Calcium and Its Functions

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Questions and Answers

What is the most common cause of hypercalcemia in a hospital population?

Excess vitamin D ingestion

Hypercalcemia of malignancy (correct)

Calcium therapy

Primary hyperparathyroidism

Which of the following symptoms is commonly associated with primary hyperparathyroidism?

Severe headaches

Fever

Lethargy (correct)

Hypercalciuria

What serum characteristic is typically observed in patients with hypercalcemia associated with malignancy?

Elevated PTH levels

High phosphate levels

Elevated vitamin D levels

Undetectable PTH levels (correct)

Which group is most likely to be affected by primary hyperparathyroidism?

Post menopausal women Signup and view all the answers

Which condition is NOT associated with hypercalcemia?

Osteoporosis Signup and view all the answers

What percentage of calcium in the body is found in bone?

99% Signup and view all the answers

Which of the following forms of calcium is considered biologically active?

Free calcium Signup and view all the answers

How does acidosis affect calcium binding to albumin?

Decreases binding Signup and view all the answers

What is the normal range of total extracellular calcium concentration?

2.2-2.6 mmol/L Signup and view all the answers

What is the primary hormone produced by the parathyroid glands that regulates calcium levels?

Parathyroid hormone (PTH) Signup and view all the answers

What happens to PTH stimulation when both calcium and magnesium levels are decreased?

PTH is decreased Signup and view all the answers

What does 'adjusted calcium' account for in clinical measurements?

Altered albumin levels Signup and view all the answers

Why is it important to measure albumin when assessing total calcium levels?

Changes in albumin can alter total calcium results Signup and view all the answers

What is a primary cause of hyperphosphatemia?

Renal failure Signup and view all the answers

Which condition is associated with severe hypophosphatemia?

Nutritional insufficiency Signup and view all the answers

What effect does hypomagnesemia have on neuromuscular function?

Impaired neuromuscular function Signup and view all the answers

How is magnesium homeostasis primarily regulated in the body?

By the kidneys Signup and view all the answers

Which deficiency can lead to hypoparathyroidism?

Severe hypomagnesemia Signup and view all the answers

What is a common consequence of hypophosphatemia related to enzyme activation?

Decreased glycolysis Signup and view all the answers

What can cause hypomagnesemia aside from nutritional insufficiency?

Prolonged nasogastric suction Signup and view all the answers

Which treatment for magnesium deficiency can lead to diarrhea?

Oral magnesium salts Signup and view all the answers

What is the main characteristic of osteoporosis?

Deterioration of bone tissue microarchitecture Signup and view all the answers

Which biochemical marker is commonly utilized to assess osteoblastic activity?

Osteocalcin Signup and view all the answers

What is a major cause of metabolic bone disease in adults?

Inadequate vitamin D levels Signup and view all the answers

What is a risk factor for developing osteoporosis?

Low dietary calcium Signup and view all the answers

Which of the following conditions is primarily associated with vitamin D deficiency in children?

Rickets Signup and view all the answers

What type of bone is commonly described as 'plastic' in Paget’s disease?

Disorganized bone Signup and view all the answers

Which of the following reflects the disturbed bone turnover in osteoporosis?

Increased bone resorption Signup and view all the answers

Which of the following factors plays a role in the pathophysiology of Paget's disease?

Genetic predisposition Signup and view all the answers

What is the primary laboratory finding associated with X-Linked Hypophosphatemia (XLH)?

Very high serum ALP levels Signup and view all the answers

What is a common consequence of untreated X-Linked Hypophosphatemia?

Rickets or osteomalacia Signup and view all the answers

Which of the following is NOT a first-line test in serum for evaluating calcium disorders?

Vitamin D levels Signup and view all the answers

Which electrolyte abnormality is commonly associated with rhabdomyolysis?

Hyperkalemia Signup and view all the answers

What symptom is NOT commonly associated with rhabdomyolysis?

Chest pain Signup and view all the answers

What is a typical investigation performed to monitor the status of a patient with rhabdomyolysis?

