application 11

Scientist Spotlight: Augustus White

Augustus White's biography includes, among other things, attending segregated schools as a boy, playing football in college, and receiving the Bronze Star for his service in the Army Medical Corp in Vietnam. He was the first African American to graduate from Stanford's school of medicine and the first African American resident in orthopedics at Yale. His research focuses on the biomechanics of the bones - especially the spine - and fracture healing. Dr. White additionally leads efforts to promote diversity in science and to explore the roles of unconscious bias in medicine.

1) Please click here Links to an external site. to read an article on Dr. White's biography. 

2) Now review the following two videos on the general topics of Dr. White's work: bone remodeling and fracture repair. 

Click hereLinks to an external site. (or copy and paste this address https://www.youtube.com/watch?v=Ux7xsXihQnY) to watch the video regarding bone remodeling. Then click hereLinks to an external site. (or copy and paste this address https://www.youtube.com/watch?v=-P6LsendHxU) to view an animation of bone fracture repair (set to some very dramatic piano music!). Note in particular what types of cells and molecules are involved and what those cells seem to be doing at different stages in these processes. Do not worry about some of the less-familiar molecule names, like all the growth factors mentioned.

After reviewing these resources, write a 250 word or more reflection with your responses. You might wish to discuss any or all of the following topics:

1)   What was most interesting or most confusing about the these resources?

2)   What can you learn from these resources about the physiology of bone remodeling and fracture healing?

3)   What do these resources tell you about the types of people that do science?

4)   What new questions do you have after reviewing these resources?

Week 7 - Estrogen & Bone: Elaborate/Evaluate

  As a result of menopause, which of the following imbalances is likely to occur?

1.   osteocytes will begin dividing frequently
2.   osteoblast activity will outpace osteoclast activity
3.   osteoclast activity will outpace osteoblast activity
4.   osteoblasts will begin dividing frequently

 Though this treatment comes with a number of potentially serious side effects, one popular treatment for osteoporosis has been hormone replacement therapy.  In that therapy, the patient takes medications containing estrogen.  The increase in estrogen levels would help treat osteoporosis by...

1.   Increasing the lifespan of osteoclasts
2.   Increasing the lifespan of osteoblasts
3.   Encouraging cell division in osteoclasts
4.   Causing apoptosis in osteblasts

Week 7 - Physical Activity Feedback Loop: Explain

 Background Fact: Older individuals are sometimes less physically active than younger individuals, which makes older individuals more at risk for osteoporosis. Interestingly, this is the same phenomenon that makes astronauts at risk for osteoporosis if spending long periods in space.
Brainteaser: Try to reason out a feedback loop that could explain how a decrease in physical activity could worsen osteoporosis.

Perhaps the main thing to consider here is how the bones know that they are experiencing less physical activity and should therefore change their strength.  In other words, what is the stimulus and the receptor in this feedback loop?  It turns out, this comes down to one of our main bone cells: the osteocyte!  Below is a brief excerpt from a scientific article published in 2012, titled  Osteocyte Signaling in Bone

 Osteocytes, the cells residing within the bone matrix and comprising 90% to 95% of the all bone cells, have long been considered quiescent bystander cells compared to the osteoblasts and osteoclasts whose activities cause bone gain and loss, and whose dysfunction lead to growth defects and osteoporosis. However, recent studies show that osteocytes play a crucial, central role in regulating the dynamic nature of bone in all its diverse functions. Osteocytes are now known to be the principal sensors for mechanical loading of bone. They produce chemicals that regulate bone formation and resorption. Osteocytes appear to be the major local orchestrator of many of bone’s functions."

Note in particular that osteocytes sense "mechanical loading," or the amount of pressure on our bones.  This sort of makes sense if you look at the picture of osteocytes above.  Those cells are squeezed in small gaps within compact bone.  You could imagine, then, that pressure placed on the bones would cause osteocytes to experience more "squeezing" in their small spaces.

lifting weightsAs the quote above points out, the osteocytes are then able to signal osteoclasts and osteoblasts to adjust bone thickness appropriately.  If you start lifting weights and putting extra pressure on your bones, your osteocytes will sense that and tell your osteoblasts to add more bone to make the bones stronger.  With stronger bones, the pressure would then be relieved.

reduced physical activityOn the other hand, if you stop performing as much physical activity (or go into orbit around Earth where you experience less gravity!), your bones would experience less pressure.  Your osteocytes would sense that and signal your osteoclasts to tell them less bone is required to meet the body's needs.  Your osteoclasts might then remove bone, which would create weaker bones and bring the pressure on the bones back up to normal levels.  Of course, that could also contribute to osteoporosis!

 Background Fact: Older individuals are sometimes less physically active than younger individuals, which makes older individuals more at risk for osteoporosis. Interestingly, this is the same phenomenon that makes astronauts at risk for osteoporosis if spending long periods in space. Space Shuttle Endeavour on Pad39A

Brainteaser: Try to reason out a feedback loop that could explain how a decrease in physical activity could worsen osteoporosis.

Take some time to consider the above scenario.  Think in particular about what cell types might be responsible for creating the condition of osteoporosis in this situation.  You're welcome to look for some answers online to explain this, but don't spend more than a few minutes doing so!

Once you have taken some time to think and find information, submit a few sentences here to record your thoughts.  You might discuss your ideas about what interactions among cells serve to create weak bones after a lack of physical activity, or just talk about what you find confusing/questions you have!

  Score for this attempt: 5 out of 5
Submitted Feb 26 at 4:05pm
This attempt took less than 1 minute.
 
Question 1
1 / 1 pts
Which of the following organs require calcium in order to function appropriately? (check all that apply)
  heart
  brain
  muscle
  bones
 
Question 2
1 / 1 pts
Which of the following has the receptors that detect blood calcium levels?
  parathyroid gland
  osteoclast
  osteoblast
  PTH
  bone
 
Question 3
1 / 1 pts
Which of the following is the most direct representation of the efferent pathway in the feedback loop that occurs in response to low blood calcium?
  osteoclast
  osteoblast
  parathyroid gland
  PTH
  raised blood calcium levels
 
Question 4
1 / 1 pts
Given everything we've studied so far in this module, what is the most likely explanation for how a person could have osteoporosis at the same time as having normal blood calcium?
  the body is taking calcium from bones in order to keep blood calcium normal
  the osteoblasts have lost their ability to effectively incorporate calcium into bone
  the parathyroid gland is interfering with Vitamin D's ability to assist in calcium absorption
  the digestive system has become insensitive to Vitamin D
  the osteoclasts are malfunctioning and breaking down bone tissue inappropriately
 
Question 5
1 / 1 pts
The feedback loop we just studied that (in our scenario) resulted in osteoporosis is an example of a...
  Rheostasis
  Positive Feedback Loop
  Negative Feedback Loop

Deviation From  Normal : Low level of Vitamin D

Receptor                         : Bone Cell

Control Center               :parathyroid gland

Efferent Pathway           :parathyroid hormone (effects on bone because of inhibition production of hormone)

Effector                          :Stimulating Osteoclasts and inhibiting  Osteoblasts

Response                       : When blood calcium levels are low, parathyroid hormone (PTH)is released, PTH stimulates osteoclasts , also PTH inhibits  osteoblasts.Osteoclasts break down bone tissue, releasing calcium into the bloodstream.PTH also inhibits osteoblasts, which are cells involved in bone deposition. By reducing calcium deposition in bone leading not enough calcium, our bones become more fragile, leading to osteoporosis.