Lymphoid System

Quick summary of the stuff I said you DON’T need to memorize for Exam 2

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As we went through each lecture, there were times when I said “this isn’t important for our exam purposes – but I included it in this lecture because _____” (usually, because it’s something I’ve heard has been on boards recently).

And I realize that is in a way okay, but also it takes some effort on your part to remember which things I said I wouldn’t test you on. And your time is short enough as it is.

So for each lecture, I’ve made a list of the things I said you did NOT have to learn for the exam. I’ve also thrown in a few things that you DO need to know, just to reiterate these important points.

I’ve already posted the lists for the Skin and Blood lectures.

Here are the lists for the remaining lectures.

Hematopoietic System

  • Slide 10: DON’T memorize the numbers in bullet point two.
  • Slide 12: DON’T memorize the stage at which erythrocyte precursors stop undergoing mitosis, or the fact that the proerythroblast is my favorite cell. DO know the names of each of these maturational stages, though, and know what makes them unique. For example, hemoglobin formation begins in the polychromatic erythroblast (you can maybe remember that because “polychromatic” means “more than one color” – and that refers to the fact that now the cytoplasm has both blue (from RNA) and red (from hemoglobin) in it.
  • Slide 21: DON’T memorize the size or the number of copies of DNA in the megakaryocyte. DO know that megakaryocytes are gigantic, though, and that the reason they get that big is because they do this weird thing called endomitosis (they replicate their DNA but don’t undergo cell division).
  • Slide 25: DON’T memorize the time it takes for neutrophils to undergo maturation, or the exact length of time they stay in the blood.
  • Slide 26: Don’t memorize the stage at which neutrophil precursors stop undergoing mitosis. DO know the names of each maturational stage though, and know what makes them unique. For example, specific (pink) granules are first seen at the myelocyte stage.

Lymphoid System

  • Slide 31: If this slide bugs you, forget it! All the important facts that you need to know from it are included in later slides.

Endocrine System

  • Slides 14-16: There are a lot of explanatory words pointing out structures on the images in these slides. DON’T memorize all of them! DO know that the anterior lobe of the pituitary arises from the roof of the mouth, and that the posterior lobe of the pituitary arises from the developing neural tube.
  • Slides 20-21: DON’T memorize the names or locations of the subdivisions (e.g., pars distalis) of the anterior pituitary.
  • Slides 29-30: Same thing: DON’T memorize the names or or locations of the subdivisions (e.g., pars nervosa) of the posterior pituitary.
  • Slide 39: This is a crazy-busy picture, and the more I look at it, the more I regret leaving it in. The only thing this diagram illustrates well is the fact that the posterior pituitary does not make its own hormones; it secretes hormones that are made by the hypothalamus. But that point is already stated on slide 34 – so you can just cross out this diagram and not lose any important, testable information.
  • Slide 47: I won’t test you on anything in this slide. This is a great diagram, though, because it shows in a pretty clear way how thyroid follicular cells create thyroid hormone, secrete it into colloid, and then (when TSH binds to their little TSH receptors) take thyroid up, process it a bit, and dump it into the blood. But this level of detail is more for biochem than for our class – so you can ignore it for now. If you ever need a concise diagram of thyroid hormone production, though, this one might help 🙂
  • Slide 48: DON’T memorize all the things thyroid hormone does. DO know that it is important for growth (during childhood) and metabolism (it stimulates pretty much every organ system in the body).
  • Slide 77: DON’T memorize what delta and F cells produce. This is great boards fodder – but there’s enough for you to memorize for this exam, and you’ll cover this stuff in physiology anyway.

Cardiovascular System

  • Slide 32: DON’T memorize the stuff on this slide. I just put it here because the following slides talk about atria, ventricles, and the conducting system, and I wanted you to have an initial diagram to refer to if that was helpful.
  • Slide 50: DON’T memorize the fact that blood flows in a coordinated fashion by day 28 (the last bullet point and its sub-bullets). DO know the approximate day at which the first heartbeat occurs.

Questions on blood, hematopoiesis, and lymphoid stuff

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Here are some questions from students from past years on the stuff we just covered. You may have some of the same questions (or maybe you didn’t even know you had some of these questions!). Anyway – maybe these will be helpful to you.

