Alveoli are sac like structures present in the lungs whereas nephrons are the basic filtration units of the kidneys.
In the alveoli, oxygen from air diffuses into the blood and carbon dioxide from blood diffuses into alveoli. In the nephrons, pressure filtration of glomerular filtrate occurs into the Bowman’s capsule.This is followed by selective reabsorption of useful materials and secretion of the waste substances in to the urine.
Alveoli excrete carbon dioxide during exhalation. Nephrons excrete excess water, salts, ions, urea, and other nitrogenous wastes.
Thus alveoli are sites of exchange of gases and oxygenation of deoxygenated blood whereas nephrons are sites of filtration of blood where water and useful substances are reabsorbed and nitrogenous wastes excreted.
Alveoli are small balloon like structures present within the lungs to increase the surface area of lungs. Their walls contain an extensive network of blood-vessels. CO2 brought by blood from rest of the body is released into the alveoli and oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body. Thus exchange of gases takes place here and the deoxygenated blood is oxygenated here.
Nephrons on the other are functional units of kidney. They are long, tubular structures, concerned with filtration of blood. They are surrounded by a rich capillary network. Different parts of nephrons absorb water and useful substances from blood and remove the harmful substances into the filtrate, which finally forms the urine.
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