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Questions and Answers
What percentage of calcium in the adult body is found in the skeleton?
Which of the following is a function of calcium in the body?
What is the role of oxalates in calcium absorption?
What is the optimal ratio of phosphate to calcium for proper absorption?
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What is the daily requirement of calcium for children?
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What happens when the concentration of plasma ionized calcium decreases?
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Which of the following is NOT a form of calcium in plasma?
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What is the effect of PTH on bones?
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What percentage of dietary calcium is absorbed?
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Which of the following increases calcium absorption by creating acidity in the gut?
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What is the role of osteoclasts in bone tissue?
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At what level of calcium in blood does it start getting excreted in urine?
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Which of the following is a factor that affects the availability of calcium in the gut?
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Which of the following induces the formation of a carrier protein important for calcium transfer across the intestinal mucosal epithelium?
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What is the term for the process of bone demineralization?
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What increases blood calcium levels by increasing osteoclast activity?
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What is the normal range of serum calcium levels?
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What is the daily requirement of phosphorus in an adult diet?
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What percentage of phosphorus in serum is bound to protein?
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What is the primary function of phosphorus in the formation of bone and teeth?
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What is the ratio of Na2HPO4:NaH2PO4 in blood?
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What is the term for intermittent muscular spasms?
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Study Notes
Calcium Metabolism
- Calcium is the most abundant mineral in the human body, with an average of 1000g in an adult body.
- 99% of calcium is found in the skeleton, and 1% is found in extracellular fluid.
Functions of Calcium
- Transmission of nerve impulses
- Formation of teeth and bone
- Muscle contraction
- Blood coagulation
- Activation of enzymes
- Secretion of hormones
Food Sources and Daily Requirement
- Food sources: milk, dairy products, cereals, fish, eggs, and cabbage
- Daily requirement: 500mg/day for adults, 1200mg/day for children, 1500mg/day for pregnancy and lactation, and 1500mg/day for the elderly
Absorption of Calcium
- Absorption occurs in the first and second parts of the duodenum
- Two mechanisms of absorption: active transport process and simple diffusion
Plasma Calcium
- Normal concentration: 9-11 mg/dL
- Calcium is present in three forms: bound to proteins (about 4mg/dL), ionized form (about 5mg/dL), and complexed with bicarbonate, citrate, or phosphate (about 1mg/dL)
- Ionized form is the only physiologically active form
Factors Affecting Calcium Absorption
- Vitamin D (calcitriol) induces the formation of a carrier protein (Calbindin) for calcium transfer
- Parathyroid hormone increases calcium transport by enhancing 1α hydroxylase activity
- pH of the intestine: acidity increases calcium absorption
- Amount of carbohydrates in the diet: lactose promotes calcium absorption
- Amount of protein in the diet: amino acids (lysine and arginine) increase calcium absorption
- Phytic acid: an anti-calcifying factor that combines with calcium to form insoluble salts
- Oxalates: present in leafy vegetables, causing formation of insoluble calcium oxalates
- Phosphate: high phosphate content causes precipitation as calcium phosphate
- Malabsorption syndromes: fatty acid is not absorbed, causing formation of insoluble calcium salt
Excretion of Calcium
- Calcium leaves the body mainly in urine and feces, but also in other body tissues and fluids, such as sweat
- Renal threshold for calcium in blood: 10mg/dL
Homeostasis of Calcium
- Plasma calcium concentration is controlled by three hormones: parathyroid hormone (PTH), calcitriol, and calcitonin
Parathyroid Hormone (PTH)
- PTH secretion is stimulated in response to decreased plasma ionized calcium
- Acts on bone to cause rapid release of calcium and increased osteoclastic resorption
- Acts on kidneys to increase calcium reabsorption and decrease renal calcium excretion
- Acts on the intestine to stimulate production of calcitriol, which increases calcium absorption
Calcitriol
- Active form of vitamin D
- Increases blood calcium level by:
- Increasing absorption of dietary calcium from the intestine
- Increasing renal tubular reabsorption of calcium
- Increasing osteoclast activity, causing bone demineralization
Calcitonin
- Secreted by parafollicular cells of the thyroid gland
Hypercalcemia and Hypocalcemia
- Hypercalcemia: serum calcium level > 11mg/dL
- Hypocalcemia: serum calcium level < 8.8mg/dL
Symptoms of Hypocalcemia
- Muscle cramps
- Paresthesia, especially in fingers
- Neuromuscular irritability, muscle twitching
- Tetany (intermittent muscular spasm)
- Seizures
- Bradycardia
- Rickets
- Osteoporosis
Phosphate Metabolism
- An adult body contains about 1 kg of phosphate, found in every cell of the body
- Daily requirement: 500mg/day
Food Sources
- Food sources: milk, dairy products, cereals, nuts
Forms of Phosphate in Serum
- Free ions (40%)
- Complex form with cations such as Ca2+, Mg2+, Na+, K+ (50%)
- Bound to protein (10%)
Functions of Phosphate
- Formation of bone and teeth
- Production of high energy phosphate compounds, such as ATP, CTP, GTP, and creatine phosphate
- Synthesis of nucleoside co-enzymes, such as NAD and NADP
- DNA and RNA synthesis, where phosphodiester linkages form the backbone of the structure
- Formation of phosphate esters, such as glucose-6-phosphate and phospholipids
- Activation of enzymes by phosphorylation
- Phosphate buffer system in blood, where the ratio of Na2HPO4:NaH2PO4 is 4:1.
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Description
Learn about the role of calcium and phosphate in the body, their absorption, regulation, and related disorders. Understand the functions of parathyroid hormone, calcitonin, and calcitriol in blood calcium regulation.
