Granulation tissue vs. granuloma

Here’s a student question from a previous year that you might find useful.
Q. I have a quick clarification question for you about the difference between granuloma and granulation tissue.  I have in my notes that “a granuloma is a type of chronic inflammation where you have macrophages that surround something indigestible like a splinter.”
How, then, would you define granulation tissue that is present in the 3-5 days following injury? Is the difference simply that granulation tissue is not necessarily something that surrounds an indigestible particle, but rather a tissue that characterized by the presence of macrophages, collagen/fibroblasts, and blood vessels?
A. Yes! You’re on the right track. I think it might be helpful to think about the differences between granulation tissue and granulomas in two categories: function and composition.
The function of granulation tissue is to provide the building blocks necessary for the healing of the injured tissue. The function of a granuloma, on the other hand, is to surround and (hopefully) digest foreign substances (splinters, difficult-to-kill bugs like mycobacterium tuberculosis).
There really isn’t any crossover, either – you don’t see granulation tissue at the site of a foreign body, and you don’t see granulomas forming in wound healing. So the functions of granulation tissue and granulomas are quite different.
Their composition is different too. Granulation tissue is composed of blood vessels, fibroblasts, and loose extracellular matrix. Granulomas are composed of macrophages and (often) a collar of surrounding lymphocytes. Macrophages do participate in wound healing, but they’re not part of granulation tissue. So the composition of granulation tissue and granulomas are very different too.

Why so sad, Prometheus?

Yeah, an eagle is pecking a little at his liver – but seriously, his face shows a disproportionate degree of anguish.

Prometheus is in a bind (literally: the painting is “Prometheus bound” by Rubens) because Zeus is pissed that he stole the secret of fire. As punishment, Zeus sends an eagle to eat Prometheus’ liver. But the liver has an incredible capacity for regeneration – so overnight, Prometheus’ liver grows back. So Zeus sends the eagle again, and the liver regenerates again…you get the idea.

While it’s probably pretty uncomfortable to have an eagle pecking at your liver, the reason Prometheus is so incredibly upset is probably because to the ancient Greeks, the liver was considered to be the seat of one’s soul and intelligence. Had the eagle been pecking at Prometheus’ spleen, say, or his kidneys, maybe it wouldn’t be such an insult. Of course, these organs can’t regenerate as prodigiously as the liver can – so although Prometheus would be less offended, he’d also be dead.