Chapter 12: Calcium

when blood calcium levels are low...

parathyroid gland releases PTH which stimulates the kidneys to convert more vitamin D to calcitriol. *calcitriol and PTH increase amount of calcium absorbed through intestinal tract, reducing amount of calcium excreted through kidneys and releasing calcium from bone

when blood calcium levels are high...

a. parathyroid glands decrease secretion of PTH, which in turn suppresses activation of vitamin D to calcitriol. Suppression of PTH and calcitriol decrease reabsorption of calcium by the kidneys, decreases absorption of calcium from the intestines and inhibits release of calcium from bone. i. Thyroid gland releases calcitonin. Calcitonin reduces reabsorption of calcium by the kidneys, increasing its loss of urine. Calcitonin stimulates bone building, removing calcium from the bloodstream.

calcium may lower blood pressure

along with potassium and magnesium

calcium may prevent colon cancer

protects the lining of the colon from damaging bile acids and cancer-promoting substances

calcium may reduce the risk of kidney stones

calcium can bind to oxalates in food and prevent absorption. with fewer oxalates filtering through kidneys, fewer stones are formed.

food sources

dairy products, bok choy, broccoli, canned salmon with bones, tofu

toxicity

hypercalcemia can cause impaired kidneys and calcium deposits *stomach upset, nausea, constipation *interfers with absorption of other minerals

deficiency

hypocalcemia may not show any symptoms but can lead to less dense, weakened bone and increased risk for osteoporosis.

true/false: americans tend to consume too little calcium

true

absorption and transport

*active transcellular transport 1. enter: vitamin D dependent membrane channel protein 2. shuttle: Ca-binding protein in cytosol 3. exit: basolateral ATPase *paracellular transport (passive diffusion)

functions

*helps build strong bones and teeth: primary mineral in hydroxyapatite crystals that provide strength and structure *muscle contraction *nerve impulses *releasing hormones *blood clotting *normal heart beat *lower blood pressure *reduce risk of colon cancer, kidney stones, and obesity

bioavailability

*influenced by other food components *vitamin D and lactose improve absorption *low protein reduces absorption *oxalates and phytates reduce bioavailability

calcium

*most abundant mineral in body *over 99% is in bones and teeth

calcium may reduce the risk of obesity

*when blood calcium is low, PTH is increased to reduce amount of calcium lost through urine and calcitriol increases in the body to enhance calcium absorption *hormne responses shift calcium into fat cells, which stimulates fat production and storage. --> opposite is true when diet is high in calcium: less calcium stored in fat cells

calcium supplements

1. calcium carbonate: most common form purchased. most effective when consumed with a meal 2. calcium citrate: can be taken throughout the day and doesn't need help of acidic juices to be absorbed. usually works best for those aged 50 and older

skeleton is made up of two types of bone:

1. cortical bone: compact, dense bone that makes up surface 2. trabecular bone: spongy, interior which has a high rate of turnover and is sensitive to change in calcium intake.