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Lysosomes - are they more specialized than what I am led to believe in basic physiology lectures?

hi! 

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there have been several different times when I came up with a version of the same question: *how do lysosomes "know" what to digest?*

example to illustrate what I mean:

* in thyroid hormone production, thyroglobulin (TGB) is taken up by the follicular cell. the endosome, full of TGB, fuses with a lysosome, which digests the TGB to release free T3/T4. 
   * how is it that the lysosome does not end up digesting the T3/T4 as well? do follicular cells express only certain kinds of enzymes that only break specific bonds within TGB and leave T3/T4 intact?

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basically - we're taught that lysosomes are these enzyme-filled bags that just digest anything they come across, but that seems very simplistic, and I am curious to know more about their heterogeneity!
gpt
Lysosomes are indeed enzyme-filled, acid bags. The main enzymes they contain are hydrolases however, which will hydrolyze your typical macromolecular bonds like peptide bonds, sugar-phosphate bonds, or glycosidic bonds,  thereby mainly digesting proteins, dna, and polysaccharides respectively. Small molecules with few or no hyrolyzable bonds will remain pretty safe. So T3 and T4 can be recycled out of the lysosome and may or may not get digested elsewhere, while the functional molecules like proteins will be digested away.