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ENDOCRINOLOGY > Bone and Calcium > Flashcards

Bone and Calcium Flashcards

1
Q

The parathyroid glands arise from the _________

A

Third and fourth branchial pouches

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2
Q

What is the half-life of PTH?

A

2-4 minutes

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3
Q

What is the function of PTH on bone, intestinal mucosa and kidney?

A
  • Bone: increases bone resorption (PTH receptor on osteoclasts)
  • Intestinal mucosa: indirectly increases calcium absorption by increasing vitamin D
  • Kidney: increases calcium reabsorption (distal convoluted tubule), inhibits phosphate reabsorption (proximal convoluted tubule), inhibits bicarbonate reabsorption
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4
Q

List 3 physiologic roles for PTHrp

A
  • Required for normal development as a regulaor of proliferation/mineralization of chondrocytes
  • Regulator of placental calcium transport
  • Regulates epithelial-mesenchymal interactions that are critical for development of mammary gland, skin and hair follicle
  • Usually local rather than systemic actions
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5
Q

What is the function of calcitonin

A
  • Inhibits osteoclast-mediated bone resorption
  • Inhibits renal resorption of phosphate (promotes renal phosphate excretion)
  • Increases renal excretion of calcium
  • Mild natriuretic effect
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6
Q

Give 2 pieces of evidence that calcitonin has little to no role on calcium homeostasis

A
  • Removal of the thyroid gland does not impact bone or calcium metabolism
  • Secretion of extremely high levels of calcitonin in medullary thyroid cancer has no effect on calcium or bone metabolism
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7
Q

List 2 clinical uses for calcitonin

A
  1. Tumor marker in MCT
  2. Treatment as an inhibitor of osteoclast bone resorption (Paget disease of bone, hypercalcemia, osteoporosis). Parenteral or nasal spray
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8
Q

List 3 dietary sources of vitamin D

A
  1. Fortified milk products
  2. Fish oils and fish liver
  3. Eggs
  4. Shiitake mushrooms
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9
Q

How is cholecalciferol (vitamin D3) converted to its active form?

A
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10
Q

FGF23 is produced by ______ and functions to ________

A

FGF23 is produced by osteocytes and functions to decrease 1,25 OH vitamin D production and excrete phosphate from kidneys

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11
Q

How do PTH and FGF23 regulate serum phosphate?

A
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12
Q

Describe the actions of vitamin D receptor

A
  • Nuclear receptor
  • Vitamin D binds VDR and forms heterodimers with retinoid X receptor (RXR)
  • VDR-RXR complex binds to vitamin D response element (VDRE) on DNA, attract co-activators
  • Transcription is initiated
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13
Q

What are the actions of vitamin D on the gut, bone and kidney?

A
  • Gut: increases calcium absorption
  • Bone: stimulates bone resorption (increased osteoclast number and activity by stimulating RANKL production)
  • Kidney: calcium and phosphate reabsorption by kidney tubules
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14
Q

What are the symptoms of hypercalcemia?

A
  • STONES
    • Renal stones, nephrocalcinosis
    • Polyuria, polydipsia
    • Uremia
  • BONES
    • Osteitis fibrosa with subperiosteal resorption, osteoclastomas, bone cysts
    • Radiologic osteoporosis
    • Osteomalacia or rickets
    • Arthritis
  • ABDOMINAL GROANS
    • Constipation
    • Indigestion, nausea, vomiting
    • Peptic ulcers
    • Pancreatitis
  • PSYCHIC MOANS
    • Lethargy, fatigue
    • Depression, memory loss
    • Psychoses/paranoia
    • Personality changes, neuroses
    • Confusion, stupor, coma
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15
Q

List a differential diagnosis for hypercalcemia

A
  • Primary hypercalcemia
    • Sporadic
    • Neonatal severe hyperparathyroidism
    • MEN1/MEN2A
    • Hyperparathyroidism-jaw tumor syndrome
    • Familial isolated (FIHP)
    • Familial hypocalciuric hypercalcemia
    • Jansen metaphyseal dysplasia
  • Lithium therapy
  • Tertiary hyperparathyroidism in chronic renal failure
  • Malignancies: humoral hypercalcemia or malignancy, PTHrP (solid tumors, adult T cell leukemia), 1,25 OH D (lymphomas), ectopic secretion of PTH (rare), local osteolytic hypercalcemia (multiple myeloma, leukemia, lymphoma)
  • Sarcoidosis or other granulomatous disease
  • Endocrinopathies: thyrotoxicosis, adrenal insufficiency, pheochromocytoma, VIPoma
  • Drug induced: vitamin A or D toxicity, thiazide diuretics, lithium, milk-alkali syndrome, estrogens, androgens, tamoxifen
  • Immobilization
  • Acute renal failure
  • Idiopathic hypercalcemia of infancy
  • ICU hypercalcemia
  • Serum protein disorders
  • Williams syndrome
  • Subcutaneous fat necrosis
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16
Q

List 3 conditions seen in hyperparathyroidism-jaw tumor syndrome. How is it inherited?

