Skeletal System Basics & Structure
If you broke down the skeletal system into its main components, what two general categories would you list?
→ Answer: The axial skeleton and the appendicular skeleton.
Which bone cell type actively builds new bone tissue?
→ Answer: Osteoblasts.
Which type of cartilage forms most of the fetal skeleton before bone takes over?
→ Answer: Hyaline cartilage.
Which bones of the skull are formed primarily by intramembranous ossification?
→ Answer: Flat bones of the skull (e.g., frontal, parietal) and parts of the mandible and clavicle.
Which process describes the continuous removal and deposition of bone tissue?
→ Answer: Bone remodeling.
What natural process causes bones to lose density as people age?
→ Answer: Decreased bone mass due to reduced osteoblast activity and loss of minerals.
Which function of bone is demonstrated when red blood cells are produced?
→ Answer: Hemopoiesis (blood cell production).
Which bone cell type is derived from white blood cells and dissolves bone tissue?
→ Answer: Osteoclasts.
What type of cartilage is found in the external ear and provides flexibility?
→ Answer: Elastic cartilage.
Which bones of the skeleton are formed primarily by endochondral ossification?
→ Answer: Most bones below the skull, especially long bones like the femur and humerus.
Which hormone stimulates osteoclast activity to increase blood calcium levels?
→ Answer: Parathyroid hormone (PTH).
Which gender is at higher risk for osteoporosis after menopause, and why?
→ Answer: Women, due to decreased estrogen which normally helps maintain bone density.
Which part of a long bone would you expect to find articular cartilage, and why?
→ Answer: The epiphyses, because they form joints and need cartilage to reduce friction and absorb shock.
What main structural difference makes compact bone denser than spongy bone?
→ Answer: Compact bone has tightly packed osteons; spongy bone has trabeculae with spaces.
Which type of cartilage is strongest and found in intervertebral discs?
→ Answer: Fibrocartilage.
During intramembranous ossification, which cell type differentiates first to initiate bone formation?
→ Answer: Mesenchymal cells differentiate into osteoblasts.
Which vitamin must be activated to calcitriol to effectively increase calcium absorption?
→ Answer: Vitamin D.
What is the first step in fracture healing?
→ Answer: Formation of a hematoma (blood clot).
What makes flat bones different from long bones in terms of shape, general role, and ossification type?
→ Answer: Flat bones are thin, often curved, and provide protection or muscle attachment, intramembranous ossification; long bones are elongated and act as levers for movement, endochondral ossification.
Why are canaliculi essential in compact bone, but less critical in spongy bone?
→ Answer: Compact bone cells are far from blood supply and need canaliculi for nutrient/waste exchange; spongy bone’s trabeculae are thinner and closer to marrow spaces.
Why does cartilage heal poorly after injury compared to bone?
→ Answer: It is avascular, so nutrients and cells required for repair diffuse slowly.
Why does endochondral ossification require a cartilage model first, unlike intramembranous ossification?
→ Answer: The cartilage provides a flexible template that is gradually replaced by bone.
Why would weightlifters have thicker bones compared to people who live sedentary lifestyles?
→ Answer: Mechanical stress stimulates osteoblast activity, increasing bone density.
Why does fracture healing slow down in elderly individuals?
→ Answer: Reduced cellular activity and decreased blood supply impair repair.
Why does the diaphysis of a long bone contain a medullary cavity, while the epiphysis does not?
→ Answer: The diaphysis provides space for marrow storage and lightens bone weight, while the epiphysis is filled with spongy bone to resist forces from many directions.
Which cell is considered the “mature” bone cell, and what is its main function?
→ Answer: Osteocytes; they maintain the bone matrix and act as mechanosensors.
In interstitial growth of cartilage, what do chondrocytes do inside their lacunae?
→ Answer: They divide and secrete new matrix internally, expanding the tissue from within.
In the epiphyseal plate, which zone is closest to the epiphysis, and what occurs there?
→ Answer: Zone of resting cartilage; it anchors the plate to the epiphysis.
