Bone Growth and Remodeling
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Questions and Answers

What type of growth occurs within the epiphyseal plate?

Interstitial growth

What is the primary function of the zone of resting cartilage?

Secures the epiphysis to the epiphyseal plate

What occurs to the chondrocytes in the zone of hypertrophic cartilage?

They cease dividing and greatly enlarge in size (hypertrophy)

What is the result of calcification in the zone of calcified cartilage?

<p>Destruction (loss) of the chondrocytes</p> Signup and view all the answers

What type of growth is responsible for an increase in the diameter or thickness of a long bone?

<p>Appositional growth</p> Signup and view all the answers

How are chondrocytes aligned in the zone of proliferating cartilage?

<p>Into longitudinal columns that look like a stack of coins</p> Signup and view all the answers

What is the last zone in the epiphyseal plate, closest to the diaphysis?

<p>Zone of ossification</p> Signup and view all the answers

What is the name of the process by which a long bone increases in length?

<p>Interstitial growth</p> Signup and view all the answers

What is the composition of zones 1-4 of the epiphyseal plate?

<p>Cartilage</p> Signup and view all the answers

What process replaces calcified cartilage with bone in the epiphyseal plate?

<p>Endochondral ossification</p> Signup and view all the answers

What is the significance of the timing of epiphyseal plate fusion in forensic anthropology?

<p>Determining age at death</p> Signup and view all the answers

How are epiphyseal plate unions scored in forensic anthropology?

<p>Open, partial union, or complete union</p> Signup and view all the answers

What is the difference in epiphyseal plate fusion timing between males and females?

<p>Female epiphyseal plates tend to fuse 1-2 years earlier</p> Signup and view all the answers

In which zones of the epiphyseal plate does growth in bone length occur?

<p>Zones 2 and 3</p> Signup and view all the answers

What type of matrix permits growth in the epiphyseal plate?

<p>Flexible matrix of hyaline cartilage</p> Signup and view all the answers

What is the relationship between growth in hyaline cartilage and bone growth?

<p>Growth in hyaline cartilage is replaced with bone</p> Signup and view all the answers

What is the significance of zone 5 in the epiphyseal plate?

<p>New bone matrix is deposited</p> Signup and view all the answers

What is the purpose of the table listing standards for selected epiphyseal plate unions?

<p>To estimate age at death</p> Signup and view all the answers

What two primary factors influence the relative activities of osteoblasts, osteocytes, and osteoclasts in bone remodeling?

<p>hormones and mechanical stress</p> Signup and view all the answers

What type of exercise has the greatest positive effect on bone density?

<p>weight training and high-impact aerobic activities</p> Signup and view all the answers

Why do females enter puberty earlier than males, and what is the consequence on their growth?

<p>Females enter puberty earlier than males, and as a result, they have fewer years of childhood growth prior to puberty, leading to shorter stature.</p> Signup and view all the answers

What happens to bone strength when mechanical stress is removed or significantly decreased?

<p>Bone strength weakens through reduction of collagen formation and demineralization.</p> Signup and view all the answers

Why do astronauts need to exercise in space to reduce the effects of bone loss?

<p>To combat the effects of lack of gravity, which leads to decreased mechanical stress and subsequent bone loss.</p> Signup and view all the answers

What is the result of consistent weight-bearing exercise on bone mass in adolescents and young adults?

<p>Increased total bone mass</p> Signup and view all the answers

What role does serotonin play in bone remodeling, and what potential disorder is being researched in relation to its abnormal levels?

<p>Serotonin plays a role in regulating the rate of bone remodeling by preventing osteoprogenitor cells from differentiating into osteoblasts when its levels are too high, and abnormally high levels are being researched for a potential link to low bone density disorders.</p> Signup and view all the answers

What happens to the bone when mechanical stress exceeds the bone's ability to remodel?

<p>The bone may be injured, leading to stress fractures.</p> Signup and view all the answers

What three hormones are involved in regulating both bone remodeling and blood calcium levels?

<p>Parathyroid hormone, calcitriol, and calcitonin.</p> Signup and view all the answers

Why is it important for individuals, especially older adults, to engage in regular weight-bearing exercise?

