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Questions and Answers
What is the initial compound converted by epidermal keratinocytes when exposed to UV radiation?
What is the initial compound converted by epidermal keratinocytes when exposed to UV radiation?
Which organ adds the first hydroxyl group in the synthesis of calcitriol?
Which organ adds the first hydroxyl group in the synthesis of calcitriol?
What is the most active form of vitamin D?
What is the most active form of vitamin D?
What additional function does calcitriol serve in the body aside from bone health?
What additional function does calcitriol serve in the body aside from bone health?
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Which step in the synthesis of calcitriol occurs last?
Which step in the synthesis of calcitriol occurs last?
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Which vitamin is synthesized through the sequential actions of the skin, liver, and kidneys?
Which vitamin is synthesized through the sequential actions of the skin, liver, and kidneys?
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What role do osteoclasts play in tooth movement during orthodontic treatment?
What role do osteoclasts play in tooth movement during orthodontic treatment?
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Which physiological processes require calcium in the body?
Which physiological processes require calcium in the body?
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What role does ultraviolet light play in vitamin D synthesis?
What role does ultraviolet light play in vitamin D synthesis?
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Which of these is a source of calcitriol besides skin synthesis?
Which of these is a source of calcitriol besides skin synthesis?
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What is the normal calcium concentration range in blood plasma?
What is the normal calcium concentration range in blood plasma?
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What happens to sodium channels when calcium levels are low in the blood?
What happens to sodium channels when calcium levels are low in the blood?
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What is a common sign of hypocalcemia induced by a blood pressure cuff?
What is a common sign of hypocalcemia induced by a blood pressure cuff?
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What percentage of the adult skeleton is exchanged with blood each year?
What percentage of the adult skeleton is exchanged with blood each year?
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What might excessive excitability of the nervous system lead to in cases of hypocalcemia?
What might excessive excitability of the nervous system lead to in cases of hypocalcemia?
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Which ion follows a pattern of electrical attraction, contributing to various physiological processes?
Which ion follows a pattern of electrical attraction, contributing to various physiological processes?
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What is the primary role of osteoblasts in bone tissue?
What is the primary role of osteoblasts in bone tissue?
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What must occur for mineral crystal formation in bone to take place?
What must occur for mineral crystal formation in bone to take place?
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Which term describes the abnormal calcification that occurs in tissues where it usually should not happen?
Which term describes the abnormal calcification that occurs in tissues where it usually should not happen?
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What is the primary function of osteoclasts?
What is the primary function of osteoclasts?
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What is a consequence of calcium homeostasis disturbance in the skeleton?
What is a consequence of calcium homeostasis disturbance in the skeleton?
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What initiates the process of mineral deposition in bone tissue?
What initiates the process of mineral deposition in bone tissue?
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What is the role of hydrogen pumps in the process of mineral resorption?
What is the role of hydrogen pumps in the process of mineral resorption?
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What happens to collagen fibers during mineral deposition in bone?
What happens to collagen fibers during mineral deposition in bone?
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What effect do anabolic steroids have on growth plates?
What effect do anabolic steroids have on growth plates?
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Which type of fracture is caused by an underlying disease, such as osteoporosis?
Which type of fracture is caused by an underlying disease, such as osteoporosis?
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What is primarily involved in the field of orthopedics?
What is primarily involved in the field of orthopedics?
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Which factor is associated with bone loss in women when consumption exceeds a specific amount?
Which factor is associated with bone loss in women when consumption exceeds a specific amount?
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Which characteristic is NOT used to classify fractures?
Which characteristic is NOT used to classify fractures?
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What is the primary role of calcitriol in calcium homeostasis?
What is the primary role of calcitriol in calcium homeostasis?
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What condition in adults may arise due to inadequate vitamin D levels?
What condition in adults may arise due to inadequate vitamin D levels?
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Which hormone is secreted when blood calcium levels are too high?
Which hormone is secreted when blood calcium levels are too high?
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How does calcitonin lower blood calcium concentration?
How does calcitonin lower blood calcium concentration?
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What is the recommended daily dietary calcium requirement?
What is the recommended daily dietary calcium requirement?
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Which of the following statements is true regarding calcitriol's effects?
Which of the following statements is true regarding calcitriol's effects?
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What is the role of osteoblasts in calcium homeostasis?
What is the role of osteoblasts in calcium homeostasis?
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What is the effect of parathyroid hormone (PTH) on calcium excretion?
What is the effect of parathyroid hormone (PTH) on calcium excretion?
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Which factor contributes to the abnormal softness of bones in children with rickets?
Which factor contributes to the abnormal softness of bones in children with rickets?
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Study Notes
Physiology of Osseous Tissue
- Mature bone is dynamic and interacts with its environment.
- It is involved in its own maintenance, growth and remodeling.
- Bone continuously exchanges minerals with tissue fluid.
- Disturbance of calcium homeostasis impacts the function of other organ systems, particularly the nervous and muscular systems.
Mineral Deposition and Resorption
- Mineral deposition (mineralization) is the process of calcium phosphate and other ions crystallizing from blood plasma to form bone tissue.
- Osteoblasts produce collagen fibers that mineralize and harden the matrix.
- Calcium and phosphate ions, specifically hydroxyapatite, are deposited along these fibers.
- For crystal formation to occur, calcium and phosphate ion concentration must surpass a critical value, known as the solubility product.
- Most tissues have inhibitors to prevent calcification, but osteoblasts neutralize these inhibitors allowing salts to precipitate in the bone matrix.
- Initial crystal formations (seed crystals) attract more calcium and phosphate from solution.
