JAYS QUIZPAD: Bone Calcium and Phosphorus Quiz

Bone Calcium & Phosphate Metabolism

• Calcium is the most abundant mineral in many animals and the human body
• Ancient Romans used calcium oxide (lime) and calcium sulfate (plaster of Paris) to set broken bones
• Sir Humphry Davy isolated calcium in 1808
• Phosphorus is the second most abundant essential mineral in the human body after calcium
• Phosphorus exists as phosphates in the human body (compounds containing the phosphate ion, PO₄³⁻)
• White phosphorus was first produced in 1669 by Hennig Brand
• Calcium and phosphorus are required for the formation of hydroxyapatite and for the strength of skeletal tissue

Role of Calcium in the Body

• Affects nerve and muscle physiology, and intracellular signal transduction pathways
• Acts as a co-factor in blood clotting
• Is a constituent of bone and teeth
• Is a major structural element in vertebrate skeletons (bones and teeth), in the form of calcium phosphate (Ca₁₀(PO₄)₆(OH)₂), also known as hydroxyapatite
• Maintains all cells and connective tissues in the body
• Is an essential component in the production of enzymes and hormones that regulate metabolism

Role of Phosphate

• Key constituent of bone and teeth
• Component of intracellular buffering, forming energy-rich bonds in ATP
• Forms co-enzymes
• Regulates blood and urinary pH
• Forms organic molecules like DNA and RNA
• Plays a role in cellular energy metabolism
• Component of macro-molecules like nucleic acids, phospholipids, and phosphoproteins

Distribution

• Total calcium in the body is 1000-1500 grams (1.5% of body weight)
• 99% of calcium is in bones
• 1% of calcium is in extracellular fluid (ECF) and plasma
• Total phosphorus in the body is 500-800 grams
• 80-90% phosphorus occurs in bones and teeth
• 10% of phosphorus occurs in red blood cells (RBCs) and plasma

Plasma Calcium and Phosphate

• Normal plasma calcium levels are 9-11 mg/dL
• Normal plasma phosphorus levels are 2.5-4.5 mg/dL
• Ionized calcium: ~5 mg/dL
• Unionized calcium: ~4 mg/dL
• Organic phosphate: ~0.5-1 mg/dL
• Inorganic phosphate: Adults ~3-4 mg/dl, Children ~5-6 mg/dL

Calcium-Phosphate Ratio

• Calcium to phosphate ratio is normally 2:1
• Increased plasma calcium levels cause a corresponding decrease in phosphate absorption

Sources of Calcium

• Best sources: Hard cheese, Milk, Dark green leafy vegetables
• Fair sources: String beans, Eggs, Bread
• Good sources: Ice-cream, Broccoli, Baked beans, Dried legumes, Dried figs

Sources of Phosphorus

• Rich sources: Milk, Meat, Fish, Poultry, Eggs
• Moderate sources: Cereals, Pulses, Nuts, Legumes, Meat

Absorption and Excretion of Calcium

• 35-40% of daily dietary calcium is absorbed by the duodenum and first half of the jejunum
• An additional 25% of calcium enters the bloodstream via secretions and sloughed mucosal cells
• About 90% of daily calcium intake is excreted in feces

Phosphorus Absorption

• 50-70% of dietary phosphorus is absorbed in the small intestine as soluble inorganic phosphate
• Almost all dietary phosphate is absorbed within the gut and then is excreted in the urine

Renal Excretion of Calcium and Phosphate

• 10% of calcium is excreted in the urine and is bound to protein and thus cannot be filtered.
• The rest is filtered through the glomeruli
• almost all of the phosphorus is excreted in the urine

Phosphorus Excretion

• Phosphorus is primarily excreted via urine
• Almost two-thirds of excreted phosphorus appears as phosphate of various cations in the urine

Renal Handling of Calcium and Phosphate

When Calcium Concentration is Low

• Reabsorption from renal tubules increases
• Calcium excretion increases markedly even with slight increases in calcium

Renal Phosphate Excretion

• Runs through an overflow mechanism
• All phosphate in the glomerular filtrate is reabsorbed when plasma phosphate levels are below 1 mmol/L

Factors Controlling Absorption

pH of the Intestine

• Acidic pH in the upper intestine (duodenum) increases calcium absorption by keeping calcium salts in a soluble state
• In the lower intestine, the more alkaline pH causes calcium salts to precipitate

Phytic Acid and Phytates

• Present in oatmeal, meat, and cereals
• Considered as anti-calcifying factors as they combine with calcium in the diet, forming insoluble salts of calcium

Oxalates

• Present in spinach and rhubarb leaves
• Form oxalate precipitates with dietary calcium, thus decreasing calcium availability

Fats

• Combine with calcium to form insoluble calcium, decreasing calcium absorption

Bile Salts

• Increase calcium absorption by promoting lipid metabolism

Protein and Amino Acids

• Increase calcium absorption as proteins form soluble complexes with calcium, keeping calcium in an absorbable form

Carbohydrates

• Lactose promotes calcium absorption by creating the acidity in the gut, favorable for the growth of acid-producing bacteria

Amount of Dietary Calcium and Phosphate

• Amount of calcium stored in the body is directly proportional to the amount of calcium absorbed
• Increased calcium and phosphate levels in the diet increase their absorption, but only up to a certain limit

Pregnancy and Growth

• During later stages of pregnancy, greater calcium absorption occurs
• 50% of absorbed calcium is used for fetal skeleton development, with the rest stored as a reserve for lactation
• Increased placental lactogen and estrogen levels cause increased vitamin D hydroxylation

Hormonal Control of Calcium and Phosphate Metabolism

• Three hormones regulate calcium and phosphate metabolism: Vitamin D, PTH, and Calcitonin

