Lecture 10: How can you keep your
bones healthy?
• Key Concepts to Review
• Homeostasis
• Hierarchical Organization
• Connective Tissues
• Bone, Tendons, Ligaments
• Bone Tissue Maintenance
• Blood Calcium Homeostasis
• Vitamin D & Calcium
• Rickets
• Osteoporosis
10/11/2016
Dr. Casey Self, Biology 118, Autumn 2015
1
Bone is connective tissue
How do connective tissues differ from
epithelial?
~ 33% protein, primarily collagen
~ 67% inorganic; calcium, phosphates…
99% of body’s calcium is in bone.
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2
Bone is dynamic.
Why does bone repair and remodel more readily than
other connective tissues?
Tendon
• Bone turnover is very high
• Repair a transverse fracture in 6
weeks
• Activity level (mechanical stress)
affects remodeling
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Bone
3
Longitudinal study of bone content in the
radius of kids in recreational gymnastics
All children tracked for at least 3 years; N = 127
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Jackowski, Baxter-Jones, Gruodyte-Raciene, et al. 2015
4
What are the functions of the
different types of bone cells?
Osteoclasts: actively transport out H+
Osteoblast: secrete bone.
Osteocyte: mature
Bones remodel by
removing , then adding
bone
http://courses.washington.edu/bonephys/Gallery/BMURemodel.swf
2-4 weeks
4-6 months
http://courses.washington.edu/bonephys/Gallery/BMURemodel.swf
Cell Activity
Bones repair by building, then removing bone
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Time
7
Calcitonin
PTH
Why & how is plasma Ca+2 regulated?
http://www.haspi.org/curriculum-medical-chemistry.html
Describe the response of the parathyroid gland
to changes in plasma calcium (Ca+2).
Chen & Goodman, 200
What is Vitamin D?
DeLuca, 2014
Calcitrol
Ages 1-18
Are many
populations
deficient in
Vitamin D?
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Wahl, Cooper, Ebeling,
et al. 2012
Adults
11
What is rickets?
Mineralization
defect
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Holick, 2006
Rickets
Schwarz, 2014
12
Why do women begin to lose bone mass at
such early ages compared to men?
Early menopause
Bone Density
g/cm2
Bone Density T-score
Osteoporosis
-1 = 10% loss
-2 = 20% loss
http://courses.washington.edu/bonephys/opmovies.html &
http://www.yourdiseaserisk.wustl.edu/hccpquiz.pl?lang=english&func=home&quiz=osteoporosis & https://americanbonehealth.org/what-you10/11/2016
13
should-know/about-t-scores
What effect did strength training have on bone
mineral density (BMD)?
What are some limitations of this study?
75+ years old
2+ years postmenopausal
12 week intervention, 3 training sessions per week
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Mats et al. 2013. Maximal strength training in postmenopausal women with osteoporosis or osteopenia. Journal of
Strength and Conditioning Research. 27(10):2879-2886
14
Compare Vit. D supplements effect on BMD (bone
mineral density) in women, average age = 59 yrs.
Lumbar spine
Reid, Bolland, & Grey, 2014
Femoral neck (femur angles into hip
Things to know or review from today’s lecture:
1.
What design & functional features do connective tissues have in common? What protein
forms most of a tendon or ligament? Why are those fibers “wavy”?
2.
Describe the differences in design & function of these bone cells: osteoblasts, osteocytes,
osteoclasts. How does an osteoclast’s shape enhance its function? Describe the
homeostasis of bone tissue formation & resorption in young adults.
3.
Describe the homeostasis loops that regulate plasma calcium, in particular calcitonin &
parathyroid hormone (PTH). Why is homeostasis of calcium so important? Diagram the
pattern of PTH release with plasma Ca+2, predict the pattern for calcitonin & plasma Ca+2
4.
How is active Vitamin D formed? What is Vitamin D derived from? What can you predict
about the water solubility of Vitamin D?
5.