- Abnormal calcification (ectopic ossification) may occur in various tissues, including lungs, brain, eyes, muscles, tendons, and arteries, leading to conditions like arteriosclerosis.
- Calculus refers to calcified masses in soft organs, such as the lungs.
- Mineral resorption is the dissolving of bone and the release of minerals back into the bloodstream.
- Osteoclasts are responsible for this process, utilizing a ruffled border.
- Hydrogen pumps secrete hydrogen ions into the space between the osteoclast and bone surface, followed by chloride ions.
- Hydrochloric acid (pH 4) dissolves bone minerals.
- Acid phosphatase enzymes digest collagen.
- Orthodontic appliances move teeth by dissolving bone ahead of the tooth where pressure is highest, and depositing bone behind the tooth where pressure is lower.
Calcium Homeostasis
- Calcium and phosphate are essential for various biological processes beyond bone structure.
- Phosphate plays a role in DNA, RNA, ATP, phospholipids, and pH buffers.
- Calcium is essential for neuron communication, muscle contractions, blood clotting, and exocytosis.
- The skeleton serves as a reservoir for these minerals, depositing and withdrawing them as needed by other functions.
- An adult body contains approximately 1,100 grams of calcium, with 99% located in the skeleton.
- This calcium exists in two forms: easily exchangeable calcium ions and a more stable hydroxyapatite reserve.
- Approximately 18% of the adult skeleton is exchanged with blood each year.
- Normal blood plasma calcium concentration ranges from 9.2 to 10.4 mg/dL, with 45% as Ca2+ diffusible across capillary walls.
- The remaining calcium is bound to plasma proteins.
Hypocalcemia
- Hypocalcemia is a deficiency of blood calcium.
- Causes include excessive excitability of the nervous system leading to muscle spasms or tetany (inability to relax).
- Hypocalcemia increases sodium channel responsiveness, leading to increased sodium influx and nerve and muscle cell excitation.
- Tetany typically begins when plasma calcium levels fall to 6 mg/dL.
- One sign of hypocalcemia is strong spasmodic flexion of the wrist and thumb, known as Trousseau's sign, often induced by a blood pressure cuff.
- Chvostek's sign, a facial spasm, is also associated with hypocalcemia, but it is not a definitive indicator.
Calcitriol
- Calcitriol is a potent form of vitamin D produced sequentially in the skin, liver, and kidneys.
- The process begins with epidermal keratinocytes converting 7-dehydrocholesterol, a steroid, to previtamin D3 using UV radiation.
- The liver adds a hydroxyl group, converting it to calcidiol.
- The kidneys add a second hydroxyl group, producing calcitriol (the most active form of vitamin D).
- Calcitriol, also found in fortified milk, functions as a hormone that increases blood calcium concentration through several mechanisms.
- It enhances calcium absorption by the small intestine.
- It promotes calcium resorption from the skeleton.
- It elevates kidney reabsorption of calcium ions, reducing urinary loss.
- Adequate vitamin D is crucial for bone deposition and proper calcium and phosphate utilization.
- Lack of vitamin D can lead to rickets in children and osteomalacia in adults, characterized by abnormal bone softness.
Calcium Homeostasis
- The daily dietary calcium requirement is approximately 1,000 mg.
- Calcitriol, calcitonin, and PTH (parathyroid hormone) work together to maintain normal blood calcium concentration.
- Calcitriol increases calcium absorption in the digestive tract and facilitates calcium resorption from bone.
- PTH, secreted by parathyroid glands, stimulates calcium resorption from bone and promotes calcium reabsorption in the kidneys.
- Calcitonin, secreted by C cells of the thyroid gland, inhibits osteoclasts and stimulates osteoblasts, lowering blood calcium concentration.
Calcitonin
- Calcitonin is secreted by C cells of the thyroid gland when blood calcium levels rise.
- It lowers blood calcium concentration in two ways:
- Inhibits osteoclasts, reducing calcium liberation from bones.
- Stimulates osteoblasts, increasing calcium deposition into the skeleton.
- Calcitonin plays a significant role in children due to their faster bone remodeling and higher calcium release.
- Estrogen has a stronger effect on bone growth than testosterone, explaining the faster growth and earlier full height attainment in girls.
- Males grow for a longer period and achieve greater height.
- Anabolic steroids can prematurely close the epiphyseal plate, leading to stunted adult stature.
- Excessive cola consumption (more than 3, 12-ounce servings) is linked to bone loss, particularly in women.
Bone Disorders
- Orthopedics, originating as the treatment of skeletal deformities in children, now encompasses preventing and correcting injuries and disorders related to bones, joints, and muscles.
- It includes designing prosthetic joints and limbs and treating athletic injuries.
Fractures and their Repairs
- A stress fracture is caused by repetitive or abnormal trauma to a bone, frequently occurring during falls, athletic activities, or military combat.
- A pathological fracture is a break in a bone weakened by a pre-existing disease, such as bone cancer or osteoporosis.
- Fractures are classified based on structural characteristics including the direction of the fracture line, whether the break penetrates the skin, and the number of bone fragments.
- Simple (closed) fractures do not penetrate the skin, while compound (open) fractures involve the skin.
- A comminuted fracture has multiple bone fragments.
- A greenstick fracture involves the bending of a bone, usually in children.
- A spiral fracture occurs when bone twists and breaks.
- A transverse fracture is straight across the bone.
- An oblique factor is angled across the bone.
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Description
Test your understanding of the physiology of osseous tissue, including its dynamic nature and mineral homeostasis. Explore the processes of mineral deposition and resorption, and how these influence bone health and function. This quiz will assess your knowledge of key concepts in bone biology.
