I can’t help but draw analogies between Beyonce and female reproductive histology. I mean, it’s BEYONCE people. Here she is in all her glory at the 2017 Grammies:
She is adorned in a beautiful golden gown and her head is surrounded by a gorgeous radiating crown. Oh, AND she’s pregnant!
Beyonce is like a primary oocyte sitting in a Graafian follicle: her crown is the corona radiata, and her dress is made of gorgeous granulosa cells. At some point she no doubt sits on a little stool, which is the cumulus oophorus.
The metaphor continues! What happens during ovulation? Beyonce sheds her gown (the granulosa cells of the Graafian follicle) and leaves the ovary, making her way down that treacherous runway to the opening of the fallopian tube. So what’s left behind? Her gorgeous golden gown! That stays in the ovary, and becomes the corpus luteum (the “yellow body”).
I’m telling you, there’s even more here. If you watch the lecture recording, you’ll see I keep saying the Graafian follicle is juicy (maybe not the best description, but hey, that’s what it looks like to me!). And Bey is most certainly juicy – she straight up says it in Cozy!
This diagram shows the different maturational stages of ovarian follicles.
Here’s a quick summary of when you see these different stages:
At birth, all you have are primordial follicles (about a million in each ovary).
At puberty, you start “recruiting” groups of about 50 primordial follicles at the beginning of each menstrual cycle.
These primordial follicles start down the pathway of maturation, moving through the stages listed above (unilaminar primary, multilaminar primary, secondary, and Graafian follicles).
Only one of the group of 50 follicles will make it to the Graafian follicle stage (the other 49 die off along the way in a process called “attrition” or “atresia”).
At the time of ovulation, the Graafian follicle ruptures, releasing the germ cell inside, which makes its way to the fallopian tube and down into the uterus.
In addition, over a woman’s lifetime, the primordial follicles in each ovary start dying off on their own (independent of the menstrual cycles). Their population dwindles over time until the age of menopause, when there are none left. Then menstrual periods cease (there are no primordial follicles left to recruit!).
By the way, here’s what is inside each follicle (spoiler: it’s always a primary oocyte):
Primordial follicle: primary oocyte (arrested part way through meiosis I)
Unilaminar primordial follicle: primary oocyte (arrested part way through meiosis I)
Multilaminar primordial follicle: primary oocyte (arrested part way through meiosis I)
Secondary follicle: primary oocyte (arrested part way through meiosis I)
Graafian follicle: primary oocyte (arrested part way through meiosis I)
Wait, what?? What about the secondary oocyte and the ovum?
At ovulation, the primary oocyte is “released” from its maturational arrest, and it turns into a secondary oocyte. YAY! This secondary oocyte starts undergoing meiosis II, but is arrested part way through.
If no fertilization occurs, the secondary oocyte will never complete meiosis II, and will be shed during menstruation.
If fertilization occurs, the secondary oocyte completes meiosis II, turning into an ovum. FINALLY!!!
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.
I got a student question a couple years ago about how to tell the difference between stomach and small intestine on histology. I love this question because I remember having the exact same issue when I was a wee medical student learning histology, and I’m not sure I ever really figured it out until I started actually teaching it!
Stomach and small intestine can be confusing when you’re first learning this stuff because 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!
You can play it at 1.5 speed and still get the same info 🙂 I talk slowly!
Here’s a little GI histology summary table that I put together. This is just one way of summarizing the material, obviously – you may have a way that works better for you! Just thought I’d share the way I did it in case you find it useful.
Here’s a short post I wrote that summarizes the high-yield points in GI histology. Totally optional, just like all of the resources I post here! Just use it if you like it 🙂
Tomorrow’s asynchronous lecture video is about the urinary system. I thought I’d share this little self-study thing I put together on the tubular segments of nephron in case you find it helpful. It just asks you to name the segments, and recall what they do and what they look like. Totally optional – if it helps, great, if not, just ignore it!
