Blood and Bone Marrow


Access to the supplemental resources for this session is password-protected and restricted to University of Michigan students. If you are a University of Michigan student enrolled in a histology course at the University of Michigan, please click on the following link and use your Kerberos-password for access to download lecture handouts and the other resources.

Resources on M+Box

Wheater's (5th ed), pgs. 46-64, Blood
Ross and Pawlina (6th ed), Chapter 10 Blood, pgs. 268-309
1.  Know the main components of peripheral blood
2.  Be able to recognize all of the cellular components found in peripheral blood by light and electron microscopy.
3.  Know the approximate abundance of various types of blood cells.
4.  Understand the functions of major plasma proteins and of the different kinds of cells.
5.  Be familiar with the general process of hematopoiesis and discriminate between lymphoid and myeloid cell lineages.
6.  Describe the organization of the bone marrow.
7.  Be able to recognize megakaryocytes in the bone marrow and understand their function in platelet production.

Normal blood smear 63x (Wright stain) WebScope ImageScope
Normal blood smear 86x (Wright stain) WebScope ImageScope
Slide 81 (blood smear, Giemsa 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.  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 arelymphocytes, 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.

122 Blood Erythrocytes (RBC) Webscope Imagescope
Erythrocytes (RBC). 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 that in contrast to the lymphocyte, neither the two platelets nor the RBCs contain nuclei. The plasma has a flocculent appearance, because the protein concentration is high and has been precipitated by the fixative.

139 Erythroblast nuclear extrusion Webscope Imagescope
Erythroblast (nuclear extrusion). When the nucleus becomes extruded during maturation of an erythrocyte, the cell becomes a reticulocyte, which is a nearly mature erythrocyte. The reticulocytes are normally found in the bone marrow (except about 1%) and still have some cellular organelles, such as mitochondria, Golgi vesicles and polysomes. This gives the cytoplasm a basophilic character.

125 Blood - Mouse Thrombocyte (platelet) Thrombocyte Webscope Imagescope
Thrombocyte. The thrombocytes or platelets are enucleate cell fragments, which originate from megakaryocytes.

126 Neutrophil Human Webscope Imagescope
Neutrophil. 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.

128 Monocyte Webscope Imagescope
Monocyte. Monocytes have a single population of azurophilic granules, which are primary lysosomes.

129 Lymphocyte - small, mouse Webscope Imagescope
Lymphocyte. Note the small amount of cytoplasm and sparse organelles (except ribosomes).

130 Blood Eosinophil Webscope Imagescope
Eosinophil. The bi-lobed nucleus, in combination with the specific granules that contain crystalloids, make it possible to identify this cell as an eosinophil.

131 Basophil - human Webscope Imagescope
Basophil. Note that the granules are true secretory granules, discharged by exocytosis. The nucleus is oval or kidney-shaped.

132 Blood - Rabbit, Process of Diapedesis and Extravasation Webscope Imagescope
Process of Diapedesis/Extravasation.

Click on a question to reveal the answer.

Why does the one sectioned in the equatorial plane appear to have a large hole in the middle?

Red blood cells are biconcave, meaning that they are shaped like a donut with a thin covering over the hole (you get an idea of this by looking at the other RBCs in the picture). Unless it is sliced exactly in the middle, the edge will be in the plane of section, but the middle portion will either be above or below, leaving what looks like a hole in the center of the cell.

1. A marrow sinus is indicated by:

View Low Mag Image

View Med Mag Image

  1. A
  2. B
  3. C
  4. D



2. The formed element indicated by the arrow:

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  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


comprises less than 1% of circulating leukocytes.

3. The formed elements indicated by the arrows:

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  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


are derived from a myeloid progenitor cell

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.


maintenance of colloid osmotic pressure.

5. The formed element indicated in the transmission electron micrograph:

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  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.


expresses ABO antigens that determine an individual's blood type.