A
  1. Benign and malignant parathyroid tumors
  2. Jaw tumors (ossifying fibromas of mandible or maxilla)
  3. Renal cysts
  4. Renal hamartomas
  5. Wilms tumor

Autosomal dominant (tumor suppressor gene CBC73)

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17
Q

What is the treatment for primary hyperparathyroidism?

A
  • Surgery
  • Cinacalcet (activates parathyroid CaSR)
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18
Q

List 3 treatments for hypercalcemia

A
  1. Hyperhydration with normal saline
  2. IV bisphosphonates (inhibit osteoclastic resorption of bone, takes 4-5 days to reach full effect)
  3. Calcitonin
  4. Denosumab (neutralizing monoclonal antibody to RANKL)
  5. Glucocorticoids in multiple myeloma, lymphoma, sarcoidosis, vitamin D/A intoxication
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19
Q

List a differential diagnosis for hypocalcemia

A
  • LOW PTH
    • Surgical, postradiation
    • Genetic
      • Di George syndrome
      • HDR or Barakat (hypoparathyroidism, sensorineural deafness, renal anomalies- GATA3 mutation)
      • HRD or Sanjad-Sakati, Kenney-Caffey (hypoparathyroidism, retardation and dysmorphism)
      • Kearns-Sayre
      • Isolated parathyroid aplasia
      • Familial isolated hypoparathyroidism
      • CHARGE syndrome
    • Autoimmune (APS-1/AIRE gene)
    • Infiltrative
    • Deposition of metals (iron- chronic transfusion, copper- Wilson disease, aluminum)
    • Functional (in hypomagnesemia)
  • PTH RESISTANCE
    • Pseudohypoparathyroidism
    • Renal insufficiency
    • Medications that block osteoclastic bone resorption (plicamycin, calcitonin, bisphosphonates, denosumab)
  • LOW VITAMIN D
    • Vitmain D deficiency
    • Hypoparathyroidism
    • Diseases associated with increased FGF23 levels
    • Pseudovitamin D deficiency rickets (CYP27B1 mutations)
  • VITAMIN D RESISTANCE
    • Hereditary vitamin D resistant rickets (inactivating VDR mutations)
  • OTHER
    • Acute hyperphosphatemia (crush injury/myonecrosis, rapid tumor lysis, parenteral phosphate administration, excessive enteral phosphate - PO4 containing antacids or enemas)
    • Acute pancreatitis
    • Citrated blood transfusion
    • Rapid, excessive skeletal mineralization (hungry bone syndrome, osteoblastic metastasis, vitamin D therapy for vit D deficiency)
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20
Q

List 3 signs and symptoms of hypocalcemia

A
  • Tetany
  • Paresthesias
  • Muscle cramping
  • Seizures
  • Organic brain syndrome
  • Cardiac: prolonged QT interval, CHF
  • Ophthalmologic: subcapsular cataract
  • Dematologic: dry flaky skin, brittle nails
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21
Q

Define Chvostek’s sign and Trousseau’s sign

A
  • Chvostek’s sign: tapping the facial nerve 2 cm anterior to earlobe, just below zygoma, response is a contraction of facial muscles (low specificity, seen in 25% of normal individuals)
  • Trousseau’s sign: inflating BP cuff 20 mm Hg above systolic for about 3 minutes, response is carpal spasm
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22
Q

How can you differentiate hypoparathyroidism from hungry bone syndrome?

