The lungs, with many alveoli of various sizes are inherently unstable. Surface tension in the lungs between the alveolar gas and the fluid lining the alveoli plays an important role here. Alveolar instability due to surface tension is produced as described below:
When two alveoli with different radius connect with each other, the amount of pressure generated (P) in each is, P= (2 × surface tension)/radius. Therefore, when the surface tension is constant, the pressure in the smaller alveolus will be more than the larger alveolus, which makes the lungs unstable. In other words, the unstable situation in the lungs is that, a smaller alveolus has higher pressure, while a larger alveolus has lower pressure. The instability is primarily caused
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This effect of carbon dioxide on the hemoglobin’s capacity to combine with oxygen is known as the Bohr effect. The physiologic advantage of the Bohr effect is that it serves to enhance O2 uptake in the lungs and delivery of O2 to tissues. Listed below are 3 situations in which the Bohr effect is beneficial to …show more content…
Moreover, vasa recta not only bring nutrients and oxygen to the medullary nephron, but also remove excess water from the medullary interstitium. The blood plasma, as it enters vasa recta is isotonic (300 mOsm) with respect to the interstitum. As plasma makes it way down into the medullary interstitial fluid, it is encountering increasingly hyperosmotic interstitial fluid (ISF). Since it’s a capillary, there is a free exchange of water and solute between the vasa recta and the medullary ISF. As plasma moves down the descending loop of Henle, due to hyperosmotic ISF, water moves out and sodium and chloride move into the bloodstream. At the end of the descending loop of Henle, the concentration of salt inside the rasa recta is around 1200 mOsm. Now, as plasma moves up the ascending loop of Henle, sodium and chloride move out and water move into the bloodstream. The ascending loop of Henle cannot remove the added water because they are water-impermeable. The vasa recta remove the water; this is why blood flow in the ascending vasa recta exceeds blood flow in the descending vasa recta. Interestingly, sodium and chloride that are moved out of the vasa recta in the ascending loop of Henle enter the descending loop of Henle and the cycle continues. The countercurrent exchange process is passive and it helps maintain an electrochemical gradient.
The final concentration