Although organs in the body do not rely primarily on their varying densities to suspend throughout the body, the densities of the organs certainly do help to sustain the suspension of themselves. Although it may look as though most of the organs have densities close to each other, even the slightest difference in density of any substance can allow floating/sinking to some degree to occur.
​
Let's start with the most obvious 'organ' in the body (which is not necessarily an organ in the first place!): the blood. Blood has a density of about 1.04 grams/cubic centimeter, which for a reference, is very close to that of water (~1 gram/cubic centimeter), which makes sense because about 92% of blood is water. Blood is located throughout the human body, as you probably know very well, and acts as a sort of cushion for the organs in the body.
​
Although many people's initial thoughts when learning this is that, "Well, of course, the organs are suspended in the blood!", but that is not entirely true. As shown in the chart above, many of the organs listed (bone, cartilage, muscle, stomach) have densities that are equal to or slightly greater than that of the blood... but wouldn't that mean the organs would sink in the body?
​
Not necessarily. Adipose tissue, which is the most common tissue that is located throughout the body, has a density of about 0.9 grams/cubic centimeter, which would obviously 'float' in the blood. This tissue surrounds almost every important bone or organ system in the body, and the attachment of that adipose tissue eventually allows the organs to 1.) remain suspended in the body and not sink all the way to your feet!, and 2.) allow not only for the suspension of the organs, but holding them steadily in place as well.
​
Some other organs, such as the heart (which is a muscle) are instead encompassed in two membranes called the visceral pleura & parietal pleura. In between these two membranes is a low-density fluid that helps to keep these organs suspended and prevents them from rubbing up against any bones that may damage them.
​
Along the same note, have you ever noticed how girls float in water better than boys? Fat has a very low density of 0.9094 grams/cubic centimeter, and compared to water, the fat is very buoyant. Females, statistically have more overall fat than males and therefore float better in water. Similarly, fat in your body essentially 'floats' to the surface of the body (closest to the skin).
​