Here’s an interactive drawing I made that shows what happens to female germ cells over time. I think it’s kind of helpful to see the numbers (and stages) of the germ cells mapped out by age – it gives you a visual sense of what happens throughout life.
I can’t post the drawing on our website because of wordpress limitations – but I was able to post it on my Pathology Student website (so when you click on the link, you’ll wind up on that website).
Okay I think I overdid it on “juicy” during class today, I kinda got sick of hearing myself say it. But I stand behind my references to Beyonce wearing a crown. I had to look it up, and here you go – Beyonce exactly as I imagined her in my head today, a goddess wearing a corona radiata.
Tomorrow we’ll talk about two types of vocal cords:
True vocal cords
False vocal cords
Most types of singing use only the true vocal cords – but there is a cool exception called Tuvan throat singing in which both the true and false cords are used. Here’s a video that showcases this singing really well.
Tomorrow we’re going to be talking about the histology of the respiratory system. It’s kind of like the GI tract, in a way, in that it consists of a series of tubes that have different histologic features. So it’s pretty easy to break down into parts (bronchi, bronchiole, etc.) and summarize.
I like to make drawings to summarize things like this – and I thought I’d share this one with you in case you find it useful. It shows how the wall of the respiratory tree changes as you go from bronchi to alveoli. There are three versions, so you can use it fully labeled, partially labeled, or unlabeled, however it suits you best. Let me know if you find it useful – if so, I’ll make more 🙂
Q. I am slightly confused about muscularis externa. Is muscularis externa only present in places where muscularis mucosa is not? For example, the oral cavity, upper esophagus, and anal canal. Is it possible for them both to be present? And muscularis is not always present as a layer in the GI tract, correct? When present does it typically present in the same layer that the muscularis mucosa would be?
A. Those are great questions! As you noted, there are two “muscularis” layers in the GI tract: the muscularis mucosa and the muscularis externa.
The muscularis mucosa is a thin little layer of smooth muscle that is part of the mucosa (which includes epithelium, lamina propria, and muscularis mucosa). It innervates the inner layers of the mucosa, and it also shows you nicely where the mucosa ends, and the submucosa begins.
The muscularis externa is a thick layer of muscle that provides the main structural support all along the GI tract. It sits between the submucosa and the serosa/adventitia.
Basically the GI tract is just a tube with four concentric layers, like this:
From inside to outside, there’s mucosa (epithelium, lamina propria, and muscularis mucosa), submucosa, muscularis externa, and serosa/adventitia.
All levels of the GI tract have this exact structure, except for:
the mouth (which I’m not allowed to discuss with you lol)
the anus (which is only slightly different…its mucosa is comprised of just epithelium, with no lamina propria or muscularis mucosa).
I think that pretty much covers it. Having said all that, here are my direct answers (in blue)!
I am slightly confused about muscularis externa. Is muscularis externa only present in places where muscularis mucosa is not? For example, the oral cavity, upper esophagus, and anal canal. No. Both the muscularis mucosa and muscularis externa are present at every level of the GI tract except for mouth and anus (as mentioned above). The upper esophagus btw is not an exception – it has the same four-layered structure you see everywhere else. Is it possible for them both to be present? Yep! And muscularis is not always present as a layer in the GI tract, correct? No – both types of muscularis layers are pretty much always present. When present does it typically present in the same layer that the muscularis mucosa would be? No – the muscularis mucosa is always part of the mucosa (the innermost of the four layers), and the muscularis externa is always located between the submucosa and serosa/adventitia.
Stomach and small intestine can be confusing when you’re first learning this stuff – they both have glands at the bottom and other structures (pits in the stomach, villi in the small intestine) on top, and it can be hard to visualize all of that in 3D.
So I made a short video explaining the difference. I think it’s easier to understand if you can see someone drawing on the pictures. I hope if some of you had the same problem that this will solve it!