It’s never too late to ask questions – I’m around and checking email today so feel free to email me. I’ve gotten some great questions about the exam last night and today – and although I don’t like to post things so close to exam time, I thought these questions were important enough to warrant sharing them with the class.
Steps in bone formation
I’ve had several questions about whether you need to memorize all the steps in intramembranous and endochondral bone formation (those wordy slides with 8 steps in intramembranous and 6 steps in endochondral ossification).
I don’t want you to memorize each step word for word (I just included those slides because without them, it’s kind of hard to see what happens from just the picture slides). What I would like you to be able to do is explain (to someone else, or just to yourself) in general what happens in each type of ossification. For example:
Intramembranous ossification happens in flat bones. There’s a bunch of mesenchyme sitting there, and the first thing that happens is some capillaries grow into that mesenchyme. Some of the mesenchymal cells turn into osteoblasts, which make bone matrix and then turn into osteocytes. At first, the bone is immature, but it gets replaced by mature bone, with compact bone on the outside and spongy bone on the inside.
Endochondral ossification happens in long bones. It starts out with just cartilage, and then the cartilage calcifies and a little bone collar develops around the long part of the bone (the diaphysis). Little things called ossification centers form in the diaphysis and in the epiphyses (the ends of the bone). Eventually, bone replaces all of that cartilage, except the epiphyseal plates and the articular cartilage. The epiphyseal plates are what makes the bone continue to grow longer and longer. They have 5 zones (resting at the top, then proliferating, hypertrophic, calcified, and ossified). The upper zones continue to proliferate and the bottom zone continues to turn into bone, until the epiphyseal plates decide to “close” or stop, which usually happens some time around/after puberty.
Cell shapes and locations
Q. In what detail do we need to know the shapes of cells in relation to their location? For example, should we know specifically that respiratory epithelium is typically pseudostratified columnar? That ependymal cells are cuboidal to low columnar? Or should we focus on the shapes in a more general aspect?
A. For the epithelium lecture, I want you to focus on the characteristics of epithelial cells themselves (their shape, etc.) rather than their specific locations (like the respiratory system). I wanted to show you real pictures of the different types of epithelium (e.g., pseudostratified columnar) and in doing so, I included the places (e.g., respiratory system). But you don’t need to memorize those places now – we’ll get to each one of them as we cover the different systems. So just know the three different shapes of lining epithelium cells, and know the difference between simple, stratified, and pseudostratified epithelium. (And also know about cilia, microvilli, etc.)
For the cells of the nervous system, you should focus on what each type of cell does (e.g., ependymal cells line the ventricles and make cerebrospinal fluid; astrocytes multiply after an injury and make a “scar”) rather than on the details of their appearance (e.g., ependymal cells are cuboidal to low columnar). You probably have a general image in your mind of each cell (neurons are big and triangular, astrocytes are star-shaped and have super long processes, oligodendrocytes are kind of round with long things that myelinate axons, microglia are little nondescript cells, etc.) – and that’s enough detail for this exam.
Q. For glandular epithelial cells, should we know about locations? For example, should we know that pancreatic acinar cells are serous secretory cells, or should we focus more on the function of serous secretory cells in general?
A. I’d like you to know the way glandular cells work (how they secrete stuff), and a little bit about the morphology (those slides at the end of the lecture that show what serous cells contain, and what goblet cells look like). But you don’t need to memorize specific locations (like the pancreas). We’ll get to that when we get to each system. I just wanted to show you real pictures of glandular epithelium like I did for lining epithelium.