<p>To increase or maintain bone mass and prevent bone loss</p> Signup and view all the answers

How does the body respond to mechanical stress on bone over time?

<p>The portions of the bone most affected by the stress develop more bone mass.</p> Signup and view all the answers

What physical characteristic is typically observed in individuals with achondroplastic dwarfism?

<p>Short stature, enlarged head, bowed lower limbs, and lordosis</p> Signup and view all the answers

What is the relationship between muscle contraction and bone growth?

<p>Muscle contraction applies stress to the bone, stimulating bone growth and increased bone density.</p> Signup and view all the answers

What is the potential connection being investigated between serotonin and low bone density disorders?

<p>Researchers are investigating whether abnormally high levels of serotonin are linked to low bone density disorders.</p> Signup and view all the answers

How does serotonin influence the process of osteoblast differentiation, and what are the implications for bone remodeling?

<p>Serotonin prevents osteoprogenitor cells from differentiating into osteoblasts, thereby affecting the rate and regulation of normal bone remodeling.</p> Signup and view all the answers

What effect does high circulating serotonin have on osteoblast differentiation, and what impact does this have on bone remodeling?

<p>High circulating serotonin prevents osteoprogenitor cells from differentiating into osteoblasts, which in turn affects the rate and regulation of normal bone remodeling.</p> Signup and view all the answers

What is the name of the process that continues to transform an infant bone into a larger version throughout an individual's lifetime?

<p>Appositional growth</p> Signup and view all the answers

What is the term for the dynamic process of continual addition of new bone tissue and removal of old bone tissue throughout a person's lifetime?

<p>Bone remodeling</p> Signup and view all the answers

What is the estimated percentage of the adult human skeleton replaced yearly through bone remodeling?

<p>About 20%</p> Signup and view all the answers

How can a physician determine whether a person has reached full height by examining x-rays of the patient's bones?

<p>By looking for the loss of the hyaline cartilage and the appearance of the remnant epiphyseal line</p> Signup and view all the answers

What is the name of the area where osteoblasts in the periosteum produce and deposit bone matrix?

<p>External circumferential lamellae</p> Signup and view all the answers

What is the term for the process of bone growth that occurs within the medullary cavity?

<p>Endochondral ossification</p> Signup and view all the answers

What type of bone is replaced at a faster rate than compact bone in the adult human skeleton?

<p>Spongy bone</p> Signup and view all the answers

What is the term for the curvature of the lumbar spine observed in individuals with achondroplastic dwarfism?

<p>Lordosis</p> Signup and view all the answers

What is the name of the layer of compact bone that forms as a remnant of the epiphyseal plate at the end of interstitial growth?

<p>Epiphyseal line</p> Signup and view all the answers

How does growth hormone stimulate bone growth, and what is the role of IGF in this process?

<p>Growth hormone stimulates liver to produce IGF, which causes cartilage proliferation at epiphyseal plate, resulting in bone elongation.</p> Signup and view all the answers

What is the effect of thyroid hormone on bone growth, and how does it influence metabolic rate of osteoblasts?

<p>Thyroid hormone stimulates bone growth by stimulating metabolic rate of osteoblasts.</p> Signup and view all the answers

How do sex hormones (estrogen and testosterone) stimulate osteoblasts and promote epiphyseal plate growth and closure?

<p>Sex hormones stimulate osteoblasts, promoting epiphyseal plate growth and closure.</p> Signup and view all the answers

What is the net effect of calcitriol on bone, and how does it relate to dietary calcium intake?

<p>The net effect of calcitriol on bone is dependent upon dietary calcium intake.</p> Signup and view all the answers

Explain why high levels of glucocorticoids can impair bone growth in children, and what is their relationship with bone loss.

<p>High levels of glucocorticoids can impair bone growth in children by increasing bone loss and inhibiting osteoblast activity.</p> Signup and view all the answers

What is the relationship between parathyroid hormone and blood calcium levels, and how does it affect bone resorption?

<p>Parathyroid hormone increases blood calcium levels by encouraging bone resorption by osteoclasts.</p> Signup and view all the answers

Explain why a young boy taking anabolic steroids (substances that have effects similar to those of testosterone) may be at risk of stunted growth.