Vitamin D

• Cholecalciferol (D₃) —Produced in the skin when exposed to sunlight
• Ergocalciferol (D₂)
• Vitamin D has minimal intrinsic biological activity and must be converted in the liver and kidneys into 1,25-dihydroxycholecalciferol for activity

Action on Bone

• Calcitriol stimulates calcium uptake in osteoblasts for deposition as calcium phosphate

Action on Kidney

• Regulates calcium and phosphate excretion via the kidneys, minimizing excretion and increasing reabsorption

Parathyroid Hormone (PTH)

• Secreted by the parathyroid glands, which are four in number, situated near the thyroid gland
• Histologically consists of chief cells which form PTH, and oxyphil cells that replace chief cells and store hormones
• The main function is to increase serum calcium levels within a critical range (9-11 mg/dL)

PTH Secretion

• Stimulatory effect of PTH secretion is caused by low plasma calcium levels—two phases rapid and slow
• Maximum PTH secretion occurs when plasma calcium levels fall below 7 mg/dL

Calcitonin

• Minor regulator of calcium and phosphate metabolism
• Secreted by parafollicular cells (C cells) of the thyroid gland
• Single chain polypeptide hormone
• Plasma concentration 10-20µg/mL
• Physiological antagonist to PTH with respect to calcium, and has the same effect on Phosphate as PTH.

Target Sites for Calcitonin

• Acts on bone (osteoclasts): decreasing serum calcium levels
• Acts on kidney and intestines, promoting calcium elimination

Influence of Other Hormones

• Includes growth hormone, insulin, testosterone, lactogen, prolactin, steroids, and thyroid hormones

Growth Hormone

• Increases intestinal calcium absorption and increases urinary calcium excretion
• Stimulates production of insulin-like growth factor in bone, which stimulates bone protein synthesis

Insulin

• Anabolic hormone favoring bone formation

Testosterone

• Causes differential growth of cartilage and resulting in differential bone development
• Acts on cartilage to increase bone growth

Thyroid Hormone

• Stimulates bone growth in infants
• Increases calcium mobilization in adults through increased bone metabolism

Glucocorticoids

• Inhibit vitamin D activity and subsequent calcium absorption in the intestine
• Inhibit protein synthesis and bone formation
• Inhibit new osteoclast formation and decrease activity of old osteoclasts

Concept of Calcium Balance

• Defined as the net gain or loss of calcium over a specified period
• Calculated by deducting calcium in feces and urine from calcium intake
• Positive calcium balance occurs in growing children
• Negative calcium balance occurs in aging adults

Osteoporosis

• Atrophy of bone—bone resorption exceeds bone deposition
• Caused by calcium or hormonal deficiencies
• Commonly seen in older people, particularly women over 60 years

Common Causes of Osteoporosis

• Lack of physical stress
• Lack of vitamin C
• Post-menopausal estrogen deficiency
• Old age
• Cushing's syndrome
• Malnutrition

Rickets

• Softening of bones in children due to vitamin D deficiency and resultant calcium and phosphate deficiency

Clinical features of Rickets

• Femoral and tibial bowing
• Growth retardation
• Weakness
• Tetany
• Susceptibility to fracture
• Irritability

Plasma Concentration of Calcium and Phosphate in Rickets

• Calcium is slightly depressed
• Phosphate is greatly depressed

Oral Manifestations in Rickets

• Development abnormalities of dentine and enamel
• Delayed eruption
• Malalignment of teeth in the jaws
• High caries index
• Abnormally wide predentine zone
• Interglobular dentine

Treatment for Rickets

• Diet rich in vitamin D and sunlight exposure
• Vitamin D supplementation may be necessary

Osteomalacia

• Softening and distortion of the skeleton
• Oral manifestations include severe periodontitis, thin or absent trabeculae, loosened teeth, weakened jaw bones

Hypophosphatasia

• Defect of the enzyme alkaline phosphatase
• Excretion of phosphoethanolamine in urine
• Clinical features vary by age: infantile form—severe rickets, childhood—loss of primary teeth, increased infection, growth retardation, rachitic-like deformation, adult—spontaneous fracture

Oral Manifestations of Hypophosphatasia

• Premature loss of primary teeth
• Gingivitis
• Radiographic features include hypocalcification, large pulp chambers, and alveolar bone loss

Hypocalcemia

• Low plasma calcium (<8.8 mg/dL)
• Symptoms may include muscle cramps, paresthesia, neuromuscular irritability, muscle twitching, tetany, seizures, bradycardia, convulsions

Causes of Hypocalcemia

• Hypoparathyroidism
• Vitamin D deficiency
• Increased calcitonin
• Deficiency of calcium, magnesium
• Hypoalbuminemia

Hypercalcemia

• High plasma calcium (>8.8 mg/dL)
• Symptoms may include anorexia, nausea, vomiting, polyuria, polydypsia, confusion, depression, psychosis, osteoporosis, pathological fractures, renal stones, ectopic calcification, and pancreatitis, increased serum alkaline phosphatase

Management of Hypercalcemia

• Adequate hydration with intravenous normal saline
• Furosemide IV to promote calcium excretion
• Steroids, if calcitriol excess is suspected

Causes and Outcomes of Calcium Deficiency

• Gluten-induced malabsorption, vitamin D deficiency, antacids, high-sugar diet, chronic steroid use can cause various issues and outcomes such as muscle spasms, bone loss, hormone disruption, high blood pressure, and abnormal blood clotting.

Test your knowledge on the dietary roles of calcium and phosphorus in human nutrition. This quiz covers recommended intakes, absorption, and the significance of these minerals in the body. Perfect for students learning about nutritional science.