Globally, where are Vitamin D deficiencies high? Explain why. What are the symptoms of a
child suffering from rickets? What causes rickets? What are some historic factors that
caused rickets? Today, when might children in the U.S. develop rickets? Explain why.
6.
Predict bone density in males vs. females with age (yrs) on the X-axis. Why do women lose
bone density faster? Why do women tend to have lower bone density than men?
7.
What role do sex hormones & growth hormones have on bone density? What are the 2
uncontrollable risk factors for osteoporosis amongst women? Do men ever develop
osteoporosis? Did Vitamin D supplements in older women affect bone density? Predict
other dietary or behavioral factors that can affect bone density.
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16
Additional Resources
1.
Arabi A, El Rassi R, & Fuleihan GE-H. (2010) Hypovitaminosis D in developing countries—prevalence, risk factors and outcomes. Nature
Reviews Endocrinology 6: 550-561.
2.
Bowen R. (1999) Vitamin D (Cholecalciferol). Pathophysiology of the Endocrine System. Colorado State University.
http://dwb.unl.edu/teacher/nsf/c10/c10links/arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/otherendo/vitamind.html
3.
Chen RA, & Goodman WG. (2004) Role of the calcium-sensing receptor in parathyroid gland physiology. American Journal of Physiology Renal Physiology 286(6): F1005-F1011 http://ajprenal.physiology.org/content/286/6/F1005
4.
DeLuca HF (2014) History of the discovery of vitamin D and its active metabolites. BoneKEy Reports 3(479).
http://www.nature.com/bonekeyreports/2014/140108/bonekey2013213/full/bonekey2013213.html
5.
Dusso AS, & Tokumoto M. (2011) Defective renal maintenance of the vitamin D endocrine system impairs vitamin D renoprotection: a
downward spiral in kidney disease. Kidney International 79: 715–729.
6.
Holick MF (2006) Resurrection of vitamin D deficiency and rickets. J Clin Invest. 116(8):2062-2072. http://www.jci.org/articles/view/29449
7.
Jackowski SA, Baxter-Jones ADG, Gruodyte-Raciene R, et al. (2015) A longitudinal study of bone area, content, density, and strength
development at the radius and tibia in children 4–12 years of age exposed to recreational gymnastics. Osteoporos Int 26:1677–1690.
8.
Reid IR, Bolland MJ, & Grey A. (2014) Effects of vitamin D supplements on bone mineral density: a systematic review and meta-analysis.
Lancet 383: 146–155.
9.
Schwarz SM. (2014) Rickets. MedScape http://emedicine.medscape.com/article/985510-overview
10. Wahl DA, Cooper C, Ebeling PR, et al. (2012) A global representation of vitamin D status in healthy populations. Archives of Osteoporosis
7(1-2): 155-172.
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17
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18
Ultraviolet light (UVB) promotes (90%) of our Vitamin D synthesis.
UVA goes deeper & can cause Folic Acid (Vitamin B9) breakdown.
Lack of folic acid can increase birth defects such as spina bifida.
In children or adults, the lack of folate can cause anemia, slower growth rates.
UVB
UVB
UVA
UVA
Melanosomes
X
Folate
folic acid B9
Folate
folic acid B9
Tanning adds pigment vesicles (melanosomes) into skin to absorb UV.
Vitamin D
N.G. Jablonski & G. Chaplin. 2000. The evolution of human skin coloration. J Human Evol. 39(1):57-106.
Hypothesis: Human skin color evolved to balance conflicting problems.
Low UV: pigmentation lost as humans moved north. High latitudes
may not get enough UV in winter to make Vitamin D.
High UV: dark skin makes enough VIt. D
(requires ~ 2-6X more UV), & folate protected.
Human skin color data
collected prior to 1940.
“Modern” Skin: Environmental mismatches can produce nutritional problems. if you have
darker skin & live far north OR if you have light skin & live near the equator
http://anthro.palomar.edu/adapt/adapt_4.htm