Saturday 25 January 2014

Histology bores

In my 1st Year Cell Biology class, we have spent quite a lot of time looking down a microscope.  Part of the training they get during the year is in how to use this tool efficiently, reliably and safely.  In this case it's not really the safety of the students (Microscope Bites Man hasn't yet happened, even as a headline in National Enquirer) but to make sure that the expensive kit survives exposure to physical and chemical (and indeed biological crud) attack on the lenses.  We have an ancient box of prepared histological sections - slices through various tissues -  lung, liver, lights etc.  Someone drove a lens through the sample of striated muscle last year and The Institute was, quite rightly, too ashamed to treat that as two half slides that could be used simultaneously by two students.  Probably because the sharbroken edge offered a clear and present danger.  Another preparation has only had the cover-slip driven in, so the the specimen is visible but so is an interesting view of propagating cracks.

Looking at prepared slides can be dead boring - I remember being bemused and adrift when I had to do it several decades ago.  So I prefaced the day with quite a long harangue about what you might get out of an hour paying attention to detail at a microscopic level.  First point was to address the different levels in the biological hierarchy at which science can be carried out. I established that they, Sport Scientists all, had already done work in another class at the whole body level - measuring the oxygen consumption of some poor bugger on a treadmill.  In 'our' Cell Biology we've looked at individual (blood) cells and I'm sure that they've done some basic biochemistry.  Histology is the in-between study of the structure and function of tissues - the characteristic cell-types that make up organs. Standard practice is that the students look at perfect specimens which makes their own preparations seem hopelessly klutzy, draw what they see and scatter a suitable number of Latinate labels - gleaned from a textbook or Google - on their representations.  Zzzzzzzzzzzz.

The problem is that it is hard to comprehend any function from the static artificially stained material on the slide.  One of the most wonderful revelations in my lifetime of science was to see red blood cellred blood cell is 8 microns across and the capillary is 9 microns in diameter - so the RBCs jam up against the slightest obstruction until more and more cells pile into the log-jam.  You can see the pressure building up until the blockage gives way and courses off down the tube in a rush. 'Histology' doesn't address that at all at all.

I also gave everyone an extra supplementary page with pictures of some standard histological sections, mostly bright pink, all labelled up and said they could cut them out and stick them in their books.  Me, I don't see the difference between looking at someone else's slide or someone else's photograph of a slide.  We then had a class discussion (aka Bob The Socratic) and we wrote up on the board interesting questions you can address in a histology class.
  • What's the difference between pictures of active and inactive mammary gland?
    • Is the ancient prepared slide active or inactive? (A: dead)
  • Why are the stripes on skeletal muscle at right angles to the fibre?
  • Why/how does lung maximise the surface are at the interface between air and capillary?
  • What is the ratio in size between alveolus and capillary?
    • Look back in your book to find out the diameter of a red blood cell.
  • How does the structure (villus and crypt) of duodenal epithelium serve its function,
Wonderfully, the thousand-thousand finger-like projections of the villi of the duodenum are replicated on a sub-cellular scale in the microvilli (aka brush-border) of certain duodenal 'goblet' cells which secrete mucus.  With pictures on the handout of active and inactive mammary gland, the obvious question was to ask "is the prepared histological slide marked mammary tissue active or inactive?"  I was called to adjudicate on this because two lads were looking down the same microscope and coming to opposite conclusions.  What I saw was a grey vista of bubbly-stuff which (and this a key piece of data) didn't move when I shifted the slide from left to right.  The students had adopted a position of some certainty and taken opposite positions in their wrangle about whether some gunk on the objective lens was active or inactive.  So we cleaned off the gunk and then brought the mammary gland tissue into focus and then we could discuss the material.

It turns out (wikipedia is a wonderful resource) that a microvilli/brush-border is not only found in goblet cells but also on the outside of a mammalian egg.  I asked the class why they thought an egg should have a brush-border and one of them piped up with increase the surface area.  I remain to be convinced of that being relevant in that cell type.  But I suggested that, if we have the genetic capability to make some cells develop a fuzzy edge to maximise secretion, maybe that can be re-purposed as a sperm-catching device.  Clearly someone is going to have to do more reading.

No comments:

Post a Comment