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Chapter 9

NUTR 1010 Chapter Notes - Chapter 9: Bone Resorption, Bone Density, Neuron


Department
Nutrition
Course Code
NUTR 1010
Professor
D E
Chapter
9

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NUTR*1010—FINAL
NUTR*1010—FINAL EXAM
CHAPTER 9—Nutirent Involved in Bone Health
How Does the Body Maintain Bone Health?
Bones are living organs that contain:
oSeveral tissues (including bone tissue)
oNerves
oCartilage
oConnective tissue
Table 9.1
Bone Composition and Structure Provide Strength and Flexibility
65% of bone tissue is make up of many minerals (mostly calcium and phosphorus)
that provide hardness
35% of bone is a mixture of organic substances that provide strength, durability, and
flexibility
oThe most important substance is collagen
Minerals form around the collagen fibres—this design enables bones to
bear weight while responding to movement
CORTICAL BONE (COMPACT BONE) - a dense bone tissue that makes up the outer
surface of all bones, as well as the entirety of most small bones of the body.
oMakes up 80% of our skeleton, contains microscopic openings that serve as
passageways for blood vessels and nerves.
oThe outer surface of all bones is cortical
oSmall bones (wrist, hands, and feet) are made of cortical
TRABECULAR BONE (SPONGY or CANCELLOUS BONE) - a porous bone tissue
that makes up only 20% of our skeleton and is found within the ends of the long
bones, inside the spinal vertebrae, inside the flat bones (breastbone, ribs, and most
bones of the skull and inside the bones of the pelvis.
oMakes up 20% of our skeleton
oFound within:
The ends of long bones (arms and legs)
Inside the spinal vertebrae
Inside flat bones (breastbone, ribs and most bones of the skull)
Inside the bones of the pelvis
oThe bones is aligned in a precise network of columns that protects the bone of
extreme stress
oHas a faster turnover rate than cortical bone—more trabecular bone is being
broken down and replenished at any given time
oMore sensitive to changes in hormones and nutritional factors
The Constant Activity of Bone Tissue Promotes Bone Health
Bone develops in a series of three processes
oBone growth
Determines bone size
Begins in the womb
Continues until early adulthood
oBone modelling
Determines bone shape
Begins in the womb
Continues until early adulthood
oBone remodelling

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NUTR*1010—FINAL
Maintains integrity of bone
Replaces old bone with new bone to maintain mineral balance
Involves bone resorption and formation
Occurs predominantly during adulthood
Bone Remodelling Maintains a Balance Between Breakdown and Repair
BONE DENSITY- the degree of compactness of bone tissue, reflecting the strength
of the bones. Peak bone density is the point at which a bone is strongest.
oPeak bone density occurs when boys are 14, and girls are 12.5 years old.
REMODELLING- the two-step process by which bone tissue is recycled; includes the
breakdown of existing bone and the formation of new bone.
oRepairs bones that have been broken or damaged
oStrengthen bone regions that are exposed to higher physical stress
RESORPTION- the process by which the surface of bone is broken down by cells
called osteoclasts.
oOSTEOCLASTS- cells that erode the surface of bones by secreting enzymes
and acids that dig grooves into the bone matrix.
oBones are broken down to:
Release calcium into the bloodstream
To help smooth rough edges from a break in the bone
OSTEOBLASTS- cells that prompt the formation of new bone matrix by laying down
the collagen-containing component of bone that is then mineralized.
Around 40 years of age, bone resorption beings to occur more rapidly than bone
formation—results in overall loss in bone density
How Do We Assess Bone Health?
Dual Energy X-Ray Absorptiometry Provides a Measure of Bone Density
DUAL ENERGY X-RAY ABSORPTION (DXA or DEXA)- currently the most accurate
tool for measuring bone density.
o15mins for a scan of the hip and lower spine
o30mins for a full body scan
oRecommended for postmenopausal women
T-SCORE- a composition of individual’s bone density to the average peak bone
density of a 30-year-old healthy adult of the same sex and race. If bone density is
normal, the T-score will be between +1 and -1.
oScore between -1 and -2.5, person has osteopenia (increased risk of fractures)
oMore than -2.5, person has osteoporosis
o+1 and -1, is normal
oMore then +1, better than normal bone mass
Other Bone Density Measurement Tools
Quantitative ultrasound technique
oUses sounds waves to measure the density of bone in heel, skin, and kneecap
Peripheral dual energy x-ray absorptiometry (pDXA)
oMeasures bone in peripheral regions of the body including wrist, heel or finger
Single energy x-ray absorptiometry
oMeasure bone density at the wrist or heel
A Profile of Nutrients That Maintain Bone Health
Calcium
Calcium composes 2% of our entire body weight
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NUTR*1010—FINAL
Functions of Calcium
99% of calcium is stored in our bones
1% is found in the blood and soft tissues
Calcium and phosphorus crystallize to form hydroxyapatite
The skeleton not only provides physical support to our bodies—it also acts as a
storehouse for calcium to assist in the regulation of blood calcium
Calcium is critical for the normal transmission of nerve impulses
oCalcium flows into nerve cells and stimulates the release of molecules called
neurotransmitters, which transfer the nerve impulses from one nerve cell to
another
When blood calcium level dangerously fall, one can experience
convulsions
Table 9.2 –Nutrients Essential to Bone Health
How Much Calcium Should We Consume?
The Adequate Intake (AI) for Calcium is:
oAdults 19-50 years: 1000mg/day
oAdults over 50 years: 1200mg/day
oBoys and Girls 15-18 years: 1300mg/day
The upper level (UL) for calcium is 2500mg/day for all ages and gender groups
BIOAVAILABILITY- the degree to which our bodies can absorb and use any given
nutrient.
The ability to absorb calcium diminishes with age, can be as low as 25%
oOur bodies cannot absorb more than 500mg of calcium at once
Dairy products are the most common source of calcium
What Happens If We Consume Too Much Calcium?
HYPERCALCEMIA- a condition marked by an abnormally high concentration of
calcium in the blood—symptoms include fatigue, muscle and joint aches, abdominal
pain, constipation, and mental confusion.
PARATHYROID HORMONE- a hormone that helps to regulate blood calcium levels.
With not enough calcium, one can acquire osteoporosis.
What Happens If We Don’t Consume Enough Calcium?
HYPOCALCEMIA- a condition characterized by an abnormally low concentration of
calcium in the blood. Symptoms include muscles spasms and convulsions.
Vitamin D
Vitamin D doesn’t always come from the diet (we can get it from sunlight)
Vitamin D is considered a hormone because it is made in one part of the body yet
regulates various activities in other parts of the body
Figure 9.5—How the body makes vitamin D
Functions of Vitamin D
CALCITRIOL (1, 25 DIHYDROXYVITAMIN D)- the primary active form of vitamin D
in the body.
oCalcitriol made by the kidneys is found in the blood and acts in the intestine
and bone to promote calcium metabolism
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