|Atlas||Wheater’s (5th ed), pgs. 46-64, Blood|
|Text||Ross and Pawlina (6th ed), Chapter 10 Blood, pgs. 268-309|
Scan around the 63x and 86x slides at high magnification to see the various kinds of blood cells that were discussed in the lecture. Most abundant, of course, are the red blood cells (RBCs) or erythrocytes, which are seen in large numbers everywhere you look. In between the RBCs you should look for small, basophilic fragments which are platelets or thrombocytes [example] that are important in blood clotting. As you continue viewing, you will see occasional white blood cells (leukocytes). Some of the white blood cells may defy identification, often because the cells were damaged during slide preparation, so look for characteristic examples, and ignore the equivocal cells. Refer to the images in your texts and from the lecture and try to find an example of each leukocyte type using the 63x and 86x slides (there’s less area to cover in these high-mag slides and the cells present are excellent, although the 63x slide does NOT contain any basophils).
The most common white blood cell is the neutrophil, which has a distinct multi-lobed nucleus (often 3-5 lobes). Also frequently seen are lymphocytes, which are small cells (often as small as RBCs) with a dark nucleus and very little cytoplasm. Another cell type is the monocyte, the largest of the blood cells. It has a large, relatively pale nucleus, and rather clear cytoplasm (granules are usually less apparent than those in the illustration in Wheater atlas). You will also see an occasional eosinophil, with prominent reddish granules filling the cytoplasm, and a nucleus with 2 (or sometimes 3) lobes. The exact color of the granules may vary from slide to slide, depending on how well the slide was prepared. In your particular slides they may be anywhere from bright red to dull brown. The remaining cell type you may see on your slides is the basophil, which is hard to find, since it constitutes less than 1% of the leukocytes (the 86x slide actually has THREE excellent examples). The cytoplasm contains large, irregular granules in a “grape-cluster” appearance that usually stain dark blue or almost black. Basophil nuclei may often appear somewhat oval-shaped, so, at first glance, they may be confused with lymphocytes. However, the presence of the large, dark-staining granules should help you distinguish them; also, remember that basophils are rare.
After you’ve done some looking on your own, here some quick links showing examples of each type of leukocyte (in order of their normal frequency in a blood smear). USE THESE LINKS ONLY AFTER HAVING TRIED TO FIND THESE CELL TYPES ON YOUR OWN!
Slide 48 (lower limb, 154mm embryo, H&E) WebScope ImageScope
Slide 45 (intervertebral disc, H&E) WebScope ImageScope
Slide 50 (decalcified bone, spider monkey, H&E) WebScope ImageScope
UCSF slide 81 (vertebrae, 7mo. fetus, trichrome) WebScope ImageScope (virtual slide courtesy of the University of California, San Francisco)
UCSF slide 83 (knee joint, 4.5mo. fetus, trichrome) WebScope ImageScope (virtual slide courtesy of the University of California, San Francisco)
UCSF slide 95 (tibia, rat, trichrome) WebScope ImageScope (virtual slide courtesy of the University of California, San Francisco)
The development of blood cells (hematopoiesis) takes place in the bone marrow found within the marrow cavity of bones. In this course you will not be required to recognize the various stages of blood cell development in bone marrow slides. However, you should have some idea of the process. Look within the marrow cavity of these slides and be sure you can see:
(1) Megakaryocytes, which are huge cells from which the platelets are formed by budding (a process only visible at the EM level).
(2) In the bone marrow in slide #48, look for marrow sinuses and cords [example], which are expanded sinusoidal (discontinuous) capillaries characteristic of marrow. When the developing blood cells in the cords are finally mature, they pass through the endothelium of these sinuses to reach the blood and are then carried out into the general circulation. The sinuses can usually be recognized by the fact that they are full of mature RBCs, and therefore are seen as pink areas in the marrow. The cords contain immature blood cells and megakaryocytes. Remember also that clusters of mature granulocytes, particularly neutrophils and eosinophils may accumulate at the margins of the cords and will move into sinuses when needed, as in response to infection or inflammation.
The sinuses in slide #48 don’t contain too many mature RBCs, so the sinuses and cords may be difficult to see. You may have better luck with slide #45 that you used to look at fibrocartilage in the intervetebral disc (the disc is in the middle of the section with two vertebral bodies on either side –the marrow is within the spongy bone of the vertebrae) [example]. Also, the UCSF collection (particularly slide 83 [example]) has some pretty good examples of marrow in which you should be able to find sinuses, cords, and megakaryocytes.
If the marrow contains mostly the blood-forming cells, it is called red marrow. If, on the other hand, there are also abundant fat cells in the marrow, it is called yellow marrow –you may see some fat cells in the marrow on slide 45, but there are enough blood-forming cells around that it would still be considered to be red marrow.