Serum creatinine Signup and view all the answers

Which treatment is NOT commonly used for rhabdomyolysis?

Calcium supplementation Signup and view all the answers

What can cause rapid destruction of skeletal muscle cells, leading to rhabdomyolysis?

Medication toxicity Signup and view all the answers

Study Notes

Calcium

Most abundant mineral in the body
Plays structural, neuromuscular, enzymatic, and signaling roles
99% of calcium is found in bone, 1% in extracellular fluid (ECF)
Calcium balance is maintained between bone, ECF, and kidneys
Extracellular total calcium levels are tightly controlled: 2.2-2.6 mmol/L
In plasma, calcium exists mainly bound to albumin (45%) and as free ionized calcium (55%)
Free ionized calcium is biologically active and is regulated by parathyroid hormone (PTH)

Calcium/Albumin Binding is Dependent on H+

Binding decreases in acidosis, leading to increased free calcium
Binding increases in alkalosis, leading to decreased free calcium

Parathyroid Glands

Four glands located near the thyroid gland
Regulate calcium homeostasis but not metabolism
Produce PTH which interacts with vitamin D to increase calcium levels
Calcium, magnesium, and phosphate levels affect PTH levels:
- Normal calcium levels, low magnesium: mild PTH stimulation
- Decreased calcium and magnesium: decreased PTH
- Increased phosphate levels: decreased calcium and increased PTH

Hypercalcemia

Most common causes include primary hyperparathyroidism and hypercalcemia of malignancy

Primary Hyperparathyroidism

Common endocrine disorder caused by adenomas, hyperplasia, and carcinomas
Most common in postmenopausal women
Often due to a parathyroid adenoma, resulting in increased PTH levels
Hypercalcemia and hypophosphatemia occur
Most individuals are asymptomatic due to calcium stability
Symptoms include muscle weakness, fatigue, bradycardia, confusion, etc.

Hypercalcemia Associated with Malignancy

Most common cause of hypercalcemia in hospitalized patients
Usually due to PTH-related protein (PTHrP) production by a tumor
PTH is often undetectable in laboratory tests
Other abnormal lab findings: very low phosphate, very high urine calcium, and low vitamin D
Clinical features include neurological, gastrointestinal, renal, cardiac, and bone symptoms

Hypercalcemia - Rare Causes

Calcium therapy
Excess vitamin D ingestion
Thiazide diuretics (Excretion of sodium)
Granulomatous diseases (synthesis of vit. D)

Phosphate

Abundant anion in the body
Important component of nucleic acids, mineral strength, and buffer
Plays key roles in phosphorylation and dephosphorylation of enzymes
80% of phosphate is found in bone
Concentrations in ECF are controlled by the kidneys, with increased excretion by PTH

Hyperphosphatemia

Increased phosphate concentrations
Most common cause is renal failure
Other causes: hypoparathyroidism, cell damage (redistribution), acidosis (buffer), and pseudohypoparathyroidism (genetic disorder causing resistance to PTH)

Hypophosphatemia

Important for enzyme activation, glycolysis, oxidative metabolism, and transmembrane transport of K+ and Ca+2
Influences secretion and action of PTH
Severe hypomagnesemia can lead to hypoparathyroidism and refractory hypocalcemia

Magnesium Homeostasis

Around 30% of dietary magnesium is absorbed in the small intestine and distributed to tissues
Largely controlled by the kidneys
Hypermagnesemia is uncommon, often associated with renal failure or antiacid use
Hypomagnesemia (magnesium deficiency in serum) has symptoms similar to hypocalcemia, including impaired neuromuscular function and muscle weakness

Hypomagnesemia - Causes

Commonly associated with nutritional insufficiency
Other causes: osmotic diuresis, prolonged diuretic use, nasogastric suction, cytotoxic therapy, and proton pump inhibitors

Hypomagnesemia - Diagnosis and Treatment

Repeated magnesium levels below 0.7 mmol/L indicate intracellular depletion
Supplementation is available in oral, intramuscular, and intravenous forms
Oral supplementation often leads to diarrhea
Parenteral supplementation is necessary in patients with diarrhea or malabsorption

