9 thoughts on “Class Forum

  1. Let me know if anyone needs help understanding homework questions. I’d be happy to point you in the right direction.

  2. Here are a few solutions so you know you have the right answer. You need to show work, however. This simply tells you that you did it correctly.
    HW Solution to problem 1.1: 0.11 cm and 0.0455.
    Problem 1.4: Takes 0.0005 s. so not diffusion limited.

    Problem 1.7 hint: FYI, I am not sure if you caught this but the renal artery flow rate is not 125 L/min. It is 1.25 L/min. solution A: males 8.6%-17.2% and females 9.4%-18.8%; B) 1.249 L/min; C) Cvein = 140.0287 mM; slight increase in [Na+] due to loss of water volume.

    Problem 1.12: Sbar = 0.9302
    Problem 1.13: 1.11 J/s expended on heart or 1.39% of energy expended on heart.
    Problem 1.15: GFR = 1.25 mL/min.

  3. In question 1.2, I take the upper or lower limit of the oxygen partial pressure of arterial and venous blood?

    Ans: Appropriately use either 95 or 70 mmHg for Po2.

    In addition, what does the question mean by “the fraction of oxygen in solution and that bound to hemoglobin in arterial and venous blood”?

    Ans: You need to determine the fraction of oxygen that is bound to hemoglobin and not bound to hemoglobin in both the arteries and the veins. Look at the equation of interest:

    Co2 = Ho2*Po2+4CHbSbar*Hct
    What does the term Ho2*Po2 represent?
    What does the term 4CHbSbar*Hct represent?
    What would Co2/ (Ho2*Po2) represent?

    These above questions should help you understand how to answer the question of interest.

    I know we have equations with which to work through the problem, but I am not sure which fractional variables they want. In short, the wording is just confusing.

    Ans: What I have written above should explain this.

    In question 1.7, I discovered the water volume fraction, but I am not sure how you were able arrived to the fraction of water filtered across the glomerulus with a renal flow rate of 1.25 L/min. What I did is that I multiplied 1.25 *60 *24 to get 1800, and then multiplied by 2 because of two kidneys to get 3600. I then times 3600 by .55 or .60, resulting in 1980 L/day and 2160 L/day. But when I divide 180 L/day by these numbers I do not achieve the percentages that you have listed. What am I missing for this section?

    Ans: You are on the right track. What you need to consider is that when it is asking for the fraction of water filtered across the glomerulus, you need to factor in the amount of the flow through the heart or cardiac output. You do not need exactly my answers (because sometimes assumeptions will be slightly different) but it needs to be pretty close. Once you factor in cardiac output, you should then have the right answer.

    For part b, are you just calculating the renal vein flow rate for water so renal artery flow rate minus the excretion of water? Thank you.

    Ans: You say flow rate minus the excretion of water but you need to be careful with your units. If I interpret the excretion of water as a volume then it would be incorrect. Be careful with units. You are on the right track.

    1. I don’t have my book yet, and the equation you mentioned for 1.2 isn’t in your slides, nor the pictures you posted.

      1. Thanks for your question. It actually is there in the post (7th line down; Co2 = Ho2*Po2+4CHbSbar*Hct). Based on what was discussed in class you should know enough information to work with that equation for the problem of interest. I’d highly recommend getting the book as it is required and you will find it very useful, of course. Perhaps you know someone in the class that you feel comfortable asking to share/use their book when they are not using it? You could always come during office hours (Monday at 9 am-10 am) or make an appointment with me to take pictures of the pages in my text book. I won’t be able to lend mine out, however. I’ll bet the university’s library also has a copy. Best wishes!

  4. I’m still waiting on the book, and I cannot enlarge the photos you left of the questions. Could you email the pages as a jpeg or maybe have an option on this website to enlarge the pictures?

    1. Browsers have a zoom-in function. I am not sure what browser you use, but that could be a solution. I also put a link for all of the images on the HW 1 QQs’ page.

  5. How should we go about solving 6.6b? Do they just want flux in some unit time and we calculate how much leaves over the course of 1 breath?

    1. My apologies for not seeing this earlier:

      If you estimate how long the gas is present in your alveoli based on your breathing (~1 s) and estimate steady state using L^2/D, you can compare steady state to how long the gas is there. Feel free to go about it considering flux and how much leaves over the course of 1 breath (that is not a bad approach either) as well.

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