Questions on blood, hematopoiesis, and lymphoid stuff

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.

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