Metabolic Bone Disease

Disorders of bone structure and function
Calcium and phosphate levels may be normal, and hypercalcemia or hypocalcemia may not be associated with marked bone changes
Main types: osteoporosis, osteomalacia/rickets, Paget's disease, and X-linked hypophosphatemia (XLH)

Bone Turnover (metabolism)

Bone is constantly broken down and reformed (bone remodeling) by osteoblasts and osteoclasts
Biochemical markers help assess disease and monitor treatment:
- Urinary hydroxyproline (collagen breakdown)
- Deoxypyridinoline (specific collagen product)
- Alkaline phosphatase (ALP)
- Osteocalcin (sensitive indicator of osteoblastic activity)

Osteoporosis

Most common bone disorder
Major cause of morbidity and mortality in the elderly
Bone turnover favors resorption
Characterized by low bone mineral density (BMD) and deterioration of bone microarchitecture
Increased susceptibility to fracture

Osteoporosis - Risk Factors

Non-modifiable: age, menopause, family history, genetic factors
Modifiable: diet, smoking, sedentary lifestyle, previous fracture, sex hormone deficiencies, alcohol, immobility

Osteoporosis - Diagnosis and Treatment

Clinical history and risk factor assessment
Bone density measurement (bone scan) is essential for diagnosis
Treatment includes oral bisphosphonates to inhibit osteoclastic function

Osteomalacia and Rickets

Defective or inadequate bone mineralization
Osteomalacia affects adults, while rickets affects children (deformities in growing bones)
Primarily due to vitamin D deficiency (inadequate ingestion or sun exposure)

Osteomalacia and Rickets - Laboratory Considerations

Low serum calcium
Increased PTH
Increased renal phosphate excretion
Low serum phosphate
Increased serum ALP
Symptoms include muscle aches and bone pain

Paget’s Disease of Bone

Increased osteoclastic and osteoblastic activity (disorganized)
Common in the elderly
Causes may be viral or genetic
Often asymptomatic

Paget’s Disease of Bone - Laboratory Considerations

No disturbance in serum calcium levels
Very high serum ALP
Elevated urinary hydroxyproline

X-Linked Hypophosphatemia (XLH)

Rare genetic disorder
Excess phosphate excretion by kidneys
Decreased phosphate absorption in intestines
Low phosphate levels in serum

X-Linked Hypophosphatemia (XLH) - Consequences

Rickets, osteomalacia, short stature, bone/joint pain, and dental problems
Treatment includes phosphate and active vitamin D supplementation

Calcium Disorders or Bone Disease - Biochemistry Testing

First line serum tests: calcium, albumin, phosphate, ALP
Follow-up tests: PTH, magnesium, 25-hydroxycholecalciferol, urine calcium excretion, specific markers of bone turnover

Skeletal Muscle Disorders (Myopathies)

Conditions leading to muscle weakness or atrophy
Causes: congenital (muscular dystrophies), infections, anoxia, toxins, drugs, muscle denervation, lack of energy molecules, severe electrolyte imbalance
Severe damage to muscle cells leads to rhabdomyolysis, releasing myoglobin and creatine kinase (CK)

Rhabdomyolysis

Rapid destruction of skeletal muscle cells, often due to injury
Releases large quantities of myoglobin, which can be toxic to the kidneys
Causes: medications, heatstroke, alcohol & drug use
Symptoms: muscle weakness, muscle pain, dark urine
Complications: renal failure, disseminated intravascular coagulation, electrolyte abnormalities (hyperkalemia, hyperphosphatemia, and hypocalcemia)

Rhabdomyolysis - Investigation and Treatment

Increased serum total CK levels
Monitoring of urea, electrolytes, alcohol and drug of abuse
Treatment: cardiac monitoring, electrolyte correction, hemodialysis

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Description

This quiz covers the critical roles of calcium in the body, including its structural and signaling functions. It also discusses calcium balance and the regulation of calcium by parathyroid hormone and its interaction with albumin. Test your knowledge on calcium physiology and its homeostasis!