& Introduction The slides for this lab are located in the “Blood and Hematopoiesis” folders on the Virtual . Blood is a specialized connective in which three types (erythrocytes, leukocytes and ) are suspended in an extracellular fluid called plasma. Plasma contains many proteins that serve to maintain osmotic pressure and homeostasis. Blood distributes oxygen, carbon dioxide, metabolites, hormones and other substances all throughout the cardiovascular system. The cells in blood have a relatively short life span and need to be replenished with new cells. These cells and their precursors are formed and mature in the bone marrow. Blood cell formation is called hematopoiesis.

Learning objectives and activities Using the Virtual Microscope:

A Identify the different cellular components of a peripheral blood smear

o Erythrocyte o o o o Lymphocyte o o Thrombocyte B Examine the major sites of hematopoiesis and differentiate between red and yellow marrow

C Identify the different myeloid stem cell derived blood cell precursors in an active marrow smear

D Complete the self-quiz to test your understanding and master your learning. Identify the different cellular components of a blood smear

Examine Slide 1 (33) and find examples of the different types of blood cell

This slide contains a normal blood smear. Not all parts of a blood smear are good for observation. Find an area where the cells are spread out (not overlapping) and appear as symmetrical discs.

i. Leukocytes At low power the leukocyte nuclei can be seen sparsely scattered throughout the smear. The large and sometimes irregularly shaped nuclei are strongly basophilic making them a prominent feature of a blood smear.

Granulocytes Find in These cells all contain granules within their cytoplasm: Slide 1a (33)

a. Neutrophil/Polymorphonucleocyte (PMN) Find in b. Eosinophil Slide 1b (33)

c. Basophil Find in Slide 1c (33)

Agranulocytes

These cells do not contain granules within their cytoplasm: Find lymphocytes in d. Lymphocyte Slide 1d(33)

e. Monocyte Find in Slide 1e (33) ii. Erythrocytes

Most of the remaining cells occupying the majority of the smear are erythrocytes. Note their distinctive shape (biconcave discs) and lack of nucleus. They are quite flexible cells. These terminally differentiated cells are Observe completely filled with the oxygen-carrying protein hemoglobin. They do not erythrocytes contain mitochondria. Histologically they can be used as an in-built scale bar in with each erythrocyte measuring approximately 7 microns. They also are a Slide 1f (33) good standard for measuring eosinophilia in . If the granules in a leukocyte exhibit more/same eosinophilia as erythrocytes it is an eosinophil. If the granules are less eosinophilic then it is a neutrophil.

iii. Thrombocytes (platelets)

At low magnification these cells are invisible. However if you increase the Observe magnification you will see these tiny cell fragments dispersed throughout the thrombocytes blood smear. Circulating platelets have about a life span of 10 days. During in Slide 1g (33) hemorrhage, platelets form a primary plug in the first step to stop bleeding. They also release factor IV from their granules to participate in the coagulation cascade.

Examine the major sites of hematopoiesis

i. Sites of hematopoiesis during fetal development The formation of blood cells (hematopoiesis) commences in the wall of the yolk sac. After the second month of development the liver and spleen become the dominant sites of hematopoiesis. After the 6th month, the formation of blood cells occurs in the bone marrow. This is the major site of formation of blood cells in normal adult humans. ii. Sites of hematopoiesis in adults Hematopoiesis in adults occurs in the bone marrow. There are two types of bone marrow in adults:

a.Red marrow Hematopoiesis occurs in red marrow which occupies the space between Observe red bone marrow trabeculae of spongy bone within the epiphysis and diaphysis of long in the section bones. The basis of hematopoiesis is a small population of hematopoietic through a rib stem cells (HSCs) in the bone marrow which can ultimately generate all Slide 2a (10) types of blood cells. Observe b. Yellow marrow regions of fatty yellow This is inactive bone marrow that contains mainly adipocytes and is found marrow in in the diaphysis of older long bones. Slide 2b (10) Identify the different myeloid stem cell derived blood cell precursors in an active bone marrow smear

Blood cells have a relatively short life span and need to be replaced with new cells. All blood cells come from one pluripotent stem cell. These Hematopoietic Stem Cells (HSCs) divide to form two stem cell populations:

1. Lymphoid stem cells

These cells differentiate to form lymphocytes. You will study lymphocytes their development, maturation and function in more detail in the lymphoid tissue module.

2. Myeloid stem cells

These cells differentiate to form all other blood cells. Follow the instructions provided to help you identify some of these cells.

i. Megakaryocytopoiesis The process by which are formed from myeloid stem cells.

