Friday, December 20, 2013

Histology

Right, so I promised a post on histology and then a migraine happened. And migraines don't give a sh*t about what you have planned to do. Things are increasingly hectic here as we get down to the 2 weeks left to move mark, and still no idea of how the actual move is going to happen (long story short the guy we hired to move us has health issues and my driver's license could not be renewed).

So, histology. What is it? How is it done? Why am I talking about it?

What is it???  Histology is the study of anatomy under the microscope. It's micro-anatomy! For reference, gross anatomy refers to the study of large structures that you can see by eye, not disgusting anatomy. The sister of histology is histopathology, the study of disease anatomy under the microscope. Scientists who study histopathology also study histology, because you need to understand what the structure looked like before the disease occurred. Histology can encompass anatomy of anything that can be seen under a microscope, human specimens, animal, plant, fungi, you get the idea. Usually specimens are sliced very, very thin, then stained with special dyes to aid the viewer.

How is it done???  First, you need to decide what you want to study. Often you choose an area or an organ or a tissue specimen. The specimen then needs to be removed and extraneous material removed (sort of like cleaning). An easy thing to study would be the structure of an organ like the spleen or liver, as these are easy to identify, remove, and prepare (they are soft). A difficult thing to study would be bone, and a really difficult thing to study is an entire area like the arm or the upper respiratory tract (where you breathe - from your nose to the sinuses). If the thing you want to study is soft, like an organ, you only have to put it in fixitive and wait. Fixatives like formalin (a derivative of formaldehyde) preserve the specimen. If you want to study something that is not soft, then (usually) you must make it soft after you fix it. If you are working with bones or cartilage, you can soak it in EDTA which is a chelating agent and decalcifies the bone. Next the specimen gets filled, or embedded with a stable compound like paraffin that will keep the structure. Formalin-fixed paraffin-embedded (FFPE) tissues have the added bonus of being stable at room temperature for decades. Possibly even centuries.
          ** Side note - the stability of FFPE specimens allows scientists to do some pretty awesome things like go to biobanks, look up specimens from say, the 1918 influenza pandemic, and make fresh samples to study with modern methods, greatly increasing our knowledge of the past. -- This in turn can inform our future. Big universities or government science facilities that store banked specimens are a huge treasure trove of new possible discoveries, or re-discovories.

Once the specimens are embedded, they are sliced until a proper depth is reached. A 'proper depth' can mean just about anything, depending on what the scientist wants to see. Once at the right area/depth, very thin slices (2-5 um) will be taken and mounted onto glass slides. This is why the tissue needs to be "soft." In order to get a thin slice that does not damage the structure, the blade must move through like butter. The blades are very sharp, but things like hard bone would still destroy the blade and the specimen.

After it is mounted onto a glass slide, the paraffin is removed, leaving just the tissue or specimen. Then a variety of stains can be used that highlight various structures. One of the most common stains in the study of anatomy is called H&E (hematoxylin and eosin). H&E are a stain and a counterstain, and depending on the structure you will see a variety of pink, deep pink, or purple colors. The nucleus of cells stains a rich purple, whereas the cytoplasm generally stains pink.

Here are some examples of H&E stained samples (pictures I took myself!). Click on the picture to enlarge it.

This is a section of a mouse lung that had a bacterial infection.
 This is a mouse lymph node, similar to the tonsils

This is a mouse sinus cavity, complete with phagocytic macrophages **EDIT I'm pretty sure it's a blood vessel inside the sinus area. (I'm not an expert)













A lot can be learned from histology, not just anatomy. This is why scientists still today use histology and histopathology, which are basically techniques first introduced over 100 years ago. Now we have some new and cool stains that can tell us more about the function of certain things, but the basics are roughly the same.

And finally - why am I talking about histology??? I am talking about it because it forms the basis of the "images" I use in my art. In my life as a scientist as I use histology and microscopes quite a bit. Because I think that what I see under the microscope is wondrous and beautiful, I decided to create art prints based off of this. Linocut printmaking is an analogous process in which you must make fine, deliberate cuts, and then add ink to reveal the final piece. This is part of the reason I chose the technique. I think it gives the same feeling as a histological picture.

So, I hope everyone has enjoyed my crash course in histology.

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