Which hormone lowers blood calcium by inhibiting osteoclast activity?
→ Answer: Calcitonin.
During fracture healing, what tissue replaces the hematoma before bone forms?
→ Answer: A fibrocartilaginous (soft) callus.
Why does compact bone dominate the diaphysis, but spongy bone is found in greater proportion at the epiphyses?
→ Answer: Compact bone resists bending stress along the shaft, while spongy bone absorbs multidirectional forces at the ends of bones.
Why might spongy bone be more metabolically active than compact bone?
→ Answer: Its trabeculae are thinner and closer to marrow/blood vessels, allowing faster remodeling.
In appositional growth, which cell layer is responsible for adding new cartilage to the outside surface?
→ Answer: Chondroblasts in the inner layer of the perichondrium.
Which zone of the epiphyseal plate is responsible for pushing the epiphysis away from the diaphysis during growth in length?
→ Answer: Zone of proliferating cartilage (chondrocyte division).
Why does bone mass decrease in astronauts who spend long periods in zero gravity?
→ Answer: Lack of mechanical stress reduces osteoblast activity, shifting balance toward bone resorption.
What is the purpose of the bony callus formed during fracture repair?
→ Answer: It stabilizes the break with new trabeculae bridging the fracture site.
Which type of marrow would you expect to be more prominent in children, and what does this indicate about their physiology?
→ Answer: Red marrow, reflecting their higher demand for blood cell production during growth.
The bone matrix contains both organic and inorganic components. Which part provides flexibility, and which provides strength?
→ Answer: Organic (collagen/proteins) = flexibility; inorganic (calcium phosphate salts) = strength and hardness.
Why does hyaline cartilage appear smooth and glassy under the microscope?
→ Answer: Because it has fine, dispersed collagen fibers that aren’t easily visible.
In appositional growth, what role do osteoblasts in the periosteum play?
→ Answer: They add new bone layers to the external surface, increasing bone diameter.
Which two organs are most critical for converting vitamin D into calcitriol?
→ Answer: The liver and kidneys.
Why might long-term immobilization in a cast contribute to bone loss?
→ Answer: Lack of mechanical stress reduces bone remodeling and leads to resorption.
How do blood vessels and nerves inside bone contribute to maintaining homeostasis?
→ Answer: Blood vessels deliver nutrients and remove waste, while nerves detect stress or injury, ensuring proper growth, repair, and remodeling.
How does the arrangement of osteons in compact bone relate to resisting mechanical stress?
→ Answer: Concentric lamellae in osteons allow compact bone to resist compressive forces along the shaft.
What structural component of hyaline cartilage allows it to resist compressive forces?
→ Answer: Proteoglycans in the ground substance that trap water.
How is the medullary cavity enlarged during appositional growth?
→ Answer: Osteoclasts resorb bone on the internal surface as osteoblasts add bone externally.
How does calcitriol indirectly affect bone strength even though it doesn’t act primarily on bone tissue?
→ Answer: It promotes intestinal calcium absorption, providing minerals for bone mineralization.
Which step in fracture healing involves remodeling the callus to restore original bone shape?
→ Answer: Bone remodeling phase.
A patient has leukemia requiring a bone marrow transplant. Why would the physician be more concerned with red marrow location than yellow marrow?
→ Answer: Because red marrow is responsible for blood cell formation, while yellow marrow mainly stores fat.
A patient with brittle bone disease (osteogenesis imperfecta) often has normal calcium but defective collagen. Which part of the matrix does this affect, and how?
→ Answer: The organic portion; bones lose flexibility and become brittle.
A child with damage to the perichondrium has difficulty expanding cartilage width. Which type of growth is impaired?
→ Answer: Appositional growth.
If the zone of hypertrophic cartilage is damaged in the growth plate, what specific process is impaired?
→ Answer: Chondrocytes enlarging and preparing the matrix for calcification, which disrupts longitudinal growth.
A patient has low PTH levels. How would this affect both blood calcium and bone remodeling?
→ Answer: Blood calcium would fall; reduced osteoclast stimulation would impair normal remodeling balance.
