Capillaries are the narrowest elements in the blood transport system of animals.

Question

Capillaries are the narrowest elements in the blood transport system of animals. They connect the arteries (the vessels that carry blood away from the heart) to the veins (the vessels that carry blood back to the heart). They are the place where the chemicals that the blood is carrying are taken from source regions (lungs for air, intestines for food, glands for hormones) and delivered to the cells that need them. There are small gaps between cells that form the capillaries that allow small molecules to diffuse from the blood to the spaces surrounding the tissues. The inner diameter of the capillary is very small – about 5-10 m. The wall of the capillary is composed of 2 layers of very thin and flat cells: endothelial cells and epithelial cells. The thickness of the capillary wall is roughly 1 µm.

A. Calculate the rate of oxygen flow across the capillary wall using the general flux equation…see additional items…Force velocity flow

B. There is also a pressure difference to consider. The capillary lumen (inside the capillary) has a pressure of 400Pa whereas the pressure in the fluid outside the capillaries is about equal to 0 Pa. Include this in the flux calculation. Does it change the flux significantly?

You will need to know the density of liquid oxygen: 1.14 x 103 kg/m3 and the diffusion constant for oxygen in water: 5 x 10-9 m 2 /sec

Note: This is a physics question.

Explanation / Answer

The density of oxygen is higher in the air outside the capillary (5 million molecules/(m)^3) compared to the density inside the capillary (0.3 million molecules/(m)^3). Therefore, the oxygen will flow down the a concentration gradient from the air outside the capillary into the capillary across the membrane,

Fick's Law tells us how a concentration difference drives flow:

J = Dn/x put values and calculates.

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