Please help with Physiology Questions

[DrJ2B]

Hey all!

You are all probably in the midst of finals and I wish you luck on them, but if you have any time to help me with a few physiology questions, I would really appreciate it. I have toiled over these questions for a while, yet I am no where nearer to a solution. Thank you all so much in advance for any help.

The power output of a muscle:

1) Is it 0 in an isometric contraction? I ask this because if I relate the physics definition of power, since there is no change in length, the power should be 0, but what length/distance is the one I would use? the length of the muscle or the length over which the movement is done?

2) When is it maximal? at loads above or at maximum active force/load or when the load approaches zero (i know that shortening velocities are higher at zero load but power is also considered load/force times the shortening velocity so it makes no sense that power output would be maximal when loads approach zero

Another evil muscle question: How many thin filaments are there for each end of the thick filament in striated muscle? According to diagrams in multiple books, it looks like 2. However, since that is only 2D, I am not sure how many there are in 3D. Six is the only other option given yet I am not sure if that makes sense.

one last question sorry for the length of the post

When is the tubular fluid in the kidney hyperosmotic to the plasma? I do not think it is the thick ascending limb because dilution occurs there. I think it is the bend of Henle's loop, but I am not sure. Could it be the proximal convoluted tubule? I am just not sure about this.

Again, thanks so much for any help

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[Childe]

P=F*d/time
1) Right. If the object doesnt move, no work is done. Hence no power. Also theoretically the length of the muscle should stay the same as well right?
2) I think power is maximal at some point in between the two you mention. The power vs. force (load) graph is not linear, more of a bell shape.

Six thin filaments surround each thick one. Since the thick filament has multiple myosin heads it is able to work on more than 1 thin filament (in 3d).

Most hyperosmotic at the bottom of henle's loop. It is also possible that the urine exiting the collecting tubule would be the same osmolarity (due to vasopressin, etc), but not normally.
Btw the overall osmolarity before you get to henle's is constant at around 300 mosm/L.

 

[DrJ2B]

Hey Childe!

Thanks so much for your reply. In reference to the power output question, isometric contraction (when the length of the muscle in not changing) does have zero output. I am trying to determine what the distance in the Force x distance in the power equation is from, the length of the muscle or the length over much something is moved. Does the power output just refer to the contraction of the muscle and the length over which it pulls a muscle (changes its length) or the distance over which the load is moved? I am still confused about this because I know isotonic contraction (where the force or load is constant) is not necessarily paired with isometric contraction, so that during isotonic contraction, the length of the muscle does change. Only when the force reaches 1.6 times the max force, does the muscle have isometric contraction for a brief period, then lengthening of the muscle occurs.

Also, do you have any websites that mention how thin and thick filaments are arranged? I do not understand why it is 6. Also is it 6 thin filaments per end of the thick filament meaning 12 total thin filaments per thick filament (both ends) or is it 3 thin filaments per end since that is the way the question is asked. My physiology text does not mention this and I could not find anything about this online.

Thank you so much again for all your help. I really appreciate it. Good luck on your finals!

 

[Childe]

Actin Myosin 3D
Theres the muscle thing. Imagine the thick filament with a bunch of heads at each end though. 6 per end, so 12 i guess.

I think the distance is relative to the muscle when discussing muscular power, making the velocity (d/t) measurement also relative to the muscle. The distance the object moves would ideally be the same (ie: all force goes into doing work on the object). But in reality with lever systems etc. it does not, so the effective work would be lower than the one used in the power equation. But the power curve is still relevant because the muscle is still performing the same motion, just a certain fraction of its force is lessened...

take this with a grain of salt of course.

And good luck to you Fortunately i finished my only final, microbiology. Unfortunately it was ridiculously hard.

 

[DrJ2B]

Hey Childe!

You are a lifesaver. Thanks so much for all your help. I am sure you did well on your microbiology exam being that you are a genius in physiology (I am very appreciative of this ). If the exam was that hard, there will probably be a nice curve so you will do well anyway. I wish I only had one final. I have 2 to go and my grades this semester are not what I expected (not bad by any means but maybe not good if I want to get into UPenn ). Have a great winter vacation! Happy Holidays!


--DrJ2B

 

[Childe]

Hehe anytime. No curve for me, ill end up with around an 88 in there (how annoying) That 5 hours would have been nice to pull an A in. Ah well.

Have a good break yourself, and let me know if you have more questions.