A patient with osteoporosis fractures a hip after a minor fall. Why does this indicate a systemic, not just local, problem?
→ Answer: The fracture reflects weakened bone density throughout the skeleton, not just at the injury site.
In cases of osteoporosis, which class of bones (by shape) is at the highest risk of fracture, and why?
→ Answer: Vertebrae (irregular bones) and long bones, especially the femur, because they bear weight and have high trabecular bone content that is vulnerable to loss.
Why would an imbalance of osteoblast and osteoclast activity result in structural weakness, even if the total bone mass stayed the same?
→ Answer: If remodeling is unbalanced, bone structure becomes disorganized, weakening architecture regardless of mass.
Why would fibrocartilage be more common in weight-bearing joints compared to hyaline cartilage?
→ Answer: Its dense collagen fibers provide tensile strength and resist compression better.
In a child with rickets, the growth plate widens abnormally. Why does this happen in terms of ossification?
→ Answer: Mineralization of cartilage is impaired, preventing normal progression to bone.
If calcitonin is overproduced, what change might occur in blood calcium, and how would this affect bone tissue?
→ Answer: Blood calcium would drop; osteoclast suppression could weaken remodeling and cause brittle bone.
Why would a fracture that crosses the epiphyseal plate be treated differently in a child than in an adult?
→ Answer: In children it risks disrupting growth; adults no longer rely on epiphyseal plates for lengthening.
Why might a fracture at the metaphysis of a child’s femur have a greater long-term consequence than a similar fracture in the shaft?
→ Answer: The metaphysis contains the growth plate; damage here can disrupt bone lengthening and cause deformities.
In Paget’s disease, bone turnover is accelerated, producing disorganized tissue. Which microscopic difference between normal compact bone and Paget’s bone explains the higher fracture risk?
→ Answer: Loss of orderly lamellae in osteons; abnormal woven bone replaces organized compact bone.
If hyaline cartilage in the trachea begins to calcify with age, how might this affect respiratory function?
→ Answer: Reduced flexibility could make the airway less able to expand, leading to breathing difficulties.
Suppose an adolescent fractures through the epiphyseal plate. Why might this injury cause unequal limb length later on?
→ Answer: Because it disrupts the zones of cartilage growth, halting or altering longitudinal bone growth.
Why might chronic kidney disease impair bone health even if dietary calcium is normal?
→ Answer: The kidneys cannot activate vitamin D to calcitriol, reducing calcium absorption and weakening bones.
In older adults, vertebral compression fractures are common. Why does trabecular bone loss make these fractures more likely?
→ Answer: Vertebrae are rich in spongy bone, which is more vulnerable to age-related resorption.
If an imaging scan reveals a loss of blood supply to part of a bone, what consequences could this have for both the bone’s structural integrity and systemic health?
→ Answer: Local bone death (avascular necrosis) can weaken structure and compromise marrow function, potentially affecting blood cell production.
A patient has damage to osteoprogenitor cells in the periosteum. How would this impact both fracture healing and the long-term ability of bone to adapt to stress?
→ Answer: It would impair new osteoblast formation, limiting repair capacity and remodeling response to stress.
Suppose a patient’s articular cartilage is wearing down (early osteoarthritis). How does the lack of perichondrium in this cartilage contribute to the poor repair capacity?
→ Answer: Articular cartilage has no perichondrium, so no chondroblasts are available for appositional growth, limiting regeneration.
A researcher blocks blood vessel invasion during endochondral ossification in an animal model. Predict the outcome for long bone development.
→ Answer: Without vascular invasion, cartilage cannot be replaced by bone, leading to shortened or malformed long bones.
In hyperparathyroidism, why would patients develop bone fragility despite high blood calcium levels?
→ Answer: Excessive PTH overstimulates osteoclasts, causing bone resorption that weakens skeletal structure.
Suppose a patient’s fracture repair produces an unusually large callus that fails to remodel fully. What functional problem might this create?
→ Answer: Abnormal bone shape could impair joint movement or increase risk of re-injury.