Q. In the notes it states that neutrophils live for hours. Is this the same for all leukocytes or do we not need to worry about the duration of the remaining leukocytes?

A. You don’t need to worry about the other leukocytes. We just talked about the circulation lifespan of neutrophils (hours), platelets (days), and erythrocytes (months) – that’s all you need to know.

Q. Just to confirm, the reticulocyte is in the blood and not the bone marrow. Additionally, I know that the reticulocyte still has RNA present. I assume there is no DNA since the nucleus is absent. Is that correct?

A. Actually, reticulocytes are produced in the marrow, and then released into the blood – so reticulocytes are in both places (marrow and blood). And yes – reticulocytes have RNA but no DNA (since the nucleus is no longer present).

Q. Is the hematopoiesis the “same” for all leukocytes – I should just keep in mind what occurs with the neutrophil and apply that same concept for the other leukocytes? I believe that you may have stated this in lecture.

A. Hematopoiesis is the same for all granulocytes (but not all leukocytes) – so once you’ve learned the neutrophil stages, you’ll know how eosinophils and basophils develop. We only covered neutrophil development, though, so you don’t need to specifically remember eosinophils and basophils.

With regard to other leukocytes: Monocyte development is pretty simple, and we didn’t cover the different stages. Lymphocyte development is also pretty simple (from a morphology standpoint…it gets pretty complicated from an immunology standpoint, but that’s from another class), and we didn’t really cover the different stages. Platelets aren’t really leukocytes – and their development is pretty simple too (we didn’t cover specific stages of megakaryocyte development though, so don’t worry about that).

The only other cell type is the red cell series – which has its own stages of development (which we did cover in class – so you should know the names and a little bit about those stages).

Q. I understand that B cells are presented antigens in the follicles of the spleen and lymph node; do these organs also present antigens to T cells or is that just done in the thymus?

A. Antigens are presented to both B and T cells in the secondary lymphoid organs (spleen, lymph nodes, MALT). Antigens are not presented to T cells in the thymus though – in fact, they’re specifically kept out of the thymus by the blood-thymus barrier! This is so T cells can undergo their education without being influenced by antigens in the blood. So the thymus is really a place for T cell maturation only (not for antigen presentation).

Q. I am having some difficulty on the concept on open versus closed circulation. I believe that I understand correctly in that all of the blood circulation in the cardiovascular system is closed. I know you had a slide in the lymphoid section that showed the red pulps’s cords and sinuses. If the blood stays in the sinuses is that considered closed circulation whereas if the blood goes into the cords is that considered open circulation?

A. Sure! Those terms only really apply to the circulation in the spleen – not to other organs. Yes – the cardiovascular system is a closed system (but we don’t really talk about “open vs. closed circulation” when we talk about the cardiovascular system – those terms are really only used when talking about the spleen).

The way you describe closed and open is exactly right! It’s as simple as that. “Closed” means that red cells come into the spleen through the arteries, and stay in the blood vessels all the way through (never leaving the splenic sinuses!), and then exit through the splenic vein. “Open” means that the red cells come in through the arteries, get to the sinuses, and then leave the sinuses, travel through the cords, and then get back into the sinuses (at a different place in the spleen!), and exit through the splenic vein.

The beauty of lymph

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We talked in class on Tuesday about lymph, which is the clear fluid that flows through lymphatic vessels and lymph nodes and eventually returns to the blood. I mentioned that the etymology of the word lymph was beautiful but I didn’t want to take up too much class time talking about it – so I’m posting the story here.

How did lymph get its name? It turns out that lymph is a combination of a couple different words: the Latin lumpa, meaning water, and the Greek nymphe, meaning spring goddess. The resulting word – lympha in Latin, lymphe in French – means clear water or a goddess of water.

I just love this so much. First of all, lumpa sounds gross, and I wouldn’t want to have to deal with that word all the time. Second, we now have an accurate description (lymph does look like clear water) overlaid with a lovely, delicate image (spring water goddess). I mean, what more could you want?

Now every time I hear lymph, lymphatic, or lymphocyte, my brain will conjure up something like this:

This is Persephone, the Greek goddess, bringing spring to the frozen tundra.