A
  • Hypoparathyroidism: low Ca, high phosphorus, low PTH
  • Hungry bone syndrome: low Ca, low phosphorus, appropriately elevated PTH
23
Q

List the genetic causes of PTH resistance (spectrum of GNAS disorders)

A
  • Pseudohypoparathyroidism 1A: PTH resistance + Albright hereditary osteodystrophy (short stature, rounded face, short neck, obesity, brachydactyly, shortened 4th and 5th metatarsals, subcutaneous ossifications, reduced intelligence, hypothyroidism, oligomenorrhea/infertility). Heterozygous mutation in GNAS
  • Pseudohypoparathyroidism 1B: isolated PTH resistance. GNAS regulatory region mutation/deletion
  • Pseudopseudohypoparathyroid: AHO phenotype with no abnormalities in calcium metabolism. Also GNAS mutation
  • Progressive osseous heteroplasia: ectopic bone formation in dermis, muscle, connective tissues, +AHO features, NO calcium or PTH abnormalities
24
Q

List 5 causes of vitamin D deficiency

A
  1. Inadequate sunlight exposure
  2. Inadequate nutrition, exclusively breastfed babies
  3. Malabsorption
  4. Short gut/gastric bypass surgery
  5. Drugs that activate catabolism (phenytoin, phenobarbital)
  6. Heavily pigmented skin (less efficient vit D production)
  7. Obesity
25
Q

List 4 functions of bone

A
  1. Rigid support to extremities and vital organs
  2. Locomotion, attachment for muscles
  3. Reservoir of ions (calcium, phosphate, magnesium, sodium)
  4. Houses hematopoietic elements
26
Q

List a differential diagnosis for rickets

A
  • Vitamin D dependent
    • 1 alpha hydroxylase deficiency
    • Vitamin D receptor mutation
  • Hypophosphatemic
    • X-linked dominant (XLH)
    • Autosomal dominant (ADHR)
    • Autosomal recessive (ARHR)
    • Tumor induced osteomalacia (TIO)
    • Hypophosphatemic rickets with hypercalciuria (HHRH)
    • HHRH, AR or X-linked recessive (XRHR)
    • Fibrous dysplasia
    • Fanconi syndrome
27
Q

List 5 classifications for osteogenesis imperfecta

A
  1. Type 1: non-deforming type (COL1A1, COL1A2)
  2. Type 2: perinatal lethal (COL1A1, COL1A2, CRTAP, LEPRE1)
  3. Type 3: progressively deforming type (COL1A1, COL1A2, CRTAP, LEPRE1, PPIB, SERPINH1, SP7, WNT1, etc)
  4. Type 4: moderate form (COL1A1, COL1A2, CRTAP, PPIB, FXBP10, SERPINF1, WNT1, etc)
  5. Type 5: OI with calcification of the interosseous membranes and/or hypertrophic callus (IFITM5)
28
Q

List 3 genetic syndromes, other than OI, that cause bone fragility in childhood

A
  • Cole-Carpenter syndrome (P4HP)
  • Ehlers-Danlos (COL1A1, COL 3A1, COL5A2, COL5A1)
  • Marfan syndrome (FBN1)
  • Homocysteinuria (CBS)
  • Osteoporosis-inducing pseudoglioma syndrome (LRP5)
  • Sponyloocular syndrome (XYLT2)
29
Q

List 8 clinical features seen in osteogenesis imperfecta

A
  1. Blue sclerae
  2. Short, deformed limbs
  3. Infancy: poor feeding, failure to thrive
  4. Infancy: wide fontanels
  5. Hypotonia
  6. Rib deformities with respiratory complications
  7. Delayed walking, waddling gait
  8. Premature loss of dentition, dentinogenesis imperfecta
  9. Joint hyperlaxity, easy bruisability
  10. Hearing loss
  11. Dysmorphisms: triangular facies, frontal bossing, limb shortening
  12. Intrauterine fractures
30
Q

List 5 clinical features seen in osteopetrosis

A
  1. Fractures
  2. Hypocalcemia
  3. Pancytopenia
  4. Blindness
  5. Deafness
  6. Facial nerve palsy
  7. Difficulties with swallowing and feeding, failure to thrive
  8. Nasal congestion
  9. Hepatosplenomegaly
  10. Nystagmus
  11. Dental abnormalities
  12. Macrocephaly, hydrocephalus
  13. Recurrent infections (esp osteomyelitis)
31
Q

What is the difference between bone modeling and remodeling?

A
  • Modeling: occurs during growth, enlargement and reshaping of the skeleton to assume final adult dimensions
  • Remodeling: occurs throughout life including after epiphyseal closure, removal of bone for homeostatic needs and in response to changes in physical stress
32
Q

What are the three cell types that are central to bone modeling/remodeling?

A
  • Osteoblasts: secretes bone matrix, initiates bone formation
  • Osteocytes: aged osteoblast that has become entombed within newly created bone, maintains a network of communication throughout bone
  • Osteoclasts: responsible for bone resorption
33
Q

Where do osteoblasts and osteoclasts come from?

