Calcium Final PDF

Minerals Average amounts of minerals in adult human body  Calcium Calcium is the most abundant mineral in the body. Bones and teeth contain about 99% of the body’s calcium ( hydroxyapatile). The other 1% is distributed in intra- and extracellular fluids. Within body fluid...

Minerals Average amounts of minerals in adult human body  Calcium Calcium is the most abundant mineral in the body. Bones and teeth contain about 99% of the body’s calcium ( hydroxyapatile). The other 1% is distributed in intra- and extracellular fluids. Within body fluids, calcium is found in its ionic form. Sources of calcium –The best food sources of calcium include milk and dairy products, especially cheese and yogurt, and selected sea- foods, such as salmon and sardines (with bones). –Some vegetables, such as broccoli and cauliflower also provide relatively high amounts of calcium. – Fortified foods and calcium supplements  Meats and grains are relatively poor sources of calcium. Vegetables such as spinach is poor sources, because they contain large amounts of oxalic acid, which binds calcium and prevents its absorption.  Digestion of calcium Calcium is present in ionic form, pond to protein and insoluble salts (calcium carbonate –calcium citrate ). Some calcium is released from the salts before absorption in about 1 hour at an acidic pH (as occurs in the stomach). Solubilization does not necessarily ensure better absorption, because free calcium can bind to other dietary constituents, limiting its bioavailability.  Absorption of calcium Two main transport processes are responsible for the absorption of calcium, which occurs along the small intestine across the intestinal mucosa : 1- Active transport (transcellularly) 2-Passive transport (paracellularly) Transcellular transport where the substances travel through the cell. Paracellular transport refers to the transfer of substances by passing through the intercellular space between the cells. 1- Active transport is interacellular (through cells) - occurs in duodenum & jejunum - requires energy(ATP) - involves calcium-binding transport protein (CBP) - stimulated by calcitriol ( active from of vitamin D). - Active transport occurs more readily during low and moderate calcium intakes. 2- Passive transport is paracellular ( between cells). - it occurs in small intestine, mostly jejunum & ileum. - no carriers or energy is needed. - Passive transport occurs more readily during higher calcium intakes.  Factors influencing calcium absorption Growth, pregnancy, and lactation increase calcium requirements and improve absorption. Growing children, for example, absorb up to 75% of dietary calcium, in contrast to adults, who average about 30% absorption.  Calcitriol ( D 3) involved in the synthesis of the calcium-binding transport protein , which binds calcium for transport into the cell. So , Vitamin D improves the absorption of calcium. With age calcium absorption becomes impaired by decreased renal calcitriol production.  High plasma phosphorus concentrations also may diminish calcitriol production in the kidney. Estrogen deficiency at menopause also decreases vitamin D–mediated calcium absorption.  Other factors influencing absorption Ingesting lactose with the calcium source appears to improve overall calcium absorption, possibly by improving solubility. protein also can enhance calcium absorption.  Phytate. inhibits calcium absorption. phytate binds calcium and decreases its availability, when present in a phytate : calcium ratio >0.2 : 1 High intake of some fibers. are also thought to bind to calcium and decrease calcium absorption.  Oxalate. chelates the calcium and decrease absorption because it has a very low solubility and increases fecal calcium excretion. Excess magnesium. Magnesium and calcium, compete with each other for intestinal absorption.  Unabsorbed dietary fatty acids found in significant quantities in the gastrointestinal tract associated with steatorrhea (>7 g of fecal fat per day) can interfere with calcium absorption by forming insoluble calcium “soaps” (calcium–fatty acid complexes) in the small intestine.  Interactions between Calcium and Selected Nutrients/Substances Nutrients/Substances Nutrients/Substances Enhancing Calcium Inhibiting Calcium Absorption Absorption Vitamin D high fiber Sugars and sugar alcohols Phytate Protein Oxalate Unabsorbed fatty acids  Transport of calcium Calcium is transported in the blood in three forms: 1. About 50% of calcium is found free (ionized) in the blood. 2. Some calcium (up to ~10%) is combined with sulfate, phosphate, or citrate. These two forms are diffusible from blood to tissues. 3. Some calcium (~40%) is bound to proteins, mainly albumin and is non diffusible.  Important note Approximately half of the calcium found in the intravascular compartment is bound to serum protein albumin. Thus, when serum albumin levels are low, total calcium levels decrease because of hypoalbuminemia.  Maintaining Calcium Balance Parathyroid hormone(PTH), calcitonin and vitamin D work together in a feedback loop to maintain calcium homeostasis which mean keep calcium within its normal range.  