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Through the Looking Glass - From Stem Cells to Tissues and Organs

Learning Resources The University of Michigan Medical School

Blood and Bone Marrow

Atlas Wheater's, pgs. 46-64, Blood
Text Ross and Pawlina (6th ed), Chapter 10 Blood, pgs. 268-309
Lab Resources

OBJECTIVES:

  1. Be able to identify the different types of blood cells at the light and electron microscopic level and describe their functions.
  2. Know the approximate abundance and lineage (lymphoid or myeloid) of each type of blood cell, and what conditions might lead to relative increases in cell types observed in a peripheral blood smear.
  3. Know the organization of bone marrow (e.g. cords and sinuses), and be able to identify megakaryocytes.

I. Blood

(see Wheater’s figures referenced below, also see Ross pgs 276-9, Plates 16 and 17)
Normal blood smear 63x (Wright stain) WebScope ImageScope
Normal blood smear 86x (Wright stain) WebScope ImageScope
Slide 81
(blood smear, Wright stain) WebScope ImageScope

Scan around the 63x and 86x slides at high magnification to see the various kinds of blood cells that were discussed in the lecture (W, pg 46).  Most abundant, of course, are the red blood cells (RBCs) or erythrocytes (W pg 47, 3.1), 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 (W pg 57, 3.10) [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) (W pg 50, 3.4).  Also frequently seen are lymphocytes, which are small cells (often as small as RBCs) with a dark nucleus and very little cytoplasm (W pg 55, 3.8).  Another cell type is the monocyte (W pg 56, 3.9), 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 W).  You will also see an occasional eosinophil (W pg 52, 3.6), 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 (W pg 54, 3.7), 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!

II. Bone Marrow

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
UCSF slide 83
(knee joint, 4.5mo. fetus, trichrome) WebScope ImageScope
UCSF slide 95
(tibia, rat, trichrome) WebScope ImageScope

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 (W pg 59, 3.12; pg 63, 3.16), 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 (W pg 59, 3.12; R pg 273, 10.20) [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.

Electron Micrograph Wall Charts

#61 ERYTHROCYTE (RBC) WebScope ImageScope RBCs are cut in several planes of section in this micrograph. Why does the one sectioned in the equatorial plane appear to have a large hole in the middle? (BL1) Note also the two platelets and that neither RBCs nor platelets contain a nucleus, in contrast to the lymphocyte. The plasma has a flocculent appearance, because the protein concentration is high and has been precipitated by the fixative.

#62 NEUTROPHIL WebScope ImageScope Remember the multi-lobed nucleus and the abundance of dense heterochromatin that you saw in the blood smear. The cytoplasm contains both azurophilic and specific granules. The distinction between these two granule populations is not very clear in this micrograph, and you are not responsible for recognizing granule types.

#63 EOSINOPHIL WebScope ImageScope The bi-lobed nucleus, in combination with the specific granules that contain crystalloids, make it possible to identify this cell as an eosinophil.

#64 BASOPHIL WebScope ImageScope Note that the granules are true secretory granules, discharged by exocytosis. The nucleus is oval or kidney-shaped.

#65 LYMPHOCYTE WebScope ImageScope Note the small amount of cytoplasm and sparse organelles (except ribosomes).

Practice Questions

  1. A marrow sinus is indicated by: Click here for low magnification image Click here for medium magnification image
    1. A
    2. B
    3. C
    4. D
    5. Answer
  2. The formed element indicated by the arrow: Click here for image
    1. comprises less than 1% of circulating leukocytes.
    2. produces platelets.
    3. is derived from a lymphoid progenitor cell.
    4. can leave the bloodstream and differentiate into a tissue macrophage.
    5. produces IgE antibodies
    6. Answer
  3. The formed elements indicated by the arrows: Click here for image
    1. express ABO antigens that determine an individual's blood type.
    2. primarily contain enzymes that regulate blood pH.
    3. are derived from a myeloid progenitor cell.
    4. contain enzymes that produce oxygen radicals.
    5. contain granules of insoluble fibrin
    6. Answer
  4. One of the primary functions of plasma albumin is:
    1. transport of triglycerides.
    2. maintenance of colloid osmotic pressure.
    3. hemostasis (blood clotting).
    4. transport of blood gases.
    5. transport of metal ions.
    6. Answer
  5. The formed element indicated in the transmission electron micrograph: Click here for image
    1. does not function properly in individuals with NADPH oxidase deficiency.
    2. in normal individuals constitutes approximately 70% of total blood volume.
    3. transports the bulk of blood CO2 as carboxyhemoglobin.
    4. is derived from a lymphoid progenitor cell.
    5. expresses ABO antigens that determine an individual's blood type.
    6. Answer