A
  • Osteoblasts: bone marrow multipotent mesenchymal stem cells (MMSCs), promoted by cytokines called bone morphogenic proteins (BMPs)
  • Osteocyte: hematopoietic stem cells, promoted by macrophage colony-stimulating factor (M-CSF) and RANK ligand
34
Q

What is osteoprotegrin (OPG)?

A

Produced by osteoblasts, it binds RANKL and prevents bringing to RANK, therefore protecting the skeleton from excessive resorption

35
Q

List a differential diagnosis for neonatal hypocalcemia

A
  • Maternal diabetes
  • Toxemia of pregnancy
  • Maternal hyperparathyroidism or hypercalcemia
  • Congenital rubella
  • Sepsis
  • SGA, IUGR, prematurity
  • Asphyxia
  • Hypomagnesemia
  • Transfusin (citrated blood products/alkali)
  • Respiratory or metabolic alkalosis
  • Ingestion of formula, evaporated/whole milk (increased phosphate load)
  • Vitamin D deficiency
  • Nutritional calcium deficiency
  • Hypomagenesemia
  • Acute/chronic renal insufficiency
  • Hypoalbuminemia (ex. nephrotic syndrome)
  • Diuretics (furosemide)
  • Organic acidemias
  • Hypoparathyroidism
36
Q

List a differential diagnosis for hypophosphatemia

A
  • Decreased intestinal absorption
    • Dietary deficiency
    • Malabsorption
    • Vomiting
    • Vitamin D deficiency or resistance
    • Phosphate-binding antacids
  • Increased urinary phosphate excretion
    • Hyperparathyroidism
    • Post renal transplantation
    • Hypophosphatemic rickets
    • Fanconi syndrome
    • Intravascular volume depletion
    • DKA (osmotic diuresis)
    • Ongogenic hypophosphatemia
    • Fibrous dysplasia
    • Drugs (diuretics, glucocorticoids, ifosfamide, cisplatin)
  • Phosphate shift to intracellular space
    • Carbohydrate loading (glucose, fructose, etc)
    • Refeeding
    • Insulin therapy
    • Respiratory alkalosis
    • Hyperventilation
    • Gram negative sepsis
    • Hungry bone syndrome
    • Tumor consumption
    • Catecholamine administration
    • Salicylate intoxication
37
Q

List a differential diagnosis for hyperphosphatemia

A
  • Increased phosphate load
    • Phosphate containing laxatives or enemas
    • Parenteral phosphate
    • Vitamin D intoxication
  • Decreased renal phosphate excretion
    • Hypoparathyroidism
    • Pseudohypoparathyroidism
    • Renal failure
    • Tumoral calcinosis
    • Hyperthyroidism
    • Acromegaly
  • Phosphate shift to extracellular space
    • Hemolysis
    • Rhabdomyolysis
    • Tumor lysis syndrome
    • Malignant hyperthermia
    • Crush injuries
    • Resipiratory or metabolic acidosis
38
Q

What is the difference between rickets and osteomalacia?

A
  • Rickets: disruption of endochondral ossification of growth plate in children whose epiphyses have not yet closed
  • Osteomalacia: deficiency in the mineralization of preformed osteoid at the trabecular, endosteal and periosteal bone surfaces in children and adults
39
Q

List 3 radiographic features of rickets

A
  • Cupping
  • Splaying/widened physis
  • Fraying/irregularity of distal metaphysis
40
Q

List 7 skeletal deformities in rickets

A
  • Genu varum (bowed legs)
  • Genu valgum (knocked knees)
  • Windswept knees
  • Swollen costochondral junctions of ribs (rachitic rosary)
  • Indentation of the lower anterior thoracic wall (Harrison’s groove)
  • Involution of the ribs and protrusion of the sternum (pigeon chest)
  • Bowing of the arms
  • Enlarged wrists
  • Expansion of cranial bones compared to facial bones (frontal bossing)
  • Softening of occipital area (craniotabes)
  • Delayed closure of fontanelles
  • Impaired development of teeth (delayed eruption, enamel hypoplasia, increased caries)
41
Q

List the 2 types of vitamin D dependent rickets

A
  1. Type 1: 1 alpha hydroxylase (CYP27B1) deficiency - treated with calcitriol and normal calcium intake
  2. Type 2: vitamin D receptor inactivation - associated with alopecia - treated with high dose calcium therapy
42
Q

