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Chapter 12

NUTR 201 Chapter Notes - Chapter 12: Hypercalcaemia, Bone Resorption, Calbindin

Foods And Nutrition
Course Code
NUTR 201

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Chapter 12: Pages 505-524, 540-551
What Are Minerals?
Mineral inorganic substance, other than water, that is required by the body for basic functions
or structure
Major minerals an essential mineral that is required in amounts greater than 100 mg daily
Common Characteristics of Major Minerals
o Most minerals work together to carry out interrelated tasks
o Calcium, magnesium, and phosphorus function together to form and strengthen the
structure of the skeleton
o Regulation of Minerals in the Body
The body maintains optimal levels of minerals, in large part by regulating
absorption (small intestine) and excretion (kidneys)
Changes in these regulatory processes ensure mineral availability and prevent
The body can store small amounts of certain minerals in the liver, bones, and
other tissues
o Dietary Sources of the Major Minerals
Animal-based products have higher mineral content than plant-based foods
Calcium The Body’s Most Abundant Mineral
Calcium (Ca) a major mineral found in bones, teeth, and blood; needed for skeletal structure,
blood clotting, muscle and nerve function, and energy metabolism
Dietary and Supplemental Sources of Calcium
o Calcium is abundant in a variety of plant- and animal-derived foods
o Other good sources:
Dark green leafy vegetables (collard greens and spinach)
Salmon and sardines (with bones)
Some legumes
o Calcium Supplements
Calcium supplements are relatively well utilized by the body, but best absorbed
when taken with a meal
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o Factors Influencing Calcium Bioavailability
Some foods contain high amounts of calcium, but it cannot be absorbed due to the
presence of the oxalates or phytates they contain
Vitamin D increased calcium absorption
Calcium absorption tends to decrease
Calcium Homeostasis is Complex
o Calcium homeostasis involves the hormones: calcitriol (active form of vitamin D),
parathyroid hormone (PTH), and calcitonin
o Responses to Low Blood Calcium
Parathyroid hormone (PTH) a hormone that is released in response to low blood
calcium concentration; stimulates the conversion of the active form of vitamin D
Calcium absorption in the small intestine requires the assistance of several
calcium transport proteins, including calbindin.
Calbindin a transport protein, made in enterocytes that assists in calcium
absorption; synthesis is stimulated by calcitriol.
Calcium absorption is increased in response to PTH release, vitamin D activation,
and calbindin synthesis
Absorption: the movement of substances from the GI tract into the blood
Reabsorption: the movement of previously absorbed substances from tissues
(such as kidneys) back into the blood
PTH stimulates the breakdown of bone, in turn releasing its calcium into the
Resorption the breakdown and assimilation of a substance in the body
Increased calcium absorption at the small intestine, reabsorption at the kidneys,
and resorption from bones increase blood calcium concentration when it is low
o Responses to High Blood Calcium
When blood calcium is high, the parathyroid glands release less PTH, which
decreases the conversion of vitamin D to calcitriol in the kidneys
Elevated blood calcium stimulates the thyroid gland to release calcitonin
Calcitonin a hormone produced in the thyroid gland in response to high blood
calcium levels
Calcitonin decreases calcium resorption from bone, absorption in the small
intestine, and reabsorption by the kidneys
Calcium is Needed For More Than Bones and Teeth
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o Structural Functions of Calcium: Bones and Teeth
Hydroxyapatite ] the mineral matrix of bones and teeth;
storage depot for calcium
Osteoblast a bone cell that promotes bone formation
Osteoclast a bone cell that promotes bone breakdown
o Regulatory Functions of Calcium
Calcium is needed for healthy vision, regulation of blood glucose, and cell
Calcium is a cofactor for several enzymes needed for energy metabolism
Calcium and Bone Health
o Calcium deficiency can result in rickets
Children with rickets have poor bone mineralization and characteristically
“bowed” bones
o Osteopenia a condition whereby bone mineral density is lower than normal
o Bone mass a measure reflecting the amount of minerals contained in bone
o Osteoporosis a bone disease characterized by reduced bone mineral density and
disruption of the microarchitecture of bone
Calcium Deficiency Also Affects Nerve and Muscle Function
o Low blood calcium can cause muscle pain, muscle spasms, and a tingling sensation in the
hands and feet
o Tetany a condition in which muscles tighten and are unable to relax
Calcium Toxicity Can Cause Kidney Stones and Calcification of Soft Tissues
o High calcium intakes are associated with impaired kidney function, formation of certain
types of kidney stones, and can interfere with the bioavailability of other nutrients, such
as iron and zinc.
o Excessive consumption of vitamin D supplements can also result in secondary calcium
Due to the stimulatory effect of vitamin D on bone resorption and subsequent
release of calcium into the blood
Recommended Intakes for Calcium
o RDA: 1000 mg/day for adults
Approximately 3-4 cups of milk
o Calcium absorption tends to decrease with age
RDA increases to 1200 mg/day at
51 years of age for women
71 years of age of men
o Tolerable Upper Intake Level (UL)
2500 mg/day for adults
2000 mg/day for adults 51+
Phosphorus A Component of Biological Membranes
Phosphorus (P) a major mineral needed for cell membranes, bone and tooth structure, DNA,
RNA, ATP, lipid transport, and a variety of metabolic reactions requiring phosphorylation
Phosphorus is Abundant in Protein-Rich Foods
o Phosphorus is naturally abundant in most foods, especially those rich in protein
o Good Sources include:
Dairy products
Meat (including poultry)
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