Podcast
Questions and Answers
In a patient with chronic kidney disease, which of the following mechanisms contributes to the development of vitamin D deficiency?
In a patient with chronic kidney disease, which of the following mechanisms contributes to the development of vitamin D deficiency?
- Impaired production of alpha-1-hydroxylase in the kidneys, reducing the conversion of 25-hydroxyvitamin D to its active form. (correct)
- Enhanced intestinal absorption of vitamin D due to increased permeability of the intestinal lining.
- Increased activity of 25-hydroxylase in the liver, leading to rapid degradation of vitamin D.
- Decreased synthesis of 7-dehydrocholesterol in the skin, limiting the availability of vitamin D3.
A child presents with bowed legs, widening of the wrists, and delayed closure of the fontanelles. Radiographic imaging reveals metaphyseal fraying. Which of the following best describes the underlying pathophysiology of these findings?
A child presents with bowed legs, widening of the wrists, and delayed closure of the fontanelles. Radiographic imaging reveals metaphyseal fraying. Which of the following best describes the underlying pathophysiology of these findings?
- Increased osteoclastic activity leading to excessive bone resorption and weakening of the bone structure.
- Inadequate synthesis of collagen fibers, leading to reduced tensile strength of the bone.
- Excessive deposition of calcium in the bone matrix, resulting in increased bone density and rigidity.
- Impaired mineralization of the osteoid matrix and epiphyseal cartilage due to vitamin D deficiency. (correct)
An elderly patient with a history of chronic kidney disease and limited sun exposure presents with bone pain and muscle weakness. Lab results show decreased serum calcium, decreased serum phosphate, and elevated parathyroid hormone (PTH). Which of the following is the most likely underlying mechanism contributing to this patient's presentation?
An elderly patient with a history of chronic kidney disease and limited sun exposure presents with bone pain and muscle weakness. Lab results show decreased serum calcium, decreased serum phosphate, and elevated parathyroid hormone (PTH). Which of the following is the most likely underlying mechanism contributing to this patient's presentation?
- Increased renal excretion of calcium and phosphate due to primary hyperparathyroidism.
- Decreased intestinal absorption of calcium and phosphate due to vitamin D deficiency. (correct)
- Increased bone resorption due to prolonged corticosteroid use.
- Enhanced bone mineralization due to excessive vitamin D supplementation.
In a patient with excessive vitamin D intake, which of the following is the most likely sequence of events leading to hypercalcemia?
In a patient with excessive vitamin D intake, which of the following is the most likely sequence of events leading to hypercalcemia?
A patient with a history of Crohn's disease presents with easy bruising and prolonged bleeding after minor trauma. Which of the following mechanisms is most likely responsible for this patient's bleeding diathesis?
A patient with a history of Crohn's disease presents with easy bruising and prolonged bleeding after minor trauma. Which of the following mechanisms is most likely responsible for this patient's bleeding diathesis?
A newborn infant born at home without vitamin K prophylaxis develops intracranial hemorrhage. Which of the following clotting factors is most directly affected by vitamin K deficiency in this patient?
A newborn infant born at home without vitamin K prophylaxis develops intracranial hemorrhage. Which of the following clotting factors is most directly affected by vitamin K deficiency in this patient?
A patient with a history of long-term warfarin therapy presents with an elevated international normalized ratio (INR) and signs of bleeding. Which of the following interventions is most appropriate to reverse the effects of warfarin in this patient?
A patient with a history of long-term warfarin therapy presents with an elevated international normalized ratio (INR) and signs of bleeding. Which of the following interventions is most appropriate to reverse the effects of warfarin in this patient?
A patient with sarcoidosis develops hypercalcemia. What is the mechanism by which sarcoidosis leads to hypercalcemia?
A patient with sarcoidosis develops hypercalcemia. What is the mechanism by which sarcoidosis leads to hypercalcemia?
A patient with pancreatic insufficiency is at risk for deficiency in which fat-soluble vitamin due to impaired micelle formation?
A patient with pancreatic insufficiency is at risk for deficiency in which fat-soluble vitamin due to impaired micelle formation?
Which of the following is the primary mechanism by which vitamin D enhances intestinal calcium absorption?
Which of the following is the primary mechanism by which vitamin D enhances intestinal calcium absorption?
Flashcards
Vitamin D's primary function
Vitamin D's primary function
Stimulates intestinal calcium absorption and renal distal tubule calcium resorption, working with PTH to regulate blood calcium.