Examine Slide 3 (34) to find examples of megakaryocytes

a. Megakaryocytes (literally ‘large nut’ cell) are formed from myeloid stem cells. They are the largest cells in a bone marrow smear and have multiple, irregular, multi-lobar nuclei. Their cytoplasm is filled with fine basophilic granules and the cell periphery is frequently folded into ruffles and protrusions. Thrombocytes are subsequently formed by fragmentation of these cytoplasmic protrusions. ii. The process by which erythrocytes are formed from myeloid stem cells.

Examine Slide 4 to find cells of the erythrocyte lineage

a. Pro-erythroblast Find a - basophilic cytoplasm pro- - a very large nucleus erythroblast - prominent nucleoli (pale ‘dots’ in the in Slide 4a nucleus)

b. Basophilic erythroblast Find a - deeply basophilic cytoplasm basophilic - large, condensed nucleus erythroblast - no visible nucleolus in Slide 4b

c. Polychromatophilic erythroblast - comparable in size to surrounding erythrocytes Find a - prominent circular nucleus polychromat - partially condensed ‘checkerboard’ nucleus ophilic - no visible nucleolus erythroblast - cytoplasm has both eosinophilic and basophilic in Slide 4c properties (hence polychromatophilic)

d. Orthochromatophilic erythroblast Find a - comparable in size to surrounding erythrocytes orthochrom - prominent circular nucleus atophilic - fully condensed nucleus (no pale specks) erythroblast - no visible nucleolus in Slide 4d - cytoplasm is almost the same color as surrounding erythrocytes (hence ‘orthochrome’ = ‘correct color’) Find a e. Reticulocyte in - comparable in size to surrounding erythrocytes Slide 4e - nucleus has been extruded - cytoplasm has a slight basophilic sheen iii. Granulocytopoiesis The process by which granulocytes are formed from myeloid stem cells.

Examine Slide 5 to find examples of cells from the lineage

a. Find a - large nucleus myeloblast - prominent nucleoli in - cytoplasm is agranular and neutral in color Slide 5a

b. Find a - large nucleus pro- - prominent nucleoli in - cytoplasm is basophilic Slide 5b - contains granules (azurophilic: blue/neutral)

c. Myelocyte Find a - large round/oval nucleus w no nucleoli n. myelocyte in - neutral granules = neutrophilic myelocyte Slide 5c - eosinophilic granules = eosinophilic myelocyte Find a - basophilic granules = basophilic myelocyte e. myelocyte in Slide 5c d. Find a - bean-shaped nucleus neutro MM in - neutral granules = neutrophilic metamyelocyte Slide 5d - eosinophilic granules = eosinophilic Find a metamyelocyte eosin MM in - basophilic granules = basophilic metamyelocyte Slide 5d

e. Band (form) cells See if there are any - horse-shoe shaped nucleus band cells in - neutral granules = neutrophilic Slide 5e - eosinophilic granules = eosinophilic band cell - basophilic granules = basophilic band cell

f. Segmented cell (‘Segs’) See if there are different - nucleus has become segmented segs in - neutral granules = segmented neutrophil Slide 5f - eosinophilic granules = segmented eosinophil - basophilic granules = segmented basophil Complete the self-quiz to test your understanding and master your learning.

In addition to all the basic tissues in slides you must be able to identify the following structures and their features:

Blood Erythrocyte, Neutrophil, PMN, Polymorphonucleocyte Eosinophil Basophil Lymphocyte Monocyte Thrombocyte, platelet

Bone marrow Erythrocyte series Pro-erythroblast Basophilic erythroblast Polychromatophilic erythroblast Orthochromatophilic erythroblast Reticulocyte Erythrocyte

Granulocyte series Myeloblast Promyelocyte Myelocyte, neutrophilic *Note: Myelocyte, eosinophilic It is not possible to accurately classify late Myelocyte, basophilic * stage basophil development because the Metamyelocyte, neutrophilic granules occlude the nucleus making it Metamyelocyte, eosinophilic difficult to see its shape. If you see Metamyelocyte, basophilic * basophilic granules in the cell you can Band cell, neutrophilic therefore return an answer of either Band cell, eosinophilic basophilic myelocyte/metamyelocyte/band Band cell, basophilic * cell/seg. Segmented cell, neutrophilic Segmented cell, eosinophilic Segmented cell, basophilic *

Megakaryocyte