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Chapter 9

Chapter 9 Summary

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University of Guelph
NUTR 1010

NUTR*1010FINAL NUTR*1010FINAL EXAM CHAPTER 9Nutirent Involved in Bone Health How Does the Body Maintain Bone Health? Bones are living organs that contain: o Several tissues (including bone tissue) o Nerves o Cartilage o Connective 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 o The most important substance is collagen Minerals form around the collagen fibresthis 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. o Makes up 80% of our skeleton, contains microscopic openings that serve as passageways for blood vessels and nerves. o The outer surface of all bones is cortical o Small 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. o Makes up 20% of our skeleton o Found 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 o The bones is aligned in a precise network of columns that protects the bone of extreme stress o Has a faster turnover rate than cortical bonemore trabecular bone is being broken down and replenished at any given time o More 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 o Bone growth Determines bone size Begins in the womb Continues until early adulthood o Bone modelling Determines bone shape Begins in the womb Continues until early adulthood o Bone remodelling NUTR*1010FINAL 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. o Peak 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. o Repairs bones that have been broken or damaged o Strengthen 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. o OSTEOCLASTS- cells that erode the surface of bones by secreting enzymes and acids that dig grooves into the bone matrix. o Bones 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 formationresults 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. o 15mins for a scan of the hip and lower spine o 30mins for a full body scan o Recommended for postmenopausal women T-SCORE- a composition of individuals 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. o Score between -1 and -2.5, person has osteopenia (increased risk of fractures) o More than -2.5, person has osteoporosis o +1 and -1, is normal o More then +1, better than normal bone mass Other Bone Density Measurement Tools Quantitative ultrasound technique o Uses sounds waves to measure the density of bone in heel, skin, and kneecap Peripheral dual energy x-ray absorptiometry (pDXA) o Measures bone in peripheral regions of the body including wrist, heel or finger Single energy x-ray absorptiometry o Measure bone density at the wrist or heel A Profile of Nutrients That Maintain Bone Health Calcium Calcium composes 2% of our entire body weightNUTR*1010FINAL 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 bodiesit 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 o Calcium 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: o Adults 19-50 years: 1000mg/day o Adults over 50 years: 1200mg/day o Boys 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%
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