Vitamin D and PTH action
Vitamin D and PTH action
Increase intestinal calcium absorption and calcium release from bones in response to low plasma calcium levels.
First Vitamin D conversion step
First Vitamin D conversion step
Occurs in the liver, converting vitamin D to 25-hydroxyvitamin D (calcidiol)
Second Vitamin D conversion step
Second Vitamin D conversion step
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Vitamin D deficiency causes
Vitamin D deficiency causes
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Rickets Pathophysiology
Rickets Pathophysiology
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Vitamin D toxicity outcomes
Vitamin D toxicity outcomes
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Vitamin K's Main Role
Vitamin K's Main Role
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Causes of Vitamin K deficiency
Causes of Vitamin K deficiency
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Vitamin K deficiency signs
Vitamin K deficiency signs
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Study Notes
Vitamin D and Calcium Regulation
- Vitamin D promotes calcium absorption in the intestines and reabsorption in the renal tubules
- Works with parathyroid hormone (PTH) to maintain blood calcium levels
- In low plasma calcium, vitamin D and PTH increase intestinal calcium absorption
- They also increase calcium and phosphate release from bone via osteoclasts
- Vitamin D triggers osteoblasts to synthesize osteocalcin, facilitating calcium deposition
Bone Mineralization
- Mineralization of the osteoid matrix and epiphyseal cartilage is vital
- Vitamin D deficiency can lead to phosphate release and decreased calcium absorption in the intestine
- It also impairs bone mineralization, mobilizes calcium and phosphates from bone, and lead to low serum calcium
Calcium-Phosphate Relationship
- Calcium and phosphate levels are inversely related
- Decreased calcium is associated with increased phosphate
Sources of Vitamin D
- The primary source of vitamin D is through skin conversion stimulated by UV light
- 7-dehydrocholesterol is converted to vitamin D3 in the skin
- Melanin in darker skin tones reduces UV conversion efficiency.
- Vitamin D is converted to 25-hydroxy vitamin D in the liver by 25-hydroxylase
- In the kidney, 25-hydroxy vitamin D is converted to 1,25-hydroxy vitamin D by alpha-1 hydroxylase
- Breast milk lacks vitamin D
Vitamin D Deficiency Causes
- Renal failure can impair vitamin D conversion in the proximal tubules
- Decreased sun exposure, heavy sunscreen use, and living in northern regions all increase the risk.
- Fat malabsorption in conditions like biliary disease, pancreatic insufficiency, and celiac disease can reduce vitamin D absorption.
- Chronic liver disease can impair vitamin D conversion
- Induction of liver enzymes (CYP450) can affect vitamin D metabolism.
Rickets (Vitamin D Deficiency in Children)
- Rickets is characterized by decreased cartilage calcification and impaired epiphyseal growth plates
- Histologically, there is more cartilage than mineralized bone
- Clinical signs include bowed legs and lumbar lordosis
- Cartilage overgrowth leads to lateral chest expansion
- "Rickety rosary" refers to cartilage overgrowth at the osteochondral junction
- Histological findings at the affected site show increased cartilage with lack of bone mineralization
Osteomalacia (Vitamin D Deficiency in Adults)
- Leads to poor bone mineralization, especially in trabecular bone
- Symptoms include bone pain and microfractures, particularly in the vertebrae and femur neck
Vitamin D Toxicity
- Prolonged sun exposure does not cause vitamin D excess
- Hypervitaminosis (excessive vitamin D intake) can cause toxicity
- Sarcoidosis is associated with granulomas producing alpha-1 hydroxylase, increasing vitamin D conversion
- The outcome is hypercalcemia
- Hypercalcemia can lead to metastatic calcifications in connective tissues and organs
- Symptoms include bone pain, cardiac arrhythmias, and short QT intervals
Vitamin K and Clotting Factors
- Vitamin K is required for clotting factors II, VII, IX, and X; and proteins S and C
- Sources of vitamin K include plants, animal tissue, and intestinal bacteria
Vitamin K Deficiency Causes
- Intestinal resection, fat malabsorption disorders, antibiotic use, and colectomy
- Warfarin inhibits vitamin K action
- Premature infants and those with immature liver function are at risk
- Newborns lacking vitamin K injections
- Clinically presents as bleeding, from small petechiae to large ecchymoses or hemorrhages
- Lab findings show prolonged PT and PTT times
- Treatment involves oral or IV vitamin K; plasma transfusions may be necessary
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