If blood calcium If blood calcium levels fall: levels rise too high: PTH is released calcitonin is from parathyroid released from thyroid gland , which gland , which helps increases calcium lower blood calcium levels. levels. The Effects of Parathyroid Hormone (PTH), Calcitriol, and Calcitonin on Calcium Balance. PTH Calcitriol Calcitonin Serum calcium ↑ ↑ ↓ Bone calcium ↓ ∗ ↑ Renal calcium reabsorption ↑ ↑ ↓ Intestinal calcium absorption ↑ ↑ No effect *Works with PTH  Calcium balance / hemostasis is controlled through an integrated response to calcium- regulating hormones that affect calcium transport at three primary sites of regulation: - Intestine - Bone - kidney. Factors Regulating Blood Calcium Level Calcitriol The calcitriol( active vitamin D) induces a calcium binding protein, Calmodulin which increases the absorption of calcium in the intestinal mucosa. Vitamin D acts independently on bone. It increases the number and activity of osteoblasts, the bone forming cells. Parathyroid Hormone (PTH) In the intestine The parathormone helps the absorption of Ca++ from the intestine via activation of vitamin D to calcitriol. In the bone PTH causes demineralization or decalcification. It increases the number of Osteoclasts, The cells responsible for bone resorption. In kidney, PTH decreases renal excretion of calcium. Calcitonin In bones , Calcitonin decreases serum calcium level by inhibiting resorption of bone. It decreases the activity of osteoclasts and increases that of osteoblasts. In kidney, calcitonin increases renal excretion of calcium. Calcitonin and PTH are antagonistic.  Functions of calcium Most absorbed calcium goes towards bone mineralization and maintenance. Other roles is mediated by calcium include : Muscle contraction. Secretion of hormones such as insulin, parathyroid hormone and calcitonin  Activation of enzymes: Calcium binding protein “Calmodulin” causes activation of various kinases enzymes such as : - Ca++-dependent protein kinases - myosin kinase - phosphorylase kinase Some other enzymes are activated directly by Ca++ without the presence of calmodulin. Examples are - pancreatic lipase - coagulation enzymes - Rennin Blood coagulation Calcium is known as factor lV (four ) in blood coagulation and play a role in the conversion of prothrombin to thrombin.  Permeability of serum through capillaries ( tiny blood vessels) is decreased by calcium which help in controlling blood pressure and presence of edema.  Excretion of Calcium – Calcium is excreted in the urine and feces, and very small amounts lost through the skin, especially with extreme sweating. – Most calcium is filtered and reabsorbed by the kidney ( 97%) Interactions of calcium with other nutrients Phosphorus : Prolonged ingestion of diets high in phosphorus and low in calcium may result in a mild hyperparathyroidism which led to calcium loss from bone.  Sodium : Sodium and calcium excretion are linked in the kidney.High amounts of sodium increase urinary Ca excretion. Caffeine: High amounts of caffeine increase urinary and gut Ca excretion  Iron : Increasing dietary calcium intake significantly decreases nonheme iron absorption. Lead : Poor dietary calcium intake increase lead absorption and is associated with lead accumulation in blood and organs Fatty acids: Calcium can diminish the absorption of fatty acids and thus influence serum lipid concentrations. - Calcium also may directly bind the fatty acids in the small intestine to form insoluble “soaps” that are excreted in the feces.  Blood Level of Calcium The normal blood level of calcium is 9 -11mg/dL. Hypercalcemia Blood calcium level is more than 11mg/dL. The major causes include : -Hyperparathyroidism - Hypothyroidism - Hypervitaminosis D. Hypocalcemia –Blood calcium level is less than 8.8mg/dL If it is lower than 7.5mg/dL, tetany will result. Tetany is a muscle contractions that fail to relax, especially in muscles of the arms and legs (extremities). The major causes include: Hypoparathyroidism Surgical removal of parathyroid glands Hyperthyroidism Renal failure Vitamin D deficiency Low protein diet.  Calcification Calcification happens when calcium builds up in body tissue, blood vessels, or organs. This buildup can harden and disrupt the body’s normal processes. Calcium is transported through the bloodstream so calcification can occur in almost any part of the body. including: Small and large arteries. Heart valves Brain Joints and tendons Soft tissues like breasts, muscles, and fat. Kidney, bladder, and gallbladder. Causes of calcification 1. Infections 2. Calcium metabolism disorders that cause hypercalcemia 3. Genetic or autoimmune disorders affecting the skeletal system and connective tissues. 4. Persistent inflammation  Deficiency of calcium Factors contributes to calcium deficiency: –Inadequate calcium intake – poor calcium absorption – excessive calcium losses or some combination of these factors.  Rickets occurs in children when the amount of calcium in bone matrix is deficient. In adults deficient in calcium, osteoporosis—the loss of bone mass (protein matrix and bone minerals) occurs. This loss of bone increases bone fragility and fracture risk. Relationship between calcium and other diseases Hypertention An inverse relationship exists between calcium intake and blood pressure which is related to the role of calcium in heart and blood vessels muscle contraction. As intake of calcium decreases, prevalence of hypertension increases. Colon cancer Calcium is thought to decrease the risk of colon cancer through its ability to bind and increase excretion of bile acids and free fatty acids, which act as promoters of cancer by inducing colon cell hyperproliferation ( abnormal rapid cell growth ). Obesity Low intakes of calcium have been associated with obesity and high body weights. High calcium intake is related to modulating fat metabolism , with decreased fat synthesis (lipogenesis) and increase fat breakdown ( lipolysis).