Cell and Tissue Biology

Terms List

The key objects to concentrate on during this lab are listed below. You need to learn 1) how to recognize each object, 2) understand it's primary functions, and 3) understand how structure is related to function.

  • Red Blood Cells
  • Neutrophils
  • Eosinophils
  • Basophils
  • Lymphocytes
  • Monocytes
  • Platelets


Blood is one of the specialized connective tissues and therefore consists of cells and intercellular substance. The cells are often referred to as "formed elements."

In the blood smear laboratory exercise and in this computer exercise you need to recognize the following formed elements: red blood cells, neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Go to the following hyperlink to access the Blood smear slide.

Blood smear

(If you have not looked at the atlas demo please do that now to familiarize yourself with the computer atlas.)

Follow the link sequence [1,1]. Click on the Mouse-over button. Moving the cursor around, you will find two of the formed elements highlighted, red blood cells and lymphocytes.

Red blood cells are 45% of the blood volume (and so are the most numerous formed element). The RBC is a soft, elastic, biconcave disc which has a diameter of roughly 7.5 Ám in the blood film, about 8.5 Ám in vivo, and about 6 Ám in tissue sections. This diameter normally varies very little and is therefore very useful as a comparison for measurement in tissue sections. The RBC is orange-red in this smear and may have a lighter staining middle. RBC's are not real cells since they lack nuclei.

The following clinical information does not need to be memorized. This is a small taste of the M2 pathology course. The size of red blood cells can be an important clinical marker for certain disease states. Macrocytosis (RBC > 9 microns) can be caused by diseases such as scurvy, aplastic anemia, impaired DNA synthesis secondary to vitamin B12 or folic acid deficiency or liver disease. Microcytosis (RBC < 6 microns) can be caused by diseases such as iron deficiency anemia, thalessemia or lead poisoning. Normal red blood cells can also be a relative size marker for identifying other abnormal cell sizes, such as the size of white blood cells in leukemic diseases.

Lymphocytes (about 30% of all leukocytes or white blood cells) all look alike in ordinary blood smears (you will learn later that there are many different types of lymphocytes, such as T and B cells). They have a very darkly staining, dense round nucleus. The diameter of the cell can vary between 8 to 12 microns. The narrow cytoplasmic rim appears clear sky-blue.

Click the Zoom Out button once and then click on link 2. In the middle of your screen is an eosinophil. They are 12 to 15 microns in diameter and have a bilobed nucleus. The cytoplasm is filled with orange-red granules. Usually 4% of the leukocytes are eosinophils, unless you are allergic to something in which case there are more.

Now Zoom Out to the 12x magnification (the original picture) and follow the sequence [2,4]. In the middle of your screen is a basophil. Basophils are so few (less than 1% of leukocytes) that most likely you will not see one in your own blood smear. They have large, numerous dark blue or purple granules that often mask the nucleus. Basophils and their connective tissue equivalents, mast cells, play an important role in defense against foreign invaders.

Zoom Out one click and then go to link 2. Find, either through the Mouse-over button or the drop-down menu, the neutrophil and the platelets.

Neutrophils are 55-60% of all blood leukocytes and 10-12 microns in diameter. The dark-staining nucleus is lobulated; young neutrophils have a stab or horseshoe shaped nucleus. There are plenty of grey and purple colored granules in the cytoplasm, but you can see through the cytoplasm (unlike in eosinophils).

Platelets are oval fragments of cytoplasm that originate from the fragmentation of giant megakaryocytes in the bone marrow. The platelets are 2-4 microns in diameter and produce clotting factors. They remain in the circulation for 8-11 days.

Zoom Out one click and then go to link 1. The large cell within the frame is a monocyte. These are large cells, 12-19 microns (compare this to the red blood cells), and are the precursors of macrophages. Cytoplasm is abundant and lacks the sky-blue color of the lymphocytes. The nucleus is much less dense than in lymphocytes; it looks spongy. Often the nucleus is horse-shoe shaped, or bent over itself (and resembles a brain).

Now it is time for a brief self quiz. Zoom Out two clicks and follow the sequence [1,9]. There are four objects that need to be identified. Try to identify them without help, then check yourself using the Mouse-over button. This blood smear slide contains many more labeled objects. Surf a bit to see how many you can identify.

In the atlas demo we suggested that you look at some of the transmission electron microscopy pictures. This is a brief exercise to help you find and recognize intracellular structures.

The structures you need to recognize are described in the lectures on cells and organelles and are: the nucleus, nucleoli, mitochondria with transverse and tubular cristae, Golgi complex, smooth and rough endoplasmic reticulum, free ribosomes, microvilli, cilia, basal bodies, lysosomes, peroxisomes, phagolysosomes, and secretory granules. Below are links to fourteen TEM slides that show all of the above structures.

TEM 1 - Nucleus, nucleoli, RER
TEM 6 - Centriole, Golgi complex
TEM 8 - Mitochondria with tubular cristae
TEM 14 - Microvilli
TEM 17 - Secretory granules, RER, Golgi compex
TEM 19 - Cilia, basal bodies
TEM 20 - Exocrine and endocrine granules, lysosomes
TEM 27 - Peroxisomes, RER
TEM 31 - Golgi complex
TEM 32 - Nucleolus
TEM 33 - Mitochondria with tranverse cristae
TEM 34 - Phagolysosomes
TEM 48 - Smooth ER, lysosomes
TEM 55 - Free ribosomes, nucleus