List 4 types of hypophosphatemic rickets (low phosphate, elevated FGF23)

A
  1. X-linked hypophosphatemic rickets - previously VDRR, mutation in PHEX
  2. Autosomal dominant hypophosphatemic rickets - activating mutation in FGF23 gene
  3. Autosomal recessive hypophosphatemic rickets - mutation in DMP1 gene
  4. Tumor induced osteomalacia (TIO) - excessive secretion of FGF23 from benign mesenchymal or mixed connective tissue tumors
  5. Fibrous dysplasia - activating mutation in GNAS
  6. Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) - AR, hypercalcemia and hypercalciuria, NORMAL FGF23
  7. X-Linked recessive hypophosphatemic rickets (XRHR) - aminoaciduria, glycosuria, proteinuria, hypercalciuria, nephrocalcinosis, renal insufficiency
  8. Fanconi syndrome - renal proximal tubules wasting phosphorus, glucose, amino acids, bicarbonate
43
Q

What is the treatment for hypophosphatemic rickets? What are the complications?

A
  • Phosphate supplements (liquid) 4-6 times per day
  • Calcitriol at supraphysiologic doses (prevent hyperparathyroidism)
  • Complications: nephrocalcinosis, hyperparathyroidism
44
Q

What is the gene involved in hypophosphatasia?

A

TNSALP (tissue non-specific alkaline phosphatate)

45
Q

What are the 5 types of hypophosphatasia?

A
  • Perinatal - lethal
  • Infantile - 50% mortality in first year
  • Childhood
  • Adult
  • Odontohypophosphatasia - prematurse exfoliation of primary teeth with intact roots or severe dental caries
46
Q

What are the lab features of hypophosphatasia?

What is the treatment?

A
  • Lab features
    • Low serum alkaline phosphatase
    • Elevated phosphoethanolamine, inorganic pyrophosphate and pyridoxal-5-phosphate
  • Treatment
    • Enzyme replacement therapy: asfotase alpha
    • OT and PT
47
Q

List 10 conditions which may predispose a child to osteoporosis

A
  • Chronic illness: leukemia/lymphoma, rheumatologic disorders, anorexia nervosa, cystic fibrosis, IBD, renal disease, transplantation, cyanotic CHD, celiac disease
  • Neuromuscular disorders: cerebral palsy, Duchenne muscular dystrophy, spina bifida, spinal musclar atrophy
  • Inborn errors of metabolism: glycogen storage disease, galactosemia, Gaucher disease
  • Endocrine/reproductive disorders: disorders of puberty, Turner syndrome, GHD, hyperthyroidism, diabetes, hyperprolactinemia, athletic amenorrhea, Cushing syndrome
  • Iatrogenic: glucocorticoids, GnRH agonists, methotrexate, cyclosporine, depo-Provera, L-thyroxine suppressive therapy
48
Q

List 3 risk factors for incomplete BMD restitution/recovery following treatment for ALL

A
  • Hypogonadism
  • Vitamin D deficiency
  • Reduced physical activity
  • Hypophosphatemia
  • Low IGF binding protein 3
49
Q

List 2 risk factors for incomplete vertebral body reshaping of fractures at diagnosis/during treatment in childhood ALL

A
  1. Moderate or severe vertebral collapse
  2. Older age (peri-pubertal and beyond)
50
Q

One must interpret pediatric BMD z-scores in the context of ____ (list 3)

A
  • Body size
  • Ethnicity
  • Pubertal staging/skeletal maturity (bone age)

*Short stature and pubertal delay underestimate BMD

51
Q

How do you diagnose pediatric osteoporosis?

A
  • Presence of vertebral fracture regardless of BMD
  • BMD Z-score of <-2.0 and clinically significant fracture history
    • 2+ long bone fractures before age 10
    • 3+ long bone fractures before age 18
52
Q

List 2 side effects of bisphosphonate therapy

A
  • Acute phase reaction (24-72 hours): fever, malaise, back and bone pain, nausea and vomiting
  • Hypocalcemia (1-3 days)
  • In adults: thrombocytopenia, uveitis, mucosal ulcerations, osteonecrosis of the jaw (ONJ), atypical sub-trochanteric or metaphyseal “fatigue fractures” (AFF)
  • Contraindicated in those with poor renal function
53
Q

How do you classify vertebral fractures according to Genant method?

A
  • 20% = normal
  • >20% = grade 1
  • >25% = grade 2
  • >40% = grade 3 (severe)

ENDOCRINOLOGY (21 decks)

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