?

Magnetic Resonance Imaging (MRI)

What joint imaging test uses contrast or air to detect ligament and cartilage tears?

Arthrography

What test is most commonly used to assess bone mineral density and predict fracture risk?

Dual-energy X-ray absorptiometry (DEXA)

What bone density test is more accurate for spine and hip fracture risk than peripheral DXA?

Dual-energy X-ray absorptiometry (DXA)

A nurse is preparing a patient for an MRI scan. Which of the following findings requires immediate follow-up with the healthcare provider?
A. The patient expresses fear of enclosed spaces
B. The patient has a metal dental filling
C. The patient has a cochlear implant
D. The patient wears contact lenses

Correct Answer: C. The patient has a cochlear implant
Rationale: Cochlear implants are contraindicated in MRI because the magnet may be displaced or damaged. Claustrophobia (A) is important but can be managed with sedation. Metal dental fillings (B) are generally safe. Contact lenses (D) are removable.

A patient returns from an arthrogram. Which of the following post-procedure findings would require the nurse to notify the provider?
A. Mild tingling in the joint
B. Clicking sensation in the joint for 24 hours
C. Crackling sensation in the joint for 48 hours
D. Increasing swelling and warmth at the injection site

Correct Answer: D. Increasing swelling and warmth at the injection site
Rationale: Swelling and warmth may indicate infection or inflammation. Mild tingling, clicking, or crackling is normal for 24–48 hours after an arthrogram.

A nurse is educating a patient scheduled for a CT scan with IV contrast. Which of the following statements made by the patient indicates a need for further teaching?
A. "I should tell you if I have allergies to iodine or shellfish."
B. "I might feel warm when the dye is injected."
C. "It’s okay to eat right before the scan."
D. "I need to lie still during the entire procedure."

Correct Answer: C. “It’s okay to eat right before the scan.”
Rationale: Patients are typically NPO prior to a CT with IV contrast to reduce the risk of nausea or complications. The other statements show understanding.

A nurse is caring for a patient post-arthrography. Which of the following instructions should the nurse give?
A. "You can resume heavy exercise right away."
B. "Take ibuprofen if you hear crackling in the joint."
C. "Keep the joint completely immobile for 48 hours."
D. "Clicking or crackling sounds in the joint are normal for up to 48 hours."

Correct Answer: D. "Clicking or crackling sounds in the joint are normal for up to 48 hours."
Rationale: These sensations are expected as air or contrast is reabsorbed. Heavy exercise (A) is avoided. NSAIDs may help but are not required for crackling (B). Complete immobility (C) isn't necessary.

A patient scheduled for an x-ray of the pelvis states, "I'm 8 weeks pregnant." What is the nurse's best action?
A. Continue with the procedure using a lead apron
B. Cancel the procedure and notify the radiologist
C. Tell the patient that x-rays are safe in early pregnancy
D. Delay the scan until after the first trimester

Correct Answer: B. Cancel the procedure and notify the radiologist
Rationale: X-rays are generally avoided in pregnancy, especially during the first trimester. The radiologist must evaluate the risk and determine if it's absolutely necessary.

What diagnostic test is used to detect bone tumors, osteomyelitis, fractures, and aseptic necrosis before they are visible on x-ray?

Bone scan

What substance is injected intravenously before performing a bone scan?

How long after the injection is a bone scan performed?

What sensation might the patient feel during radioisotope injection for a bone scan?

What should the patient do before a bone scan to prevent interference with imaging pelvic bones?

What post-procedure instruction helps with radioisotope elimination?

Radioisotope

2 to 3 hours

Flushing or warmth

Empty the bladder

Encourage increased fluid intake