Physiology Practice Problems
Taken from Feher [3].
Poblem set 1.2
#18) The free diffusion coefficient of oxygen in aqueous solution is about 1.5 x 10-5 cm2 s-1. If the diffusion distance between the air and the blood is 0.5 µm, about how long is the diffusion time?
Solution:
rearrange equation for t and plug in values for D and lamda where:
D= 1.5 x 10-5 cm2 s-1 = 2 x 10-9 m2 s-1
lamda= 0.5 x 10-6 m
Answer:
t= 62.5 µs
Problem set 2.2
#14) The kidney filters plasma to produce an ultrafiltrate, which is the first step in the formation of urine. This filtrate is called an ultrafiltrate because the kidney can retain even small particles like plasma proteins. The force behind ultrafiltration is the blood pressure. The kidney ultrafiltration occurs at a structure called the glomerulus, which is a group of small blood vessels (capillaries) that are closely joined to another structure, the Bowman's capsule, that forms a double-walled cup for the collection of the ultrafiltrate. The filtration barrier is a combination of the capillary walls and the structure in the Bowman's capsule.
Calculate the glomerular filtration rate (GFR) assuming a total area for both kidneys is 1.5 m2 and a driving force P= 20 mm Hg. The GFR is the total volume of ultrafiltrate produced per min. Its units should be in cm3 min-1. Use Lp= 0.638 x 10-8 cm3/(dyne•s).
Solution: osmotic flow equation assumes blood is mostly water, Poiseuille's equation assumes the tube is a cylinder. Since delta x is not given, use osmotic flow.
Qv= GFR (flow rate)
A= 1.5 m2
P= 20 mm Hg
Lp= hydraulic conductivity (ease with which fluid passes through pores)
use 0.638 x 10-08 cm3/(dyne•s)
Answer:
153 cm3/min