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November 1, 2009 at 10:00 pm #12159loopyloo91Participant
Hi there!!
I am revising a bit for a biology test on tuesday – but i can’t for the life of me work out the answer to these questions:
Okay here is the info from the passage:
At a particular point in time in a healthy human adult, the following measurements were made:
1. The total blood output from both ventricles was 10.08 litres per min
2. The aorta leaving the left ventricle had a mean diameter of 2cm
3. 40% of the blood passing through the aorta went to the skeletal muscles
4. The maximum blood pressure in the aorta was 160mm Hg
5. Volume of a cylinder = 2(pi)r
Area of a circle = (pi)r^2
1ml = 1 cubic cm
In a cylinder, velovity = volume per unit time / cross sectional area
6. (pi) should be approximated to equal 3
Note:
1. Some of the above data are redundant
2. There are insufficient data to answer one of the following questions. Correct identification of this fact carries the marks
3. Your answers must specify units e.g. cm, mm s^1, etc.
Okay so the questions are as follows:
1. What volume of blood goes to the lungs every minute?
2. Ignoring blood lost from the aorta into the coronary circulationm what is the mean velocity of blood per second in the aorta?
3. If the mean velocity of blood flowing through the skeletal muscle capillary beds is 1 mm s^1, what is the mean total cross sectional area of the muscle capillaries?
4. If the pressure of the blood reaching the glomeruli of the kidneys is 40mm Hg, what is the approximate flow rate of blood through the capillaries
5. The cross sectional area of the veins returning blood to the heart is greater than the cross sectional area of the arteries leaving the heart. What is the consequence of this for the realtive rates of flow in arteries and veins? (Your answer should not exceed 50 words).

November 1, 2009 at 10:31 pm #94303mithParticipant
1. easy, it’s 10.08/2 liters/min since you only want it from one ventricle.
2. use the same rate as in 1, divide by cross sectional area
3. ok, you should be able to do this one, remember mass conservation.
4. i think this is the trick question
5. draw a conclusion from above. im guessing they’re saying flow speed. 
November 2, 2009 at 10:50 am #94333loopyloo91Participant
Thanks very much for the help, mith:P
I thought about dividing by 2 to get the volume of blood leaving only the right ventricle, but surely the volume of blood leaving both ventricles is not exactly the same? Could it really be that easy?
And i thought that for question 4 – you could rearrange the formula they give you in the formula list to get –
Cross Sectional Area = Volume per unit time/velocity
Think this would work??
I’ve tried it myself but couldn’t get an answer, so you’re probably right and this is the trick question ðŸ˜€
Thanks for the advice,
Laura x.

November 2, 2009 at 3:33 pm #94342mithParticipant
well for 1, you’d have to assume that you have a constant volume of blood. think about what would happen if there was an imbalance.
the problem with 4 is you have a pressure term which you can’t really relate to velocity. usually flow within a pipe is a sum of pressure difference and viscous and other frictional forces.

November 2, 2009 at 11:09 pm #94351loopyloo91Participant
Hi, me again…
I was trying question three – but i don’t know what i am doing wrong…
I have never done any kind of physics at all so this fluid dynamics stuff is all new to me ðŸ˜•
But this is what i’ve been doing, perhaps you can tell me where i’m going wrong?
This is Question 3:
I have taken the equation from the paper which states that:
velocity = volume per unit time / cross sectional area (CSA)
and changed it round so that:
CSA = volume per unit time / velocity
So i have taken that 40% of the blood pumped from the ventricles travels to the skeletal muscles. That makes it a total volume of 4.032 l min^1.
4.032 l min^1 is the same as 0.0672 l s^1.
So 0.0672 l = 67.2 mm
Which makes it 67.2 mm s^1 over the velocity (which is given in the question as 1 mm s^1).
67.2 mm s^1 / 1 mm s^1
= 67.2 mm^2.
And this = 6.72cm^2.
But this seems quite large to me… can the mean total cross sectional area of the muscle capillaries really be as big as 6.72 cm sqaured??
I always think of capillaries in terms of um, not cm!!

November 3, 2009 at 1:22 am #94355MissMParticipant
Hi, I have this exact same test on Wednesday and found this looking for help online.
In Q3 the volume should be 40% of 5.04 not 10.08.
This is because 5.04L was pumped into the lung circulatory system, the other 5.04L went into the body ie. the skeletal muscle.

November 3, 2009 at 4:08 am #94370mithParticipant
Check your plumbing.

November 4, 2009 at 1:10 am #94455MissMParticipant
I don’t understand, plumbing?


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