Here’s a drawing I made showing 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 🙂
Nice job on the exam!! Everyone is done with the exam, and so I wanted to let you know that there are several questions that I will be rescoring/adjusting. Unfortunately, no matter how many times I check and recheck my exams, it seems that there is always the possibility of a typo I didn’t catch, or some additional answer being correct, or some other thing like confusing wording.
Here are the questions that posed problems, along with my solution for resolving each question.
Question 14
This question stem was worded in a way that could be interpreted as “which cell is the last to always contain a nucleus?” In that case, the correct answer would be A) polychromatic erythroblast (same thing as polychromatic normoblast), since the orthochromatic erythroblast only contains a nucleus for part of its lifespan (it then gets extruded). So I am accepting both A and C as correct answers.
Question 20
In class, we talked about selection occurring in the cortex. However, someone brought up that you guys learned in another class that positive selection occurs in the cortex, while negative selection occurs in the medulla. So since D is correct, I am also accepting that as a correct answer (and changing my slides for next year!).
Question 27
This was confusing to some because although the histology slide showing thyroid tissue showed eosinophilic fluid (colloid) within the follicles, the text slide didn’t use the word eosinophilic. And I’ve said several times that I don’t want you memorizing slides. There were people who picked other answers too for different reasons. So I think it was confusing enough that I am adding a point to everyone’s score for this question. The reason I don’t just throw the question out, by the way, is because that in a way punishes the people who got the right answer. So I feel this is the most fair way to handle questions like these.
Question 28
This question stem confused some people, because instead of “islets” I said “islands” which is not a word we used in lecture. So I am adding a point to everyone’s score for this question as well.
Question 38
I didn’t realize this, but there was a typo on slide 51 of the Cardiovascular System lecture:
The last bullet point should say “…from right to left atrium.” So I am giving credit for A (right ventricle to left ventricle), even though it’s incorrect, in addition to the correct answer (C: right atrium to left atrium), because of the typo on this slide.
Please read this next paragraph!
Regarding this last question, I want to make sure you all understand this concept, because maybe I didn’t explain it well enough in class. The foramen ovale is a valve-covered hole that exists between the two atria, allowing blood to flow from the high-pressure right atrium into the low-pressure left atrium. It is one of the cool little heart structures (like the ductus arteriosus) that exist in utero to take some pressure of the right side of the heart (so it doesn’t get gigantic) and puts a little more pressure on the left side of the heart (to allow it to become big and strong enough to pump blood through the body after birth). These structures almost always close after birth (if they don’t, you can run into problems – but we’ll talk about those next year in Systemic Pathology. Please let me know if you have any questions on this!
Bottom line
Okay – that’s it for questions – whew! I’m not allowed to rescore the exam until I return from vacation – so unfortunately you won’t see your Canvas score change for a few weeks. But you can determine, from the above information, what your new score will be on your own 🙂
Two new things have come up today: one has to do with randomly appearing passcodes, and the other is just a reminder that you have to use a laptop (not an iPad) for the exam.
Passcode
I found another glitch in the system: no matter how many times I turn OFF the student passcode setting in Canvas, and saving the exam, Canvas keeps turning it on. Not sure why this is an issue with this exam (it didn’t happen for our first exam).
So I’ve decided to leave the Passcode setting on, and set it to “HistoExam2.” I will do this for everyone’s exam, including those with accommodations. Hopefully Canvas keeps it that way and doesn’t pick another random passcode. If it does, Dr. G. can look in Canvas and let you know what the new passcode is. For those with accommodations, I am sending you a separate email with instructions on how to reach me if this is an issue.
iPads
I was reminded today that iPads do not work with HonorLock. There were some issues with this during our Mock Exam, and we were all reminded that you need to use a laptop, not an iPad, for taking the exam. If you need a laptop, you can borrow one from Dental IT. They are on the 16th floor of Moos Tower; if you get off the elevators, and walk in the opposite direction from the big face, IT is the second door on the right.
As always, please let me know if you have any questions about this stuff or anything else!