<p>The high levels of testosterone-like substances can accelerate bone growth, leading to premature closure of the epiphyseal plate, resulting in stunted growth.</p> Signup and view all the answers

How do hormones such as growth hormone, thyroid hormone, and sex hormones regulate bone growth and maintenance?

<p>These hormones regulate bone growth and maintenance by stimulating or inhibiting chondrocyte, osteoblast, and osteoclast activity.</p> Signup and view all the answers

What is the relationship between calcitonin and osteoclast activity, and how does it affect bone growth?

<p>Calcitonin promotes calcium deposition in bone and inhibits osteoclast activity, leading to increased bone growth.</p> Signup and view all the answers

Explain how hormonal imbalances can lead to skeletal system disorders, and provide examples.

<p>Hormonal imbalances can lead to skeletal system disorders by disrupting the regulation of bone growth and maintenance, e.g. excess glucocorticoids can lead to bone loss.</p> Signup and view all the answers

Study Notes

Bone Growth and Bone Remodeling

  • Bone growth and bone remodeling begin during embryologic development and continue throughout a person's lifetime
  • Bone growth can occur in two ways: interstitial growth (growth in length) and appositional growth (growth in diameter or thickness)

Interstitial Growth (Growth in Length)

  • Occurs within the epiphyseal plate, which has five distinct microscopic zones:
    • Zone of resting cartilage: small chondrocytes distributed throughout the cartilage matrix, secures the epiphysis to the epiphyseal plate
    • Zone of proliferating cartilage: chondrocytes undergo rapid mitotic cell division, enlarge slightly, and become aligned into longitudinal columns
    • Zone of hypertrophic cartilage: chondrocytes cease dividing and greatly enlarge in size, resorbing matrix as they hypertrophy
    • Zone of calcified cartilage: minerals are deposited in the matrix between the columns of lacunae, limiting diffusion of nutrients and resulting in destruction of chondrocytes
    • Zone of ossification: walls break down between lacunae, forming longitudinal channels invaded by capillaries and osteoprogenitor cells from the medullary cavity
  • Growth in length occurs through the combination of chondrocyte proliferation and hypertrophy in zones 2 and 3, and subsequent replacement of cartilage with bone tissue in zone 5

Appositional Growth (Growth in Diameter or Thickness)

  • Occurs within the periosteum, where osteoblasts produce and deposit bone matrix in layers parallel to the surface (external circumferential lamellae)
  • As new bone is laid down at the periphery, osteoclasts resorb bone matrix within the medullary cavity, expanding the cavity and increasing the bone's diameter
  • Appositional growth continues throughout an individual's lifetime

Bone Remodeling

  • The process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue (bone resorption) that occurs at both the periosteal and endosteal surfaces of a bone
  • About 20% of the adult human skeleton is replaced yearly, with compact bone replaced at a slower rate than spongy bone
  • Mechanical stress (weight-bearing movement and exercise) affects bone remodeling, with increased stress leading to increased bone mass and strength
  • Hormones (such as growth hormone, thyroid hormone, and sex hormones) also influence bone growth and remodeling

Hormones That Influence Bone Growth and Bone Remodeling

  • Growth hormone: stimulates liver to produce insulin-like growth factor (IGF), which promotes cartilage proliferation at the epiphyseal plate
  • Thyroid hormone: stimulates bone growth by influencing the basal metabolic rate of bone cells
  • Sex hormones (estrogen and testosterone): promote osteoblast activity and bone formation, especially during puberty
  • Calcitonin: promotes calcium deposition in bone and inhibits osteoclast activity
  • Parathyroid hormone: increases blood calcium levels by encouraging bone resorption by osteoclasts
  • Calcitriol: stimulates absorption of calcium ions from the small intestine into the blood, which may cause a net decrease in calcium loss from bone
  • Glucocorticoids: increase bone loss and, in children, impair growth at the epiphyseal plate
  • Serotonin: inhibits osteoprogenitor cells from differentiating into osteoblasts when levels are chronically high

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Learn about bone growth and remodeling, including the five zones of the epiphyseal plate, interstitial growth, and appositional growth.

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