My exhaustion and poor attendance at lecture today are going to make this a short one.
TIL: Part of the reason congestive heart failure is so bad for lower body edema (fluid retention and swelling) is that the kidneys try to help but only make things worse. First of all, the main effect on blood circulation for CHF patients is that the overworked heart can't pump enough blood, so blood collects in the veins (this is where the "congested" in CHF comes from: congested veins of blood). As the blood pools, higher than normal pressure builds up in the capillaries, causing fluid leakage and swelling. No bueno.
Then the kidney tries to help. The kidney is blind to all of the above things happening but notices that there is less blood on the arterial side of the circulation, resulting in low blood pressure. In a normal healthy person, the kidney can fix that! Using a cascade of hormones called the aldosterone-renin-angiotensin axis, the kidney starts retaining sodium and consequently water in the blood it filters. A healthy heart would then increase output and restore normal blood pressure, but a heart in CHF already can't pump all the blood it has pooling in the venous system. So the heart is like, "Can't... pump... anymore..." and the kidneys are like, "HERE, HAVE SOME MOAR BLOOD TO PUMP! YOU'RE WELCOME!" Thanks kidneys.
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